Merge libc++ trunk r366426, resolve conflicts, and add FREEBSD-Xlist.

[FreeBSD/FreeBSD.git] / contrib / libxo / libxo / libxo.c

/*
 * Copyright (c) 2014-2019, Juniper Networks, Inc.
 * All rights reserved.
 * This SOFTWARE is licensed under the LICENSE provided in the
 * ../Copyright file. By downloading, installing, copying, or otherwise
 * using the SOFTWARE, you agree to be bound by the terms of that
 * LICENSE.
 * Phil Shafer, July 2014
 *
 * This is the implementation of libxo, the formatting library that
 * generates multiple styles of output from a single code path.
 * Command line utilities can have their normal text output while
 * automation tools can see XML or JSON output, and web tools can use
 * HTML output that encodes the text output annotated with additional
 * information.  Specialized encoders can be built that allow custom
 * encoding including binary ones like CBOR, thrift, protobufs, etc.
 *
 * Full documentation is available in ./doc/libxo.txt or online at:
 *   http://juniper.github.io/libxo/libxo-manual.html
 *
 * For first time readers, the core bits of code to start looking at are:
 * - xo_do_emit() -- parse and emit a set of fields
 * - xo_do_emit_fields -- the central function of the library
 * - xo_do_format_field() -- handles formatting a single field
 * - xo_transiton() -- the state machine that keeps things sane
 * and of course the "xo_handle_t" data structure, which carries all
 * configuration and state.
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <stddef.h>
#include <wchar.h>
#include <locale.h>
#include <sys/types.h>
#include <stdarg.h>
#include <string.h>
#include <errno.h>
#include <limits.h>
#include <ctype.h>
#include <wctype.h>
#include <getopt.h>

#include "xo_config.h"
#include "xo.h"
#include "xo_encoder.h"
#include "xo_buf.h"
#include "xo_explicit.h"

/*
 * We ask wcwidth() to do an impossible job, really.  It's supposed to
 * need to tell us the number of columns consumed to display a unicode
 * character.  It returns that number without any sort of context, but
 * we know they are characters whose glyph differs based on placement
 * (end of word, middle of word, etc) and many that affect characters
 * previously emitted.  Without content, it can't hope to tell us.
 * But it's the only standard tool we've got, so we use it.  We would
 * use wcswidth() but it typically just loops through adding the results
 * of wcwidth() calls in an entirely unhelpful way.
 *
 * Even then, there are many poor implementations (macosx), so we have
 * to carry our own.  We could have configure.ac test this (with
 * something like 'assert(wcwidth(0x200d) == 0)'), but it would have
 * to run a binary, which breaks cross-compilation.  Hmm... I could
 * run this test at init time and make a warning for our dear user.
 *
 * Anyhow, it remains a best-effort sort of thing.  And it's all made
 * more hopeless because we assume the display code doing the rendering is
 * playing by the same rules we are.  If it display 0x200d as a square
 * box or a funky question mark, the output will be hosed.
 */
#ifdef LIBXO_WCWIDTH
#include "xo_wcwidth.h"
#else /* LIBXO_WCWIDTH */
#define xo_wcwidth(_x) wcwidth(_x)
#endif /* LIBXO_WCWIDTH */

#ifdef HAVE_STDIO_EXT_H
#include <stdio_ext.h>
#endif /* HAVE_STDIO_EXT_H */

/*
 * humanize_number is a great function, unless you don't have it.  So
 * we carry one in our pocket.
 */
#ifdef HAVE_HUMANIZE_NUMBER
#include <libutil.h>
#define xo_humanize_number humanize_number 
#else /* HAVE_HUMANIZE_NUMBER */
#include "xo_humanize.h"
#endif /* HAVE_HUMANIZE_NUMBER */

#ifdef HAVE_GETTEXT
#include <libintl.h>
#endif /* HAVE_GETTEXT */

/* Rather lame that we can't count on these... */
#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

/*
 * Three styles of specifying thread-local variables are supported.
 * configure.ac has the brains to run each possibility through the
 * compiler and see what works; we are left to define the THREAD_LOCAL
 * macro to the right value.  Most toolchains (clang, gcc) use
 * "before", but some (borland) use "after" and I've heard of some
 * (ms) that use __declspec.  Any others out there?
 */
#define THREAD_LOCAL_before 1
#define THREAD_LOCAL_after 2
#define THREAD_LOCAL_declspec 3

#ifndef HAVE_THREAD_LOCAL
#define THREAD_LOCAL(_x) _x
#elif HAVE_THREAD_LOCAL == THREAD_LOCAL_before
#define THREAD_LOCAL(_x) __thread _x
#elif HAVE_THREAD_LOCAL == THREAD_LOCAL_after
#define THREAD_LOCAL(_x) _x __thread
#elif HAVE_THREAD_LOCAL == THREAD_LOCAL_declspec
#define THREAD_LOCAL(_x) __declspec(_x)
#else
#error unknown thread-local setting
#endif /* HAVE_THREADS_H */

const char xo_version[] = LIBXO_VERSION;
const char xo_version_extra[] = LIBXO_VERSION_EXTRA;
static const char xo_default_format[] = "%s";

#ifndef UNUSED
#define UNUSED __attribute__ ((__unused__))
#endif /* UNUSED */

#define XO_INDENT_BY 2  /* Amount to indent when pretty printing */
#define XO_DEPTH        128      /* Default stack depth */
#define XO_MAX_ANCHOR_WIDTH (8*1024) /* Anything wider is just silly */

#define XO_FAILURE_NAME "failure"

/* Flags for the stack frame */
typedef unsigned xo_xsf_flags_t; /* XSF_* flags */
#define XSF_NOT_FIRST   (1<<0)  /* Not the first element */
#define XSF_LIST        (1<<1)  /* Frame is a list */
#define XSF_INSTANCE    (1<<2)  /* Frame is an instance */
#define XSF_DTRT        (1<<3)  /* Save the name for DTRT mode */

#define XSF_CONTENT     (1<<4)  /* Some content has been emitted */
#define XSF_EMIT        (1<<5)  /* Some field has been emitted */
#define XSF_EMIT_KEY    (1<<6)  /* A key has been emitted */
#define XSF_EMIT_LEAF_LIST (1<<7) /* A leaf-list field has been emitted */

/* These are the flags we propagate between markers and their parents */
#define XSF_MARKER_FLAGS \
 (XSF_NOT_FIRST | XSF_CONTENT | XSF_EMIT | XSF_EMIT_KEY | XSF_EMIT_LEAF_LIST )

/*
 * Turn the transition between two states into a number suitable for
 * a "switch" statement.
 */
#define XSS_TRANSITION(_old, _new) ((_old) << 8 | (_new))

/*
 * xo_stack_t: As we open and close containers and levels, we
 * create a stack of frames to track them.  This is needed for
 * XOF_WARN and XOF_XPATH.
 */
typedef struct xo_stack_s {
    xo_xsf_flags_t xs_flags;    /* Flags for this frame */
    xo_state_t xs_state;        /* State for this stack frame */
    char *xs_name;              /* Name (for XPath value) */
    char *xs_keys;              /* XPath predicate for any key fields */
} xo_stack_t;

/*
 * libxo supports colors and effects, for those who like them.
 * XO_COL_* ("colors") refers to fancy ansi codes, while X__EFF_*
 * ("effects") are bits since we need to maintain state.
 */
typedef uint8_t xo_color_t;
#define XO_COL_DEFAULT          0
#define XO_COL_BLACK            1
#define XO_COL_RED              2
#define XO_COL_GREEN            3
#define XO_COL_YELLOW           4
#define XO_COL_BLUE             5
#define XO_COL_MAGENTA          6
#define XO_COL_CYAN             7
#define XO_COL_WHITE            8

#define XO_NUM_COLORS           9

/*
 * Yes, there's no blink.  We're civilized.  We like users.  Blink
 * isn't something one does to someone you like.  Friends don't let
 * friends use blink.  On friends.  You know what I mean.  Blink is
 * like, well, it's like bursting into show tunes at a funeral.  It's
 * just not done.  Not something anyone wants.  And on those rare
 * instances where it might actually be appropriate, it's still wrong,
 * since it's likely done by the wrong person for the wrong reason.
 * Just like blink.  And if I implemented blink, I'd be like a funeral
 * director who adds "Would you like us to burst into show tunes?" on
 * the list of questions asked while making funeral arrangements.
 * It's formalizing wrongness in the wrong way.  And we're just too
 * civilized to do that.  Hhhmph!
 */
#define XO_EFF_RESET            (1<<0)
#define XO_EFF_NORMAL           (1<<1)
#define XO_EFF_BOLD             (1<<2)
#define XO_EFF_UNDERLINE        (1<<3)
#define XO_EFF_INVERSE          (1<<4)

#define XO_EFF_CLEAR_BITS XO_EFF_RESET /* Reset gets reset, surprisingly */

typedef uint8_t xo_effect_t;
typedef struct xo_colors_s {
    xo_effect_t xoc_effects;    /* Current effect set */
    xo_color_t xoc_col_fg;      /* Foreground color */
    xo_color_t xoc_col_bg;      /* Background color */
} xo_colors_t;

/*
 * xo_handle_t: this is the principle data structure for libxo.
 * It's used as a store for state, options, content, and all manor
 * of other information.
 */
struct xo_handle_s {
    xo_xof_flags_t xo_flags;    /* Flags (XOF_*) from the user*/
    xo_xof_flags_t xo_iflags;   /* Internal flags (XOIF_*) */
    xo_style_t xo_style;        /* XO_STYLE_* value */
    unsigned short xo_indent;   /* Indent level (if pretty) */
    unsigned short xo_indent_by; /* Indent amount (tab stop) */
    xo_write_func_t xo_write;   /* Write callback */
    xo_close_func_t xo_close;   /* Close callback */
    xo_flush_func_t xo_flush;   /* Flush callback */
    xo_formatter_t xo_formatter; /* Custom formating function */
    xo_checkpointer_t xo_checkpointer; /* Custom formating support function */
    void *xo_opaque;            /* Opaque data for write function */
    xo_buffer_t xo_data;        /* Output data */
    xo_buffer_t xo_fmt;         /* Work area for building format strings */
    xo_buffer_t xo_attrs;       /* Work area for building XML attributes */
    xo_buffer_t xo_predicate;   /* Work area for building XPath predicates */
    xo_stack_t *xo_stack;       /* Stack pointer */
    int xo_depth;               /* Depth of stack */
    int xo_stack_size;          /* Size of the stack */
    xo_info_t *xo_info;         /* Info fields for all elements */
    int xo_info_count;          /* Number of info entries */
    va_list xo_vap;             /* Variable arguments (stdargs) */
    char *xo_leading_xpath;     /* A leading XPath expression */
    mbstate_t xo_mbstate;       /* Multi-byte character conversion state */
    ssize_t xo_anchor_offset;   /* Start of anchored text */
    ssize_t xo_anchor_columns;  /* Number of columns since the start anchor */
    ssize_t xo_anchor_min_width; /* Desired width of anchored text */
    ssize_t xo_units_offset;    /* Start of units insertion point */
    ssize_t xo_columns; /* Columns emitted during this xo_emit call */
#ifndef LIBXO_TEXT_ONLY
    xo_color_t xo_color_map_fg[XO_NUM_COLORS]; /* Foreground color mappings */
    xo_color_t xo_color_map_bg[XO_NUM_COLORS]; /* Background color mappings */
#endif /* LIBXO_TEXT_ONLY */
    xo_colors_t xo_colors;      /* Current color and effect values */
    xo_buffer_t xo_color_buf;   /* HTML: buffer of colors and effects */
    char *xo_version;           /* Version string */
    int xo_errno;               /* Saved errno for "%m" */
    char *xo_gt_domain;         /* Gettext domain, suitable for dgettext(3) */
    xo_encoder_func_t xo_encoder; /* Encoding function */
    void *xo_private;           /* Private data for external encoders */
};

/* Flag operations */
#define XOF_BIT_ISSET(_flag, _bit)      (((_flag) & (_bit)) ? 1 : 0)
#define XOF_BIT_SET(_flag, _bit)        do { (_flag) |= (_bit); } while (0)
#define XOF_BIT_CLEAR(_flag, _bit)      do { (_flag) &= ~(_bit); } while (0)

#define XOF_ISSET(_xop, _bit) XOF_BIT_ISSET(_xop->xo_flags, _bit)
#define XOF_SET(_xop, _bit) XOF_BIT_SET(_xop->xo_flags, _bit)
#define XOF_CLEAR(_xop, _bit) XOF_BIT_CLEAR(_xop->xo_flags, _bit)

#define XOIF_ISSET(_xop, _bit) XOF_BIT_ISSET(_xop->xo_iflags, _bit)
#define XOIF_SET(_xop, _bit) XOF_BIT_SET(_xop->xo_iflags, _bit)
#define XOIF_CLEAR(_xop, _bit) XOF_BIT_CLEAR(_xop->xo_iflags, _bit)

/* Internal flags */
#define XOIF_REORDER    XOF_BIT(0) /* Reordering fields; record field info */
#define XOIF_DIV_OPEN   XOF_BIT(1) /* A <div> is open */
#define XOIF_TOP_EMITTED XOF_BIT(2) /* The top JSON braces have been emitted */
#define XOIF_ANCHOR     XOF_BIT(3) /* An anchor is in place  */

#define XOIF_UNITS_PENDING XOF_BIT(4) /* We have a units-insertion pending */
#define XOIF_INIT_IN_PROGRESS XOF_BIT(5) /* Init of handle is in progress */
#define XOIF_MADE_OUTPUT XOF_BIT(6)      /* Have already made output */

/* Flags for formatting functions */
typedef unsigned long xo_xff_flags_t;
#define XFF_COLON       (1<<0)  /* Append a ":" */
#define XFF_COMMA       (1<<1)  /* Append a "," iff there's more output */
#define XFF_WS          (1<<2)  /* Append a blank */
#define XFF_ENCODE_ONLY (1<<3)  /* Only emit for encoding styles (XML, JSON) */

#define XFF_QUOTE       (1<<4)  /* Force quotes */
#define XFF_NOQUOTE     (1<<5)  /* Force no quotes */
#define XFF_DISPLAY_ONLY (1<<6) /* Only emit for display styles (text, html) */
#define XFF_KEY         (1<<7)  /* Field is a key (for XPath) */

#define XFF_XML         (1<<8)  /* Force XML encoding style (for XPath) */
#define XFF_ATTR        (1<<9)  /* Escape value using attribute rules (XML) */
#define XFF_BLANK_LINE  (1<<10) /* Emit a blank line */
#define XFF_NO_OUTPUT   (1<<11) /* Do not make any output */

#define XFF_TRIM_WS     (1<<12) /* Trim whitespace off encoded values */
#define XFF_LEAF_LIST   (1<<13) /* A leaf-list (list of values) */
#define XFF_UNESCAPE    (1<<14) /* Need to printf-style unescape the value */
#define XFF_HUMANIZE    (1<<15) /* Humanize the value (for display styles) */

#define XFF_HN_SPACE    (1<<16) /* Humanize: put space before suffix */
#define XFF_HN_DECIMAL  (1<<17) /* Humanize: add one decimal place if <10 */
#define XFF_HN_1000     (1<<18) /* Humanize: use 1000, not 1024 */
#define XFF_GT_FIELD    (1<<19) /* Call gettext() on a field */

#define XFF_GT_PLURAL   (1<<20) /* Call dngettext to find plural form */
#define XFF_ARGUMENT    (1<<21) /* Content provided via argument */

/* Flags to turn off when we don't want i18n processing */
#define XFF_GT_FLAGS (XFF_GT_FIELD | XFF_GT_PLURAL)

/*
 * Normal printf has width and precision, which for strings operate as
 * min and max number of columns.  But this depends on the idea that
 * one byte means one column, which UTF-8 and multi-byte characters
 * pitches on its ear.  It may take 40 bytes of data to populate 14
 * columns, but we can't go off looking at 40 bytes of data without the
 * caller's permission for fear/knowledge that we'll generate core files.
 * 
 * So we make three values, distinguishing between "max column" and
 * "number of bytes that we will inspect inspect safely" We call the
 * later "size", and make the format "%[[<min>].[[<size>].<max>]]s".
 *
 * Under the "first do no harm" theory, we default "max" to "size".
 * This is a reasonable assumption for folks that don't grok the
 * MBS/WCS/UTF-8 world, and while it will be annoying, it will never
 * be evil.
 *
 * For example, xo_emit("{:tag/%-14.14s}", buf) will make 14
 * columns of output, but will never look at more than 14 bytes of the
 * input buffer.  This is mostly compatible with printf and caller's
 * expectations.
 *
 * In contrast xo_emit("{:tag/%-14..14s}", buf) will look at however
 * many bytes (or until a NUL is seen) are needed to fill 14 columns
 * of output.  xo_emit("{:tag/%-14.*.14s}", xx, buf) will look at up
 * to xx bytes (or until a NUL is seen) in order to fill 14 columns
 * of output.
 *
 * It's fairly amazing how a good idea (handle all languages of the
 * world) blows such a big hole in the bottom of the fairly weak boat
 * that is C string handling.  The simplicity and completenesss are
 * sunk in ways we haven't even begun to understand.
 */
#define XF_WIDTH_MIN    0       /* Minimal width */
#define XF_WIDTH_SIZE   1       /* Maximum number of bytes to examine */
#define XF_WIDTH_MAX    2       /* Maximum width */
#define XF_WIDTH_NUM    3       /* Numeric fields in printf (min.size.max) */

/* Input and output string encodings */
#define XF_ENC_WIDE     1       /* Wide characters (wchar_t) */
#define XF_ENC_UTF8     2       /* UTF-8 */
#define XF_ENC_LOCALE   3       /* Current locale */

/*
 * A place to parse printf-style format flags for each field
 */
typedef struct xo_format_s {
    unsigned char xf_fc;        /* Format character */
    unsigned char xf_enc;       /* Encoding of the string (XF_ENC_*) */
    unsigned char xf_skip;      /* Skip this field */
    unsigned char xf_lflag;     /* 'l' (long) */
    unsigned char xf_hflag;;    /* 'h' (half) */
    unsigned char xf_jflag;     /* 'j' (intmax_t) */
    unsigned char xf_tflag;     /* 't' (ptrdiff_t) */
    unsigned char xf_zflag;     /* 'z' (size_t) */
    unsigned char xf_qflag;     /* 'q' (quad_t) */
    unsigned char xf_seen_minus; /* Seen a minus */
    int xf_leading_zero;        /* Seen a leading zero (zero fill)  */
    unsigned xf_dots;           /* Seen one or more '.'s */
    int xf_width[XF_WIDTH_NUM]; /* Width/precision/size numeric fields */
    unsigned xf_stars;          /* Seen one or more '*'s */
    unsigned char xf_star[XF_WIDTH_NUM]; /* Seen one or more '*'s */
} xo_format_t;

/*
 * This structure represents the parsed field information, suitable for
 * processing by xo_do_emit and anything else that needs to parse fields.
 * Note that all pointers point to the main format string.
 *
 * XXX This is a first step toward compilable or cachable format
 * strings.  We can also cache the results of dgettext when no format
 * is used, assuming the 'p' modifier has _not_ been set.
 */
typedef struct xo_field_info_s {
    xo_xff_flags_t xfi_flags;   /* Flags for this field */
    unsigned xfi_ftype;         /* Field type, as character (e.g. 'V') */
    const char *xfi_start;   /* Start of field in the format string */
    const char *xfi_content;    /* Field's content */
    const char *xfi_format;     /* Field's Format */
    const char *xfi_encoding;   /* Field's encoding format */
    const char *xfi_next;       /* Next character in format string */
    ssize_t xfi_len;            /* Length of field */
    ssize_t xfi_clen;           /* Content length */
    ssize_t xfi_flen;           /* Format length */
    ssize_t xfi_elen;           /* Encoding length */
    unsigned xfi_fnum;          /* Field number (if used; 0 otherwise) */
    unsigned xfi_renum;         /* Reordered number (0 == no renumbering) */
} xo_field_info_t;

/*
 * We keep a 'default' handle to allow callers to avoid having to
 * allocate one.  Passing NULL to any of our functions will use
 * this default handle.  Most functions have a variant that doesn't
 * require a handle at all, since most output is to stdout, which
 * the default handle handles handily.
 */
static THREAD_LOCAL(xo_handle_t) xo_default_handle;
static THREAD_LOCAL(int) xo_default_inited;
static int xo_locale_inited;
static const char *xo_program;

/*
 * To allow libxo to be used in diverse environment, we allow the
 * caller to give callbacks for memory allocation.
 */
xo_realloc_func_t xo_realloc = realloc;
xo_free_func_t xo_free = free;

/* Forward declarations */
static void
xo_failure (xo_handle_t *xop, const char *fmt, ...);

static ssize_t
xo_transition (xo_handle_t *xop, xo_xof_flags_t flags, const char *name,
               xo_state_t new_state);

static int
xo_set_options_simple (xo_handle_t *xop, const char *input);

static int
xo_color_find (const char *str);

static void
xo_buf_append_div (xo_handle_t *xop, const char *class, xo_xff_flags_t flags,
                   const char *name, ssize_t nlen,
                   const char *value, ssize_t vlen,
                   const char *fmt, ssize_t flen,
                   const char *encoding, ssize_t elen);

static void
xo_anchor_clear (xo_handle_t *xop);

/*
 * xo_style is used to retrieve the current style.  When we're built
 * for "text only" mode, we use this function to drive the removal
 * of most of the code in libxo.  We return a constant and the compiler
 * happily removes the non-text code that is not longer executed.  This
 * trims our code nicely without needing to trampel perfectly readable
 * code with ifdefs.
 */
static inline xo_style_t
xo_style (xo_handle_t *xop UNUSED)
{
#ifdef LIBXO_TEXT_ONLY
    return XO_STYLE_TEXT;
#else /* LIBXO_TEXT_ONLY */
    return xop->xo_style;
#endif /* LIBXO_TEXT_ONLY */
}

/*
 * Allow the compiler to optimize out non-text-only code while
 * still compiling it.
 */
static inline int
xo_text_only (void)
{
#ifdef LIBXO_TEXT_ONLY
    return TRUE;
#else /* LIBXO_TEXT_ONLY */
    return FALSE;
#endif /* LIBXO_TEXT_ONLY */
}

/*
 * Callback to write data to a FILE pointer
 */
static xo_ssize_t
xo_write_to_file (void *opaque, const char *data)
{
    FILE *fp = (FILE *) opaque;

    return fprintf(fp, "%s", data);
}

/*
 * Callback to close a file
 */
static void
xo_close_file (void *opaque)
{
    FILE *fp = (FILE *) opaque;

    fclose(fp);
}

/*
 * Callback to flush a FILE pointer
 */
static int
xo_flush_file (void *opaque)
{
    FILE *fp = (FILE *) opaque;

    return fflush(fp);
}

/*
 * Use a rotating stock of buffers to make a printable string
 */
#define XO_NUMBUFS 8
#define XO_SMBUFSZ 128

static const char *
xo_printable (const char *str)
{
    static THREAD_LOCAL(char) bufset[XO_NUMBUFS][XO_SMBUFSZ];
    static THREAD_LOCAL(int) bufnum = 0;

    if (str == NULL)
        return "";

    if (++bufnum == XO_NUMBUFS)
        bufnum = 0;

    char *res = bufset[bufnum], *cp, *ep;

    for (cp = res, ep = res + XO_SMBUFSZ - 1; *str && cp < ep; cp++, str++) {
        if (*str == '\n') {
            *cp++ = '\\';
            *cp = 'n';
        } else if (*str == '\r') {
            *cp++ = '\\';
            *cp = 'r';
        } else if (*str == '\"') {
            *cp++ = '\\';
            *cp = '"';
        } else 
            *cp = *str;
    }

    *cp = '\0';
    return res;
}

static int
xo_depth_check (xo_handle_t *xop, int depth)
{
    xo_stack_t *xsp;

    if (depth >= xop->xo_stack_size) {
        depth += XO_DEPTH;      /* Extra room */

        xsp = xo_realloc(xop->xo_stack, sizeof(xop->xo_stack[0]) * depth);
        if (xsp == NULL) {
            xo_failure(xop, "xo_depth_check: out of memory (%d)", depth);
            return -1;
        }

        int count = depth - xop->xo_stack_size;

        bzero(xsp + xop->xo_stack_size, count * sizeof(*xsp));
        xop->xo_stack_size = depth;
        xop->xo_stack = xsp;
    }

    return 0;
}

void
xo_no_setlocale (void)
{
    xo_locale_inited = 1;       /* Skip initialization */
}

/*
 * For XML, the first character of a tag cannot be numeric, but people
 * will likely not notice.  So we people-proof them by forcing a leading
 * underscore if they use invalid tags.  Note that this doesn't cover
 * all broken tags, just this fairly specific case.
 */
static const char *
xo_xml_leader_len (xo_handle_t *xop, const char *name, xo_ssize_t nlen)
{
    if (name == NULL || isalpha(name[0]) || name[0] == '_')
        return "";

    xo_failure(xop, "invalid XML tag name: '%.*s'", nlen, name);
    return "_";
}

static const char *
xo_xml_leader (xo_handle_t *xop, const char *name)
{
    return xo_xml_leader_len(xop, name, strlen(name));
}

/*
 * We need to decide if stdout is line buffered (_IOLBF).  Lacking a
 * standard way to decide this (e.g. getlinebuf()), we have configure
 * look to find __flbf, which glibc supported.  If not, we'll rely on
 * isatty, with the assumption that terminals are the only thing
 * that's line buffered.  We _could_ test for "steam._flags & _IOLBF",
 * which is all __flbf does, but that's even tackier.  Like a
 * bedazzled Elvis outfit on an ugly lap dog sort of tacky.  Not
 * something we're willing to do.
 */
static int
xo_is_line_buffered (FILE *stream)
{
#if HAVE___FLBF
    if (__flbf(stream))
        return 1;
#else /* HAVE___FLBF */
    if (isatty(fileno(stream)))
        return 1;
#endif /* HAVE___FLBF */
    return 0;
}

/*
 * Initialize an xo_handle_t, using both static defaults and
 * the global settings from the LIBXO_OPTIONS environment
 * variable.
 */
static void
xo_init_handle (xo_handle_t *xop)
{
    xop->xo_opaque = stdout;
    xop->xo_write = xo_write_to_file;
    xop->xo_flush = xo_flush_file;

    if (xo_is_line_buffered(stdout))
        XOF_SET(xop, XOF_FLUSH_LINE);

    /*
     * We need to initialize the locale, which isn't really pretty.
     * Libraries should depend on their caller to set up the
     * environment.  But we really can't count on the caller to do
     * this, because well, they won't.  Trust me.
     */
    if (!xo_locale_inited) {
        xo_locale_inited = 1;   /* Only do this once */

        const char *cp = getenv("LC_CTYPE");
        if (cp == NULL)
            cp = getenv("LANG");
        if (cp == NULL)
            cp = getenv("LC_ALL");
        if (cp == NULL)
            cp = "C";           /* Default for C programs */
        (void) setlocale(LC_CTYPE, cp);
    }

    /*
     * Initialize only the xo_buffers we know we'll need; the others
     * can be allocated as needed.
     */
    xo_buf_init(&xop->xo_data);
    xo_buf_init(&xop->xo_fmt);

    if (XOIF_ISSET(xop, XOIF_INIT_IN_PROGRESS))
        return;
    XOIF_SET(xop, XOIF_INIT_IN_PROGRESS);

    xop->xo_indent_by = XO_INDENT_BY;
    xo_depth_check(xop, XO_DEPTH);

    XOIF_CLEAR(xop, XOIF_INIT_IN_PROGRESS);
}

/*
 * Initialize the default handle.
 */
static void
xo_default_init (void)
{
    xo_handle_t *xop = &xo_default_handle;

    xo_init_handle(xop);

#if !defined(NO_LIBXO_OPTIONS)
    if (!XOF_ISSET(xop, XOF_NO_ENV)) {
       char *env = getenv("LIBXO_OPTIONS");

       if (env)
           xo_set_options_simple(xop, env);

    }
#endif /* NO_LIBXO_OPTIONS */

    xo_default_inited = 1;
}

/*
 * Cheap convenience function to return either the argument, or
 * the internal handle, after it has been initialized.  The usage
 * is:
 *    xop = xo_default(xop);
 */
static xo_handle_t *
xo_default (xo_handle_t *xop)
{
    if (xop == NULL) {
        if (xo_default_inited == 0)
            xo_default_init();
        xop = &xo_default_handle;
    }

    return xop;
}

/*
 * Return the number of spaces we should be indenting.  If
 * we are pretty-printing, this is indent * indent_by.
 */
static int
xo_indent (xo_handle_t *xop)
{
    int rc = 0;

    xop = xo_default(xop);

    if (XOF_ISSET(xop, XOF_PRETTY)) {
        rc = xop->xo_indent * xop->xo_indent_by;
        if (XOIF_ISSET(xop, XOIF_TOP_EMITTED))
            rc += xop->xo_indent_by;
    }

    return (rc > 0) ? rc : 0;
}

static void
xo_buf_indent (xo_handle_t *xop, int indent)
{
    xo_buffer_t *xbp = &xop->xo_data;

    if (indent <= 0)
        indent = xo_indent(xop);

    if (!xo_buf_has_room(xbp, indent))
        return;

    memset(xbp->xb_curp, ' ', indent);
    xbp->xb_curp += indent;
}

static char xo_xml_amp[] = "&amp;";
static char xo_xml_lt[] = "&lt;";
static char xo_xml_gt[] = "&gt;";
static char xo_xml_quot[] = "&quot;";

static ssize_t
xo_escape_xml (xo_buffer_t *xbp, ssize_t len, xo_xff_flags_t flags)
{
    ssize_t slen;
    ssize_t delta = 0;
    char *cp, *ep, *ip;
    const char *sp;
    int attr = XOF_BIT_ISSET(flags, XFF_ATTR);

    for (cp = xbp->xb_curp, ep = cp + len; cp < ep; cp++) {
        /* We're subtracting 2: 1 for the NUL, 1 for the char we replace */
        if (*cp == '<')
            delta += sizeof(xo_xml_lt) - 2;
        else if (*cp == '>')
            delta += sizeof(xo_xml_gt) - 2;
        else if (*cp == '&')
            delta += sizeof(xo_xml_amp) - 2;
        else if (attr && *cp == '"')
            delta += sizeof(xo_xml_quot) - 2;
    }

    if (delta == 0)             /* Nothing to escape; bail */
        return len;

    if (!xo_buf_has_room(xbp, delta)) /* No room; bail, but don't append */
        return 0;

    ep = xbp->xb_curp;
    cp = ep + len;
    ip = cp + delta;
    do {
        cp -= 1;
        ip -= 1;

        if (*cp == '<')
            sp = xo_xml_lt;
        else if (*cp == '>')
            sp = xo_xml_gt;
        else if (*cp == '&')
            sp = xo_xml_amp;
        else if (attr && *cp == '"')
            sp = xo_xml_quot;
        else {
            *ip = *cp;
            continue;
        }

        slen = strlen(sp);
        ip -= slen - 1;
        memcpy(ip, sp, slen);
        
    } while (cp > ep && cp != ip);

    return len + delta;
}

static ssize_t
xo_escape_json (xo_buffer_t *xbp, ssize_t len, xo_xff_flags_t flags UNUSED)
{
    ssize_t delta = 0;
    char *cp, *ep, *ip;

    for (cp = xbp->xb_curp, ep = cp + len; cp < ep; cp++) {
        if (*cp == '\\' || *cp == '"')
            delta += 1;
        else if (*cp == '\n' || *cp == '\r')
            delta += 1;
    }

    if (delta == 0)             /* Nothing to escape; bail */
        return len;

    if (!xo_buf_has_room(xbp, delta)) /* No room; bail, but don't append */
        return 0;

    ep = xbp->xb_curp;
    cp = ep + len;
    ip = cp + delta;
    do {
        cp -= 1;
        ip -= 1;

        if (*cp == '\\' || *cp == '"') {
            *ip-- = *cp;
            *ip = '\\';
        } else if (*cp == '\n') {
            *ip-- = 'n';
            *ip = '\\';
        } else if (*cp == '\r') {
            *ip-- = 'r';
            *ip = '\\';
        } else {
            *ip = *cp;
        }
        
    } while (cp > ep && cp != ip);

    return len + delta;
}

/*
 * PARAM-VALUE     = UTF-8-STRING ; characters '"', '\' and
 *                                ; ']' MUST be escaped.
 */
static ssize_t
xo_escape_sdparams (xo_buffer_t *xbp, ssize_t len, xo_xff_flags_t flags UNUSED)
{
    ssize_t delta = 0;
    char *cp, *ep, *ip;

    for (cp = xbp->xb_curp, ep = cp + len; cp < ep; cp++) {
        if (*cp == '\\' || *cp == '"' || *cp == ']')
            delta += 1;
    }

    if (delta == 0)             /* Nothing to escape; bail */
        return len;

    if (!xo_buf_has_room(xbp, delta)) /* No room; bail, but don't append */
        return 0;

    ep = xbp->xb_curp;
    cp = ep + len;
    ip = cp + delta;
    do {
        cp -= 1;
        ip -= 1;

        if (*cp == '\\' || *cp == '"' || *cp == ']') {
            *ip-- = *cp;
            *ip = '\\';
        } else {
            *ip = *cp;
        }
        
    } while (cp > ep && cp != ip);

    return len + delta;
}

static void
xo_buf_escape (xo_handle_t *xop, xo_buffer_t *xbp,
               const char *str, ssize_t len, xo_xff_flags_t flags)
{
    if (!xo_buf_has_room(xbp, len))
        return;

    memcpy(xbp->xb_curp, str, len);

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
    case XO_STYLE_HTML:
        len = xo_escape_xml(xbp, len, flags);
        break;

    case XO_STYLE_JSON:
        len = xo_escape_json(xbp, len, flags);
        break;

    case XO_STYLE_SDPARAMS:
        len = xo_escape_sdparams(xbp, len, flags);
        break;
    }

    xbp->xb_curp += len;
}

/*
 * Write the current contents of the data buffer using the handle's
 * xo_write function.
 */
static ssize_t
xo_write (xo_handle_t *xop)
{
    ssize_t rc = 0;
    xo_buffer_t *xbp = &xop->xo_data;

    if (xbp->xb_curp != xbp->xb_bufp) {
        xo_buf_append(xbp, "", 1); /* Append ending NUL */
        xo_anchor_clear(xop);
        if (xop->xo_write)
            rc = xop->xo_write(xop->xo_opaque, xbp->xb_bufp);
        xbp->xb_curp = xbp->xb_bufp;
    }

    /* Turn off the flags that don't survive across writes */
    XOIF_CLEAR(xop, XOIF_UNITS_PENDING);

    return rc;
}

/*
 * Format arguments into our buffer.  If a custom formatter has been set,
 * we use that to do the work; otherwise we vsnprintf().
 */
static ssize_t
xo_vsnprintf (xo_handle_t *xop, xo_buffer_t *xbp, const char *fmt, va_list vap)
{
    va_list va_local;
    ssize_t rc;
    ssize_t left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);

    va_copy(va_local, vap);

    if (xop->xo_formatter)
        rc = xop->xo_formatter(xop, xbp->xb_curp, left, fmt, va_local);
    else
        rc = vsnprintf(xbp->xb_curp, left, fmt, va_local);

    if (rc >= left) {
        if (!xo_buf_has_room(xbp, rc)) {
            va_end(va_local);
            return -1;
        }

        /*
         * After we call vsnprintf(), the stage of vap is not defined.
         * We need to copy it before we pass.  Then we have to do our
         * own logic below to move it along.  This is because the
         * implementation can have va_list be a pointer (bsd) or a
         * structure (macosx) or anything in between.
         */

        va_end(va_local);       /* Reset vap to the start */
        va_copy(va_local, vap);

        left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
        if (xop->xo_formatter)
            rc = xop->xo_formatter(xop, xbp->xb_curp, left, fmt, va_local);
        else
            rc = vsnprintf(xbp->xb_curp, left, fmt, va_local);
    }
    va_end(va_local);

    return rc;
}

/*
 * Print some data through the handle.
 */
static ssize_t
xo_printf_v (xo_handle_t *xop, const char *fmt, va_list vap)
{
    xo_buffer_t *xbp = &xop->xo_data;
    ssize_t left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
    ssize_t rc;
    va_list va_local;

    va_copy(va_local, vap);

    rc = vsnprintf(xbp->xb_curp, left, fmt, va_local);

    if (rc >= left) {
        if (!xo_buf_has_room(xbp, rc)) {
            va_end(va_local);
            return -1;
        }

        va_end(va_local);       /* Reset vap to the start */
        va_copy(va_local, vap);

        left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
        rc = vsnprintf(xbp->xb_curp, left, fmt, va_local);
    }

    va_end(va_local);

    if (rc > 0)
        xbp->xb_curp += rc;

    return rc;
}

static ssize_t
xo_printf (xo_handle_t *xop, const char *fmt, ...)
{
    ssize_t rc;
    va_list vap;

    va_start(vap, fmt);

    rc = xo_printf_v(xop, fmt, vap);

    va_end(vap);
    return rc;
}

/*
 * These next few function are make The Essential UTF-8 Ginsu Knife.
 * Identify an input and output character, and convert it.
 */
static uint8_t xo_utf8_data_bits[5] = { 0, 0x7f, 0x1f, 0x0f, 0x07 };
static uint8_t xo_utf8_len_bits[5]  = { 0, 0x00, 0xc0, 0xe0, 0xf0 };

/*
 * If the byte has a high-bit set, it's UTF-8, not ASCII.
 */
static int
xo_is_utf8 (char ch)
{
    return (ch & 0x80);
}

/*
 * Look at the high bits of the first byte to determine the length
 * of the UTF-8 character.
 */
static inline ssize_t
xo_utf8_to_wc_len (const char *buf)
{
    uint8_t bval = (uint8_t) *buf;
    ssize_t len;

    if ((bval & 0x80) == 0x0)
        len = 1;
    else if ((bval & 0xe0) == 0xc0)
        len = 2;
    else if ((bval & 0xf0) == 0xe0)
        len = 3;
    else if ((bval & 0xf8) == 0xf0)
        len = 4;
    else
        len = -1;

    return len;
}

static ssize_t
xo_buf_utf8_len (xo_handle_t *xop, const char *buf, ssize_t bufsiz)
{
    unsigned b = (unsigned char) *buf;
    ssize_t len, i;

    len = xo_utf8_to_wc_len(buf);
    if (len < 0) {
        xo_failure(xop, "invalid UTF-8 data: %02hhx", b);
        return -1;
    }

    if (len > bufsiz) {
        xo_failure(xop, "invalid UTF-8 data (short): %02hhx (%d/%d)",
                   b, len, bufsiz);
        return -1;
    }

    for (i = 2; i < len; i++) {
        b = (unsigned char ) buf[i];
        if ((b & 0xc0) != 0x80) {
            xo_failure(xop, "invalid UTF-8 data (byte %d): %x", i, b);
            return -1;
        }
    }

    return len;
}

/*
 * Build a wide character from the input buffer; the number of
 * bits we pull off the first character is dependent on the length,
 * but we put 6 bits off all other bytes.
 */
static inline wchar_t
xo_utf8_char (const char *buf, ssize_t len)
{
    /* Most common case: singleton byte */
    if (len == 1)
        return (unsigned char) buf[0];

    ssize_t i;
    wchar_t wc;
    const unsigned char *cp = (const unsigned char *) buf;

    wc = *cp & xo_utf8_data_bits[len];
    for (i = 1; i < len; i++) {
        wc <<= 6;               /* Low six bits have data */
        wc |= cp[i] & 0x3f;
        if ((cp[i] & 0xc0) != 0x80)
            return (wchar_t) -1;
    }

    return wc;
}

/*
 * Determine the number of bytes needed to encode a wide character.
 */
static ssize_t
xo_utf8_emit_len (wchar_t wc)
{
    ssize_t len;

    if ((wc & ((1 << 7) - 1)) == wc) /* Simple case */
        len = 1;
    else if ((wc & ((1 << 11) - 1)) == wc)
        len = 2;
    else if ((wc & ((1 << 16) - 1)) == wc)
        len = 3;
    else if ((wc & ((1 << 21) - 1)) == wc)
        len = 4;
    else
        len = -1;               /* Invalid */

    return len;
}

/*
 * Emit one wide character into the given buffer
 */
static void
xo_utf8_emit_char (char *buf, ssize_t len, wchar_t wc)
{
    ssize_t i;

    if (len == 1) { /* Simple case */
        buf[0] = wc & 0x7f;
        return;
    }

    /* Start with the low bits and insert them, six bits at a time */
    for (i = len - 1; i >= 0; i--) {
        buf[i] = 0x80 | (wc & 0x3f);
        wc >>= 6;               /* Drop the low six bits */
    }

    /* Finish off the first byte with the length bits */
    buf[0] &= xo_utf8_data_bits[len]; /* Clear out the length bits */
    buf[0] |= xo_utf8_len_bits[len]; /* Drop in new length bits */
}

/*
 * Append a single UTF-8 character to a buffer, converting it to locale
 * encoding.  Returns the number of columns consumed by that character,
 * as best we can determine it.
 */
static ssize_t
xo_buf_append_locale_from_utf8 (xo_handle_t *xop, xo_buffer_t *xbp,
                                const char *ibuf, ssize_t ilen)
{
    wchar_t wc;
    ssize_t len;

    /*
     * Build our wide character from the input buffer; the number of
     * bits we pull off the first character is dependent on the length,
     * but we put 6 bits off all other bytes.
     */
    wc = xo_utf8_char(ibuf, ilen);
    if (wc == (wchar_t) -1) {
        xo_failure(xop, "invalid UTF-8 byte sequence");
        return 0;
    }

    if (XOF_ISSET(xop, XOF_NO_LOCALE)) {
        if (!xo_buf_has_room(xbp, ilen))
            return 0;

        memcpy(xbp->xb_curp, ibuf, ilen);
        xbp->xb_curp += ilen;

    } else {
        if (!xo_buf_has_room(xbp, MB_LEN_MAX + 1))
            return 0;

        bzero(&xop->xo_mbstate, sizeof(xop->xo_mbstate));
        len = wcrtomb(xbp->xb_curp, wc, &xop->xo_mbstate);

        if (len <= 0) {
            xo_failure(xop, "could not convert wide char: %lx",
                       (unsigned long) wc);
            return 0;
        }
        xbp->xb_curp += len;
    }

    return xo_wcwidth(wc);
}

/*
 * Append a UTF-8 string to a buffer, converting it into locale encoding
 */
static void
xo_buf_append_locale (xo_handle_t *xop, xo_buffer_t *xbp,
                      const char *cp, ssize_t len)
{
    const char *sp = cp, *ep = cp + len;
    ssize_t save_off = xbp->xb_bufp - xbp->xb_curp;
    ssize_t slen;
    int cols = 0;

    for ( ; cp < ep; cp++) {
        if (!xo_is_utf8(*cp)) {
            cols += 1;
            continue;
        }

        /*
         * We're looking at a non-ascii UTF-8 character.
         * First we copy the previous data.
         * Then we need find the length and validate it.
         * Then we turn it into a wide string.
         * Then we turn it into a localized string.
         * Then we repeat.  Isn't i18n fun?
         */
        if (sp != cp)
            xo_buf_append(xbp, sp, cp - sp); /* Append previous data */

        slen = xo_buf_utf8_len(xop, cp, ep - cp);
        if (slen <= 0) {
            /* Bad data; back it all out */
            xbp->xb_curp = xbp->xb_bufp + save_off;
            return;
        }

        cols += xo_buf_append_locale_from_utf8(xop, xbp, cp, slen);

        /* Next time through, we'll start at the next character */
        cp += slen - 1;
        sp = cp + 1;
    }

    /* Update column values */
    if (XOF_ISSET(xop, XOF_COLUMNS))
        xop->xo_columns += cols;
    if (XOIF_ISSET(xop, XOIF_ANCHOR))
        xop->xo_anchor_columns += cols;

    /* Before we fall into the basic logic below, we need reset len */
    len = ep - sp;
    if (len != 0) /* Append trailing data */
        xo_buf_append(xbp, sp, len);
}

/*
 * Append the given string to the given buffer, without escaping or
 * character set conversion.  This is the straight copy to the data
 * buffer with no fanciness.
 */
static void
xo_data_append (xo_handle_t *xop, const char *str, ssize_t len)
{
    xo_buf_append(&xop->xo_data, str, len);
}

/*
 * Append the given string to the given buffer
 */
static void
xo_data_escape (xo_handle_t *xop, const char *str, ssize_t len)
{
    xo_buf_escape(xop, &xop->xo_data, str, len, 0);
}

#ifdef LIBXO_NO_RETAIN
/*
 * Empty implementations of the retain logic
 */

void
xo_retain_clear_all (void)
{
    return;
}

void
xo_retain_clear (const char *fmt UNUSED)
{
    return;
}
static void
xo_retain_add (const char *fmt UNUSED, xo_field_info_t *fields UNUSED,
                unsigned num_fields UNUSED)
{
    return;
}

static int
xo_retain_find (const char *fmt UNUSED, xo_field_info_t **valp UNUSED,
                 unsigned *nump UNUSED)
{
    return -1;
}

#else /* !LIBXO_NO_RETAIN */
/*
 * Retain: We retain parsed field definitions to enhance performance,
 * especially inside loops.  We depend on the caller treating the format
 * strings as immutable, so that we can retain pointers into them.  We
 * hold the pointers in a hash table, so allow quick access.  Retained
 * information is retained until xo_retain_clear is called.
 */

/*
 * xo_retain_entry_t holds information about one retained set of
 * parsed fields.
 */
typedef struct xo_retain_entry_s {
    struct xo_retain_entry_s *xre_next; /* Pointer to next (older) entry */
    unsigned long xre_hits;              /* Number of times we've hit */
    const char *xre_format;              /* Pointer to format string */
    unsigned xre_num_fields;             /* Number of fields saved */
    xo_field_info_t *xre_fields;         /* Pointer to fields */
} xo_retain_entry_t;

/*
 * xo_retain_t holds a complete set of parsed fields as a hash table.
 */
#ifndef XO_RETAIN_SIZE
#define XO_RETAIN_SIZE 6
#endif /* XO_RETAIN_SIZE */
#define RETAIN_HASH_SIZE (1<<XO_RETAIN_SIZE)

typedef struct xo_retain_s {
    xo_retain_entry_t *xr_bucket[RETAIN_HASH_SIZE];
} xo_retain_t;

static THREAD_LOCAL(xo_retain_t) xo_retain;
static THREAD_LOCAL(unsigned) xo_retain_count;

/*
 * Simple hash function based on Thomas Wang's paper.  The original is
 * gone, but an archive is available on the Way Back Machine:
 *
 * http://web.archive.org/web/20071223173210/\
 *     http://www.concentric.net/~Ttwang/tech/inthash.htm
 *
 * For our purposes, we can assume the low four bits are uninteresting
 * since any string less that 16 bytes wouldn't be worthy of
 * retaining.  We toss the high bits also, since these bits are likely
 * to be common among constant format strings.  We then run Wang's
 * algorithm, and cap the result at RETAIN_HASH_SIZE.
 */
static unsigned
xo_retain_hash (const char *fmt)
{
    volatile uintptr_t iptr = (uintptr_t) (const void *) fmt;

    /* Discard low four bits and high bits; they aren't interesting */
    uint32_t val = (uint32_t) ((iptr >> 4) & (((1 << 24) - 1)));

    val = (val ^ 61) ^ (val >> 16);
    val = val + (val << 3);
    val = val ^ (val >> 4);
    val = val * 0x3a8f05c5;     /* My large prime number */
    val = val ^ (val >> 15);
    val &= RETAIN_HASH_SIZE - 1;

    return val;
}       

/*
 * Walk all buckets, clearing all retained entries
 */
void
xo_retain_clear_all (void)
{
    int i;
    xo_retain_entry_t *xrep, *next;

    for (i = 0; i < RETAIN_HASH_SIZE; i++) {
        for (xrep = xo_retain.xr_bucket[i]; xrep; xrep = next) {
            next = xrep->xre_next;
            xo_free(xrep);
        }
        xo_retain.xr_bucket[i] = NULL;
    }
    xo_retain_count = 0;
}

/*
 * Walk all buckets, clearing all retained entries
 */
void
xo_retain_clear (const char *fmt)
{
    xo_retain_entry_t **xrepp;
    unsigned hash = xo_retain_hash(fmt);

    for (xrepp = &xo_retain.xr_bucket[hash]; *xrepp;
         xrepp = &(*xrepp)->xre_next) {
        if ((*xrepp)->xre_format == fmt) {
            *xrepp = (*xrepp)->xre_next;
            xo_retain_count -= 1;
            return;
        }
    }
}

/*
 * Search the hash for an entry matching 'fmt'; return it's fields.
 */
static int
xo_retain_find (const char *fmt, xo_field_info_t **valp, unsigned *nump)
{
    if (xo_retain_count == 0)
        return -1;

    unsigned hash = xo_retain_hash(fmt);
    xo_retain_entry_t *xrep;

    for (xrep = xo_retain.xr_bucket[hash]; xrep != NULL;
         xrep = xrep->xre_next) {
        if (xrep->xre_format == fmt) {
            *valp = xrep->xre_fields;
            *nump = xrep->xre_num_fields;
            xrep->xre_hits += 1;
            return 0;
        }
    }

    return -1;
}

static void
xo_retain_add (const char *fmt, xo_field_info_t *fields, unsigned num_fields)
{
    unsigned hash = xo_retain_hash(fmt);
    xo_retain_entry_t *xrep;
    ssize_t sz = sizeof(*xrep) + (num_fields + 1) * sizeof(*fields);
    xo_field_info_t *xfip;

    xrep = xo_realloc(NULL, sz);
    if (xrep == NULL)
        return;

    xfip = (xo_field_info_t *) &xrep[1];
    memcpy(xfip, fields, num_fields * sizeof(*fields));

    bzero(xrep, sizeof(*xrep));

    xrep->xre_format = fmt;
    xrep->xre_fields = xfip;
    xrep->xre_num_fields = num_fields;

    /* Record the field info in the retain bucket */
    xrep->xre_next = xo_retain.xr_bucket[hash];
    xo_retain.xr_bucket[hash] = xrep;
    xo_retain_count += 1;
}

#endif /* !LIBXO_NO_RETAIN */

/*
 * Generate a warning.  Normally, this is a text message written to
 * standard error.  If the XOF_WARN_XML flag is set, then we generate
 * XMLified content on standard output.
 */
static void
xo_warn_hcv (xo_handle_t *xop, int code, int check_warn,
             const char *fmt, va_list vap)
{
    xop = xo_default(xop);
    if (check_warn && !XOF_ISSET(xop, XOF_WARN))
        return;

    if (fmt == NULL)
        return;

    ssize_t len = strlen(fmt);
    ssize_t plen = xo_program ? strlen(xo_program) : 0;
    char *newfmt = alloca(len + 1 + plen + 2); /* NUL, and ": " */

    if (plen) {
        memcpy(newfmt, xo_program, plen);
        newfmt[plen++] = ':';
        newfmt[plen++] = ' ';
    }

    memcpy(newfmt + plen, fmt, len);
    newfmt[len + plen] = '\0';

    if (XOF_ISSET(xop, XOF_WARN_XML)) {
        static char err_open[] = "<error>";
        static char err_close[] = "</error>";
        static char msg_open[] = "<message>";
        static char msg_close[] = "</message>";

        xo_buffer_t *xbp = &xop->xo_data;

        xo_buf_append(xbp, err_open, sizeof(err_open) - 1);
        xo_buf_append(xbp, msg_open, sizeof(msg_open) - 1);

        va_list va_local;
        va_copy(va_local, vap);

        ssize_t left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
        ssize_t rc = vsnprintf(xbp->xb_curp, left, newfmt, vap);

        if (rc >= left) {
            if (!xo_buf_has_room(xbp, rc)) {
                va_end(va_local);
                return;
            }

            va_end(vap);        /* Reset vap to the start */
            va_copy(vap, va_local);

            left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
            rc = vsnprintf(xbp->xb_curp, left, fmt, vap);
        }

        va_end(va_local);

        rc = xo_escape_xml(xbp, rc, 1);
        xbp->xb_curp += rc;

        xo_buf_append(xbp, msg_close, sizeof(msg_close) - 1);
        xo_buf_append(xbp, err_close, sizeof(err_close) - 1);

        if (code >= 0) {
            const char *msg = strerror(code);

            if (msg) {
                xo_buf_append(xbp, ": ", 2);
                xo_buf_append(xbp, msg, strlen(msg));
            }
        }

        xo_buf_append(xbp, "\n", 1); /* Append newline and NUL to string */
        (void) xo_write(xop);

    } else {
        vfprintf(stderr, newfmt, vap);
        if (code >= 0) {
            const char *msg = strerror(code);

            if (msg)
                fprintf(stderr, ": %s", msg);
        }
        fprintf(stderr, "\n");
    }
}

void
xo_warn_hc (xo_handle_t *xop, int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(xop, code, 0, fmt, vap);
    va_end(vap);
}

void
xo_warn_c (int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(NULL, code, 0, fmt, vap);
    va_end(vap);
}

void
xo_warn (const char *fmt, ...)
{
    int code = errno;
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(NULL, code, 0, fmt, vap);
    va_end(vap);
}

void
xo_warnx (const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(NULL, -1, 0, fmt, vap);
    va_end(vap);
}

void
xo_err (int eval, const char *fmt, ...)
{
    int code = errno;
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(NULL, code, 0, fmt, vap);
    va_end(vap);
    xo_finish();
    exit(eval);
}

void
xo_errx (int eval, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(NULL, -1, 0, fmt, vap);
    va_end(vap);
    xo_finish();
    exit(eval);
}

void
xo_errc (int eval, int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(NULL, code, 0, fmt, vap);
    va_end(vap);
    xo_finish();
    exit(eval);
}

/*
 * Generate a warning.  Normally, this is a text message written to
 * standard error.  If the XOF_WARN_XML flag is set, then we generate
 * XMLified content on standard output.
 */
void
xo_message_hcv (xo_handle_t *xop, int code, const char *fmt, va_list vap)
{
    static char msg_open[] = "<message>";
    static char msg_close[] = "</message>";
    xo_buffer_t *xbp;
    ssize_t rc;
    va_list va_local;

    xop = xo_default(xop);

    if (fmt == NULL || *fmt == '\0')
        return;

    int need_nl = (fmt[strlen(fmt) - 1] != '\n');

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        xbp = &xop->xo_data;
        if (XOF_ISSET(xop, XOF_PRETTY))
            xo_buf_indent(xop, xop->xo_indent_by);
        xo_buf_append(xbp, msg_open, sizeof(msg_open) - 1);

        va_copy(va_local, vap);

        ssize_t left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);

        rc = vsnprintf(xbp->xb_curp, left, fmt, vap);
        if (rc >= left) {
            if (!xo_buf_has_room(xbp, rc)) {
                va_end(va_local);
                return;
            }

            va_end(vap);        /* Reset vap to the start */
            va_copy(vap, va_local);

            left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
            rc = vsnprintf(xbp->xb_curp, left, fmt, vap);
        }

        va_end(va_local);

        rc = xo_escape_xml(xbp, rc, 0);
        xbp->xb_curp += rc;

        if (need_nl && code > 0) {
            const char *msg = strerror(code);

            if (msg) {
                xo_buf_append(xbp, ": ", 2);
                xo_buf_append(xbp, msg, strlen(msg));
            }
        }

        if (need_nl)
            xo_buf_append(xbp, "\n", 1); /* Append newline and NUL to string */

        xo_buf_append(xbp, msg_close, sizeof(msg_close) - 1);

        if (XOF_ISSET(xop, XOF_PRETTY))
            xo_buf_append(xbp, "\n", 1); /* Append newline and NUL to string */

        (void) xo_write(xop);
        break;

    case XO_STYLE_HTML:
        {
            char buf[BUFSIZ], *bp = buf, *cp;
            ssize_t bufsiz = sizeof(buf);
            ssize_t rc2;

            va_copy(va_local, vap);

            rc = vsnprintf(bp, bufsiz, fmt, va_local);
            if (rc > bufsiz) {
                bufsiz = rc + BUFSIZ;
                bp = alloca(bufsiz);
                va_end(va_local);
                va_copy(va_local, vap);
                rc = vsnprintf(bp, bufsiz, fmt, va_local);
            }

            va_end(va_local);
            cp = bp + rc;

            if (need_nl) {
                rc2 = snprintf(cp, bufsiz - rc, "%s%s\n",
                               (code > 0) ? ": " : "",
                               (code > 0) ? strerror(code) : "");
                if (rc2 > 0)
                    rc += rc2;
            }

            xo_buf_append_div(xop, "message", 0, NULL, 0, bp, rc,
                              NULL, 0, NULL, 0);
        }
        break;

    case XO_STYLE_JSON:
    case XO_STYLE_SDPARAMS:
    case XO_STYLE_ENCODER:
        /* No means of representing messages */
        return;

    case XO_STYLE_TEXT:
        rc = xo_printf_v(xop, fmt, vap);
        /*
         * XXX need to handle UTF-8 widths
         */
        if (rc > 0) {
            if (XOF_ISSET(xop, XOF_COLUMNS))
                xop->xo_columns += rc;
            if (XOIF_ISSET(xop, XOIF_ANCHOR))
                xop->xo_anchor_columns += rc;
        }

        if (need_nl && code > 0) {
            const char *msg = strerror(code);

            if (msg) {
                xo_printf(xop, ": %s", msg);
            }
        }
        if (need_nl)
            xo_printf(xop, "\n");

        break;
    }

    switch (xo_style(xop)) {
    case XO_STYLE_HTML:
        if (XOIF_ISSET(xop, XOIF_DIV_OPEN)) {
            static char div_close[] = "</div>";

            XOIF_CLEAR(xop, XOIF_DIV_OPEN);
            xo_data_append(xop, div_close, sizeof(div_close) - 1);

            if (XOF_ISSET(xop, XOF_PRETTY))
                xo_data_append(xop, "\n", 1);
        }
        break;
    }

    (void) xo_flush_h(xop);
}

void
xo_message_hc (xo_handle_t *xop, int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_message_hcv(xop, code, fmt, vap);
    va_end(vap);
}

void
xo_message_c (int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_message_hcv(NULL, code, fmt, vap);
    va_end(vap);
}

void
xo_message_e (const char *fmt, ...)
{
    int code = errno;
    va_list vap;

    va_start(vap, fmt);
    xo_message_hcv(NULL, code, fmt, vap);
    va_end(vap);
}

void
xo_message (const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_message_hcv(NULL, 0, fmt, vap);
    va_end(vap);
}

static void
xo_failure (xo_handle_t *xop, const char *fmt, ...)
{
    if (!XOF_ISSET(xop, XOF_WARN))
        return;

    va_list vap;

    va_start(vap, fmt);
    xo_warn_hcv(xop, -1, 1, fmt, vap);
    va_end(vap);
}

/**
 * Create a handle for use by later libxo functions.
 *
 * Note: normal use of libxo does not require a distinct handle, since
 * the default handle (used when NULL is passed) generates text on stdout.
 *
 * @param style Style of output desired (XO_STYLE_* value)
 * @param flags Set of XOF_* flags in use with this handle
 * @return Newly allocated handle
 * @see xo_destroy
 */
xo_handle_t *
xo_create (xo_style_t style, xo_xof_flags_t flags)
{
    xo_handle_t *xop = xo_realloc(NULL, sizeof(*xop));

    if (xop) {
        bzero(xop, sizeof(*xop));

        xop->xo_style = style;
        XOF_SET(xop, flags);
        xo_init_handle(xop);
        xop->xo_style = style;  /* Reset style (see LIBXO_OPTIONS) */
    }

    return xop;
}

/**
 * Create a handle that will write to the given file.  Use
 * the XOF_CLOSE_FP flag to have the file closed on xo_destroy().
 *
 * @param fp FILE pointer to use
 * @param style Style of output desired (XO_STYLE_* value)
 * @param flags Set of XOF_* flags to use with this handle
 * @return Newly allocated handle
 * @see xo_destroy
 */
xo_handle_t *
xo_create_to_file (FILE *fp, xo_style_t style, xo_xof_flags_t flags)
{
    xo_handle_t *xop = xo_create(style, flags);

    if (xop) {
        xop->xo_opaque = fp;
        xop->xo_write = xo_write_to_file;
        xop->xo_close = xo_close_file;
        xop->xo_flush = xo_flush_file;
    }

    return xop;
}

/**
 * Set the default handler to output to a file.
 *
 * @param xop libxo handle
 * @param fp FILE pointer to use
 * @return 0 on success, non-zero on failure
 */
int
xo_set_file_h (xo_handle_t *xop, FILE *fp)
{
    xop = xo_default(xop);

    if (fp == NULL) {
        xo_failure(xop, "xo_set_file: NULL fp");
        return -1;
    }

    xop->xo_opaque = fp;
    xop->xo_write = xo_write_to_file;
    xop->xo_close = xo_close_file;
    xop->xo_flush = xo_flush_file;

    return 0;
}

/**
 * Set the default handler to output to a file.
 *
 * @param fp FILE pointer to use
 * @return 0 on success, non-zero on failure
 */
int
xo_set_file (FILE *fp)
{
    return xo_set_file_h(NULL, fp);
}

/**
 * Release any resources held by the handle.
 *
 * @param xop XO handle to alter (or NULL for default handle)
 */
void
xo_destroy (xo_handle_t *xop_arg)
{
    xo_handle_t *xop = xo_default(xop_arg);

    xo_flush_h(xop);

    if (xop->xo_close && XOF_ISSET(xop, XOF_CLOSE_FP))
        xop->xo_close(xop->xo_opaque);

    xo_free(xop->xo_stack);
    xo_buf_cleanup(&xop->xo_data);
    xo_buf_cleanup(&xop->xo_fmt);
    xo_buf_cleanup(&xop->xo_predicate);
    xo_buf_cleanup(&xop->xo_attrs);
    xo_buf_cleanup(&xop->xo_color_buf);

    if (xop->xo_version)
        xo_free(xop->xo_version);

    if (xop_arg == NULL) {
        bzero(&xo_default_handle, sizeof(xo_default_handle));
        xo_default_inited = 0;
    } else
        xo_free(xop);
}

/**
 * Record a new output style to use for the given handle (or default if
 * handle is NULL).  This output style will be used for any future output.
 *
 * @param xop XO handle to alter (or NULL for default handle)
 * @param style new output style (XO_STYLE_*)
 */
void
xo_set_style (xo_handle_t *xop, xo_style_t style)
{
    xop = xo_default(xop);
    xop->xo_style = style;
}

/**
 * Return the current style of a handle
 *
 * @param xop XO handle to access
 * @return The handle's current style
 */
xo_style_t
xo_get_style (xo_handle_t *xop)
{
    xop = xo_default(xop);
    return xo_style(xop);
}

/**
 * Return the XO_STYLE_* value matching a given name
 *
 * @param name String name of a style
 * @return XO_STYLE_* value
 */
static int
xo_name_to_style (const char *name)
{
    if (strcmp(name, "xml") == 0)
        return XO_STYLE_XML;
    else if (strcmp(name, "json") == 0)
        return XO_STYLE_JSON;
    else if (strcmp(name, "encoder") == 0)
        return XO_STYLE_ENCODER;
    else if (strcmp(name, "text") == 0)
        return XO_STYLE_TEXT;
    else if (strcmp(name, "html") == 0)
        return XO_STYLE_HTML;
    else if (strcmp(name, "sdparams") == 0)
        return XO_STYLE_SDPARAMS;

    return -1;
}

/*
 * Indicate if the style is an "encoding" one as opposed to a "display" one.
 */
static int
xo_style_is_encoding (xo_handle_t *xop)
{
    if (xo_style(xop) == XO_STYLE_JSON
        || xo_style(xop) == XO_STYLE_XML
        || xo_style(xop) == XO_STYLE_SDPARAMS
        || xo_style(xop) == XO_STYLE_ENCODER)
        return 1;
    return 0;
}

/* Simple name-value mapping */
typedef struct xo_mapping_s {
    xo_xff_flags_t xm_value;    /* Flag value */
    const char *xm_name;        /* String name */
} xo_mapping_t;

static xo_xff_flags_t
xo_name_lookup (xo_mapping_t *map, const char *value, ssize_t len)
{
    if (len == 0)
        return 0;

    if (len < 0)
        len = strlen(value);

    while (isspace((int) *value)) {
        value += 1;
        len -= 1;
    }

    while (isspace((int) value[len]))
        len -= 1;

    if (*value == '\0')
        return 0;

    for ( ; map->xm_name; map++)
        if (strncmp(map->xm_name, value, len) == 0)
            return map->xm_value;

    return 0;
}

#ifdef NOT_NEEDED_YET
static const char *
xo_value_lookup (xo_mapping_t *map, xo_xff_flags_t value)
{
    if (value == 0)
        return NULL;

    for ( ; map->xm_name; map++)
        if (map->xm_value == value)
            return map->xm_name;

    return NULL;
}
#endif /* NOT_NEEDED_YET */

static xo_mapping_t xo_xof_names[] = {
    { XOF_COLOR_ALLOWED, "color" },
    { XOF_COLOR, "color-force" },
    { XOF_COLUMNS, "columns" },
    { XOF_DTRT, "dtrt" },
    { XOF_FLUSH, "flush" },
    { XOF_FLUSH_LINE, "flush-line" },
    { XOF_IGNORE_CLOSE, "ignore-close" },
    { XOF_INFO, "info" },
    { XOF_KEYS, "keys" },
    { XOF_LOG_GETTEXT, "log-gettext" },
    { XOF_LOG_SYSLOG, "log-syslog" },
    { XOF_NO_HUMANIZE, "no-humanize" },
    { XOF_NO_LOCALE, "no-locale" },
    { XOF_RETAIN_NONE, "no-retain" },
    { XOF_NO_TOP, "no-top" },
    { XOF_NOT_FIRST, "not-first" },
    { XOF_PRETTY, "pretty" },
    { XOF_RETAIN_ALL, "retain" },
    { XOF_UNDERSCORES, "underscores" },
    { XOF_UNITS, "units" },
    { XOF_WARN, "warn" },
    { XOF_WARN_XML, "warn-xml" },
    { XOF_XPATH, "xpath" },
    { 0, NULL }
};

/* Options available via the environment variable ($LIBXO_OPTIONS) */
static xo_mapping_t xo_xof_simple_names[] = {
    { XOF_COLOR_ALLOWED, "color" },
    { XOF_FLUSH, "flush" },
    { XOF_FLUSH_LINE, "flush-line" },
    { XOF_NO_HUMANIZE, "no-humanize" },
    { XOF_NO_LOCALE, "no-locale" },
    { XOF_RETAIN_NONE, "no-retain" },
    { XOF_PRETTY, "pretty" },
    { XOF_RETAIN_ALL, "retain" },
    { XOF_UNDERSCORES, "underscores" },
    { XOF_WARN, "warn" },
    { 0, NULL }
};

/*
 * Convert string name to XOF_* flag value.
 * Not all are useful.  Or safe.  Or sane.
 */
static unsigned
xo_name_to_flag (const char *name)
{
    return (unsigned) xo_name_lookup(xo_xof_names, name, -1);
}

/**
 * Set the style of an libxo handle based on a string name
 *
 * @param xop XO handle
 * @param name String value of name
 * @return 0 on success, non-zero on failure
 */
int
xo_set_style_name (xo_handle_t *xop, const char *name)
{
    if (name == NULL)
        return -1;

    int style = xo_name_to_style(name);

    if (style < 0)
        return -1;

    xo_set_style(xop, style);
    return 0;
}

/*
 * Fill in the color map, based on the input string; currently unimplemented
 * Look for something like "colors=red/blue+green/yellow" as fg/bg pairs.
 */
static void
xo_set_color_map (xo_handle_t *xop, char *value)
{
    if (xo_text_only())
        return;

    char *cp, *ep, *vp, *np;
    ssize_t len = value ? strlen(value) + 1 : 0;
    int num = 1, fg, bg;

    for (cp = value, ep = cp + len - 1; cp && *cp && cp < ep; cp = np) {
        np = strchr(cp, '+');
        if (np)
            *np++ = '\0';

        vp = strchr(cp, '/');
        if (vp)
            *vp++ = '\0';

        fg = *cp ? xo_color_find(cp) : -1;
        bg = (vp && *vp) ? xo_color_find(vp) : -1;

#ifndef LIBXO_TEXT_ONLY
        xop->xo_color_map_fg[num] = (fg < 0) ? num : fg;
        xop->xo_color_map_bg[num] = (bg < 0) ? num : bg;
#endif /* LIBXO_TEXT_ONLY */

        if (++num > XO_NUM_COLORS)
            break;
    }

    /* If no color initialization happened, then we don't need the map */
    if (num > 0)
        XOF_SET(xop, XOF_COLOR_MAP);
    else
        XOF_CLEAR(xop, XOF_COLOR_MAP);

#ifndef LIBXO_TEXT_ONLY
    /* Fill in the rest of the colors with the defaults */
    for ( ; num < XO_NUM_COLORS; num++)
        xop->xo_color_map_fg[num] = xop->xo_color_map_bg[num] = num;
#endif /* LIBXO_TEXT_ONLY */
}

static int
xo_set_options_simple (xo_handle_t *xop, const char *input)
{
    xo_xof_flags_t new_flag;
    char *cp, *ep, *vp, *np, *bp;
    ssize_t len = strlen(input) + 1;

    bp = alloca(len);
    memcpy(bp, input, len);

    for (cp = bp, ep = cp + len - 1; cp && cp < ep; cp = np) {
        np = strchr(cp, ',');
        if (np)
            *np++ = '\0';

        vp = strchr(cp, '=');
        if (vp)
            *vp++ = '\0';

        if (strcmp("colors", cp) == 0) {
            xo_set_color_map(xop, vp);
            continue;
        }

        new_flag = xo_name_lookup(xo_xof_simple_names, cp, -1);
        if (new_flag != 0) {
            XOF_SET(xop, new_flag);
        } else if (strcmp(cp, "no-color") == 0) {
            XOF_CLEAR(xop, XOF_COLOR_ALLOWED);
        } else {
            xo_failure(xop, "unknown simple option: %s", cp);
            return -1;
        }
    }

    return 0;
}

/**
 * Set the options for a handle using a string of options
 * passed in.  The input is a comma-separated set of names
 * and optional values: "xml,pretty,indent=4"
 *
 * @param xop XO handle
 * @param input Comma-separated set of option values
 * @return 0 on success, non-zero on failure
 */
int
xo_set_options (xo_handle_t *xop, const char *input)
{
    char *cp, *ep, *vp, *np, *bp;
    int style = -1, new_style, rc = 0;
    ssize_t len;
    xo_xof_flags_t new_flag;

    if (input == NULL)
        return 0;

    xop = xo_default(xop);

#ifdef LIBXO_COLOR_ON_BY_DEFAULT
    /* If the installer used --enable-color-on-by-default, then we allow it */
    XOF_SET(xop, XOF_COLOR_ALLOWED);
#endif /* LIBXO_COLOR_ON_BY_DEFAULT */

    /*
     * We support a simpler, old-school style of giving option
     * also, using a single character for each option.  It's
     * ideal for lazy people, such as myself.
     */
    if (*input == ':') {
        ssize_t sz;

        for (input++ ; *input; input++) {
            switch (*input) {
            case 'c':
                XOF_SET(xop, XOF_COLOR_ALLOWED);
                break;

            case 'f':
                XOF_SET(xop, XOF_FLUSH);
                break;

            case 'F':
                XOF_SET(xop, XOF_FLUSH_LINE);
                break;

            case 'g':
                XOF_SET(xop, XOF_LOG_GETTEXT);
                break;

            case 'H':
                xop->xo_style = XO_STYLE_HTML;
                break;

            case 'I':
                XOF_SET(xop, XOF_INFO);
                break;

            case 'i':
                sz = strspn(input + 1, "0123456789");
                if (sz > 0) {
                    xop->xo_indent_by = atoi(input + 1);
                    input += sz - 1;    /* Skip value */
                }
                break;

            case 'J':
                xop->xo_style = XO_STYLE_JSON;
                break;

            case 'k':
                XOF_SET(xop, XOF_KEYS);
                break;

            case 'n':
                XOF_SET(xop, XOF_NO_HUMANIZE);
                break;

            case 'P':
                XOF_SET(xop, XOF_PRETTY);
                break;

            case 'T':
                xop->xo_style = XO_STYLE_TEXT;
                break;

            case 'U':
                XOF_SET(xop, XOF_UNITS);
                break;

            case 'u':
                XOF_SET(xop, XOF_UNDERSCORES);
                break;

            case 'W':
                XOF_SET(xop, XOF_WARN);
                break;

            case 'X':
                xop->xo_style = XO_STYLE_XML;
                break;

            case 'x':
                XOF_SET(xop, XOF_XPATH);
                break;
            }
        }
        return 0;
    }

    len = strlen(input) + 1;
    bp = alloca(len);
    memcpy(bp, input, len);

    for (cp = bp, ep = cp + len - 1; cp && cp < ep; cp = np) {
        np = strchr(cp, ',');
        if (np)
            *np++ = '\0';

        vp = strchr(cp, '=');
        if (vp)
            *vp++ = '\0';

        if (strcmp("colors", cp) == 0) {
            xo_set_color_map(xop, vp);
            continue;
        }

        /*
         * For options, we don't allow "encoder" since we want to
         * handle it explicitly below as "encoder=xxx".
         */
        new_style = xo_name_to_style(cp);
        if (new_style >= 0 && new_style != XO_STYLE_ENCODER) {
            if (style >= 0)
                xo_warnx("ignoring multiple styles: '%s'", cp);
            else
                style = new_style;
        } else {
            new_flag = xo_name_to_flag(cp);
            if (new_flag != 0)
                XOF_SET(xop, new_flag);
            else if (strcmp(cp, "no-color") == 0)
                XOF_CLEAR(xop, XOF_COLOR_ALLOWED);
            else if (strcmp(cp, "indent") == 0) {
                if (vp)
                    xop->xo_indent_by = atoi(vp);
                else
                    xo_failure(xop, "missing value for indent option");
            } else if (strcmp(cp, "encoder") == 0) {
                if (vp == NULL)
                    xo_failure(xop, "missing value for encoder option");
                else {
                    if (xo_encoder_init(xop, vp)) {
                        xo_failure(xop, "encoder not found: %s", vp);
                        rc = -1;
                    }
                }
                
            } else {
                xo_warnx("unknown libxo option value: '%s'", cp);
                rc = -1;
            }
        }
    }

    if (style > 0)
        xop->xo_style= style;

    return rc;
}

/**
 * Set one or more flags for a given handle (or default if handle is NULL).
 * These flags will affect future output.
 *
 * @param xop XO handle to alter (or NULL for default handle)
 * @param flags Flags to be set (XOF_*)
 */
void
xo_set_flags (xo_handle_t *xop, xo_xof_flags_t flags)
{
    xop = xo_default(xop);

    XOF_SET(xop, flags);
}

/**
 * Accessor to return the current set of flags for a handle
 * @param xop XO handle
 * @return Current set of flags
 */
xo_xof_flags_t
xo_get_flags (xo_handle_t *xop)
{
    xop = xo_default(xop);

    return xop->xo_flags;
}

/**
 * strndup with a twist: len < 0 means len = strlen(str)
 */
static char *
xo_strndup (const char *str, ssize_t len)
{
    if (len < 0)
        len = strlen(str);

    char *cp = xo_realloc(NULL, len + 1);
    if (cp) {
        memcpy(cp, str, len);
        cp[len] = '\0';
    }

    return cp;
}

/**
 * Record a leading prefix for the XPath we generate.  This allows the
 * generated data to be placed within an XML hierarchy but still have
 * accurate XPath expressions.
 *
 * @param xop XO handle to alter (or NULL for default handle)
 * @param path The XPath expression
 */
void
xo_set_leading_xpath (xo_handle_t *xop, const char *path)
{
    xop = xo_default(xop);

    if (xop->xo_leading_xpath) {
        xo_free(xop->xo_leading_xpath);
        xop->xo_leading_xpath = NULL;
    }

    if (path == NULL)
        return;

    xop->xo_leading_xpath = xo_strndup(path, -1);
}

/**
 * Record the info data for a set of tags
 *
 * @param xop XO handle to alter (or NULL for default handle)
 * @param info Info data (xo_info_t) to be recorded (or NULL) (MUST BE SORTED)
 * @pararm count Number of entries in info (or -1 to count them ourselves)
 */
void
xo_set_info (xo_handle_t *xop, xo_info_t *infop, int count)
{
    xop = xo_default(xop);

    if (count < 0 && infop) {
        xo_info_t *xip;

        for (xip = infop, count = 0; xip->xi_name; xip++, count++)
            continue;
    }

    xop->xo_info = infop;
    xop->xo_info_count = count;
}

/**
 * Set the formatter callback for a handle.  The callback should
 * return a newly formatting contents of a formatting instruction,
 * meaning the bits inside the braces.
 */
void
xo_set_formatter (xo_handle_t *xop, xo_formatter_t func,
                  xo_checkpointer_t cfunc)
{
    xop = xo_default(xop);

    xop->xo_formatter = func;
    xop->xo_checkpointer = cfunc;
}

/**
 * Clear one or more flags for a given handle (or default if handle is NULL).
 * These flags will affect future output.
 *
 * @param xop XO handle to alter (or NULL for default handle)
 * @param flags Flags to be cleared (XOF_*)
 */
void
xo_clear_flags (xo_handle_t *xop, xo_xof_flags_t flags)
{
    xop = xo_default(xop);

    XOF_CLEAR(xop, flags);
}

static const char *
xo_state_name (xo_state_t state)
{
    static const char *names[] = {
        "init",
        "open_container",
        "close_container",
        "open_list",
        "close_list",
        "open_instance",
        "close_instance",
        "open_leaf_list",
        "close_leaf_list",
        "discarding",
        "marker",
        "emit",
        "emit_leaf_list",
        "finish",
        NULL
    };

    if (state < (sizeof(names) / sizeof(names[0])))
        return names[state];

    return "unknown";
}

static void
xo_line_ensure_open (xo_handle_t *xop, xo_xff_flags_t flags UNUSED)
{
    static char div_open[] = "<div class=\"line\">";
    static char div_open_blank[] = "<div class=\"blank-line\">";

    if (XOF_ISSET(xop, XOF_CONTINUATION)) {
        XOF_CLEAR(xop, XOF_CONTINUATION);
        XOIF_SET(xop, XOIF_DIV_OPEN);
        return;
    }

    if (XOIF_ISSET(xop, XOIF_DIV_OPEN))
        return;

    if (xo_style(xop) != XO_STYLE_HTML)
        return;

    XOIF_SET(xop, XOIF_DIV_OPEN);
    if (flags & XFF_BLANK_LINE)
        xo_data_append(xop, div_open_blank, sizeof(div_open_blank) - 1);
    else
        xo_data_append(xop, div_open, sizeof(div_open) - 1);

    if (XOF_ISSET(xop, XOF_PRETTY))
        xo_data_append(xop, "\n", 1);
}

static void
xo_line_close (xo_handle_t *xop)
{
    static char div_close[] = "</div>";

    switch (xo_style(xop)) {
    case XO_STYLE_HTML:
        if (!XOIF_ISSET(xop, XOIF_DIV_OPEN))
            xo_line_ensure_open(xop, 0);

        XOIF_CLEAR(xop, XOIF_DIV_OPEN);
        xo_data_append(xop, div_close, sizeof(div_close) - 1);

        if (XOF_ISSET(xop, XOF_PRETTY))
            xo_data_append(xop, "\n", 1);
        break;

    case XO_STYLE_TEXT:
        xo_data_append(xop, "\n", 1);
        break;
    }
}

static int
xo_info_compare (const void *key, const void *data)
{
    const char *name = key;
    const xo_info_t *xip = data;

    return strcmp(name, xip->xi_name);
}


static xo_info_t *
xo_info_find (xo_handle_t *xop, const char *name, ssize_t nlen)
{
    xo_info_t *xip;
    char *cp = alloca(nlen + 1); /* Need local copy for NUL termination */

    memcpy(cp, name, nlen);
    cp[nlen] = '\0';

    xip = bsearch(cp, xop->xo_info, xop->xo_info_count,
                  sizeof(xop->xo_info[0]), xo_info_compare);
    return xip;
}

#define CONVERT(_have, _need) (((_have) << 8) | (_need))

/*
 * Check to see that the conversion is safe and sane.
 */
static int
xo_check_conversion (xo_handle_t *xop, int have_enc, int need_enc)
{
    switch (CONVERT(have_enc, need_enc)) {
    case CONVERT(XF_ENC_UTF8, XF_ENC_UTF8):
    case CONVERT(XF_ENC_UTF8, XF_ENC_LOCALE):
    case CONVERT(XF_ENC_WIDE, XF_ENC_UTF8):
    case CONVERT(XF_ENC_WIDE, XF_ENC_LOCALE):
    case CONVERT(XF_ENC_LOCALE, XF_ENC_LOCALE):
    case CONVERT(XF_ENC_LOCALE, XF_ENC_UTF8):
        return 0;

    default:
        xo_failure(xop, "invalid conversion (%c:%c)", have_enc, need_enc);
        return 1;
    }
}

static int
xo_format_string_direct (xo_handle_t *xop, xo_buffer_t *xbp,
                         xo_xff_flags_t flags,
                         const wchar_t *wcp, const char *cp,
                         ssize_t len, int max,
                         int need_enc, int have_enc)
{
    int cols = 0;
    wchar_t wc = 0;
    ssize_t ilen, olen;
    ssize_t width;
    int attr = XOF_BIT_ISSET(flags, XFF_ATTR);
    const char *sp;

    if (len > 0 && !xo_buf_has_room(xbp, len))
        return 0;

    for (;;) {
        if (len == 0)
            break;

        if (cp) {
            if (*cp == '\0')
                break;
            if ((flags & XFF_UNESCAPE) && (*cp == '\\' || *cp == '%')) {
                cp += 1;
                len -= 1;
                if (len == 0 || *cp == '\0')
                    break;
            }
        }

        if (wcp && *wcp == L'\0')
            break;

        ilen = 0;

        switch (have_enc) {
        case XF_ENC_WIDE:               /* Wide character */
            wc = *wcp++;
            ilen = 1;
            break;

        case XF_ENC_UTF8:               /* UTF-8 */
            ilen = xo_utf8_to_wc_len(cp);
            if (ilen < 0) {
                xo_failure(xop, "invalid UTF-8 character: %02hhx", *cp);
                return -1;      /* Can't continue; we can't find the end */
            }

            if (len > 0 && len < ilen) {
                len = 0;        /* Break out of the loop */
                continue;
            }

            wc = xo_utf8_char(cp, ilen);
            if (wc == (wchar_t) -1) {
                xo_failure(xop, "invalid UTF-8 character: %02hhx/%d",
                           *cp, ilen);
                return -1;      /* Can't continue; we can't find the end */
            }
            cp += ilen;
            break;

        case XF_ENC_LOCALE:             /* Native locale */
            ilen = (len > 0) ? len : MB_LEN_MAX;
            ilen = mbrtowc(&wc, cp, ilen, &xop->xo_mbstate);
            if (ilen < 0) {             /* Invalid data; skip */
                xo_failure(xop, "invalid mbs char: %02hhx", *cp);
                wc = L'?';
                ilen = 1;
            }

            if (ilen == 0) {            /* Hit a wide NUL character */
                len = 0;
                continue;
            }

            cp += ilen;
            break;
        }

        /* Reduce len, but not below zero */
        if (len > 0) {
            len -= ilen;
            if (len < 0)
                len = 0;
        }

        /*
         * Find the width-in-columns of this character, which must be done
         * in wide characters, since we lack a mbswidth() function.  If
         * it doesn't fit
         */
        width = xo_wcwidth(wc);
        if (width < 0)
            width = iswcntrl(wc) ? 0 : 1;

        if (xo_style(xop) == XO_STYLE_TEXT || xo_style(xop) == XO_STYLE_HTML) {
            if (max > 0 && cols + width > max)
                break;
        }

        switch (need_enc) {
        case XF_ENC_UTF8:

            /* Output in UTF-8 needs to be escaped, based on the style */
            switch (xo_style(xop)) {
            case XO_STYLE_XML:
            case XO_STYLE_HTML:
                if (wc == '<')
                    sp = xo_xml_lt;
                else if (wc == '>')
                    sp = xo_xml_gt;
                else if (wc == '&')
                    sp = xo_xml_amp;
                else if (attr && wc == '"')
                    sp = xo_xml_quot;
                else
                    break;

                ssize_t slen = strlen(sp);
                if (!xo_buf_has_room(xbp, slen - 1))
                    return -1;

                memcpy(xbp->xb_curp, sp, slen);
                xbp->xb_curp += slen;
                goto done_with_encoding; /* Need multi-level 'break' */

            case XO_STYLE_JSON:
                if (wc != '\\' && wc != '"' && wc != '\n' && wc != '\r')
                    break;

                if (!xo_buf_has_room(xbp, 2))
                    return -1;

                *xbp->xb_curp++ = '\\';
                if (wc == '\n')
                    wc = 'n';
                else if (wc == '\r')
                    wc = 'r';
                else wc = wc & 0x7f;

                *xbp->xb_curp++ = wc;
                goto done_with_encoding;

            case XO_STYLE_SDPARAMS:
                if (wc != '\\' && wc != '"' && wc != ']')
                    break;

                if (!xo_buf_has_room(xbp, 2))
                    return -1;

                *xbp->xb_curp++ = '\\';
                wc = wc & 0x7f;
                *xbp->xb_curp++ = wc;
                goto done_with_encoding;
            }

            olen = xo_utf8_emit_len(wc);
            if (olen < 0) {
                xo_failure(xop, "ignoring bad length");
                continue;
            }

            if (!xo_buf_has_room(xbp, olen))
                return -1;

            xo_utf8_emit_char(xbp->xb_curp, olen, wc);
            xbp->xb_curp += olen;
            break;

        case XF_ENC_LOCALE:
            if (!xo_buf_has_room(xbp, MB_LEN_MAX + 1))
                return -1;

            olen = wcrtomb(xbp->xb_curp, wc, &xop->xo_mbstate);
            if (olen <= 0) {
                xo_failure(xop, "could not convert wide char: %lx",
                           (unsigned long) wc);
                width = 1;
                *xbp->xb_curp++ = '?';
            } else
                xbp->xb_curp += olen;
            break;
        }

    done_with_encoding:
        cols += width;
    }

    return cols;
}

static int
xo_needed_encoding (xo_handle_t *xop)
{
    if (XOF_ISSET(xop, XOF_UTF8)) /* Check the override flag */
        return XF_ENC_UTF8;

    if (xo_style(xop) == XO_STYLE_TEXT) /* Text means locale */
        return XF_ENC_LOCALE;

    return XF_ENC_UTF8;         /* Otherwise, we love UTF-8 */
}

static ssize_t
xo_format_string (xo_handle_t *xop, xo_buffer_t *xbp, xo_xff_flags_t flags,
                  xo_format_t *xfp)
{
    static char null[] = "(null)";
    static char null_no_quotes[] = "null";

    char *cp = NULL;
    wchar_t *wcp = NULL;
    ssize_t len;
    ssize_t cols = 0, rc = 0;
    ssize_t off = xbp->xb_curp - xbp->xb_bufp, off2;
    int need_enc = xo_needed_encoding(xop);

    if (xo_check_conversion(xop, xfp->xf_enc, need_enc))
        return 0;

    len = xfp->xf_width[XF_WIDTH_SIZE];

    if (xfp->xf_fc == 'm') {
        cp = strerror(xop->xo_errno);
        if (len < 0)
            len = cp ? strlen(cp) : 0;
        goto normal_string;

    } else if (xfp->xf_enc == XF_ENC_WIDE) {
        wcp = va_arg(xop->xo_vap, wchar_t *);
        if (xfp->xf_skip)
            return 0;

        /*
         * Dont' deref NULL; use the traditional "(null)" instead
         * of the more accurate "who's been a naughty boy, then?".
         */
        if (wcp == NULL) {
            cp = null;
            len = sizeof(null) - 1;
        }

    } else {
        cp = va_arg(xop->xo_vap, char *); /* UTF-8 or native */

    normal_string:
        if (xfp->xf_skip)
            return 0;

        /* Echo "Dont' deref NULL" logic */
        if (cp == NULL) {
            if ((flags & XFF_NOQUOTE) && xo_style_is_encoding(xop)) {
                cp = null_no_quotes;
                len = sizeof(null_no_quotes) - 1;
            } else {
                cp = null;
                len = sizeof(null) - 1;
            }
        }

        /*
         * Optimize the most common case, which is "%s".  We just
         * need to copy the complete string to the output buffer.
         */
        if (xfp->xf_enc == need_enc
                && xfp->xf_width[XF_WIDTH_MIN] < 0
                && xfp->xf_width[XF_WIDTH_SIZE] < 0
                && xfp->xf_width[XF_WIDTH_MAX] < 0
                && !(XOIF_ISSET(xop, XOIF_ANCHOR)
                     || XOF_ISSET(xop, XOF_COLUMNS))) {
            len = strlen(cp);
            xo_buf_escape(xop, xbp, cp, len, flags);

            /*
             * Our caller expects xb_curp left untouched, so we have
             * to reset it and return the number of bytes written to
             * the buffer.
             */
            off2 = xbp->xb_curp - xbp->xb_bufp;
            rc = off2 - off;
            xbp->xb_curp = xbp->xb_bufp + off;

            return rc;
        }
    }

    cols = xo_format_string_direct(xop, xbp, flags, wcp, cp, len,
                                   xfp->xf_width[XF_WIDTH_MAX],
                                   need_enc, xfp->xf_enc);
    if (cols < 0)
        goto bail;

    /*
     * xo_buf_append* will move xb_curp, so we save/restore it.
     */
    off2 = xbp->xb_curp - xbp->xb_bufp;
    rc = off2 - off;
    xbp->xb_curp = xbp->xb_bufp + off;

    if (cols < xfp->xf_width[XF_WIDTH_MIN]) {
        /*
         * Find the number of columns needed to display the string.
         * If we have the original wide string, we just call wcswidth,
         * but if we did the work ourselves, then we need to do it.
         */
        int delta = xfp->xf_width[XF_WIDTH_MIN] - cols;
        if (!xo_buf_has_room(xbp, xfp->xf_width[XF_WIDTH_MIN]))
            goto bail;

        /*
         * If seen_minus, then pad on the right; otherwise move it so
         * we can pad on the left.
         */
        if (xfp->xf_seen_minus) {
            cp = xbp->xb_curp + rc;
        } else {
            cp = xbp->xb_curp;
            memmove(xbp->xb_curp + delta, xbp->xb_curp, rc);
        }

        /* Set the padding */
        memset(cp, (xfp->xf_leading_zero > 0) ? '0' : ' ', delta);
        rc += delta;
        cols += delta;
    }

    if (XOF_ISSET(xop, XOF_COLUMNS))
        xop->xo_columns += cols;
    if (XOIF_ISSET(xop, XOIF_ANCHOR))
        xop->xo_anchor_columns += cols;

    return rc;

 bail:
    xbp->xb_curp = xbp->xb_bufp + off;
    return 0;
}

/*
 * Look backwards in a buffer to find a numeric value
 */
static int
xo_buf_find_last_number (xo_buffer_t *xbp, ssize_t start_offset)
{
    int rc = 0;                 /* Fail with zero */
    int digit = 1;
    char *sp = xbp->xb_bufp;
    char *cp = sp + start_offset;

    while (--cp >= sp)
        if (isdigit((int) *cp))
            break;

    for ( ; cp >= sp; cp--) {
        if (!isdigit((int) *cp))
            break;
        rc += (*cp - '0') * digit;
        digit *= 10;
    }

    return rc;
}

static ssize_t
xo_count_utf8_cols (const char *str, ssize_t len)
{
    ssize_t tlen;
    wchar_t wc;
    ssize_t cols = 0;
    const char *ep = str + len;

    while (str < ep) {
        tlen = xo_utf8_to_wc_len(str);
        if (tlen < 0)           /* Broken input is very bad */
            return cols;

        wc = xo_utf8_char(str, tlen);
        if (wc == (wchar_t) -1)
            return cols;

        /* We only print printable characters */
        if (iswprint((wint_t) wc)) {
            /*
             * Find the width-in-columns of this character, which must be done
             * in wide characters, since we lack a mbswidth() function.
             */
            ssize_t width = xo_wcwidth(wc);
            if (width < 0)
                width = iswcntrl(wc) ? 0 : 1;

            cols += width;
        }

        str += tlen;
    }

    return cols;
}

#ifdef HAVE_GETTEXT
static inline const char *
xo_dgettext (xo_handle_t *xop, const char *str)
{
    const char *domainname = xop->xo_gt_domain;
    const char *res;

    res = dgettext(domainname, str);

    if (XOF_ISSET(xop, XOF_LOG_GETTEXT))
        fprintf(stderr, "xo: gettext: %s%s%smsgid \"%s\" returns \"%s\"\n",
                domainname ? "domain \"" : "", xo_printable(domainname),
                domainname ? "\", " : "", xo_printable(str), xo_printable(res));

    return res;
}

static inline const char *
xo_dngettext (xo_handle_t *xop, const char *sing, const char *plural,
              unsigned long int n)
{
    const char *domainname = xop->xo_gt_domain;
    const char *res;

    res = dngettext(domainname, sing, plural, n);
    if (XOF_ISSET(xop, XOF_LOG_GETTEXT))
        fprintf(stderr, "xo: gettext: %s%s%s"
                "msgid \"%s\", msgid_plural \"%s\" (%lu) returns \"%s\"\n",
                domainname ? "domain \"" : "", 
                xo_printable(domainname), domainname ? "\", " : "",
                xo_printable(sing),
                xo_printable(plural), n, xo_printable(res));

    return res;
}
#else /* HAVE_GETTEXT */
static inline const char *
xo_dgettext (xo_handle_t *xop UNUSED, const char *str)
{
    return str;
}

static inline const char *
xo_dngettext (xo_handle_t *xop UNUSED, const char *singular,
              const char *plural, unsigned long int n)
{
    return (n == 1) ? singular : plural;
}
#endif /* HAVE_GETTEXT */

/*
 * This is really _re_formatting, since the normal format code has
 * generated a beautiful string into xo_data, starting at
 * start_offset.  We need to see if it's plural, which means
 * comma-separated options, or singular.  Then we make the appropriate
 * call to d[n]gettext() to get the locale-based version.  Note that
 * both input and output of gettext() this should be UTF-8.
 */
static ssize_t
xo_format_gettext (xo_handle_t *xop, xo_xff_flags_t flags,
                   ssize_t start_offset, ssize_t cols, int need_enc)
{
    xo_buffer_t *xbp = &xop->xo_data;

    if (!xo_buf_has_room(xbp, 1))
        return cols;

    xbp->xb_curp[0] = '\0'; /* NUL-terminate the input string */
    
    char *cp = xbp->xb_bufp + start_offset;
    ssize_t len = xbp->xb_curp - cp;
    const char *newstr = NULL;

    /*
     * The plural flag asks us to look backwards at the last numeric
     * value rendered and disect the string into two pieces.
     */
    if (flags & XFF_GT_PLURAL) {
        int n = xo_buf_find_last_number(xbp, start_offset);
        char *two = memchr(cp, (int) ',', len);
        if (two == NULL) {
            xo_failure(xop, "no comma in plural gettext field: '%s'", cp);
            return cols;
        }

        if (two == cp) {
            xo_failure(xop, "nothing before comma in plural gettext "
                       "field: '%s'", cp);
            return cols;
        }

        if (two == xbp->xb_curp) {
            xo_failure(xop, "nothing after comma in plural gettext "
                       "field: '%s'", cp);
            return cols;
        }

        *two++ = '\0';
        if (flags & XFF_GT_FIELD) {
            newstr = xo_dngettext(xop, cp, two, n);
        } else {
            /* Don't do a gettext() look up, just get the plural form */
            newstr = (n == 1) ? cp : two;
        }

        /*
         * If we returned the first string, optimize a bit by
         * backing up over comma
         */
        if (newstr == cp) {
            xbp->xb_curp = two - 1; /* One for comma */
            /*
             * If the caller wanted UTF8, we're done; nothing changed,
             * but we need to count the columns used.
             */
            if (need_enc == XF_ENC_UTF8)
                return xo_count_utf8_cols(cp, xbp->xb_curp - cp);
        }

    } else {
        /* The simple case (singular) */
        newstr = xo_dgettext(xop, cp);

        if (newstr == cp) {
            /* If the caller wanted UTF8, we're done; nothing changed */
            if (need_enc == XF_ENC_UTF8)
                return cols;
        }
    }

    /*
     * Since the new string string might be in gettext's buffer or
     * in the buffer (as the plural form), we make a copy.
     */
    ssize_t nlen = strlen(newstr);
    char *newcopy = alloca(nlen + 1);
    memcpy(newcopy, newstr, nlen + 1);

    xbp->xb_curp = xbp->xb_bufp + start_offset; /* Reset the buffer */
    return xo_format_string_direct(xop, xbp, flags, NULL, newcopy, nlen, 0,
                                   need_enc, XF_ENC_UTF8);
}

static void
xo_data_append_content (xo_handle_t *xop, const char *str, ssize_t len,
                        xo_xff_flags_t flags)
{
    int cols;
    int need_enc = xo_needed_encoding(xop);
    ssize_t start_offset = xo_buf_offset(&xop->xo_data);

    cols = xo_format_string_direct(xop, &xop->xo_data, XFF_UNESCAPE | flags,
                                   NULL, str, len, -1,
                                   need_enc, XF_ENC_UTF8);
    if (flags & XFF_GT_FLAGS)
        cols = xo_format_gettext(xop, flags, start_offset, cols, need_enc);

    if (XOF_ISSET(xop, XOF_COLUMNS))
        xop->xo_columns += cols;
    if (XOIF_ISSET(xop, XOIF_ANCHOR))
        xop->xo_anchor_columns += cols;
}

/**
 * Bump one of the 'width' values in a format strings (e.g. "%40.50.60s").
 * @param xfp Formatting instructions
 * @param digit Single digit (0-9) of input
 */
static void
xo_bump_width (xo_format_t *xfp, int digit)
{
    int *ip = &xfp->xf_width[xfp->xf_dots];

    *ip = ((*ip > 0) ? *ip : 0) * 10 + digit;
}

static ssize_t
xo_trim_ws (xo_buffer_t *xbp, ssize_t len)
{
    char *cp, *sp, *ep;
    ssize_t delta;

    /* First trim leading space */
    for (cp = sp = xbp->xb_curp, ep = cp + len; cp < ep; cp++) {
        if (*cp != ' ')
            break;
    }

    delta = cp - sp;
    if (delta) {
        len -= delta;
        memmove(sp, cp, len);
    }

    /* Then trim off the end */
    for (cp = xbp->xb_curp, sp = ep = cp + len; cp < ep; ep--) {
        if (ep[-1] != ' ')
            break;
    }

    delta = sp - ep;
    if (delta) {
        len -= delta;
        cp[len] = '\0';
    }

    return len;
}

/*
 * Interface to format a single field.  The arguments are in xo_vap,
 * and the format is in 'fmt'.  If 'xbp' is null, we use xop->xo_data;
 * this is the most common case.
 */
static ssize_t
xo_do_format_field (xo_handle_t *xop, xo_buffer_t *xbp,
                const char *fmt, ssize_t flen, xo_xff_flags_t flags)
{
    xo_format_t xf;
    const char *cp, *ep, *sp, *xp = NULL;
    ssize_t rc, cols;
    int style = (flags & XFF_XML) ? XO_STYLE_XML : xo_style(xop);
    unsigned make_output = !(flags & XFF_NO_OUTPUT) ? 1 : 0;
    int need_enc = xo_needed_encoding(xop);
    int real_need_enc = need_enc;
    ssize_t old_cols = xop->xo_columns;

    /* The gettext interface is UTF-8, so we'll need that for now */
    if (flags & XFF_GT_FIELD)
        need_enc = XF_ENC_UTF8;

    if (xbp == NULL)
        xbp = &xop->xo_data;

    ssize_t start_offset = xo_buf_offset(xbp);

    for (cp = fmt, ep = fmt + flen; cp < ep; cp++) {
        /*
         * Since we're starting a new field, save the starting offset.
         * We'll need this later for field-related operations.
         */

        if (*cp != '%') {
        add_one:
            if (xp == NULL)
                xp = cp;

            if (*cp == '\\' && cp[1] != '\0')
                cp += 1;
            continue;

        } if (cp + 1 < ep && cp[1] == '%') {
            cp += 1;
            goto add_one;
        }

        if (xp) {
            if (make_output) {
                cols = xo_format_string_direct(xop, xbp, flags | XFF_UNESCAPE,
                                               NULL, xp, cp - xp, -1,
                                               need_enc, XF_ENC_UTF8);
                if (XOF_ISSET(xop, XOF_COLUMNS))
                    xop->xo_columns += cols;
                if (XOIF_ISSET(xop, XOIF_ANCHOR))
                    xop->xo_anchor_columns += cols;
            }

            xp = NULL;
        }

        bzero(&xf, sizeof(xf));
        xf.xf_leading_zero = -1;
        xf.xf_width[0] = xf.xf_width[1] = xf.xf_width[2] = -1;

        /*
         * "%@" starts an XO-specific set of flags:
         *   @X@ - XML-only field; ignored if style isn't XML
         */
        if (cp[1] == '@') {
            for (cp += 2; cp < ep; cp++) {
                if (*cp == '@') {
                    break;
                }
                if (*cp == '*') {
                    /*
                     * '*' means there's a "%*.*s" value in vap that
                     * we want to ignore
                     */
                    if (!XOF_ISSET(xop, XOF_NO_VA_ARG))
                        va_arg(xop->xo_vap, int);
                }
            }
        }

        /* Hidden fields are only visible to JSON and XML */
        if (XOF_ISSET(xop, XFF_ENCODE_ONLY)) {
            if (style != XO_STYLE_XML
                    && !xo_style_is_encoding(xop))
                xf.xf_skip = 1;
        } else if (XOF_ISSET(xop, XFF_DISPLAY_ONLY)) {
            if (style != XO_STYLE_TEXT
                    && xo_style(xop) != XO_STYLE_HTML)
                xf.xf_skip = 1;
        }

        if (!make_output)
            xf.xf_skip = 1;

        /*
         * Looking at one piece of a format; find the end and
         * call snprintf.  Then advance xo_vap on our own.
         *
         * Note that 'n', 'v', and '$' are not supported.
         */
        sp = cp;                /* Save start pointer */
        for (cp += 1; cp < ep; cp++) {
            if (*cp == 'l')
                xf.xf_lflag += 1;
            else if (*cp == 'h')
                xf.xf_hflag += 1;
            else if (*cp == 'j')
                xf.xf_jflag += 1;
            else if (*cp == 't')
                xf.xf_tflag += 1;
            else if (*cp == 'z')
                xf.xf_zflag += 1;
            else if (*cp == 'q')
                xf.xf_qflag += 1;
            else if (*cp == '.') {
                if (++xf.xf_dots >= XF_WIDTH_NUM) {
                    xo_failure(xop, "Too many dots in format: '%s'", fmt);
                    return -1;
                }
            } else if (*cp == '-')
                xf.xf_seen_minus = 1;
            else if (isdigit((int) *cp)) {
                if (xf.xf_leading_zero < 0)
                    xf.xf_leading_zero = (*cp == '0');
                xo_bump_width(&xf, *cp - '0');
            } else if (*cp == '*') {
                xf.xf_stars += 1;
                xf.xf_star[xf.xf_dots] = 1;
            } else if (strchr("diouxXDOUeEfFgGaAcCsSpm", *cp) != NULL)
                break;
            else if (*cp == 'n' || *cp == 'v') {
                xo_failure(xop, "unsupported format: '%s'", fmt);
                return -1;
            }
        }

        if (cp == ep)
            xo_failure(xop, "field format missing format character: %s",
                          fmt);

        xf.xf_fc = *cp;

        if (!XOF_ISSET(xop, XOF_NO_VA_ARG)) {
            if (*cp == 's' || *cp == 'S') {
                /* Handle "%*.*.*s" */
                int s;
                for (s = 0; s < XF_WIDTH_NUM; s++) {
                    if (xf.xf_star[s]) {
                        xf.xf_width[s] = va_arg(xop->xo_vap, int);
                        
                        /* Normalize a negative width value */
                        if (xf.xf_width[s] < 0) {
                            if (s == 0) {
                                xf.xf_width[0] = -xf.xf_width[0];
                                xf.xf_seen_minus = 1;
                            } else
                                xf.xf_width[s] = -1; /* Ignore negative values */
                        }
                    }
                }
            }
        }

        /* If no max is given, it defaults to size */
        if (xf.xf_width[XF_WIDTH_MAX] < 0 && xf.xf_width[XF_WIDTH_SIZE] >= 0)
            xf.xf_width[XF_WIDTH_MAX] = xf.xf_width[XF_WIDTH_SIZE];

        if (xf.xf_fc == 'D' || xf.xf_fc == 'O' || xf.xf_fc == 'U')
            xf.xf_lflag = 1;

        if (!xf.xf_skip) {
            xo_buffer_t *fbp = &xop->xo_fmt;
            ssize_t len = cp - sp + 1;
            if (!xo_buf_has_room(fbp, len + 1))
                return -1;

            char *newfmt = fbp->xb_curp;
            memcpy(newfmt, sp, len);
            newfmt[0] = '%';    /* If we skipped over a "%@...@s" format */
            newfmt[len] = '\0';

            /*
             * Bad news: our strings are UTF-8, but the stock printf
             * functions won't handle field widths for wide characters
             * correctly.  So we have to handle this ourselves.
             */
            if (xop->xo_formatter == NULL
                    && (xf.xf_fc == 's' || xf.xf_fc == 'S'
                        || xf.xf_fc == 'm')) {

                xf.xf_enc = (xf.xf_fc == 'm') ? XF_ENC_UTF8
                    : (xf.xf_lflag || (xf.xf_fc == 'S')) ? XF_ENC_WIDE
                    : xf.xf_hflag ? XF_ENC_LOCALE : XF_ENC_UTF8;

                rc = xo_format_string(xop, xbp, flags, &xf);

                if ((flags & XFF_TRIM_WS) && xo_style_is_encoding(xop))
                    rc = xo_trim_ws(xbp, rc);

            } else {
                ssize_t columns = rc = xo_vsnprintf(xop, xbp, newfmt,
                                                    xop->xo_vap);

                if (rc > 0) {
                    /*
                     * For XML and HTML, we need "&<>" processing; for JSON,
                     * it's quotes.  Text gets nothing.
                     */
                    switch (style) {
                    case XO_STYLE_XML:
                        if (flags & XFF_TRIM_WS)
                            columns = rc = xo_trim_ws(xbp, rc);
                        /* FALLTHRU */
                    case XO_STYLE_HTML:
                        rc = xo_escape_xml(xbp, rc, (flags & XFF_ATTR));
                        break;

                    case XO_STYLE_JSON:
                        if (flags & XFF_TRIM_WS)
                            columns = rc = xo_trim_ws(xbp, rc);
                        rc = xo_escape_json(xbp, rc, 0);
                        break;

                    case XO_STYLE_SDPARAMS:
                        if (flags & XFF_TRIM_WS)
                            columns = rc = xo_trim_ws(xbp, rc);
                        rc = xo_escape_sdparams(xbp, rc, 0);
                        break;

                    case XO_STYLE_ENCODER:
                        if (flags & XFF_TRIM_WS)
                            columns = rc = xo_trim_ws(xbp, rc);
                        break;
                    }

                    /*
                     * We can assume all the non-%s data we've
                     * added is ASCII, so the columns and bytes are the
                     * same.  xo_format_string handles all the fancy
                     * string conversions and updates xo_anchor_columns
                     * accordingly.
                     */
                    if (XOF_ISSET(xop, XOF_COLUMNS))
                        xop->xo_columns += columns;
                    if (XOIF_ISSET(xop, XOIF_ANCHOR))
                        xop->xo_anchor_columns += columns;
                }
            }

            if (rc > 0)
                xbp->xb_curp += rc;
        }

        /*
         * Now for the tricky part: we need to move the argument pointer
         * along by the amount needed.
         */
        if (!XOF_ISSET(xop, XOF_NO_VA_ARG)) {

            if (xf.xf_fc == 's' ||xf.xf_fc == 'S') {
                /*
                 * The 'S' and 's' formats are normally handled in
                 * xo_format_string, but if we skipped it, then we
                 * need to pop it.
                 */
                if (xf.xf_skip)
                    va_arg(xop->xo_vap, char *);

            } else if (xf.xf_fc == 'm') {
                /* Nothing on the stack for "%m" */

            } else {
                int s;
                for (s = 0; s < XF_WIDTH_NUM; s++) {
                    if (xf.xf_star[s])
                        va_arg(xop->xo_vap, int);
                }

                if (strchr("diouxXDOU", xf.xf_fc) != NULL) {
                    if (xf.xf_hflag > 1) {
                        va_arg(xop->xo_vap, int);

                    } else if (xf.xf_hflag > 0) {
                        va_arg(xop->xo_vap, int);

                    } else if (xf.xf_lflag > 1) {
                        va_arg(xop->xo_vap, unsigned long long);

                    } else if (xf.xf_lflag > 0) {
                        va_arg(xop->xo_vap, unsigned long);

                    } else if (xf.xf_jflag > 0) {
                        va_arg(xop->xo_vap, intmax_t);

                    } else if (xf.xf_tflag > 0) {
                        va_arg(xop->xo_vap, ptrdiff_t);

                    } else if (xf.xf_zflag > 0) {
                        va_arg(xop->xo_vap, size_t);

                    } else if (xf.xf_qflag > 0) {
                        va_arg(xop->xo_vap, quad_t);

                    } else {
                        va_arg(xop->xo_vap, int);
                    }
                } else if (strchr("eEfFgGaA", xf.xf_fc) != NULL)
                    if (xf.xf_lflag)
                        va_arg(xop->xo_vap, long double);
                    else
                        va_arg(xop->xo_vap, double);

                else if (xf.xf_fc == 'C' || (xf.xf_fc == 'c' && xf.xf_lflag))
                    va_arg(xop->xo_vap, wint_t);

                else if (xf.xf_fc == 'c')
                    va_arg(xop->xo_vap, int);

                else if (xf.xf_fc == 'p')
                    va_arg(xop->xo_vap, void *);
            }
        }
    }

    if (xp) {
        if (make_output) {
            cols = xo_format_string_direct(xop, xbp, flags | XFF_UNESCAPE,
                                           NULL, xp, cp - xp, -1,
                                           need_enc, XF_ENC_UTF8);

            if (XOF_ISSET(xop, XOF_COLUMNS))
                xop->xo_columns += cols;
            if (XOIF_ISSET(xop, XOIF_ANCHOR))
                xop->xo_anchor_columns += cols;
        }

        xp = NULL;
    }

    if (flags & XFF_GT_FLAGS) {
        /*
         * Handle gettext()ing the field by looking up the value
         * and then copying it in, while converting to locale, if
         * needed.
         */
        ssize_t new_cols = xo_format_gettext(xop, flags, start_offset,
                                         old_cols, real_need_enc);
        
        if (XOF_ISSET(xop, XOF_COLUMNS))
            xop->xo_columns += new_cols - old_cols;
        if (XOIF_ISSET(xop, XOIF_ANCHOR))
            xop->xo_anchor_columns += new_cols - old_cols;
    }

    return 0;
}

/*
 * Remove any numeric precision/width format from the format string by
 * inserting the "%" after the [0-9]+, returning the substring.
 */
static char *
xo_fix_encoding (xo_handle_t *xop UNUSED, char *encoding)
{
    char *cp = encoding;

    if (cp[0] != '%' || !isdigit((int) cp[1]))
        return encoding;

    for (cp += 2; *cp; cp++) {
        if (!isdigit((int) *cp))
            break;
    }

    *--cp = '%';                /* Back off and insert the '%' */

    return cp;
}

static void
xo_color_append_html (xo_handle_t *xop)
{
    /*
     * If the color buffer has content, we add it now.  It's already
     * prebuilt and ready, since we want to add it to every <div>.
     */
    if (!xo_buf_is_empty(&xop->xo_color_buf)) {
        xo_buffer_t *xbp = &xop->xo_color_buf;

        xo_data_append(xop, xbp->xb_bufp, xbp->xb_curp - xbp->xb_bufp);
    }
}

/*
 * A wrapper for humanize_number that autoscales, since the
 * HN_AUTOSCALE flag scales as needed based on the size of
 * the output buffer, not the size of the value.  I also
 * wish HN_DECIMAL was more imperative, without the <10
 * test.  But the boat only goes where we want when we hold
 * the rudder, so xo_humanize fixes part of the problem.
 */
static ssize_t
xo_humanize (char *buf, ssize_t len, uint64_t value, int flags)
{
    int scale = 0;

    if (value) {
        uint64_t left = value;

        if (flags & HN_DIVISOR_1000) {
            for ( ; left; scale++)
                left /= 1000;
        } else {
            for ( ; left; scale++)
                left /= 1024;
        }
        scale -= 1;
    }
    
    return xo_humanize_number(buf, len, value, "", scale, flags);
}

/*
 * This is an area where we can save information from the handle for
 * later restoration.  We need to know what data was rendered to know
 * what needs cleaned up.
 */
typedef struct xo_humanize_save_s {
    ssize_t xhs_offset;         /* Saved xo_offset */
    ssize_t xhs_columns;        /* Saved xo_columns */
    ssize_t xhs_anchor_columns; /* Saved xo_anchor_columns */
} xo_humanize_save_t;

/*
 * Format a "humanized" value for a numeric, meaning something nice
 * like "44M" instead of "44470272".  We autoscale, choosing the
 * most appropriate value for K/M/G/T/P/E based on the value given.
 */
static void
xo_format_humanize (xo_handle_t *xop, xo_buffer_t *xbp,
                    xo_humanize_save_t *savep, xo_xff_flags_t flags)
{
    if (XOF_ISSET(xop, XOF_NO_HUMANIZE))
        return;

    ssize_t end_offset = xbp->xb_curp - xbp->xb_bufp;
    if (end_offset == savep->xhs_offset) /* Huh? Nothing to render */
        return;

    /*
     * We have a string that's allegedly a number. We want to
     * humanize it, which means turning it back into a number
     * and calling xo_humanize_number on it.
     */
    uint64_t value;
    char *ep;

    xo_buf_append(xbp, "", 1); /* NUL-terminate it */

    value = strtoull(xbp->xb_bufp + savep->xhs_offset, &ep, 0);
    if (!(value == ULLONG_MAX && errno == ERANGE)
        && (ep != xbp->xb_bufp + savep->xhs_offset)) {
        /*
         * There are few values where humanize_number needs
         * more bytes than the original value.  I've used
         * 10 as a rectal number to cover those scenarios.
         */
        if (xo_buf_has_room(xbp, 10)) {
            xbp->xb_curp = xbp->xb_bufp + savep->xhs_offset;

            ssize_t rc;
            ssize_t left = (xbp->xb_bufp + xbp->xb_size) - xbp->xb_curp;
            int hn_flags = HN_NOSPACE; /* On by default */

            if (flags & XFF_HN_SPACE)
                hn_flags &= ~HN_NOSPACE;

            if (flags & XFF_HN_DECIMAL)
                hn_flags |= HN_DECIMAL;

            if (flags & XFF_HN_1000)
                hn_flags |= HN_DIVISOR_1000;

            rc = xo_humanize(xbp->xb_curp, left, value, hn_flags);
            if (rc > 0) {
                xbp->xb_curp += rc;
                xop->xo_columns = savep->xhs_columns + rc;
                xop->xo_anchor_columns = savep->xhs_anchor_columns + rc;
            }
        }
    }
}

/*
 * Convenience function that either append a fixed value (if one is
 * given) or formats a field using a format string.  If it's
 * encode_only, then we can't skip formatting the field, since it may
 * be pulling arguments off the stack.
 */
static inline void
xo_simple_field (xo_handle_t *xop, unsigned encode_only,
                      const char *value, ssize_t vlen,
                      const char *fmt, ssize_t flen, xo_xff_flags_t flags)
{
    if (encode_only)
        flags |= XFF_NO_OUTPUT;

    if (vlen == 0)
        xo_do_format_field(xop, NULL, fmt, flen, flags);
    else if (!encode_only)
        xo_data_append_content(xop, value, vlen, flags);
}

/*
 * Html mode: append a <div> to the output buffer contain a field
 * along with all the supporting information indicated by the flags.
 */
static void
xo_buf_append_div (xo_handle_t *xop, const char *class, xo_xff_flags_t flags,
                   const char *name, ssize_t nlen,
                   const char *value, ssize_t vlen,
                   const char *fmt, ssize_t flen,
                   const char *encoding, ssize_t elen)
{
    static char div_start[] = "<div class=\"";
    static char div_tag[] = "\" data-tag=\"";
    static char div_xpath[] = "\" data-xpath=\"";
    static char div_key[] = "\" data-key=\"key";
    static char div_end[] = "\">";
    static char div_close[] = "</div>";

    /* The encoding format defaults to the normal format */
    if (encoding == NULL && fmt != NULL) {
        char *enc  = alloca(flen + 1);
        memcpy(enc, fmt, flen);
        enc[flen] = '\0';
        encoding = xo_fix_encoding(xop, enc);
        elen = strlen(encoding);
    }

    /*
     * To build our XPath predicate, we need to save the va_list before
     * we format our data, and then restore it before we format the
     * xpath expression.
     * Display-only keys implies that we've got an encode-only key
     * elsewhere, so we don't use them from making predicates.
     */
    int need_predidate = 
        (name && (flags & XFF_KEY) && !(flags & XFF_DISPLAY_ONLY)
         && XOF_ISSET(xop, XOF_XPATH)) ? 1 : 0;

    if (need_predidate) {
        va_list va_local;

        va_copy(va_local, xop->xo_vap);
        if (xop->xo_checkpointer)
            xop->xo_checkpointer(xop, xop->xo_vap, 0);

        /*
         * Build an XPath predicate expression to match this key.
         * We use the format buffer.
         */
        xo_buffer_t *pbp = &xop->xo_predicate;
        pbp->xb_curp = pbp->xb_bufp; /* Restart buffer */

        xo_buf_append(pbp, "[", 1);
        xo_buf_escape(xop, pbp, name, nlen, 0);
        if (XOF_ISSET(xop, XOF_PRETTY))
            xo_buf_append(pbp, " = '", 4);
        else
            xo_buf_append(pbp, "='", 2);

        xo_xff_flags_t pflags = flags | XFF_XML | XFF_ATTR;
        pflags &= ~(XFF_NO_OUTPUT | XFF_ENCODE_ONLY);
        xo_do_format_field(xop, pbp, encoding, elen, pflags);

        xo_buf_append(pbp, "']", 2);

        /* Now we record this predicate expression in the stack */
        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];
        ssize_t olen = xsp->xs_keys ? strlen(xsp->xs_keys) : 0;
        ssize_t dlen = pbp->xb_curp - pbp->xb_bufp;

        char *cp = xo_realloc(xsp->xs_keys, olen + dlen + 1);
        if (cp) {
            memcpy(cp + olen, pbp->xb_bufp, dlen);
            cp[olen + dlen] = '\0';
            xsp->xs_keys = cp;
        }

        /* Now we reset the xo_vap as if we were never here */
        va_end(xop->xo_vap);
        va_copy(xop->xo_vap, va_local);
        va_end(va_local);
        if (xop->xo_checkpointer)
            xop->xo_checkpointer(xop, xop->xo_vap, 1);
    }

    if (flags & XFF_ENCODE_ONLY) {
        /*
         * Even if this is encode-only, we need to go through the
         * work of formatting it to make sure the args are cleared
         * from xo_vap.  This is not true when vlen is zero, since
         * that means our "value" isn't on the stack.
         */
        xo_simple_field(xop, TRUE, NULL, 0, encoding, elen, flags);
        return;
    }

    xo_line_ensure_open(xop, 0);

    if (XOF_ISSET(xop, XOF_PRETTY))
        xo_buf_indent(xop, xop->xo_indent_by);

    xo_data_append(xop, div_start, sizeof(div_start) - 1);
    xo_data_append(xop, class, strlen(class));

    /*
     * If the color buffer has content, we add it now.  It's already
     * prebuilt and ready, since we want to add it to every <div>.
     */
    if (!xo_buf_is_empty(&xop->xo_color_buf)) {
        xo_buffer_t *xbp = &xop->xo_color_buf;

        xo_data_append(xop, xbp->xb_bufp, xbp->xb_curp - xbp->xb_bufp);
    }

    if (name) {
        xo_data_append(xop, div_tag, sizeof(div_tag) - 1);
        xo_data_escape(xop, name, nlen);

        /*
         * Save the offset at which we'd place units.  See xo_format_units.
         */
        if (XOF_ISSET(xop, XOF_UNITS)) {
            XOIF_SET(xop, XOIF_UNITS_PENDING);
            /*
             * Note: We need the '+1' here because we know we've not
             * added the closing quote.  We add one, knowing the quote
             * will be added shortly.
             */
            xop->xo_units_offset =
                xop->xo_data.xb_curp -xop->xo_data.xb_bufp + 1;
        }

        if (XOF_ISSET(xop, XOF_XPATH)) {
            int i;
            xo_stack_t *xsp;

            xo_data_append(xop, div_xpath, sizeof(div_xpath) - 1);
            if (xop->xo_leading_xpath)
                xo_data_append(xop, xop->xo_leading_xpath,
                               strlen(xop->xo_leading_xpath));

            for (i = 0; i <= xop->xo_depth; i++) {
                xsp = &xop->xo_stack[i];
                if (xsp->xs_name == NULL)
                    continue;

                /*
                 * XSS_OPEN_LIST and XSS_OPEN_LEAF_LIST stack frames
                 * are directly under XSS_OPEN_INSTANCE frames so we
                 * don't need to put these in our XPath expressions.
                 */
                if (xsp->xs_state == XSS_OPEN_LIST
                        || xsp->xs_state == XSS_OPEN_LEAF_LIST)
                    continue;

                xo_data_append(xop, "/", 1);
                xo_data_escape(xop, xsp->xs_name, strlen(xsp->xs_name));
                if (xsp->xs_keys) {
                    /* Don't show keys for the key field */
                    if (i != xop->xo_depth || !(flags & XFF_KEY))
                        xo_data_append(xop, xsp->xs_keys, strlen(xsp->xs_keys));
                }
            }

            xo_data_append(xop, "/", 1);
            xo_data_escape(xop, name, nlen);
        }

        if (XOF_ISSET(xop, XOF_INFO) && xop->xo_info) {
            static char in_type[] = "\" data-type=\"";
            static char in_help[] = "\" data-help=\"";

            xo_info_t *xip = xo_info_find(xop, name, nlen);
            if (xip) {
                if (xip->xi_type) {
                    xo_data_append(xop, in_type, sizeof(in_type) - 1);
                    xo_data_escape(xop, xip->xi_type, strlen(xip->xi_type));
                }
                if (xip->xi_help) {
                    xo_data_append(xop, in_help, sizeof(in_help) - 1);
                    xo_data_escape(xop, xip->xi_help, strlen(xip->xi_help));
                }
            }
        }

        if ((flags & XFF_KEY) && XOF_ISSET(xop, XOF_KEYS))
            xo_data_append(xop, div_key, sizeof(div_key) - 1);
    }

    xo_buffer_t *xbp = &xop->xo_data;
    ssize_t base_offset = xbp->xb_curp - xbp->xb_bufp;

    xo_data_append(xop, div_end, sizeof(div_end) - 1);

    xo_humanize_save_t save;    /* Save values for humanizing logic */

    save.xhs_offset = xbp->xb_curp - xbp->xb_bufp;
    save.xhs_columns = xop->xo_columns;
    save.xhs_anchor_columns = xop->xo_anchor_columns;

    xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);

    if (flags & XFF_HUMANIZE) {
        /*
         * Unlike text style, we want to retain the original value and
         * stuff it into the "data-number" attribute.
         */
        static const char div_number[] = "\" data-number=\"";
        ssize_t div_len = sizeof(div_number) - 1;

        ssize_t end_offset = xbp->xb_curp - xbp->xb_bufp;
        ssize_t olen = end_offset - save.xhs_offset;

        char *cp = alloca(olen + 1);
        memcpy(cp, xbp->xb_bufp + save.xhs_offset, olen);
        cp[olen] = '\0';

        xo_format_humanize(xop, xbp, &save, flags);

        if (xo_buf_has_room(xbp, div_len + olen)) {
            ssize_t new_offset = xbp->xb_curp - xbp->xb_bufp;


            /* Move the humanized string off to the left */
            memmove(xbp->xb_bufp + base_offset + div_len + olen,
                    xbp->xb_bufp + base_offset, new_offset - base_offset);

            /* Copy the data_number attribute name */
            memcpy(xbp->xb_bufp + base_offset, div_number, div_len);

            /* Copy the original long value */
            memcpy(xbp->xb_bufp + base_offset + div_len, cp, olen);
            xbp->xb_curp += div_len + olen;
        }
    }

    xo_data_append(xop, div_close, sizeof(div_close) - 1);

    if (XOF_ISSET(xop, XOF_PRETTY))
        xo_data_append(xop, "\n", 1);
}

static void
xo_format_text (xo_handle_t *xop, const char *str, ssize_t len)
{
    switch (xo_style(xop)) {
    case XO_STYLE_TEXT:
        xo_buf_append_locale(xop, &xop->xo_data, str, len);
        break;

    case XO_STYLE_HTML:
        xo_buf_append_div(xop, "text", 0, NULL, 0, str, len, NULL, 0, NULL, 0);
        break;
    }
}

static void
xo_format_title (xo_handle_t *xop, xo_field_info_t *xfip,
                 const char *value, ssize_t vlen)
{
    const char *fmt = xfip->xfi_format;
    ssize_t flen = xfip->xfi_flen;
    xo_xff_flags_t flags = xfip->xfi_flags;

    static char div_open[] = "<div class=\"title";
    static char div_middle[] = "\">";
    static char div_close[] = "</div>";

    if (flen == 0) {
        fmt = "%s";
        flen = 2;
    }

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
    case XO_STYLE_JSON:
    case XO_STYLE_SDPARAMS:
    case XO_STYLE_ENCODER:
        /*
         * Even though we don't care about text, we need to do
         * enough parsing work to skip over the right bits of xo_vap.
         */
        xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
        return;
    }

    xo_buffer_t *xbp = &xop->xo_data;
    ssize_t start = xbp->xb_curp - xbp->xb_bufp;
    ssize_t left = xbp->xb_size - start;
    ssize_t rc;

    if (xo_style(xop) == XO_STYLE_HTML) {
        xo_line_ensure_open(xop, 0);
        if (XOF_ISSET(xop, XOF_PRETTY))
            xo_buf_indent(xop, xop->xo_indent_by);
        xo_buf_append(&xop->xo_data, div_open, sizeof(div_open) - 1);
        xo_color_append_html(xop);
        xo_buf_append(&xop->xo_data, div_middle, sizeof(div_middle) - 1);
    }

    start = xbp->xb_curp - xbp->xb_bufp; /* Reset start */
    if (vlen) {
        char *newfmt = alloca(flen + 1);
        memcpy(newfmt, fmt, flen);
        newfmt[flen] = '\0';

        /* If len is non-zero, the format string apply to the name */
        char *newstr = alloca(vlen + 1);
        memcpy(newstr, value, vlen);
        newstr[vlen] = '\0';

        if (newstr[vlen - 1] == 's') {
            char *bp;

            rc = snprintf(NULL, 0, newfmt, newstr);
            if (rc > 0) {
                /*
                 * We have to do this the hard way, since we might need
                 * the columns.
                 */
                bp = alloca(rc + 1);
                rc = snprintf(bp, rc + 1, newfmt, newstr);

                xo_data_append_content(xop, bp, rc, flags);
            }
            goto move_along;

        } else {
            rc = snprintf(xbp->xb_curp, left, newfmt, newstr);
            if (rc >= left) {
                if (!xo_buf_has_room(xbp, rc))
                    return;
                left = xbp->xb_size - (xbp->xb_curp - xbp->xb_bufp);
                rc = snprintf(xbp->xb_curp, left, newfmt, newstr);
            }

            if (rc > 0) {
                if (XOF_ISSET(xop, XOF_COLUMNS))
                    xop->xo_columns += rc;
                if (XOIF_ISSET(xop, XOIF_ANCHOR))
                    xop->xo_anchor_columns += rc;
            }
        }

    } else {
        xo_do_format_field(xop, NULL, fmt, flen, flags);

        /* xo_do_format_field moved curp, so we need to reset it */
        rc = xbp->xb_curp - (xbp->xb_bufp + start);
        xbp->xb_curp = xbp->xb_bufp + start;
    }

    /* If we're styling HTML, then we need to escape it */
    if (xo_style(xop) == XO_STYLE_HTML) {
        rc = xo_escape_xml(xbp, rc, 0);
    }

    if (rc > 0)
        xbp->xb_curp += rc;

 move_along:
    if (xo_style(xop) == XO_STYLE_HTML) {
        xo_data_append(xop, div_close, sizeof(div_close) - 1);
        if (XOF_ISSET(xop, XOF_PRETTY))
            xo_data_append(xop, "\n", 1);
    }
}

/*
 * strspn() with a string length
 */
static ssize_t
xo_strnspn (const char *str, size_t len,  const char *accept)
{
    ssize_t i;
    const char *cp, *ep;

    for (i = 0, cp = str, ep = str + len; cp < ep && *cp != '\0'; i++, cp++) {
        if (strchr(accept, *cp) == NULL)
            break;
    }

    return i;
}

/*
 * Decide if a format string should be considered "numeric",
 * in the sense that the number does not need to be quoted.
 * This means that it consists only of a single numeric field
 * with nothing exotic or "interesting".  This means that
 * static values are never considered numeric.
 */
static int
xo_format_is_numeric (const char *fmt, ssize_t flen)
{
    if (flen <= 0 || *fmt++ != '%') /* Must start with '%' */
        return FALSE;
    flen -= 1;

    /* Handle leading flags; don't want "#" since JSON can't handle hex */
    ssize_t spn = xo_strnspn(fmt, flen, "0123456789.*+ -");
    if (spn >= flen)
        return FALSE;

    fmt += spn;                 /* Move along the input string */
    flen -= spn;

    /* Handle the length modifiers */
    spn = xo_strnspn(fmt, flen, "hljtqz");
    if (spn >= flen)
        return FALSE;

    fmt += spn;                 /* Move along the input string */
    flen -= spn;

    if (flen != 1)              /* Should only be one character left */
        return FALSE;

    return (strchr("diouDOUeEfFgG", *fmt) == NULL) ? FALSE : TRUE;
}

/*
 * Update the stack flags using the object flags, allowing callers
 * to monkey with the stack flags without even knowing they exist.
 */
static void
xo_stack_set_flags (xo_handle_t *xop)
{
    if (XOF_ISSET(xop, XOF_NOT_FIRST)) {
        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];

        xsp->xs_flags |= XSF_NOT_FIRST;
        XOF_CLEAR(xop, XOF_NOT_FIRST);
    }
}

static void
xo_format_prep (xo_handle_t *xop, xo_xff_flags_t flags)
{
    if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST) {
        xo_data_append(xop, ",", 1);
        if (!(flags & XFF_LEAF_LIST) && XOF_ISSET(xop, XOF_PRETTY))
            xo_data_append(xop, "\n", 1);
    } else
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
}

#if 0
/* Useful debugging function */
void
xo_arg (xo_handle_t *xop);
void
xo_arg (xo_handle_t *xop)
{
    xop = xo_default(xop);
    fprintf(stderr, "0x%x", va_arg(xop->xo_vap, unsigned));
}
#endif /* 0 */

static void
xo_format_value (xo_handle_t *xop, const char *name, ssize_t nlen,
                 const char *value, ssize_t vlen,
                 const char *fmt, ssize_t flen,
                 const char *encoding, ssize_t elen, xo_xff_flags_t flags)
{
    int pretty = XOF_ISSET(xop, XOF_PRETTY);
    int quote;

    /*
     * Before we emit a value, we need to know that the frame is ready.
     */
    xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];

    if (flags & XFF_LEAF_LIST) {
        /*
         * Check if we've already started to emit normal leafs
         * or if we're not in a leaf list.
         */
        if ((xsp->xs_flags & (XSF_EMIT | XSF_EMIT_KEY))
            || !(xsp->xs_flags & XSF_EMIT_LEAF_LIST)) {
            char nbuf[nlen + 1];
            memcpy(nbuf, name, nlen);
            nbuf[nlen] = '\0';

            ssize_t rc = xo_transition(xop, 0, nbuf, XSS_EMIT_LEAF_LIST);
            if (rc < 0)
                flags |= XFF_DISPLAY_ONLY | XFF_ENCODE_ONLY;
            else
                xop->xo_stack[xop->xo_depth].xs_flags |= XSF_EMIT_LEAF_LIST;
        }

        xsp = &xop->xo_stack[xop->xo_depth];
        if (xsp->xs_name) {
            name = xsp->xs_name;
            nlen = strlen(name);
        }

    } else if (flags & XFF_KEY) {
        /* Emitting a 'k' (key) field */
        if ((xsp->xs_flags & XSF_EMIT) && !(flags & XFF_DISPLAY_ONLY)) {
            xo_failure(xop, "key field emitted after normal value field: '%.*s'",
                       nlen, name);

        } else if (!(xsp->xs_flags & XSF_EMIT_KEY)) {
            char nbuf[nlen + 1];
            memcpy(nbuf, name, nlen);
            nbuf[nlen] = '\0';

            ssize_t rc = xo_transition(xop, 0, nbuf, XSS_EMIT);
            if (rc < 0)
                flags |= XFF_DISPLAY_ONLY | XFF_ENCODE_ONLY;
            else
                xop->xo_stack[xop->xo_depth].xs_flags |= XSF_EMIT_KEY;

            xsp = &xop->xo_stack[xop->xo_depth];
            xsp->xs_flags |= XSF_EMIT_KEY;
        }

    } else {
        /* Emitting a normal value field */
        if ((xsp->xs_flags & XSF_EMIT_LEAF_LIST)
            || !(xsp->xs_flags & XSF_EMIT)) {
            char nbuf[nlen + 1];
            memcpy(nbuf, name, nlen);
            nbuf[nlen] = '\0';

            ssize_t rc = xo_transition(xop, 0, nbuf, XSS_EMIT);
            if (rc < 0)
                flags |= XFF_DISPLAY_ONLY | XFF_ENCODE_ONLY;
            else
                xop->xo_stack[xop->xo_depth].xs_flags |= XSF_EMIT;

            xsp = &xop->xo_stack[xop->xo_depth];
            xsp->xs_flags |= XSF_EMIT;
        }
    }

    xo_buffer_t *xbp = &xop->xo_data;
    xo_humanize_save_t save;    /* Save values for humanizing logic */

    const char *leader = xo_xml_leader_len(xop, name, nlen);

    switch (xo_style(xop)) {
    case XO_STYLE_TEXT:
        if (flags & XFF_ENCODE_ONLY)
            flags |= XFF_NO_OUTPUT;

        save.xhs_offset = xbp->xb_curp - xbp->xb_bufp;
        save.xhs_columns = xop->xo_columns;
        save.xhs_anchor_columns = xop->xo_anchor_columns;

        xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);

        if (flags & XFF_HUMANIZE)
            xo_format_humanize(xop, xbp, &save, flags);
        break;

    case XO_STYLE_HTML:
        if (flags & XFF_ENCODE_ONLY)
            flags |= XFF_NO_OUTPUT;

        xo_buf_append_div(xop, "data", flags, name, nlen, value, vlen,
                          fmt, flen, encoding, elen);
        break;

    case XO_STYLE_XML:
        /*
         * Even though we're not making output, we still need to
         * let the formatting code handle the va_arg popping.
         */
        if (flags & XFF_DISPLAY_ONLY) {
            xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
            break;
        }

        if (encoding) {
            fmt = encoding;
            flen = elen;
        } else {
            char *enc  = alloca(flen + 1);
            memcpy(enc, fmt, flen);
            enc[flen] = '\0';
            fmt = xo_fix_encoding(xop, enc);
            flen = strlen(fmt);
        }

        if (nlen == 0) {
            static char missing[] = "missing-field-name";
            xo_failure(xop, "missing field name: %s", fmt);
            name = missing;
            nlen = sizeof(missing) - 1;
        }

        if (pretty)
            xo_buf_indent(xop, -1);
        xo_data_append(xop, "<", 1);
        if (*leader)
            xo_data_append(xop, leader, 1);
        xo_data_escape(xop, name, nlen);

        if (xop->xo_attrs.xb_curp != xop->xo_attrs.xb_bufp) {
            xo_data_append(xop, xop->xo_attrs.xb_bufp,
                           xop->xo_attrs.xb_curp - xop->xo_attrs.xb_bufp);
            xop->xo_attrs.xb_curp = xop->xo_attrs.xb_bufp;
        }

        /*
         * We indicate 'key' fields using the 'key' attribute.  While
         * this is really committing the crime of mixing meta-data with
         * data, it's often useful.  Especially when format meta-data is
         * difficult to come by.
         */
        if ((flags & XFF_KEY) && XOF_ISSET(xop, XOF_KEYS)) {
            static char attr[] = " key=\"key\"";
            xo_data_append(xop, attr, sizeof(attr) - 1);
        }

        /*
         * Save the offset at which we'd place units.  See xo_format_units.
         */
        if (XOF_ISSET(xop, XOF_UNITS)) {
            XOIF_SET(xop, XOIF_UNITS_PENDING);
            xop->xo_units_offset = xop->xo_data.xb_curp -xop->xo_data.xb_bufp;
        }

        xo_data_append(xop, ">", 1);

        xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);

        xo_data_append(xop, "</", 2);
        if (*leader)
            xo_data_append(xop, leader, 1);
        xo_data_escape(xop, name, nlen);
        xo_data_append(xop, ">", 1);
        if (pretty)
            xo_data_append(xop, "\n", 1);
        break;

    case XO_STYLE_JSON:
        if (flags & XFF_DISPLAY_ONLY) {
            xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
            break;
        }

        if (encoding) {
            fmt = encoding;
            flen = elen;
        } else {
            char *enc  = alloca(flen + 1);
            memcpy(enc, fmt, flen);
            enc[flen] = '\0';
            fmt = xo_fix_encoding(xop, enc);
            flen = strlen(fmt);
        }

        xo_stack_set_flags(xop);

        int first = (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            ? 0 : 1;

        xo_format_prep(xop, flags);

        if (flags & XFF_QUOTE)
            quote = 1;
        else if (flags & XFF_NOQUOTE)
            quote = 0;
        else if (vlen != 0)
            quote = 1;
        else if (flen == 0) {
            quote = 0;
            fmt = "true";       /* JSON encodes empty tags as a boolean true */
            flen = 4;
        } else if (xo_format_is_numeric(fmt, flen))
            quote = 0;
        else
            quote = 1;

        if (nlen == 0) {
            static char missing[] = "missing-field-name";
            xo_failure(xop, "missing field name: %s", fmt);
            name = missing;
            nlen = sizeof(missing) - 1;
        }

        if (flags & XFF_LEAF_LIST) {
            if (!first && pretty)
                xo_data_append(xop, "\n", 1);
            if (pretty)
                xo_buf_indent(xop, -1);
        } else {
            if (pretty)
                xo_buf_indent(xop, -1);
            xo_data_append(xop, "\"", 1);

            xbp = &xop->xo_data;
            ssize_t off = xbp->xb_curp - xbp->xb_bufp;

            xo_data_escape(xop, name, nlen);

            if (XOF_ISSET(xop, XOF_UNDERSCORES)) {
                ssize_t coff = xbp->xb_curp - xbp->xb_bufp;
                for ( ; off < coff; off++)
                    if (xbp->xb_bufp[off] == '-')
                        xbp->xb_bufp[off] = '_';
            }
            xo_data_append(xop, "\":", 2);
            if (pretty)
                xo_data_append(xop, " ", 1);
        }

        if (quote)
            xo_data_append(xop, "\"", 1);

        xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);

        if (quote)
            xo_data_append(xop, "\"", 1);
        break;

    case XO_STYLE_SDPARAMS:
        if (flags & XFF_DISPLAY_ONLY) {
            xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
            break;
        }

        if (encoding) {
            fmt = encoding;
            flen = elen;
        } else {
            char *enc  = alloca(flen + 1);
            memcpy(enc, fmt, flen);
            enc[flen] = '\0';
            fmt = xo_fix_encoding(xop, enc);
            flen = strlen(fmt);
        }

        if (nlen == 0) {
            static char missing[] = "missing-field-name";
            xo_failure(xop, "missing field name: %s", fmt);
            name = missing;
            nlen = sizeof(missing) - 1;
        }

        xo_data_escape(xop, name, nlen);
        xo_data_append(xop, "=\"", 2);

        xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);

        xo_data_append(xop, "\" ", 2);
        break;

    case XO_STYLE_ENCODER:
        if (flags & XFF_DISPLAY_ONLY) {
            xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
            break;
        }

        if (flags & XFF_QUOTE)
            quote = 1;
        else if (flags & XFF_NOQUOTE)
            quote = 0;
        else if (flen == 0) {
            quote = 0;
            fmt = "true";       /* JSON encodes empty tags as a boolean true */
            flen = 4;
        } else if (strchr("diouxXDOUeEfFgGaAcCp", fmt[flen - 1]) == NULL)
            quote = 1;
        else
            quote = 0;

        if (encoding) {
            fmt = encoding;
            flen = elen;
        } else {
            char *enc  = alloca(flen + 1);
            memcpy(enc, fmt, flen);
            enc[flen] = '\0';
            fmt = xo_fix_encoding(xop, enc);
            flen = strlen(fmt);
        }

        if (nlen == 0) {
            static char missing[] = "missing-field-name";
            xo_failure(xop, "missing field name: %s", fmt);
            name = missing;
            nlen = sizeof(missing) - 1;
        }

        ssize_t name_offset = xo_buf_offset(&xop->xo_data);
        xo_data_append(xop, name, nlen);
        xo_data_append(xop, "", 1);

        ssize_t value_offset = xo_buf_offset(&xop->xo_data);

        xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);

        xo_data_append(xop, "", 1);

        xo_encoder_handle(xop, quote ? XO_OP_STRING : XO_OP_CONTENT,
                          xo_buf_data(&xop->xo_data, name_offset),
                          xo_buf_data(&xop->xo_data, value_offset), flags);
        xo_buf_reset(&xop->xo_data);
        break;
    }
}

static void
xo_set_gettext_domain (xo_handle_t *xop, xo_field_info_t *xfip,
                       const char *str, ssize_t len)
{
    const char *fmt = xfip->xfi_format;
    ssize_t flen = xfip->xfi_flen;

    /* Start by discarding previous domain */
    if (xop->xo_gt_domain) {
        xo_free(xop->xo_gt_domain);
        xop->xo_gt_domain = NULL;
    }

    /* An empty {G:} means no domainname */
    if (len == 0 && flen == 0)
        return;

    ssize_t start_offset = -1;
    if (len == 0 && flen != 0) {
        /* Need to do format the data to get the domainname from args */
        start_offset = xop->xo_data.xb_curp - xop->xo_data.xb_bufp;
        xo_do_format_field(xop, NULL, fmt, flen, 0);

        ssize_t end_offset = xop->xo_data.xb_curp - xop->xo_data.xb_bufp;
        len = end_offset - start_offset;
        str = xop->xo_data.xb_bufp + start_offset;
    }

    xop->xo_gt_domain = xo_strndup(str, len);

    /* Reset the current buffer point to avoid emitting the name as output */
    if (start_offset >= 0)
        xop->xo_data.xb_curp = xop->xo_data.xb_bufp + start_offset;
}

static void
xo_format_content (xo_handle_t *xop, const char *class_name,
                   const char *tag_name,
                   const char *value, ssize_t vlen,
                   const char *fmt, ssize_t flen,
                   xo_xff_flags_t flags)
{
    switch (xo_style(xop)) {
    case XO_STYLE_TEXT:
        xo_simple_field(xop, FALSE, value, vlen, fmt, flen, flags);
        break;

    case XO_STYLE_HTML:
        xo_buf_append_div(xop, class_name, flags, NULL, 0,
                          value, vlen, fmt, flen, NULL, 0);
        break;

    case XO_STYLE_XML:
    case XO_STYLE_JSON:
    case XO_STYLE_SDPARAMS:
        if (tag_name) {
            xo_open_container_h(xop, tag_name);
            xo_format_value(xop, "message", 7, value, vlen,
                            fmt, flen, NULL, 0, flags);
            xo_close_container_h(xop, tag_name);

        } else {
            /*
             * Even though we don't care about labels, we need to do
             * enough parsing work to skip over the right bits of xo_vap.
             */
            xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
        }
        break;

    case XO_STYLE_ENCODER:
        xo_simple_field(xop, TRUE, value, vlen, fmt, flen, flags);
        break;
    }
}

static const char *xo_color_names[] = {
    "default",  /* XO_COL_DEFAULT */
    "black",    /* XO_COL_BLACK */
    "red",      /* XO_CLOR_RED */
    "green",    /* XO_COL_GREEN */
    "yellow",   /* XO_COL_YELLOW */
    "blue",     /* XO_COL_BLUE */
    "magenta",  /* XO_COL_MAGENTA */
    "cyan",     /* XO_COL_CYAN */
    "white",    /* XO_COL_WHITE */
    NULL
};

static int
xo_color_find (const char *str)
{
    int i;

    for (i = 0; xo_color_names[i]; i++) {
        if (strcmp(xo_color_names[i], str) == 0)
            return i;
    }

    return -1;
}

static const char *xo_effect_names[] = {
    "reset",                    /* XO_EFF_RESET */
    "normal",                   /* XO_EFF_NORMAL */
    "bold",                     /* XO_EFF_BOLD */
    "underline",                /* XO_EFF_UNDERLINE */
    "inverse",                  /* XO_EFF_INVERSE */
    NULL
};

static const char *xo_effect_on_codes[] = {
    "0",                        /* XO_EFF_RESET */
    "0",                        /* XO_EFF_NORMAL */
    "1",                        /* XO_EFF_BOLD */
    "4",                        /* XO_EFF_UNDERLINE */
    "7",                        /* XO_EFF_INVERSE */
    NULL
};

#if 0
/*
 * See comment below re: joy of terminal standards.  These can
 * be use by just adding:
 * +    if (newp->xoc_effects & bit)
 *          code = xo_effect_on_codes[i];
 * +    else
 * +        code = xo_effect_off_codes[i];
 * in xo_color_handle_text.
 */
static const char *xo_effect_off_codes[] = {
    "0",                        /* XO_EFF_RESET */
    "0",                        /* XO_EFF_NORMAL */
    "21",                       /* XO_EFF_BOLD */
    "24",                       /* XO_EFF_UNDERLINE */
    "27",                       /* XO_EFF_INVERSE */
    NULL
};
#endif /* 0 */

static int
xo_effect_find (const char *str)
{
    int i;

    for (i = 0; xo_effect_names[i]; i++) {
        if (strcmp(xo_effect_names[i], str) == 0)
            return i;
    }

    return -1;
}

static void
xo_colors_parse (xo_handle_t *xop, xo_colors_t *xocp, char *str)
{
    if (xo_text_only())
        return;

    char *cp, *ep, *np, *xp;
    ssize_t len = strlen(str);
    int rc;

    /*
     * Possible tokens: colors, bg-colors, effects, no-effects, "reset".
     */
    for (cp = str, ep = cp + len - 1; cp && cp < ep; cp = np) {
        /* Trim leading whitespace */
        while (isspace((int) *cp))
            cp += 1;

        np = strchr(cp, ',');
        if (np)
            *np++ = '\0';

        /* Trim trailing whitespace */
        xp = cp + strlen(cp) - 1;
        while (isspace(*xp) && xp > cp)
            *xp-- = '\0';

        if (cp[0] == 'f' && cp[1] == 'g' && cp[2] == '-') {
            rc = xo_color_find(cp + 3);
            if (rc < 0)
                goto unknown;

            xocp->xoc_col_fg = rc;

        } else if (cp[0] == 'b' && cp[1] == 'g' && cp[2] == '-') {
            rc = xo_color_find(cp + 3);
            if (rc < 0)
                goto unknown;
            xocp->xoc_col_bg = rc;

        } else if (cp[0] == 'n' && cp[1] == 'o' && cp[2] == '-') {
            rc = xo_effect_find(cp + 3);
            if (rc < 0)
                goto unknown;
            xocp->xoc_effects &= ~(1 << rc);

        } else {
            rc = xo_effect_find(cp);
            if (rc < 0)
                goto unknown;
            xocp->xoc_effects |= 1 << rc;

            switch (1 << rc) {
            case XO_EFF_RESET:
                xocp->xoc_col_fg = xocp->xoc_col_bg = 0;
                /* Note: not "|=" since we want to wipe out the old value */
                xocp->xoc_effects = XO_EFF_RESET;
                break;

            case XO_EFF_NORMAL:
                xocp->xoc_effects &= ~(XO_EFF_BOLD | XO_EFF_UNDERLINE
                                      | XO_EFF_INVERSE | XO_EFF_NORMAL);
                break;
            }
        }
        continue;

    unknown:
        if (XOF_ISSET(xop, XOF_WARN))
            xo_failure(xop, "unknown color/effect string detected: '%s'", cp);
    }
}

static inline int
xo_colors_enabled (xo_handle_t *xop UNUSED)
{
#ifdef LIBXO_TEXT_ONLY
    return 0;
#else /* LIBXO_TEXT_ONLY */
    return XOF_ISSET(xop, XOF_COLOR);
#endif /* LIBXO_TEXT_ONLY */
}

/*
 * If the color map is in use (--libxo colors=xxxx), then update
 * the incoming foreground and background colors from the map.
 */
static void
xo_colors_update (xo_handle_t *xop UNUSED, xo_colors_t *newp UNUSED)
{
#ifndef LIBXO_TEXT_ONLY
    xo_color_t fg = newp->xoc_col_fg;
    if (XOF_ISSET(xop, XOF_COLOR_MAP) && fg < XO_NUM_COLORS)
        fg = xop->xo_color_map_fg[fg]; /* Fetch from color map */
    newp->xoc_col_fg = fg;

    xo_color_t bg = newp->xoc_col_bg;
    if (XOF_ISSET(xop, XOF_COLOR_MAP) && bg < XO_NUM_COLORS)
        bg = xop->xo_color_map_bg[bg]; /* Fetch from color map */
    newp->xoc_col_bg = bg;
#endif /* LIBXO_TEXT_ONLY */
}

static void
xo_colors_handle_text (xo_handle_t *xop, xo_colors_t *newp)
{
    char buf[BUFSIZ];
    char *cp = buf, *ep = buf + sizeof(buf);
    unsigned i, bit;
    xo_colors_t *oldp = &xop->xo_colors;
    const char *code = NULL;

    /*
     * Start the buffer with an escape.  We don't want to add the '['
     * now, since we let xo_effect_text_add unconditionally add the ';'.
     * We'll replace the first ';' with a '[' when we're done.
     */
    *cp++ = 0x1b;               /* Escape */

    /*
     * Terminals were designed back in the age before "certainty" was
     * invented, when standards were more what you'd call "guidelines"
     * than actual rules.  Anyway we can't depend on them to operate
     * correctly.  So when display attributes are changed, we punt,
     * reseting them all and turning back on the ones we want to keep.
     * Longer, but should be completely reliable.  Savvy?
     */
    if (oldp->xoc_effects != (newp->xoc_effects & oldp->xoc_effects)) {
        newp->xoc_effects |= XO_EFF_RESET;
        oldp->xoc_effects = 0;
    }

    for (i = 0, bit = 1; xo_effect_names[i]; i++, bit <<= 1) {
        if ((newp->xoc_effects & bit) == (oldp->xoc_effects & bit))
            continue;

        code = xo_effect_on_codes[i];

        cp += snprintf(cp, ep - cp, ";%s", code);
        if (cp >= ep)
            return;             /* Should not occur */

        if (bit == XO_EFF_RESET) {
            /* Mark up the old value so we can detect current values as new */
            oldp->xoc_effects = 0;
            oldp->xoc_col_fg = oldp->xoc_col_bg = XO_COL_DEFAULT;
        }
    }

    xo_color_t fg = newp->xoc_col_fg;
    if (fg != oldp->xoc_col_fg) {
        cp += snprintf(cp, ep - cp, ";3%u",
                       (fg != XO_COL_DEFAULT) ? fg - 1 : 9);
    }

    xo_color_t bg = newp->xoc_col_bg;
    if (bg != oldp->xoc_col_bg) {
        cp += snprintf(cp, ep - cp, ";4%u",
                       (bg != XO_COL_DEFAULT) ? bg - 1 : 9);
    }

    if (cp - buf != 1 && cp < ep - 3) {
        buf[1] = '[';           /* Overwrite leading ';' */
        *cp++ = 'm';
        *cp = '\0';
        xo_buf_append(&xop->xo_data, buf, cp - buf);
    }
}

static void
xo_colors_handle_html (xo_handle_t *xop, xo_colors_t *newp)
{
    xo_colors_t *oldp = &xop->xo_colors;

    /*
     * HTML colors are mostly trivial: fill in xo_color_buf with
     * a set of class tags representing the colors and effects.
     */

    /* If nothing changed, then do nothing */
    if (oldp->xoc_effects == newp->xoc_effects
        && oldp->xoc_col_fg == newp->xoc_col_fg
        && oldp->xoc_col_bg == newp->xoc_col_bg)
        return;

    unsigned i, bit;
    xo_buffer_t *xbp = &xop->xo_color_buf;

    xo_buf_reset(xbp);          /* We rebuild content after each change */

    for (i = 0, bit = 1; xo_effect_names[i]; i++, bit <<= 1) {
        if (!(newp->xoc_effects & bit))
            continue;

        xo_buf_append_str(xbp, " effect-");
        xo_buf_append_str(xbp, xo_effect_names[i]);
    }

    const char *fg = NULL;
    const char *bg = NULL;

    if (newp->xoc_col_fg != XO_COL_DEFAULT)
        fg = xo_color_names[newp->xoc_col_fg];
    if (newp->xoc_col_bg != XO_COL_DEFAULT)
        bg = xo_color_names[newp->xoc_col_bg];

    if (newp->xoc_effects & XO_EFF_INVERSE) {
        const char *tmp = fg;
        fg = bg;
        bg = tmp;
        if (fg == NULL)
            fg = "inverse";
        if (bg == NULL)
            bg = "inverse";

    }

    if (fg) {
        xo_buf_append_str(xbp, " color-fg-");
        xo_buf_append_str(xbp, fg);
    }

    if (bg) {
        xo_buf_append_str(xbp, " color-bg-");
        xo_buf_append_str(xbp, bg);
    }
}

static void
xo_format_colors (xo_handle_t *xop, xo_field_info_t *xfip,
                  const char *value, ssize_t vlen)
{
    const char *fmt = xfip->xfi_format;
    ssize_t flen = xfip->xfi_flen;

    xo_buffer_t xb;

    /* If the string is static and we've in an encoding style, bail */
    if (vlen != 0 && xo_style_is_encoding(xop))
        return;

    xo_buf_init(&xb);

    if (vlen)
        xo_buf_append(&xb, value, vlen);
    else if (flen)
        xo_do_format_field(xop, &xb, fmt, flen, 0);
    else
        xo_buf_append(&xb, "reset", 6); /* Default if empty */

    if (xo_colors_enabled(xop)) {
        switch (xo_style(xop)) {
        case XO_STYLE_TEXT:
        case XO_STYLE_HTML:
            xo_buf_append(&xb, "", 1);

            xo_colors_t xoc = xop->xo_colors;
            xo_colors_parse(xop, &xoc, xb.xb_bufp);
            xo_colors_update(xop, &xoc);

            if (xo_style(xop) == XO_STYLE_TEXT) {
                /*
                 * Text mode means emitting the colors as ANSI character
                 * codes.  This will allow people who like colors to have
                 * colors.  The issue is, of course conflicting with the
                 * user's perfectly reasonable color scheme.  Which leads
                 * to the hell of LSCOLORS, where even app need to have
                 * customization hooks for adjusting colors.  Instead we
                 * provide a simpler-but-still-annoying answer where one
                 * can map colors to other colors.
                 */
                xo_colors_handle_text(xop, &xoc);
                xoc.xoc_effects &= ~XO_EFF_RESET; /* After handling it */

            } else {
                /*
                 * HTML output is wrapped in divs, so the color information
                 * must appear in every div until cleared.  Most pathetic.
                 * Most unavoidable.
                 */
                xoc.xoc_effects &= ~XO_EFF_RESET; /* Before handling effects */
                xo_colors_handle_html(xop, &xoc);
            }

            xop->xo_colors = xoc;
            break;

        case XO_STYLE_XML:
        case XO_STYLE_JSON:
        case XO_STYLE_SDPARAMS:
        case XO_STYLE_ENCODER:
            /*
             * Nothing to do; we did all that work just to clear the stack of
             * formatting arguments.
             */
            break;
        }
    }

    xo_buf_cleanup(&xb);
}

static void
xo_format_units (xo_handle_t *xop, xo_field_info_t *xfip,
                 const char *value, ssize_t vlen)
{
    const char *fmt = xfip->xfi_format;
    ssize_t flen = xfip->xfi_flen;
    xo_xff_flags_t flags = xfip->xfi_flags;

    static char units_start_xml[] = " units=\"";
    static char units_start_html[] = " data-units=\"";

    if (!XOIF_ISSET(xop, XOIF_UNITS_PENDING)) {
        xo_format_content(xop, "units", NULL, value, vlen, fmt, flen, flags);
        return;
    }

    xo_buffer_t *xbp = &xop->xo_data;
    ssize_t start = xop->xo_units_offset;
    ssize_t stop = xbp->xb_curp - xbp->xb_bufp;

    if (xo_style(xop) == XO_STYLE_XML)
        xo_buf_append(xbp, units_start_xml, sizeof(units_start_xml) - 1);
    else if (xo_style(xop) == XO_STYLE_HTML)
        xo_buf_append(xbp, units_start_html, sizeof(units_start_html) - 1);
    else
        return;

    if (vlen)
        xo_data_escape(xop, value, vlen);
    else
        xo_do_format_field(xop, NULL, fmt, flen, flags);

    xo_buf_append(xbp, "\"", 1);

    ssize_t now = xbp->xb_curp - xbp->xb_bufp;
    ssize_t delta = now - stop;
    if (delta <= 0) {           /* Strange; no output to move */
        xbp->xb_curp = xbp->xb_bufp + stop; /* Reset buffer to prior state */
        return;
    }

    /*
     * Now we're in it alright.  We've need to insert the unit value
     * we just created into the right spot.  We make a local copy,
     * move it and then insert our copy.  We know there's room in the
     * buffer, since we're just moving this around.
     */
    char *buf = alloca(delta);

    memcpy(buf, xbp->xb_bufp + stop, delta);
    memmove(xbp->xb_bufp + start + delta, xbp->xb_bufp + start, stop - start);
    memmove(xbp->xb_bufp + start, buf, delta);
}

static ssize_t
xo_find_width (xo_handle_t *xop, xo_field_info_t *xfip,
               const char *value, ssize_t vlen)
{
    const char *fmt = xfip->xfi_format;
    ssize_t flen = xfip->xfi_flen;

    long width = 0;
    char *bp;
    char *cp;

    if (vlen) {
        bp = alloca(vlen + 1);  /* Make local NUL-terminated copy of value */
        memcpy(bp, value, vlen);
        bp[vlen] = '\0';

        width = strtol(bp, &cp, 0);
        if (width == LONG_MIN || width == LONG_MAX || bp == cp || *cp != '\0') {
            width = 0;
            xo_failure(xop, "invalid width for anchor: '%s'", bp);
        }
    } else if (flen) {
        /*
         * We really expect the format for width to be "{:/%d}" or
         * "{:/%u}", so if that's the case, we just grab our width off
         * the argument list.  But we need to avoid optimized logic if
         * there's a custom formatter.
         */
        if (xop->xo_formatter == NULL && flen == 2
                && strncmp("%d", fmt, flen) == 0) {
            if (!XOF_ISSET(xop, XOF_NO_VA_ARG))
                width = va_arg(xop->xo_vap, int);
        } else if (xop->xo_formatter == NULL && flen == 2
                   && strncmp("%u", fmt, flen) == 0) {
            if (!XOF_ISSET(xop, XOF_NO_VA_ARG))
                width = va_arg(xop->xo_vap, unsigned);
        } else {
            /*
             * So we have a format and it's not a simple one like
             * "{:/%d}".  That means we need to format the field,
             * extract the value from the formatted output, and then
             * discard that output.
             */
            int anchor_was_set = FALSE;
            xo_buffer_t *xbp = &xop->xo_data;
            ssize_t start_offset = xo_buf_offset(xbp);
            bp = xo_buf_cur(xbp);       /* Save start of the string */
            cp = NULL;

            if (XOIF_ISSET(xop, XOIF_ANCHOR)) {
                XOIF_CLEAR(xop, XOIF_ANCHOR);
                anchor_was_set = TRUE;
            }

            ssize_t rc = xo_do_format_field(xop, xbp, fmt, flen, 0);
            if (rc >= 0) {
                xo_buf_append(xbp, "", 1); /* Append a NUL */

                width = strtol(bp, &cp, 0);
                if (width == LONG_MIN || width == LONG_MAX
                        || bp == cp || *cp != '\0') {
                    width = 0;
                    xo_failure(xop, "invalid width for anchor: '%s'", bp);
                }
            }

            /* Reset the cur pointer to where we found it */
            xbp->xb_curp = xbp->xb_bufp + start_offset;
            if (anchor_was_set)
                XOIF_SET(xop, XOIF_ANCHOR);
        }
    }

    return width;
}

static void
xo_anchor_clear (xo_handle_t *xop)
{
    XOIF_CLEAR(xop, XOIF_ANCHOR);
    xop->xo_anchor_offset = 0;
    xop->xo_anchor_columns = 0;
    xop->xo_anchor_min_width = 0;
}

/*
 * An anchor is a marker used to delay field width implications.
 * Imagine the format string "{[:10}{min:%d}/{cur:%d}/{max:%d}{:]}".
 * We are looking for output like "     1/4/5"
 *
 * To make this work, we record the anchor and then return to
 * format it when the end anchor tag is seen.
 */
static void
xo_anchor_start (xo_handle_t *xop, xo_field_info_t *xfip,
                 const char *value, ssize_t vlen)
{
    if (XOIF_ISSET(xop, XOIF_ANCHOR))
        xo_failure(xop, "the anchor already recording is discarded");

    XOIF_SET(xop, XOIF_ANCHOR);
    xo_buffer_t *xbp = &xop->xo_data;
    xop->xo_anchor_offset = xbp->xb_curp - xbp->xb_bufp;
    xop->xo_anchor_columns = 0;

    /*
     * Now we find the width, if possible.  If it's not there,
     * we'll get it on the end anchor.
     */
    xop->xo_anchor_min_width = xo_find_width(xop, xfip, value, vlen);
}

static void
xo_anchor_stop (xo_handle_t *xop, xo_field_info_t *xfip,
                 const char *value, ssize_t vlen)
{
    if (!XOIF_ISSET(xop, XOIF_ANCHOR)) {
        xo_failure(xop, "no start anchor");
        return;
    }

    XOIF_CLEAR(xop, XOIF_UNITS_PENDING);

    ssize_t width = xo_find_width(xop, xfip, value, vlen);
    if (width == 0)
        width = xop->xo_anchor_min_width;

    if (width == 0)             /* No width given; nothing to do */
        goto done;

    xo_buffer_t *xbp = &xop->xo_data;
    ssize_t start = xop->xo_anchor_offset;
    ssize_t stop = xbp->xb_curp - xbp->xb_bufp;
    ssize_t abswidth = (width > 0) ? width : -width;
    ssize_t blen = abswidth - xop->xo_anchor_columns;

    if (blen <= 0)              /* Already over width */
        goto done;

    if (abswidth > XO_MAX_ANCHOR_WIDTH) {
        xo_failure(xop, "width over %u are not supported",
                   XO_MAX_ANCHOR_WIDTH);
        goto done;
    }

    /* Make a suitable padding field and emit it */
    char *buf = alloca(blen);
    memset(buf, ' ', blen);
    xo_format_content(xop, "padding", NULL, buf, blen, NULL, 0, 0);

    if (width < 0)              /* Already left justified */
        goto done;

    ssize_t now = xbp->xb_curp - xbp->xb_bufp;
    ssize_t delta = now - stop;
    if (delta <= 0)             /* Strange; no output to move */
        goto done;

    /*
     * Now we're in it alright.  We've need to insert the padding data
     * we just created (which might be an HTML <div> or text) before
     * the formatted data.  We make a local copy, move it and then
     * insert our copy.  We know there's room in the buffer, since
     * we're just moving this around.
     */
    if (delta > blen)
        buf = alloca(delta);    /* Expand buffer if needed */

    memcpy(buf, xbp->xb_bufp + stop, delta);
    memmove(xbp->xb_bufp + start + delta, xbp->xb_bufp + start, stop - start);
    memmove(xbp->xb_bufp + start, buf, delta);

 done:
    xo_anchor_clear(xop);
}

static const char *
xo_class_name (int ftype)
{
    switch (ftype) {
    case 'D': return "decoration";
    case 'E': return "error";
    case 'L': return "label";
    case 'N': return "note";
    case 'P': return "padding";
    case 'W': return "warning";
    }

    return NULL;
}

static const char *
xo_tag_name (int ftype)
{
    switch (ftype) {
    case 'E': return "__error";
    case 'W': return "__warning";
    }

    return NULL;
}

static int
xo_role_wants_default_format (int ftype)
{
    switch (ftype) {
        /* These roles can be completely empty and/or without formatting */
    case 'C':
    case 'G':
    case '[':
    case ']':
        return 0;
    }

    return 1;
}

static xo_mapping_t xo_role_names[] = {
    { 'C', "color" },
    { 'D', "decoration" },
    { 'E', "error" },
    { 'L', "label" },
    { 'N', "note" },
    { 'P', "padding" },
    { 'T', "title" },
    { 'U', "units" },
    { 'V', "value" },
    { 'W', "warning" },
    { '[', "start-anchor" },
    { ']', "stop-anchor" },
    { 0, NULL }
};

#define XO_ROLE_EBRACE  '{'     /* Escaped braces */
#define XO_ROLE_TEXT    '+'
#define XO_ROLE_NEWLINE '\n'

static xo_mapping_t xo_modifier_names[] = {
    { XFF_ARGUMENT, "argument" },
    { XFF_COLON, "colon" },
    { XFF_COMMA, "comma" },
    { XFF_DISPLAY_ONLY, "display" },
    { XFF_ENCODE_ONLY, "encoding" },
    { XFF_GT_FIELD, "gettext" },
    { XFF_HUMANIZE, "humanize" },
    { XFF_HUMANIZE, "hn" },
    { XFF_HN_SPACE, "hn-space" },
    { XFF_HN_DECIMAL, "hn-decimal" },
    { XFF_HN_1000, "hn-1000" },
    { XFF_KEY, "key" },
    { XFF_LEAF_LIST, "leaf-list" },
    { XFF_LEAF_LIST, "list" },
    { XFF_NOQUOTE, "no-quotes" },
    { XFF_NOQUOTE, "no-quote" },
    { XFF_GT_PLURAL, "plural" },
    { XFF_QUOTE, "quotes" },
    { XFF_QUOTE, "quote" },
    { XFF_TRIM_WS, "trim" },
    { XFF_WS, "white" },
    { 0, NULL }
};

#ifdef NOT_NEEDED_YET
static xo_mapping_t xo_modifier_short_names[] = {
    { XFF_COLON, "c" },
    { XFF_DISPLAY_ONLY, "d" },
    { XFF_ENCODE_ONLY, "e" },
    { XFF_GT_FIELD, "g" },
    { XFF_HUMANIZE, "h" },
    { XFF_KEY, "k" },
    { XFF_LEAF_LIST, "l" },
    { XFF_NOQUOTE, "n" },
    { XFF_GT_PLURAL, "p" },
    { XFF_QUOTE, "q" },
    { XFF_TRIM_WS, "t" },
    { XFF_WS, "w" },
    { 0, NULL }
};
#endif /* NOT_NEEDED_YET */

static int
xo_count_fields (xo_handle_t *xop UNUSED, const char *fmt)
{
    int rc = 1;
    const char *cp;

    for (cp = fmt; *cp; cp++)
        if (*cp == '{' || *cp == '\n')
            rc += 1;

    return rc * 2 + 1;
}

/*
 * The field format is:
 *  '{' modifiers ':' content [ '/' print-fmt [ '/' encode-fmt ]] '}'
 * Roles are optional and include the following field types:
 *   'D': decoration; something non-text and non-data (colons, commmas)
 *   'E': error message
 *   'G': gettext() the entire string; optional domainname as content
 *   'L': label; text preceding data
 *   'N': note; text following data
 *   'P': padding; whitespace
 *   'T': Title, where 'content' is a column title
 *   'U': Units, where 'content' is the unit label
 *   'V': value, where 'content' is the name of the field (the default)
 *   'W': warning message
 *   '[': start a section of anchored text
 *   ']': end a section of anchored text
 * The following modifiers are also supported:
 *   'a': content is provided via argument (const char *), not descriptor
 *   'c': flag: emit a colon after the label
 *   'd': field is only emitted for display styles (text and html)
 *   'e': field is only emitted for encoding styles (xml and json)
 *   'g': gettext() the field
 *   'h': humanize a numeric value (only for display styles)
 *   'k': this field is a key, suitable for XPath predicates
 *   'l': a leaf-list, a simple list of values
 *   'n': no quotes around this field
 *   'p': the field has plural gettext semantics (ngettext)
 *   'q': add quotes around this field
 *   't': trim whitespace around the value
 *   'w': emit a blank after the label
 * The print-fmt and encode-fmt strings is the printf-style formating
 * for this data.  JSON and XML will use the encoding-fmt, if present.
 * If the encode-fmt is not provided, it defaults to the print-fmt.
 * If the print-fmt is not provided, it defaults to 's'.
 */
static const char *
xo_parse_roles (xo_handle_t *xop, const char *fmt,
                const char *basep, xo_field_info_t *xfip)
{
    const char *sp;
    unsigned ftype = 0;
    xo_xff_flags_t flags = 0;
    uint8_t fnum = 0;

    for (sp = basep; sp && *sp; sp++) {
        if (*sp == ':' || *sp == '/' || *sp == '}')
            break;

        if (*sp == '\\') {
            if (sp[1] == '\0') {
                xo_failure(xop, "backslash at the end of string");
                return NULL;
            }

            /* Anything backslashed is ignored */
            sp += 1;
            continue;
        }

        if (*sp == ',') {
            const char *np;
            for (np = ++sp; *np; np++)
                if (*np == ':' || *np == '/' || *np == '}' || *np == ',')
                    break;

            ssize_t slen = np - sp;
            if (slen > 0) {
                xo_xff_flags_t value;

                value = xo_name_lookup(xo_role_names, sp, slen);
                if (value)
                    ftype = value;
                else {
                    value = xo_name_lookup(xo_modifier_names, sp, slen);
                    if (value)
                        flags |= value;
                    else
                        xo_failure(xop, "unknown keyword ignored: '%.*s'",
                                   slen, sp);
                }
            }

            sp = np - 1;
            continue;
        }

        switch (*sp) {
        case 'C':
        case 'D':
        case 'E':
        case 'G':
        case 'L':
        case 'N':
        case 'P':
        case 'T':
        case 'U':
        case 'V':
        case 'W':
        case '[':
        case ']':
            if (ftype != 0) {
                xo_failure(xop, "field descriptor uses multiple types: '%s'",
                           xo_printable(fmt));
                return NULL;
            }
            ftype = *sp;
            break;

        case '0':
        case '1':
        case '2':
        case '3':
        case '4':
        case '5':
        case '6':
        case '7':
        case '8':
        case '9':
            fnum = (fnum * 10) + (*sp - '0');
            break;

        case 'a':
            flags |= XFF_ARGUMENT;
            break;

        case 'c':
            flags |= XFF_COLON;
            break;

        case 'd':
            flags |= XFF_DISPLAY_ONLY;
            break;

        case 'e':
            flags |= XFF_ENCODE_ONLY;
            break;

        case 'g':
            flags |= XFF_GT_FIELD;
            break;

        case 'h':
            flags |= XFF_HUMANIZE;
            break;

        case 'k':
            flags |= XFF_KEY;
            break;

        case 'l':
            flags |= XFF_LEAF_LIST;
            break;

        case 'n':
            flags |= XFF_NOQUOTE;
            break;

        case 'p':
            flags |= XFF_GT_PLURAL;
            break;

        case 'q':
            flags |= XFF_QUOTE;
            break;

        case 't':
            flags |= XFF_TRIM_WS;
            break;

        case 'w':
            flags |= XFF_WS;
            break;

        default:
            xo_failure(xop, "field descriptor uses unknown modifier: '%s'",
                       xo_printable(fmt));
            /*
             * No good answer here; a bad format will likely
             * mean a core file.  We just return and hope
             * the caller notices there's no output, and while
             * that seems, well, bad, there's nothing better.
             */
            return NULL;
        }

        if (ftype == 'N' || ftype == 'U') {
            if (flags & XFF_COLON) {
                xo_failure(xop, "colon modifier on 'N' or 'U' field ignored: "
                           "'%s'", xo_printable(fmt));
                flags &= ~XFF_COLON;
            }
        }
    }

    xfip->xfi_flags = flags;
    xfip->xfi_ftype = ftype ?: 'V';
    xfip->xfi_fnum = fnum;

    return sp;
}

/*
 * Number any remaining fields that need numbers.  Note that some
 * field types (text, newline, escaped braces) never get numbers.
 */
static void
xo_gettext_finish_numbering_fields (xo_handle_t *xop UNUSED,
                                    const char *fmt UNUSED,
                                    xo_field_info_t *fields)
{
    xo_field_info_t *xfip;
    unsigned fnum, max_fields;
    uint64_t bits = 0;

    /* First make a list of add the explicitly used bits */
    for (xfip = fields, fnum = 0; xfip->xfi_ftype; xfip++) {
        switch (xfip->xfi_ftype) {
        case XO_ROLE_NEWLINE:   /* Don't get numbered */
        case XO_ROLE_TEXT:
        case XO_ROLE_EBRACE:
        case 'G':
            continue;
        }

        fnum += 1;
        if (fnum >= 63)
            break;

        if (xfip->xfi_fnum)
            bits |= 1 << xfip->xfi_fnum;
    }

    max_fields = fnum;

    for (xfip = fields, fnum = 0; xfip->xfi_ftype; xfip++) {
        switch (xfip->xfi_ftype) {
        case XO_ROLE_NEWLINE:   /* Don't get numbered */
        case XO_ROLE_TEXT:
        case XO_ROLE_EBRACE:
        case 'G':
            continue;
        }

        if (xfip->xfi_fnum != 0)
            continue;

        /* Find the next unassigned field */
        for (fnum++; bits & (1 << fnum); fnum++)
            continue;

        if (fnum > max_fields)
            break;

        xfip->xfi_fnum = fnum;  /* Mark the field number */
        bits |= 1 << fnum;      /* Mark it used */
    }
}

/*
 * The format string uses field numbers, so we need to whiffle through it
 * and make sure everything's sane and lovely.
 */
static int
xo_parse_field_numbers (xo_handle_t *xop, const char *fmt,
                        xo_field_info_t *fields, unsigned num_fields)
{
    xo_field_info_t *xfip;
    unsigned field, fnum;
    uint64_t bits = 0;

    for (xfip = fields, field = 0; field < num_fields; xfip++, field++) {
        /* Fields default to 1:1 with natural position */
        if (xfip->xfi_fnum == 0)
            xfip->xfi_fnum = field + 1;
        else if (xfip->xfi_fnum > num_fields) {
            xo_failure(xop, "field number exceeds number of fields: '%s'", fmt);
            return -1;
        }

        fnum = xfip->xfi_fnum - 1; /* Move to zero origin */
        if (fnum < 64) {        /* Only test what fits */
            if (bits & (1 << fnum)) {
                xo_failure(xop, "field number %u reused: '%s'",
                           xfip->xfi_fnum, fmt);
                return -1;
            }
            bits |= 1 << fnum;
        }
    }

    return 0;
}

static int
xo_parse_fields (xo_handle_t *xop, xo_field_info_t *fields,
                 unsigned num_fields, const char *fmt)
{
    const char *cp, *sp, *ep, *basep;
    unsigned field = 0;
    xo_field_info_t *xfip = fields;
    unsigned seen_fnum = 0;

    for (cp = fmt; *cp && field < num_fields; field++, xfip++) {
        xfip->xfi_start = cp;

        if (*cp == '\n') {
            xfip->xfi_ftype = XO_ROLE_NEWLINE;
            xfip->xfi_len = 1;
            cp += 1;
            continue;
        }

        if (*cp != '{') {
            /* Normal text */
            for (sp = cp; *sp; sp++) {
                if (*sp == '{' || *sp == '\n')
                    break;
            }

            xfip->xfi_ftype = XO_ROLE_TEXT;
            xfip->xfi_content = cp;
            xfip->xfi_clen = sp - cp;
            xfip->xfi_next = sp;

            cp = sp;
            continue;
        }

        if (cp[1] == '{') {     /* Start of {{escaped braces}} */
            xfip->xfi_start = cp + 1; /* Start at second brace */
            xfip->xfi_ftype = XO_ROLE_EBRACE;

            cp += 2;    /* Skip over _both_ characters */
            for (sp = cp; *sp; sp++) {
                if (*sp == '}' && sp[1] == '}')
                    break;
            }
            if (*sp == '\0') {
                xo_failure(xop, "missing closing '}}': '%s'",
                           xo_printable(fmt));
                return -1;
            }

            xfip->xfi_len = sp - xfip->xfi_start + 1;

            /* Move along the string, but don't run off the end */
            if (*sp == '}' && sp[1] == '}')
                sp += 2;
            cp = *sp ? sp : sp;
            xfip->xfi_next = cp;
            continue;
        }

        /* We are looking at the start of a field definition */
        xfip->xfi_start = basep = cp + 1;

        const char *format = NULL;
        ssize_t flen = 0;

        /* Looking at roles and modifiers */
        sp = xo_parse_roles(xop, fmt, basep, xfip);
        if (sp == NULL) {
            /* xo_failure has already been called */
            return -1;
        }

        if (xfip->xfi_fnum)
            seen_fnum = 1;

        /* Looking at content */
        if (*sp == ':') {
            for (ep = ++sp; *sp; sp++) {
                if (*sp == '}' || *sp == '/')
                    break;
                if (*sp == '\\') {
                    if (sp[1] == '\0') {
                        xo_failure(xop, "backslash at the end of string");
                        return -1;
                    }
                    sp += 1;
                    continue;
                }
            }
            if (ep != sp) {
                xfip->xfi_clen = sp - ep;
                xfip->xfi_content = ep;
            }
        } else {
            xo_failure(xop, "missing content (':'): '%s'", xo_printable(fmt));
            return -1;
        }

        /* Looking at main (display) format */
        if (*sp == '/') {
            for (ep = ++sp; *sp; sp++) {
                if (*sp == '}' || *sp == '/')
                    break;
                if (*sp == '\\') {
                    if (sp[1] == '\0') {
                        xo_failure(xop, "backslash at the end of string");
                        return -1;
                    }
                    sp += 1;
                    continue;
                }
            }
            flen = sp - ep;
            format = ep;
        }

        /* Looking at encoding format */
        if (*sp == '/') {
            for (ep = ++sp; *sp; sp++) {
                if (*sp == '}')
                    break;
            }

            xfip->xfi_encoding = ep;
            xfip->xfi_elen = sp - ep;
        }

        if (*sp != '}') {
            xo_failure(xop, "missing closing '}': %s", xo_printable(fmt));
            return -1;
        }

        xfip->xfi_len = sp - xfip->xfi_start;
        xfip->xfi_next = ++sp;

        /* If we have content, then we have a default format */
        if (xfip->xfi_clen || format || (xfip->xfi_flags & XFF_ARGUMENT)) {
            if (format) {
                xfip->xfi_format = format;
                xfip->xfi_flen = flen;
            } else if (xo_role_wants_default_format(xfip->xfi_ftype)) {
                xfip->xfi_format = xo_default_format;
                xfip->xfi_flen = 2;
            }
        }

        cp = sp;
    }

    int rc = 0;

    /*
     * If we saw a field number on at least one field, then we need
     * to enforce some rules and/or guidelines.
     */
    if (seen_fnum)
        rc = xo_parse_field_numbers(xop, fmt, fields, field);

    return rc;
}

/*
 * We are passed a pointer to a format string just past the "{G:}"
 * field.  We build a simplified version of the format string.
 */
static int
xo_gettext_simplify_format (xo_handle_t *xop UNUSED,
                       xo_buffer_t *xbp,
                       xo_field_info_t *fields,
                       int this_field,
                       const char *fmt UNUSED,
                       xo_simplify_field_func_t field_cb)
{
    unsigned ftype;
    xo_xff_flags_t flags;
    int field = this_field + 1;
    xo_field_info_t *xfip;
    char ch;

    for (xfip = &fields[field]; xfip->xfi_ftype; xfip++, field++) {
        ftype = xfip->xfi_ftype;
        flags = xfip->xfi_flags;

        if ((flags & XFF_GT_FIELD) && xfip->xfi_content && ftype != 'V') {
            if (field_cb)
                field_cb(xfip->xfi_content, xfip->xfi_clen,
                         (flags & XFF_GT_PLURAL) ? 1 : 0);
        }

        switch (ftype) {
        case 'G':
            /* Ignore gettext roles */
            break;

        case XO_ROLE_NEWLINE:
            xo_buf_append(xbp, "\n", 1);
            break;

        case XO_ROLE_EBRACE:
            xo_buf_append(xbp, "{", 1);
            xo_buf_append(xbp, xfip->xfi_content, xfip->xfi_clen);
            xo_buf_append(xbp, "}", 1);
            break;

        case XO_ROLE_TEXT:
            xo_buf_append(xbp, xfip->xfi_content, xfip->xfi_clen);
            break;

        default:
            xo_buf_append(xbp, "{", 1);
            if (ftype != 'V') {
                ch = ftype;
                xo_buf_append(xbp, &ch, 1);
            }

            unsigned fnum = xfip->xfi_fnum ?: 0;
            if (fnum) {
                char num[12];
                /* Field numbers are origin 1, not 0, following printf(3) */
                snprintf(num, sizeof(num), "%u", fnum);
                xo_buf_append(xbp, num, strlen(num));
            }

            xo_buf_append(xbp, ":", 1);
            xo_buf_append(xbp, xfip->xfi_content, xfip->xfi_clen);
            xo_buf_append(xbp, "}", 1);
        }
    }

    xo_buf_append(xbp, "", 1);
    return 0;
}

void
xo_dump_fields (xo_field_info_t *); /* Fake prototype for debug function */
void
xo_dump_fields (xo_field_info_t *fields)
{
    xo_field_info_t *xfip;

    for (xfip = fields; xfip->xfi_ftype; xfip++) {
        printf("%lu(%u): %lx [%c/%u] [%.*s] [%.*s] [%.*s]\n",
               (unsigned long) (xfip - fields), xfip->xfi_fnum,
               (unsigned long) xfip->xfi_flags,
               isprint((int) xfip->xfi_ftype) ? xfip->xfi_ftype : ' ',
               xfip->xfi_ftype,
               (int) xfip->xfi_clen, xfip->xfi_content ?: "", 
               (int) xfip->xfi_flen, xfip->xfi_format ?: "", 
               (int) xfip->xfi_elen, xfip->xfi_encoding ?: "");
    }
}

#ifdef HAVE_GETTEXT
/*
 * Find the field that matches the given field number
 */
static xo_field_info_t *
xo_gettext_find_field (xo_field_info_t *fields, unsigned fnum)
{
    xo_field_info_t *xfip;

    for (xfip = fields; xfip->xfi_ftype; xfip++)
        if (xfip->xfi_fnum == fnum)
            return xfip;

    return NULL;
}

/*
 * At this point, we need to consider if the fields have been reordered,
 * such as "The {:adjective} {:noun}" to "La {:noun} {:adjective}".
 *
 * We need to rewrite the new_fields using the old fields order,
 * so that we can render the message using the arguments as they
 * appear on the stack.  It's a lot of work, but we don't really
 * want to (eventually) fall into the standard printf code which
 * means using the arguments straight (and in order) from the
 * varargs we were originally passed.
 */
static void
xo_gettext_rewrite_fields (xo_handle_t *xop UNUSED,
                           xo_field_info_t *fields, unsigned max_fields)
{
    xo_field_info_t tmp[max_fields];
    bzero(tmp, max_fields * sizeof(tmp[0]));

    unsigned fnum = 0;
    xo_field_info_t *newp, *outp, *zp;
    for (newp = fields, outp = tmp; newp->xfi_ftype; newp++, outp++) {
        switch (newp->xfi_ftype) {
        case XO_ROLE_NEWLINE:   /* Don't get numbered */
        case XO_ROLE_TEXT:
        case XO_ROLE_EBRACE:
        case 'G':
            *outp = *newp;
            outp->xfi_renum = 0;
            continue;
        }

        zp = xo_gettext_find_field(fields, ++fnum);
        if (zp == NULL) {       /* Should not occur */
            *outp = *newp;
            outp->xfi_renum = 0;
            continue;
        }

        *outp = *zp;
        outp->xfi_renum = newp->xfi_fnum;
    }

    memcpy(fields, tmp, max_fields * sizeof(tmp[0]));
}

/*
 * We've got two lists of fields, the old list from the original
 * format string and the new one from the parsed gettext reply.  The
 * new list has the localized words, where the old list has the
 * formatting information.  We need to combine them into a single list
 * (the new list).
 *
 * If the list needs to be reordered, then we've got more serious work
 * to do.
 */
static int
xo_gettext_combine_formats (xo_handle_t *xop, const char *fmt UNUSED,
                    const char *gtfmt, xo_field_info_t *old_fields,
                    xo_field_info_t *new_fields, unsigned new_max_fields,
                    int *reorderedp)
{
    int reordered = 0;
    xo_field_info_t *newp, *oldp, *startp = old_fields;

    xo_gettext_finish_numbering_fields(xop, fmt, old_fields);

    for (newp = new_fields; newp->xfi_ftype; newp++) {
        switch (newp->xfi_ftype) {
        case XO_ROLE_NEWLINE:
        case XO_ROLE_TEXT:
        case XO_ROLE_EBRACE:
            continue;

        case 'V':
            for (oldp = startp; oldp->xfi_ftype; oldp++) {
                if (oldp->xfi_ftype != 'V')
                    continue;
                if (newp->xfi_clen != oldp->xfi_clen
                    || strncmp(newp->xfi_content, oldp->xfi_content,
                               oldp->xfi_clen) != 0) {
                    reordered = 1;
                    continue;
                }
                startp = oldp + 1;
                break;
            }

            /* Didn't find it on the first pass (starting from start) */
            if (oldp->xfi_ftype == 0) {
                for (oldp = old_fields; oldp < startp; oldp++) {
                    if (oldp->xfi_ftype != 'V')
                        continue;
                    if (newp->xfi_clen != oldp->xfi_clen)
                        continue;
                    if (strncmp(newp->xfi_content, oldp->xfi_content,
                                oldp->xfi_clen) != 0)
                        continue;
                    reordered = 1;
                    break;
                }
                if (oldp == startp) {
                    /* Field not found */
                    xo_failure(xop, "post-gettext format can't find field "
                               "'%.*s' in format '%s'",
                               newp->xfi_clen, newp->xfi_content,
                               xo_printable(gtfmt));
                    return -1;
                }
            }
            break;

        default:
            /*
             * Other fields don't have names for us to use, so if
             * the types aren't the same, then we'll have to assume
             * the original field is a match.
             */
            for (oldp = startp; oldp->xfi_ftype; oldp++) {
                if (oldp->xfi_ftype == 'V') /* Can't go past these */
                    break;
                if (oldp->xfi_ftype == newp->xfi_ftype)
                    goto copy_it; /* Assumably we have a match */
            }
            continue;
        }

        /*
         * Found a match; copy over appropriate fields
         */
    copy_it:
        newp->xfi_flags = oldp->xfi_flags;
        newp->xfi_fnum = oldp->xfi_fnum;
        newp->xfi_format = oldp->xfi_format;
        newp->xfi_flen = oldp->xfi_flen;
        newp->xfi_encoding = oldp->xfi_encoding;
        newp->xfi_elen = oldp->xfi_elen;
    }

    *reorderedp = reordered;
    if (reordered) {
        xo_gettext_finish_numbering_fields(xop, fmt, new_fields);
        xo_gettext_rewrite_fields(xop, new_fields, new_max_fields);
    }

    return 0;
}

/*
 * We don't want to make gettext() calls here with a complete format
 * string, since that means changing a flag would mean a
 * labor-intensive re-translation expense.  Instead we build a
 * simplified form with a reduced level of detail, perform a lookup on
 * that string and then re-insert the formating info.
 *
 * So something like:
 *   xo_emit("{G:}close {:fd/%ld} returned {g:error/%m} {:test/%6.6s}\n", ...)
 * would have a lookup string of:
 *   "close {:fd} returned {:error} {:test}\n"
 *
 * We also need to handling reordering of fields, where the gettext()
 * reply string uses fields in a different order than the original
 * format string:
 *   "cluse-a {:fd} retoorned {:test}.  Bork {:error} Bork. Bork.\n"
 * If we have to reorder fields within the message, then things get
 * complicated.  See xo_gettext_rewrite_fields.
 *
 * Summary: i18n aighn't cheap.
 */
static const char *
xo_gettext_build_format (xo_handle_t *xop,
                         xo_field_info_t *fields, int this_field,
                         const char *fmt, char **new_fmtp)
{
    if (xo_style_is_encoding(xop))
        goto bail;

    xo_buffer_t xb;
    xo_buf_init(&xb);

    if (xo_gettext_simplify_format(xop, &xb, fields,
                                   this_field, fmt, NULL))
        goto bail2;

    const char *gtfmt = xo_dgettext(xop, xb.xb_bufp);
    if (gtfmt == NULL || gtfmt == fmt || strcmp(gtfmt, fmt) == 0)
        goto bail2;

    char *new_fmt = xo_strndup(gtfmt, -1);
    if (new_fmt == NULL)
        goto bail2;

    xo_buf_cleanup(&xb);

    *new_fmtp = new_fmt;
    return new_fmt;

 bail2:
        xo_buf_cleanup(&xb);
 bail:
    *new_fmtp = NULL;
    return fmt;
}

static void
xo_gettext_rebuild_content (xo_handle_t *xop, xo_field_info_t *fields,
                            ssize_t *fstart, unsigned min_fstart,
                            ssize_t *fend, unsigned max_fend)
{
    xo_field_info_t *xfip;
    char *buf;
    ssize_t base = fstart[min_fstart];
    ssize_t blen = fend[max_fend] - base;
    xo_buffer_t *xbp = &xop->xo_data;

    if (blen == 0)
        return;

    buf = xo_realloc(NULL, blen);
    if (buf == NULL)
        return;

    memcpy(buf, xbp->xb_bufp + fstart[min_fstart], blen); /* Copy our data */

    unsigned field = min_fstart, len, fnum;
    ssize_t soff, doff = base;
    xo_field_info_t *zp;

    /*
     * Be aware there are two competing views of "field number": we
     * want the user to thing in terms of "The {1:size}" where {G:},
     * newlines, escaped braces, and text don't have numbers.  But is
     * also the internal view, where we have an array of
     * xo_field_info_t and every field have an index.  fnum, fstart[]
     * and fend[] are the latter, but xfi_renum is the former.
     */
    for (xfip = fields + field; xfip->xfi_ftype; xfip++, field++) {
        fnum = field;
        if (xfip->xfi_renum) {
            zp = xo_gettext_find_field(fields, xfip->xfi_renum);
            fnum = zp ? zp - fields : field;
        }

        soff = fstart[fnum];
        len = fend[fnum] - soff;

        if (len > 0) {
            soff -= base;
            memcpy(xbp->xb_bufp + doff, buf + soff, len);
            doff += len;
        }
    }

    xo_free(buf);
}
#else  /* HAVE_GETTEXT */
static const char *
xo_gettext_build_format (xo_handle_t *xop UNUSED,
                         xo_field_info_t *fields UNUSED,
                         int this_field UNUSED,
                         const char *fmt UNUSED, char **new_fmtp)
{
    *new_fmtp = NULL;
    return fmt;
}

static int
xo_gettext_combine_formats (xo_handle_t *xop UNUSED, const char *fmt UNUSED,
                    const char *gtfmt UNUSED,
                    xo_field_info_t *old_fields UNUSED,
                    xo_field_info_t *new_fields UNUSED,
                    unsigned new_max_fields UNUSED,
                    int *reorderedp UNUSED)
{
    return -1;
}

static void
xo_gettext_rebuild_content (xo_handle_t *xop UNUSED,
                    xo_field_info_t *fields UNUSED,
                    ssize_t *fstart UNUSED, unsigned min_fstart UNUSED,
                    ssize_t *fend UNUSED, unsigned max_fend UNUSED)
{
    return;
}
#endif /* HAVE_GETTEXT */

/*
 * Emit a set of fields.  This is really the core of libxo.
 */
static ssize_t
xo_do_emit_fields (xo_handle_t *xop, xo_field_info_t *fields,
                   unsigned max_fields, const char *fmt)
{
    int gettext_inuse = 0;
    int gettext_changed = 0;
    int gettext_reordered = 0;
    unsigned ftype;
    xo_xff_flags_t flags;
    xo_field_info_t *new_fields = NULL;
    xo_field_info_t *xfip;
    unsigned field;
    ssize_t rc = 0;

    int flush = XOF_ISSET(xop, XOF_FLUSH);
    int flush_line = XOF_ISSET(xop, XOF_FLUSH_LINE);
    char *new_fmt = NULL;

    if (XOIF_ISSET(xop, XOIF_REORDER) || xo_style(xop) == XO_STYLE_ENCODER)
        flush_line = 0;

    /*
     * Some overhead for gettext; if the fields in the msgstr returned
     * by gettext are reordered, then we need to record start and end
     * for each field.  We'll go ahead and render the fields in the
     * normal order, but later we can then reconstruct the reordered
     * fields using these fstart/fend values.
     */
    unsigned flimit = max_fields * 2; /* Pessimistic limit */
    unsigned min_fstart = flimit - 1;
    unsigned max_fend = 0;            /* Highest recorded fend[] entry */
    ssize_t fstart[flimit];
    bzero(fstart, flimit * sizeof(fstart[0]));
    ssize_t fend[flimit];
    bzero(fend, flimit * sizeof(fend[0]));

    for (xfip = fields, field = 0; field < max_fields && xfip->xfi_ftype;
         xfip++, field++) {
        ftype = xfip->xfi_ftype;
        flags = xfip->xfi_flags;

        /* Record field start offset */
        if (gettext_reordered) {
            fstart[field] = xo_buf_offset(&xop->xo_data);
            if (min_fstart > field)
                min_fstart = field;
        }

        const char *content = xfip->xfi_content;
        ssize_t clen = xfip->xfi_clen;

        if (flags & XFF_ARGUMENT) {
            /*
             * Argument flag means the content isn't given in the descriptor,
             * but as a UTF-8 string ('const char *') argument in xo_vap.
             */
            content = va_arg(xop->xo_vap, char *);
            clen = content ? strlen(content) : 0;
        }

        if (ftype == XO_ROLE_NEWLINE) {
            xo_line_close(xop);
            if (flush_line && xo_flush_h(xop) < 0)
                return -1;
            goto bottom;

        } else if (ftype == XO_ROLE_EBRACE) {
            xo_format_text(xop, xfip->xfi_start, xfip->xfi_len);
            goto bottom;

        } else if (ftype == XO_ROLE_TEXT) {
            /* Normal text */
            xo_format_text(xop, xfip->xfi_content, xfip->xfi_clen);
            goto bottom;
        }

        /*
         * Notes and units need the 'w' flag handled before the content.
         */
        if (ftype == 'N' || ftype == 'U') {
            if (flags & XFF_WS) {
                xo_format_content(xop, "padding", NULL, " ", 1,
                                  NULL, 0, flags);
                flags &= ~XFF_WS; /* Prevent later handling of this flag */
            }
        }

        if (ftype == 'V')
            xo_format_value(xop, content, clen, NULL, 0,
                            xfip->xfi_format, xfip->xfi_flen,
                            xfip->xfi_encoding, xfip->xfi_elen, flags);
        else if (ftype == '[')
            xo_anchor_start(xop, xfip, content, clen);
        else if (ftype == ']')
            xo_anchor_stop(xop, xfip, content, clen);
        else if (ftype == 'C')
            xo_format_colors(xop, xfip, content, clen);

        else if (ftype == 'G') {
            /*
             * A {G:domain} field; disect the domain name and translate
             * the remaining portion of the input string.  If the user
             * didn't put the {G:} at the start of the format string, then
             * assumably they just want us to translate the rest of it.
             * Since gettext returns strings in a static buffer, we make
             * a copy in new_fmt.
             */
            xo_set_gettext_domain(xop, xfip, content, clen);

            if (!gettext_inuse) { /* Only translate once */
                gettext_inuse = 1;
                if (new_fmt) {
                    xo_free(new_fmt);
                    new_fmt = NULL;
                }

                xo_gettext_build_format(xop, fields, field,
                                        xfip->xfi_next, &new_fmt);
                if (new_fmt) {
                    gettext_changed = 1;

                    unsigned new_max_fields = xo_count_fields(xop, new_fmt);

                    if (++new_max_fields < max_fields)
                        new_max_fields = max_fields;

                    /* Leave a blank slot at the beginning */
                    ssize_t sz = (new_max_fields + 1) * sizeof(xo_field_info_t);
                    new_fields = alloca(sz);
                    bzero(new_fields, sz);

                    if (!xo_parse_fields(xop, new_fields + 1,
                                         new_max_fields, new_fmt)) {
                        gettext_reordered = 0;

                        if (!xo_gettext_combine_formats(xop, fmt, new_fmt,
                                        fields, new_fields + 1,
                                        new_max_fields, &gettext_reordered)) {

                            if (gettext_reordered) {
                                if (XOF_ISSET(xop, XOF_LOG_GETTEXT))
                                    xo_failure(xop, "gettext finds reordered "
                                               "fields in '%s' and '%s'",
                                               xo_printable(fmt),
                                               xo_printable(new_fmt));
                                flush_line = 0; /* Must keep at content */
                                XOIF_SET(xop, XOIF_REORDER);
                            }

                            field = -1; /* Will be incremented at top of loop */
                            xfip = new_fields;
                            max_fields = new_max_fields;
                        }
                    }
                }
            }
            continue;

        } else  if (clen || xfip->xfi_format) {

            const char *class_name = xo_class_name(ftype);
            if (class_name)
                xo_format_content(xop, class_name, xo_tag_name(ftype),
                                  content, clen,
                                  xfip->xfi_format, xfip->xfi_flen, flags);
            else if (ftype == 'T')
                xo_format_title(xop, xfip, content, clen);
            else if (ftype == 'U')
                xo_format_units(xop, xfip, content, clen);
            else
                xo_failure(xop, "unknown field type: '%c'", ftype);
        }

        if (flags & XFF_COLON)
            xo_format_content(xop, "decoration", NULL, ":", 1, NULL, 0, 0);

        if (flags & XFF_WS)
            xo_format_content(xop, "padding", NULL, " ", 1, NULL, 0, 0);

    bottom:
        /* Record the end-of-field offset */
        if (gettext_reordered) {
            fend[field] = xo_buf_offset(&xop->xo_data);
            max_fend = field;
        }
    }

    if (gettext_changed && gettext_reordered) {
        /* Final step: rebuild the content using the rendered fields */
        xo_gettext_rebuild_content(xop, new_fields + 1, fstart, min_fstart,
                                   fend, max_fend);
    }

    XOIF_CLEAR(xop, XOIF_REORDER);

    /*
     * If we've got enough data, flush it.
     */
    if (xo_buf_offset(&xop->xo_data) > XO_BUF_HIGH_WATER)
        flush = 1;

    /* If we don't have an anchor, write the text out */
    if (flush && !XOIF_ISSET(xop, XOIF_ANCHOR)) {
        if (xo_flush_h(xop) < 0)
            rc = -1;
    }

    if (new_fmt)
        xo_free(new_fmt);

    /*
     * We've carried the gettext domainname inside our handle just for
     * convenience, but we need to ensure it doesn't survive across
     * xo_emit calls.
     */
    if (xop->xo_gt_domain) {
        xo_free(xop->xo_gt_domain);
        xop->xo_gt_domain = NULL;
    }

    return (rc < 0) ? rc : xop->xo_columns;
}

/*
 * Parse and emit a set of fields
 */
static int
xo_do_emit (xo_handle_t *xop, xo_emit_flags_t flags, const char *fmt)
{
    xop->xo_columns = 0;        /* Always reset it */
    xop->xo_errno = errno;      /* Save for "%m" */

    if (fmt == NULL)
        return 0;

    unsigned max_fields;
    xo_field_info_t *fields = NULL;

    /* Adjust XOEF_RETAIN based on global flags */
    if (XOF_ISSET(xop, XOF_RETAIN_ALL))
        flags |= XOEF_RETAIN;
    if (XOF_ISSET(xop, XOF_RETAIN_NONE))
        flags &= ~XOEF_RETAIN;

    /*
     * Check for 'retain' flag, telling us to retain the field
     * information.  If we've already saved it, then we can avoid
     * re-parsing the format string.
     */
    if (!(flags & XOEF_RETAIN)
        || xo_retain_find(fmt, &fields, &max_fields) != 0
        || fields == NULL) {

        /* Nothing retained; parse the format string */
        max_fields = xo_count_fields(xop, fmt);
        fields = alloca(max_fields * sizeof(fields[0]));
        bzero(fields, max_fields * sizeof(fields[0]));

        if (xo_parse_fields(xop, fields, max_fields, fmt))
            return -1;          /* Warning already displayed */

        if (flags & XOEF_RETAIN) {
            /* Retain the info */
            xo_retain_add(fmt, fields, max_fields);
        }
    }

    return xo_do_emit_fields(xop, fields, max_fields, fmt);
}

/*
 * Rebuild a format string in a gettext-friendly format.  This function
 * is exposed to tools can perform this function.  See xo(1).
 */
char *
xo_simplify_format (xo_handle_t *xop, const char *fmt, int with_numbers,
                    xo_simplify_field_func_t field_cb)
{
    xop = xo_default(xop);

    xop->xo_columns = 0;        /* Always reset it */
    xop->xo_errno = errno;      /* Save for "%m" */

    unsigned max_fields = xo_count_fields(xop, fmt);
    xo_field_info_t fields[max_fields];

    bzero(fields, max_fields * sizeof(fields[0]));

    if (xo_parse_fields(xop, fields, max_fields, fmt))
        return NULL;            /* Warning already displayed */

    xo_buffer_t xb;
    xo_buf_init(&xb);

    if (with_numbers)
        xo_gettext_finish_numbering_fields(xop, fmt, fields);

    if (xo_gettext_simplify_format(xop, &xb, fields, -1, fmt, field_cb))
        return NULL;

    return xb.xb_bufp;
}

xo_ssize_t
xo_emit_hv (xo_handle_t *xop, const char *fmt, va_list vap)
{
    ssize_t rc;

    xop = xo_default(xop);
    va_copy(xop->xo_vap, vap);
    rc = xo_do_emit(xop, 0, fmt);
    va_end(xop->xo_vap);
    bzero(&xop->xo_vap, sizeof(xop->xo_vap));

    return rc;
}

xo_ssize_t
xo_emit_h (xo_handle_t *xop, const char *fmt, ...)
{
    ssize_t rc;

    xop = xo_default(xop);
    va_start(xop->xo_vap, fmt);
    rc = xo_do_emit(xop, 0, fmt);
    va_end(xop->xo_vap);
    bzero(&xop->xo_vap, sizeof(xop->xo_vap));

    return rc;
}

xo_ssize_t
xo_emit (const char *fmt, ...)
{
    xo_handle_t *xop = xo_default(NULL);
    ssize_t rc;

    va_start(xop->xo_vap, fmt);
    rc = xo_do_emit(xop, 0, fmt);
    va_end(xop->xo_vap);
    bzero(&xop->xo_vap, sizeof(xop->xo_vap));

    return rc;
}

xo_ssize_t
xo_emit_hvf (xo_handle_t *xop, xo_emit_flags_t flags,
             const char *fmt, va_list vap)
{
    ssize_t rc;

    xop = xo_default(xop);
    va_copy(xop->xo_vap, vap);
    rc = xo_do_emit(xop, flags, fmt);
    va_end(xop->xo_vap);
    bzero(&xop->xo_vap, sizeof(xop->xo_vap));

    return rc;
}

xo_ssize_t
xo_emit_hf (xo_handle_t *xop, xo_emit_flags_t flags, const char *fmt, ...)
{
    ssize_t rc;

    xop = xo_default(xop);
    va_start(xop->xo_vap, fmt);
    rc = xo_do_emit(xop, flags, fmt);
    va_end(xop->xo_vap);
    bzero(&xop->xo_vap, sizeof(xop->xo_vap));

    return rc;
}

xo_ssize_t
xo_emit_f (xo_emit_flags_t flags, const char *fmt, ...)
{
    xo_handle_t *xop = xo_default(NULL);
    ssize_t rc;

    va_start(xop->xo_vap, fmt);
    rc = xo_do_emit(xop, flags, fmt);
    va_end(xop->xo_vap);
    bzero(&xop->xo_vap, sizeof(xop->xo_vap));

    return rc;
}

/*
 * Emit a single field by providing the info information typically provided
 * inside the field description (role, modifiers, and formats).  This is
 * a convenience function to avoid callers using snprintf to build field
 * descriptions.
 */
xo_ssize_t
xo_emit_field_hv (xo_handle_t *xop, const char *rolmod, const char *contents,
                  const char *fmt, const char *efmt,
                  va_list vap)
{
    ssize_t rc;

    xop = xo_default(xop);

    if (rolmod == NULL)
        rolmod = "V";

    xo_field_info_t xfi;

    bzero(&xfi, sizeof(xfi));

    const char *cp;
    cp = xo_parse_roles(xop, rolmod, rolmod, &xfi);
    if (cp == NULL)
        return -1;

    xfi.xfi_start = fmt;
    xfi.xfi_content = contents;
    xfi.xfi_format = fmt;
    xfi.xfi_encoding = efmt;
    xfi.xfi_clen = contents ? strlen(contents) : 0;
    xfi.xfi_flen = fmt ? strlen(fmt) : 0;
    xfi.xfi_elen = efmt ? strlen(efmt) : 0;

    /* If we have content, then we have a default format */
    if (contents && fmt == NULL
                && xo_role_wants_default_format(xfi.xfi_ftype)) {
        xfi.xfi_format = xo_default_format;
        xfi.xfi_flen = 2;
    }

    va_copy(xop->xo_vap, vap);

    rc = xo_do_emit_fields(xop, &xfi, 1, fmt ?: contents ?: "field");

    va_end(xop->xo_vap);

    return rc;
}

xo_ssize_t
xo_emit_field_h (xo_handle_t *xop, const char *rolmod, const char *contents,
                 const char *fmt, const char *efmt, ...)
{
    ssize_t rc;
    va_list vap;

    va_start(vap, efmt);
    rc = xo_emit_field_hv(xop, rolmod, contents, fmt, efmt, vap);
    va_end(vap);

    return rc;
}

xo_ssize_t
xo_emit_field (const char *rolmod, const char *contents,
               const char *fmt, const char *efmt, ...)
{
    ssize_t rc;
    va_list vap;

    va_start(vap, efmt);
    rc = xo_emit_field_hv(NULL, rolmod, contents, fmt, efmt, vap);
    va_end(vap);

    return rc;
}

xo_ssize_t
xo_attr_hv (xo_handle_t *xop, const char *name, const char *fmt, va_list vap)
{
    const ssize_t extra = 5;    /* space, equals, quote, quote, and nul */
    xop = xo_default(xop);

    ssize_t rc = 0;
    ssize_t nlen = strlen(name);
    xo_buffer_t *xbp = &xop->xo_attrs;
    ssize_t name_offset, value_offset;

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        if (!xo_buf_has_room(xbp, nlen + extra))
            return -1;

        *xbp->xb_curp++ = ' ';
        memcpy(xbp->xb_curp, name, nlen);
        xbp->xb_curp += nlen;
        *xbp->xb_curp++ = '=';
        *xbp->xb_curp++ = '"';

        rc = xo_vsnprintf(xop, xbp, fmt, vap);

        if (rc >= 0) {
            rc = xo_escape_xml(xbp, rc, 1);
            xbp->xb_curp += rc;
        }

        if (!xo_buf_has_room(xbp, 2))
            return -1;

        *xbp->xb_curp++ = '"';
        *xbp->xb_curp = '\0';

        rc += nlen + extra;
        break;

    case XO_STYLE_ENCODER:
        name_offset = xo_buf_offset(xbp);
        xo_buf_append(xbp, name, nlen);
        xo_buf_append(xbp, "", 1);

        value_offset = xo_buf_offset(xbp);
        rc = xo_vsnprintf(xop, xbp, fmt, vap);
        if (rc >= 0) {
            xbp->xb_curp += rc;
            *xbp->xb_curp = '\0';
            rc = xo_encoder_handle(xop, XO_OP_ATTRIBUTE,
                                   xo_buf_data(xbp, name_offset),
                                   xo_buf_data(xbp, value_offset), 0);
        }
    }

    return rc;
}

xo_ssize_t
xo_attr_h (xo_handle_t *xop, const char *name, const char *fmt, ...)
{
    ssize_t rc;
    va_list vap;

    va_start(vap, fmt);
    rc = xo_attr_hv(xop, name, fmt, vap);
    va_end(vap);

    return rc;
}

xo_ssize_t
xo_attr (const char *name, const char *fmt, ...)
{
    ssize_t rc;
    va_list vap;

    va_start(vap, fmt);
    rc = xo_attr_hv(NULL, name, fmt, vap);
    va_end(vap);

    return rc;
}

static void
xo_depth_change (xo_handle_t *xop, const char *name,
                 int delta, int indent, xo_state_t state, xo_xsf_flags_t flags)
{
    if (xo_style(xop) == XO_STYLE_HTML || xo_style(xop) == XO_STYLE_TEXT)
        indent = 0;

    if (XOF_ISSET(xop, XOF_DTRT))
        flags |= XSF_DTRT;

    if (delta >= 0) {                   /* Push operation */
        if (xo_depth_check(xop, xop->xo_depth + delta))
            return;

        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth + delta];
        xsp->xs_flags = flags;
        xsp->xs_state = state;
        xo_stack_set_flags(xop);

        if (name == NULL)
            name = XO_FAILURE_NAME;

        xsp->xs_name = xo_strndup(name, -1);

    } else {                    /* Pop operation */
        if (xop->xo_depth == 0) {
            if (!XOF_ISSET(xop, XOF_IGNORE_CLOSE))
                xo_failure(xop, "close with empty stack: '%s'", name);
            return;
        }

        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];
        if (XOF_ISSET(xop, XOF_WARN)) {
            const char *top = xsp->xs_name;
            if (top != NULL && name != NULL && strcmp(name, top) != 0) {
                xo_failure(xop, "incorrect close: '%s' .vs. '%s'",
                              name, top);
                return;
            } 
            if ((xsp->xs_flags & XSF_LIST) != (flags & XSF_LIST)) {
                xo_failure(xop, "list close on list confict: '%s'",
                              name);
                return;
            }
            if ((xsp->xs_flags & XSF_INSTANCE) != (flags & XSF_INSTANCE)) {
                xo_failure(xop, "list close on instance confict: '%s'",
                              name);
                return;
            }
        }

        if (xsp->xs_name) {
            xo_free(xsp->xs_name);
            xsp->xs_name = NULL;
        }
        if (xsp->xs_keys) {
            xo_free(xsp->xs_keys);
            xsp->xs_keys = NULL;
        }
    }

    xop->xo_depth += delta;     /* Record new depth */
    xop->xo_indent += indent;
}

void
xo_set_depth (xo_handle_t *xop, int depth)
{
    xop = xo_default(xop);

    if (xo_depth_check(xop, depth))
        return;

    xop->xo_depth += depth;
    xop->xo_indent += depth;

    /*
     * Handling the "top wrapper" for JSON is a bit of a pain.  Here
     * we need to detect that the depth has been changed to set the
     * "XOIF_TOP_EMITTED" flag correctly.
     */
    if (xop->xo_style == XO_STYLE_JSON
        && !XOF_ISSET(xop, XOF_NO_TOP) && xop->xo_depth > 0)
        XOIF_SET(xop, XOIF_TOP_EMITTED);
}

static xo_xsf_flags_t
xo_stack_flags (xo_xof_flags_t xflags)
{
    if (xflags & XOF_DTRT)
        return XSF_DTRT;
    return 0;
}

static void
xo_emit_top (xo_handle_t *xop, const char *ppn)
{
    xo_printf(xop, "%*s{%s", xo_indent(xop), "", ppn);
    XOIF_SET(xop, XOIF_TOP_EMITTED);

    if (xop->xo_version) {
        xo_printf(xop, "%*s\"__version\": \"%s\", %s",
                  xo_indent(xop), "", xop->xo_version, ppn);
        xo_free(xop->xo_version);
        xop->xo_version = NULL;
    }
}

static ssize_t
xo_do_open_container (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    ssize_t rc = 0;
    const char *ppn = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
    const char *pre_nl = "";

    if (name == NULL) {
        xo_failure(xop, "NULL passed for container name");
        name = XO_FAILURE_NAME;
    }

    const char *leader = xo_xml_leader(xop, name);
    flags |= xop->xo_flags;     /* Pick up handle flags */

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        rc = xo_printf(xop, "%*s<%s%s", xo_indent(xop), "", leader, name);

        if (xop->xo_attrs.xb_curp != xop->xo_attrs.xb_bufp) {
            rc += xop->xo_attrs.xb_curp - xop->xo_attrs.xb_bufp;
            xo_data_append(xop, xop->xo_attrs.xb_bufp,
                           xop->xo_attrs.xb_curp - xop->xo_attrs.xb_bufp);
            xop->xo_attrs.xb_curp = xop->xo_attrs.xb_bufp;
        }

        rc += xo_printf(xop, ">%s", ppn);
        break;

    case XO_STYLE_JSON:
        xo_stack_set_flags(xop);

        if (!XOF_ISSET(xop, XOF_NO_TOP)
                && !XOIF_ISSET(xop, XOIF_TOP_EMITTED))
            xo_emit_top(xop, ppn);

        if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? ",\n" : ", ";
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;

        rc = xo_printf(xop, "%s%*s\"%s\": {%s",
                       pre_nl, xo_indent(xop), "", name, ppn);
        break;

    case XO_STYLE_SDPARAMS:
        break;

    case XO_STYLE_ENCODER:
        rc = xo_encoder_handle(xop, XO_OP_OPEN_CONTAINER, name, NULL, flags);
        break;
    }

    xo_depth_change(xop, name, 1, 1, XSS_OPEN_CONTAINER,
                    xo_stack_flags(flags));

    return rc;
}

xo_ssize_t
xo_open_container_hf (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    return xo_transition(xop, flags, name, XSS_OPEN_CONTAINER);
}

xo_ssize_t
xo_open_container_h (xo_handle_t *xop, const char *name)
{
    return xo_open_container_hf(xop, 0, name);
}

xo_ssize_t
xo_open_container (const char *name)
{
    return xo_open_container_hf(NULL, 0, name);
}

xo_ssize_t
xo_open_container_hd (xo_handle_t *xop, const char *name)
{
    return xo_open_container_hf(xop, XOF_DTRT, name);
}

xo_ssize_t
xo_open_container_d (const char *name)
{
    return xo_open_container_hf(NULL, XOF_DTRT, name);
}

static int
xo_do_close_container (xo_handle_t *xop, const char *name)
{
    xop = xo_default(xop);

    ssize_t rc = 0;
    const char *ppn = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
    const char *pre_nl = "";

    if (name == NULL) {
        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];

        name = xsp->xs_name;
        if (name) {
            ssize_t len = strlen(name) + 1;
            /* We need to make a local copy; xo_depth_change will free it */
            char *cp = alloca(len);
            memcpy(cp, name, len);
            name = cp;
        } else if (!(xsp->xs_flags & XSF_DTRT)) {
            xo_failure(xop, "missing name without 'dtrt' mode");
            name = XO_FAILURE_NAME;
        }
    }

    const char *leader = xo_xml_leader(xop, name);

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        xo_depth_change(xop, name, -1, -1, XSS_CLOSE_CONTAINER, 0);
        rc = xo_printf(xop, "%*s</%s%s>%s", xo_indent(xop), "", leader, name, ppn);
        break;

    case XO_STYLE_JSON:
        xo_stack_set_flags(xop);

        pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
        ppn = (xop->xo_depth <= 1) ? pre_nl : "";
        ppn = "";

        xo_depth_change(xop, name, -1, -1, XSS_CLOSE_CONTAINER, 0);
        rc = xo_printf(xop, "%s%*s}%s", pre_nl, xo_indent(xop), "", ppn);
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
        break;

    case XO_STYLE_HTML:
    case XO_STYLE_TEXT:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_CONTAINER, 0);
        break;

    case XO_STYLE_SDPARAMS:
        break;

    case XO_STYLE_ENCODER:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_CONTAINER, 0);
        rc = xo_encoder_handle(xop, XO_OP_CLOSE_CONTAINER, name, NULL, 0);
        break;
    }

    return rc;
}

xo_ssize_t
xo_close_container_h (xo_handle_t *xop, const char *name)
{
    return xo_transition(xop, 0, name, XSS_CLOSE_CONTAINER);
}

xo_ssize_t
xo_close_container (const char *name)
{
    return xo_close_container_h(NULL, name);
}

xo_ssize_t
xo_close_container_hd (xo_handle_t *xop)
{
    return xo_close_container_h(xop, NULL);
}

xo_ssize_t
xo_close_container_d (void)
{
    return xo_close_container_h(NULL, NULL);
}

static int
xo_do_open_list (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    ssize_t rc = 0;
    int indent = 0;

    xop = xo_default(xop);

    const char *ppn = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
    const char *pre_nl = "";

    switch (xo_style(xop)) {
    case XO_STYLE_JSON:

        indent = 1;
        if (!XOF_ISSET(xop, XOF_NO_TOP)
                && !XOIF_ISSET(xop, XOIF_TOP_EMITTED))
            xo_emit_top(xop, ppn);

        if (name == NULL) {
            xo_failure(xop, "NULL passed for list name");
            name = XO_FAILURE_NAME;
        }

        xo_stack_set_flags(xop);

        if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? ",\n" : ", ";
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;

        rc = xo_printf(xop, "%s%*s\"%s\": [%s",
                       pre_nl, xo_indent(xop), "", name, ppn);
        break;

    case XO_STYLE_ENCODER:
        rc = xo_encoder_handle(xop, XO_OP_OPEN_LIST, name, NULL, flags);
        break;
    }

    xo_depth_change(xop, name, 1, indent, XSS_OPEN_LIST,
                    XSF_LIST | xo_stack_flags(flags));

    return rc;
}

xo_ssize_t
xo_open_list_hf (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    return xo_transition(xop, flags, name, XSS_OPEN_LIST);
}

xo_ssize_t
xo_open_list_h (xo_handle_t *xop, const char *name)
{
    return xo_open_list_hf(xop, 0, name);
}

xo_ssize_t
xo_open_list (const char *name)
{
    return xo_open_list_hf(NULL, 0, name);
}

xo_ssize_t
xo_open_list_hd (xo_handle_t *xop, const char *name)
{
    return xo_open_list_hf(xop, XOF_DTRT, name);
}

xo_ssize_t
xo_open_list_d (const char *name)
{
    return xo_open_list_hf(NULL, XOF_DTRT, name);
}

static int
xo_do_close_list (xo_handle_t *xop, const char *name)
{
    ssize_t rc = 0;
    const char *pre_nl = "";

    if (name == NULL) {
        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];

        name = xsp->xs_name;
        if (name) {
            ssize_t len = strlen(name) + 1;
            /* We need to make a local copy; xo_depth_change will free it */
            char *cp = alloca(len);
            memcpy(cp, name, len);
            name = cp;
        } else if (!(xsp->xs_flags & XSF_DTRT)) {
            xo_failure(xop, "missing name without 'dtrt' mode");
            name = XO_FAILURE_NAME;
        }
    }

    switch (xo_style(xop)) {
    case XO_STYLE_JSON:
        if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;

        xo_depth_change(xop, name, -1, -1, XSS_CLOSE_LIST, XSF_LIST);
        rc = xo_printf(xop, "%s%*s]", pre_nl, xo_indent(xop), "");
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
        break;

    case XO_STYLE_ENCODER:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_LIST, XSF_LIST);
        rc = xo_encoder_handle(xop, XO_OP_CLOSE_LIST, name, NULL, 0);
        break;

    default:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_LIST, XSF_LIST);
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
        break;
    }

    return rc;
}

xo_ssize_t
xo_close_list_h (xo_handle_t *xop, const char *name)
{
    return xo_transition(xop, 0, name, XSS_CLOSE_LIST);
}

xo_ssize_t
xo_close_list (const char *name)
{
    return xo_close_list_h(NULL, name);
}

xo_ssize_t
xo_close_list_hd (xo_handle_t *xop)
{
    return xo_close_list_h(xop, NULL);
}

xo_ssize_t
xo_close_list_d (void)
{
    return xo_close_list_h(NULL, NULL);
}

static int
xo_do_open_leaf_list (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    ssize_t rc = 0;
    int indent = 0;

    xop = xo_default(xop);

    const char *ppn = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
    const char *pre_nl = "";

    switch (xo_style(xop)) {
    case XO_STYLE_JSON:
        indent = 1;

        if (!XOF_ISSET(xop, XOF_NO_TOP)) {
            if (!XOIF_ISSET(xop, XOIF_TOP_EMITTED)) {
                xo_printf(xop, "%*s{%s", xo_indent(xop), "", ppn);
                XOIF_SET(xop, XOIF_TOP_EMITTED);
            }
        }

        if (name == NULL) {
            xo_failure(xop, "NULL passed for list name");
            name = XO_FAILURE_NAME;
        }

        xo_stack_set_flags(xop);

        if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? ",\n" : ", ";
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;

        rc = xo_printf(xop, "%s%*s\"%s\": [%s",
                       pre_nl, xo_indent(xop), "", name, ppn);
        break;

    case XO_STYLE_ENCODER:
        rc = xo_encoder_handle(xop, XO_OP_OPEN_LEAF_LIST, name, NULL, flags);
        break;
    }

    xo_depth_change(xop, name, 1, indent, XSS_OPEN_LEAF_LIST,
                    XSF_LIST | xo_stack_flags(flags));

    return rc;
}

static int
xo_do_close_leaf_list (xo_handle_t *xop, const char *name)
{
    ssize_t rc = 0;
    const char *pre_nl = "";

    if (name == NULL) {
        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];

        name = xsp->xs_name;
        if (name) {
            ssize_t len = strlen(name) + 1;
            /* We need to make a local copy; xo_depth_change will free it */
            char *cp = alloca(len);
            memcpy(cp, name, len);
            name = cp;
        } else if (!(xsp->xs_flags & XSF_DTRT)) {
            xo_failure(xop, "missing name without 'dtrt' mode");
            name = XO_FAILURE_NAME;
        }
    }

    switch (xo_style(xop)) {
    case XO_STYLE_JSON:
        if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;

        xo_depth_change(xop, name, -1, -1, XSS_CLOSE_LEAF_LIST, XSF_LIST);
        rc = xo_printf(xop, "%s%*s]", pre_nl, xo_indent(xop), "");
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
        break;

    case XO_STYLE_ENCODER:
        rc = xo_encoder_handle(xop, XO_OP_CLOSE_LEAF_LIST, name, NULL, 0);
        /* FALLTHRU */

    default:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_LEAF_LIST, XSF_LIST);
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
        break;
    }

    return rc;
}

static int
xo_do_open_instance (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    xop = xo_default(xop);

    ssize_t rc = 0;
    const char *ppn = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
    const char *pre_nl = "";

    if (name == NULL) {
        xo_failure(xop, "NULL passed for instance name");
        name = XO_FAILURE_NAME;
    }

    const char *leader = xo_xml_leader(xop, name);
    flags |= xop->xo_flags;

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        rc = xo_printf(xop, "%*s<%s%s", xo_indent(xop), "", leader, name);

        if (xop->xo_attrs.xb_curp != xop->xo_attrs.xb_bufp) {
            rc += xop->xo_attrs.xb_curp - xop->xo_attrs.xb_bufp;
            xo_data_append(xop, xop->xo_attrs.xb_bufp,
                           xop->xo_attrs.xb_curp - xop->xo_attrs.xb_bufp);
            xop->xo_attrs.xb_curp = xop->xo_attrs.xb_bufp;
        }

        rc += xo_printf(xop, ">%s", ppn);
        break;

    case XO_STYLE_JSON:
        xo_stack_set_flags(xop);

        if (xop->xo_stack[xop->xo_depth].xs_flags & XSF_NOT_FIRST)
            pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? ",\n" : ", ";
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;

        rc = xo_printf(xop, "%s%*s{%s",
                       pre_nl, xo_indent(xop), "", ppn);
        break;

    case XO_STYLE_SDPARAMS:
        break;

    case XO_STYLE_ENCODER:
        rc = xo_encoder_handle(xop, XO_OP_OPEN_INSTANCE, name, NULL, flags);
        break;
    }

    xo_depth_change(xop, name, 1, 1, XSS_OPEN_INSTANCE, xo_stack_flags(flags));

    return rc;
}

xo_ssize_t
xo_open_instance_hf (xo_handle_t *xop, xo_xof_flags_t flags, const char *name)
{
    return xo_transition(xop, flags, name, XSS_OPEN_INSTANCE);
}

xo_ssize_t
xo_open_instance_h (xo_handle_t *xop, const char *name)
{
    return xo_open_instance_hf(xop, 0, name);
}

xo_ssize_t
xo_open_instance (const char *name)
{
    return xo_open_instance_hf(NULL, 0, name);
}

xo_ssize_t
xo_open_instance_hd (xo_handle_t *xop, const char *name)
{
    return xo_open_instance_hf(xop, XOF_DTRT, name);
}

xo_ssize_t
xo_open_instance_d (const char *name)
{
    return xo_open_instance_hf(NULL, XOF_DTRT, name);
}

static int
xo_do_close_instance (xo_handle_t *xop, const char *name)
{
    xop = xo_default(xop);

    ssize_t rc = 0;
    const char *ppn = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";
    const char *pre_nl = "";

    if (name == NULL) {
        xo_stack_t *xsp = &xop->xo_stack[xop->xo_depth];

        name = xsp->xs_name;
        if (name) {
            ssize_t len = strlen(name) + 1;
            /* We need to make a local copy; xo_depth_change will free it */
            char *cp = alloca(len);
            memcpy(cp, name, len);
            name = cp;
        } else if (!(xsp->xs_flags & XSF_DTRT)) {
            xo_failure(xop, "missing name without 'dtrt' mode");
            name = XO_FAILURE_NAME;
        }
    }

    const char *leader = xo_xml_leader(xop, name);

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        xo_depth_change(xop, name, -1, -1, XSS_CLOSE_INSTANCE, 0);
        rc = xo_printf(xop, "%*s</%s%s>%s", xo_indent(xop), "", leader, name, ppn);
        break;

    case XO_STYLE_JSON:
        pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";

        xo_depth_change(xop, name, -1, -1, XSS_CLOSE_INSTANCE, 0);
        rc = xo_printf(xop, "%s%*s}", pre_nl, xo_indent(xop), "");
        xop->xo_stack[xop->xo_depth].xs_flags |= XSF_NOT_FIRST;
        break;

    case XO_STYLE_HTML:
    case XO_STYLE_TEXT:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_INSTANCE, 0);
        break;

    case XO_STYLE_SDPARAMS:
        break;

    case XO_STYLE_ENCODER:
        xo_depth_change(xop, name, -1, 0, XSS_CLOSE_INSTANCE, 0);
        rc = xo_encoder_handle(xop, XO_OP_CLOSE_INSTANCE, name, NULL, 0);
        break;
    }

    return rc;
}

xo_ssize_t
xo_close_instance_h (xo_handle_t *xop, const char *name)
{
    return xo_transition(xop, 0, name, XSS_CLOSE_INSTANCE);
}

xo_ssize_t
xo_close_instance (const char *name)
{
    return xo_close_instance_h(NULL, name);
}

xo_ssize_t
xo_close_instance_hd (xo_handle_t *xop)
{
    return xo_close_instance_h(xop, NULL);
}

xo_ssize_t
xo_close_instance_d (void)
{
    return xo_close_instance_h(NULL, NULL);
}

static int
xo_do_close_all (xo_handle_t *xop, xo_stack_t *limit)
{
    xo_stack_t *xsp;
    ssize_t rc = 0;
    xo_xsf_flags_t flags;

    for (xsp = &xop->xo_stack[xop->xo_depth]; xsp >= limit; xsp--) {
        switch (xsp->xs_state) {
        case XSS_INIT:
            /* Nothing */
            rc = 0;
            break;

        case XSS_OPEN_CONTAINER:
            rc = xo_do_close_container(xop, NULL);
            break;

        case XSS_OPEN_LIST:
            rc = xo_do_close_list(xop, NULL);
            break;

        case XSS_OPEN_INSTANCE:
            rc = xo_do_close_instance(xop, NULL);
            break;

        case XSS_OPEN_LEAF_LIST:
            rc = xo_do_close_leaf_list(xop, NULL);
            break;

        case XSS_MARKER:
            flags = xsp->xs_flags & XSF_MARKER_FLAGS;
            xo_depth_change(xop, xsp->xs_name, -1, 0, XSS_MARKER, 0);
            xop->xo_stack[xop->xo_depth].xs_flags |= flags;
            rc = 0;
            break;
        }

        if (rc < 0)
            xo_failure(xop, "close %d failed: %d", xsp->xs_state, rc);
    }

    return 0;
}

/*
 * This function is responsible for clearing out whatever is needed
 * to get to the desired state, if possible.
 */
static int
xo_do_close (xo_handle_t *xop, const char *name, xo_state_t new_state)
{
    xo_stack_t *xsp, *limit = NULL;
    ssize_t rc;
    xo_state_t need_state = new_state;

    if (new_state == XSS_CLOSE_CONTAINER)
        need_state = XSS_OPEN_CONTAINER;
    else if (new_state == XSS_CLOSE_LIST)
        need_state = XSS_OPEN_LIST;
    else if (new_state == XSS_CLOSE_INSTANCE)
        need_state = XSS_OPEN_INSTANCE;
    else if (new_state == XSS_CLOSE_LEAF_LIST)
        need_state = XSS_OPEN_LEAF_LIST;
    else if (new_state == XSS_MARKER)
        need_state = XSS_MARKER;
    else
        return 0; /* Unknown or useless new states are ignored */

    for (xsp = &xop->xo_stack[xop->xo_depth]; xsp > xop->xo_stack; xsp--) {
        /*
         * Marker's normally stop us from going any further, unless
         * we are popping a marker (new_state == XSS_MARKER).
         */
        if (xsp->xs_state == XSS_MARKER && need_state != XSS_MARKER) {
            if (name) {
                xo_failure(xop, "close (xo_%s) fails at marker '%s'; "
                           "not found '%s'",
                           xo_state_name(new_state),
                           xsp->xs_name, name);
                return 0;

            } else {
                limit = xsp;
                xo_failure(xop, "close stops at marker '%s'", xsp->xs_name);
            }
            break;
        }
        
        if (xsp->xs_state != need_state)
            continue;

        if (name && xsp->xs_name && strcmp(name, xsp->xs_name) != 0)
            continue;

        limit = xsp;
        break;
    }

    if (limit == NULL) {
        xo_failure(xop, "xo_%s can't find match for '%s'",
                   xo_state_name(new_state), name);
        return 0;
    }

    rc = xo_do_close_all(xop, limit);

    return rc;
}

/*
 * We are in a given state and need to transition to the new state.
 */
static ssize_t
xo_transition (xo_handle_t *xop, xo_xof_flags_t flags, const char *name,
               xo_state_t new_state)
{
    xo_stack_t *xsp;
    ssize_t rc = 0;
    int old_state, on_marker;

    xop = xo_default(xop);

    xsp = &xop->xo_stack[xop->xo_depth];
    old_state = xsp->xs_state;
    on_marker = (old_state == XSS_MARKER);

    /* If there's a marker on top of the stack, we need to find a real state */
    while (old_state == XSS_MARKER) {
        if (xsp == xop->xo_stack)
            break;
        xsp -= 1;
        old_state = xsp->xs_state;
    }

    /*
     * At this point, the list of possible states are:
     *   XSS_INIT, XSS_OPEN_CONTAINER, XSS_OPEN_LIST,
     *   XSS_OPEN_INSTANCE, XSS_OPEN_LEAF_LIST, XSS_DISCARDING
     */
    switch (XSS_TRANSITION(old_state, new_state)) {

    open_container:
    case XSS_TRANSITION(XSS_INIT, XSS_OPEN_CONTAINER):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_OPEN_CONTAINER):
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_OPEN_CONTAINER):
       rc = xo_do_open_container(xop, flags, name);
       break;

    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_OPEN_CONTAINER):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_list(xop, NULL);
        if (rc >= 0)
            goto open_container;
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_OPEN_CONTAINER):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, NULL);
        if (rc >= 0)
            goto open_container;
        break;

    /*close_container:*/
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_CLOSE_CONTAINER):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close(xop, name, new_state);
        break;

    case XSS_TRANSITION(XSS_INIT, XSS_CLOSE_CONTAINER):
        /* This is an exception for "xo --close" */
        rc = xo_do_close_container(xop, name);
        break;

    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_CLOSE_CONTAINER):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_CLOSE_CONTAINER):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close(xop, name, new_state);
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_CLOSE_CONTAINER):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, NULL);
        if (rc >= 0)
            rc = xo_do_close(xop, name, new_state);
        break;

    open_list:
    case XSS_TRANSITION(XSS_INIT, XSS_OPEN_LIST):
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_OPEN_LIST):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_OPEN_LIST):
        rc = xo_do_open_list(xop, flags, name);
        break;

    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_OPEN_LIST):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_list(xop, NULL);
        if (rc >= 0)
            goto open_list;
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_OPEN_LIST):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, NULL);
        if (rc >= 0)
            goto open_list;
        break;

    /*close_list:*/
    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_CLOSE_LIST):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close(xop, name, new_state);
        break;

    case XSS_TRANSITION(XSS_INIT, XSS_CLOSE_LIST):
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_CLOSE_LIST):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_CLOSE_LIST):
    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_CLOSE_LIST):
        rc = xo_do_close(xop, name, new_state);
        break;

    open_instance:
    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_OPEN_INSTANCE):
        rc = xo_do_open_instance(xop, flags, name);
        break;

    case XSS_TRANSITION(XSS_INIT, XSS_OPEN_INSTANCE):
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_OPEN_INSTANCE):
        rc = xo_do_open_list(xop, flags, name);
        if (rc >= 0)
            goto open_instance;
        break;

    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_OPEN_INSTANCE):
        if (on_marker) {
            rc = xo_do_open_list(xop, flags, name);
        } else {
            rc = xo_do_close_instance(xop, NULL);
        }
        if (rc >= 0)
            goto open_instance;
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_OPEN_INSTANCE):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, NULL);
        if (rc >= 0)
            goto open_instance;
        break;

    /*close_instance:*/
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_CLOSE_INSTANCE):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_instance(xop, name);
        break;

    case XSS_TRANSITION(XSS_INIT, XSS_CLOSE_INSTANCE):
        /* This one makes no sense; ignore it */
        xo_failure(xop, "xo_close_instance ignored when called from "
                   "initial state ('%s')", name ?: "(unknown)");
        break;

    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_CLOSE_INSTANCE):
    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_CLOSE_INSTANCE):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close(xop, name, new_state);
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_CLOSE_INSTANCE):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, NULL);
        if (rc >= 0)
            rc = xo_do_close(xop, name, new_state);
        break;

    open_leaf_list:
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_OPEN_LEAF_LIST):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_OPEN_LEAF_LIST):
    case XSS_TRANSITION(XSS_INIT, XSS_OPEN_LEAF_LIST):
        rc = xo_do_open_leaf_list(xop, flags, name);
        break;

    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_OPEN_LEAF_LIST):
    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_OPEN_LEAF_LIST):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_list(xop, NULL);
        if (rc >= 0)
            goto open_leaf_list;
        break;

    /*close_leaf_list:*/
    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_CLOSE_LEAF_LIST):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, name);
        break;

    case XSS_TRANSITION(XSS_INIT, XSS_CLOSE_LEAF_LIST):
        /* Makes no sense; ignore */
        xo_failure(xop, "xo_close_leaf_list ignored when called from "
                   "initial state ('%s')", name ?: "(unknown)");
        break;

    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_CLOSE_LEAF_LIST):
    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_CLOSE_LEAF_LIST):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_CLOSE_LEAF_LIST):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close(xop, name, new_state);
        break;

    /*emit:*/
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_EMIT):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_EMIT):
        break;

    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_EMIT):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close(xop, NULL, XSS_CLOSE_LIST);
        break;

    case XSS_TRANSITION(XSS_INIT, XSS_EMIT):
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_EMIT):
        if (on_marker)
            goto marker_prevents_close;
        rc = xo_do_close_leaf_list(xop, NULL);
        break;

    /*emit_leaf_list:*/
    case XSS_TRANSITION(XSS_INIT, XSS_EMIT_LEAF_LIST):
    case XSS_TRANSITION(XSS_OPEN_CONTAINER, XSS_EMIT_LEAF_LIST):
    case XSS_TRANSITION(XSS_OPEN_INSTANCE, XSS_EMIT_LEAF_LIST):
        rc = xo_do_open_leaf_list(xop, flags, name);
        break;

    case XSS_TRANSITION(XSS_OPEN_LEAF_LIST, XSS_EMIT_LEAF_LIST):
        break;

    case XSS_TRANSITION(XSS_OPEN_LIST, XSS_EMIT_LEAF_LIST):
        /*
         * We need to be backward compatible with the pre-xo_open_leaf_list
         * API, where both lists and leaf-lists were opened as lists.  So
         * if we find an open list that hasn't had anything written to it,
         * we'll accept it.
         */
        break;

    default:
        xo_failure(xop, "unknown transition: (%u -> %u)",
                   xsp->xs_state, new_state);
    }

    /* Handle the flush flag */
    if (rc >= 0 && XOF_ISSET(xop, XOF_FLUSH))
        if (xo_flush_h(xop) < 0)
            rc = -1;

    /* We have now official made output */
    XOIF_SET(xop, XOIF_MADE_OUTPUT);

    return rc;

 marker_prevents_close:
    xo_failure(xop, "marker '%s' prevents transition from %s to %s",
               xop->xo_stack[xop->xo_depth].xs_name,
               xo_state_name(old_state), xo_state_name(new_state));
    return -1;
}

xo_ssize_t
xo_open_marker_h (xo_handle_t *xop, const char *name)
{
    xop = xo_default(xop);

    xo_depth_change(xop, name, 1, 0, XSS_MARKER,
                    xop->xo_stack[xop->xo_depth].xs_flags & XSF_MARKER_FLAGS);

    return 0;
}

xo_ssize_t
xo_open_marker (const char *name)
{
    return xo_open_marker_h(NULL, name);
}

xo_ssize_t
xo_close_marker_h (xo_handle_t *xop, const char *name)
{
    xop = xo_default(xop);

    return xo_do_close(xop, name, XSS_MARKER);
}

xo_ssize_t
xo_close_marker (const char *name)
{
    return xo_close_marker_h(NULL, name);
}

/*
 * Record custom output functions into the xo handle, allowing
 * integration with a variety of output frameworks.
 */
void
xo_set_writer (xo_handle_t *xop, void *opaque, xo_write_func_t write_func,
               xo_close_func_t close_func, xo_flush_func_t flush_func)
{
    xop = xo_default(xop);

    xop->xo_opaque = opaque;
    xop->xo_write = write_func;
    xop->xo_close = close_func;
    xop->xo_flush = flush_func;
}

void
xo_set_allocator (xo_realloc_func_t realloc_func, xo_free_func_t free_func)
{
    xo_realloc = realloc_func;
    xo_free = free_func;
}

xo_ssize_t
xo_flush_h (xo_handle_t *xop)
{
    ssize_t rc;

    xop = xo_default(xop);

    switch (xo_style(xop)) {
    case XO_STYLE_ENCODER:
        xo_encoder_handle(xop, XO_OP_FLUSH, NULL, NULL, 0);
    }

    rc = xo_write(xop);
    if (rc >= 0 && xop->xo_flush)
        if (xop->xo_flush(xop->xo_opaque) < 0)
            return -1;

    return rc;
}

xo_ssize_t
xo_flush (void)
{
    return xo_flush_h(NULL);
}

xo_ssize_t
xo_finish_h (xo_handle_t *xop)
{
    const char *open_if_empty = "";
    xop = xo_default(xop);

    if (!XOF_ISSET(xop, XOF_NO_CLOSE))
        xo_do_close_all(xop, xop->xo_stack);

    switch (xo_style(xop)) {
    case XO_STYLE_JSON:
        if (!XOF_ISSET(xop, XOF_NO_TOP)) {
            const char *pre_nl = XOF_ISSET(xop, XOF_PRETTY) ? "\n" : "";

            if (XOIF_ISSET(xop, XOIF_TOP_EMITTED))
                XOIF_CLEAR(xop, XOIF_TOP_EMITTED); /* Turn off before output */
            else if (!XOIF_ISSET(xop, XOIF_MADE_OUTPUT)) {
                open_if_empty = "{ ";
                pre_nl = "";
            }

            xo_printf(xop, "%s%*s%s}\n",
                      pre_nl, xo_indent(xop), "", open_if_empty);
        }
        break;

    case XO_STYLE_ENCODER:
        xo_encoder_handle(xop, XO_OP_FINISH, NULL, NULL, 0);
        break;
    }

    return xo_flush_h(xop);
}

xo_ssize_t
xo_finish (void)
{
    return xo_finish_h(NULL);
}

/*
 * xo_finish_atexit is suitable for atexit() calls, to force clear up
 * and finalizing output.
 */
void
xo_finish_atexit (void)
{
    (void) xo_finish_h(NULL);
}

/*
 * Generate an error message, such as would be displayed on stderr
 */
void
xo_error_hv (xo_handle_t *xop, const char *fmt, va_list vap)
{
    xop = xo_default(xop);

    /*
     * If the format string doesn't end with a newline, we pop
     * one on ourselves.
     */
    ssize_t len = strlen(fmt);
    if (len > 0 && fmt[len - 1] != '\n') {
        char *newfmt = alloca(len + 2);
        memcpy(newfmt, fmt, len);
        newfmt[len] = '\n';
        newfmt[len] = '\0';
        fmt = newfmt;
    }

    switch (xo_style(xop)) {
    case XO_STYLE_TEXT:
        vfprintf(stderr, fmt, vap);
        break;

    case XO_STYLE_HTML:
        va_copy(xop->xo_vap, vap);
        
        xo_buf_append_div(xop, "error", 0, NULL, 0, NULL, 0,
                          fmt, strlen(fmt), NULL, 0);

        if (XOIF_ISSET(xop, XOIF_DIV_OPEN))
            xo_line_close(xop);

        xo_write(xop);

        va_end(xop->xo_vap);
        bzero(&xop->xo_vap, sizeof(xop->xo_vap));
        break;

    case XO_STYLE_XML:
    case XO_STYLE_JSON:
        va_copy(xop->xo_vap, vap);

        xo_open_container_h(xop, "error");
        xo_format_value(xop, "message", 7, NULL, 0,
                        fmt, strlen(fmt), NULL, 0, 0);
        xo_close_container_h(xop, "error");

        va_end(xop->xo_vap);
        bzero(&xop->xo_vap, sizeof(xop->xo_vap));
        break;

    case XO_STYLE_SDPARAMS:
    case XO_STYLE_ENCODER:
        break;
    }
}

void
xo_error_h (xo_handle_t *xop, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_error_hv(xop, fmt, vap);
    va_end(vap);
}

/*
 * Generate an error message, such as would be displayed on stderr
 */
void
xo_error (const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_error_hv(NULL, fmt, vap);
    va_end(vap);
}

/*
 * Parse any libxo-specific options from the command line, removing them
 * so the main() argument parsing won't see them.  We return the new value
 * for argc or -1 for error.  If an error occurred, the program should
 * exit.  A suitable error message has already been displayed.
 */
int
xo_parse_args (int argc, char **argv)
{
    static char libxo_opt[] = "--libxo";
    char *cp;
    int i, save;

    /* Save our program name for xo_err and friends */
    xo_program = argv[0];
    cp = strrchr(xo_program, '/');
    if (cp)
        xo_program = cp + 1;

    xo_handle_t *xop = xo_default(NULL);

    for (save = i = 1; i < argc; i++) {
        if (argv[i] == NULL
            || strncmp(argv[i], libxo_opt, sizeof(libxo_opt) - 1) != 0) {
            if (save != i)
                argv[save] = argv[i];
            save += 1;
            continue;
        }

        cp = argv[i] + sizeof(libxo_opt) - 1;
        if (*cp == '\0') {
            cp = argv[++i];
            if (cp == NULL) {
                xo_warnx("missing libxo option");
                return -1;
            }
                
            if (xo_set_options(xop, cp) < 0)
                return -1;
        } else if (*cp == ':') {
            if (xo_set_options(xop, cp) < 0)
                return -1;

        } else if (*cp == '=') {
            if (xo_set_options(xop, ++cp) < 0)
                return -1;

        } else if (*cp == '-') {
            cp += 1;
            if (strcmp(cp, "check") == 0) {
                exit(XO_HAS_LIBXO);

            } else {
                xo_warnx("unknown libxo option: '%s'", argv[i]);
                return -1;
            }
        } else {
                xo_warnx("unknown libxo option: '%s'", argv[i]);
            return -1;
        }
    }

    /*
     * We only want to do color output on terminals, but we only want
     * to do this if the user has asked for color.
     */
    if (XOF_ISSET(xop, XOF_COLOR_ALLOWED) && isatty(1))
        XOF_SET(xop, XOF_COLOR);

    argv[save] = NULL;
    return save;
}

/*
 * Debugging function that dumps the current stack of open libxo constructs,
 * suitable for calling from the debugger.
 */
void
xo_dump_stack (xo_handle_t *xop)
{
    int i;
    xo_stack_t *xsp;

    xop = xo_default(xop);

    fprintf(stderr, "Stack dump:\n");

    xsp = xop->xo_stack;
    for (i = 1, xsp++; i <= xop->xo_depth; i++, xsp++) {
        fprintf(stderr, "   [%d] %s '%s' [%x]\n",
                i, xo_state_name(xsp->xs_state),
                xsp->xs_name ?: "--", xsp->xs_flags);
    }
}

/*
 * Record the program name used for error messages
 */
void
xo_set_program (const char *name)
{
    xo_program = name;
}

void
xo_set_version_h (xo_handle_t *xop, const char *version)
{
    xop = xo_default(xop);

    if (version == NULL || strchr(version, '"') != NULL)
        return;

    if (!xo_style_is_encoding(xop))
        return;

    switch (xo_style(xop)) {
    case XO_STYLE_XML:
        /* For XML, we record this as an attribute for the first tag */
        xo_attr_h(xop, "version", "%s", version);
        break;

    case XO_STYLE_JSON:
        /*
         * For JSON, we record the version string in our handle, and emit
         * it in xo_emit_top.
         */
        xop->xo_version = xo_strndup(version, -1);
        break;

    case XO_STYLE_ENCODER:
        xo_encoder_handle(xop, XO_OP_VERSION, NULL, version, 0);
        break;
    }
}

/*
 * Set the version number for the API content being carried through
 * the xo handle.
 */
void
xo_set_version (const char *version)
{
    xo_set_version_h(NULL, version);
}

/*
 * Generate a warning.  Normally, this is a text message written to
 * standard error.  If the XOF_WARN_XML flag is set, then we generate
 * XMLified content on standard output.
 */
void
xo_emit_warn_hcv (xo_handle_t *xop, int as_warning, int code,
                  const char *fmt, va_list vap)
{
    xop = xo_default(xop);

    if (fmt == NULL)
        return;

    xo_open_marker_h(xop, "xo_emit_warn_hcv");
    xo_open_container_h(xop, as_warning ? "__warning" : "__error");

    if (xo_program)
        xo_emit("{wc:program}", xo_program);

    if (xo_style(xop) == XO_STYLE_XML || xo_style(xop) == XO_STYLE_JSON) {
        va_list ap;
        xo_handle_t temp;

        bzero(&temp, sizeof(temp));
        temp.xo_style = XO_STYLE_TEXT;
        xo_buf_init(&temp.xo_data);
        xo_depth_check(&temp, XO_DEPTH);

        va_copy(ap, vap);
        (void) xo_emit_hv(&temp, fmt, ap);
        va_end(ap);

        xo_buffer_t *src = &temp.xo_data;
        xo_format_value(xop, "message", 7, src->xb_bufp,
                        src->xb_curp - src->xb_bufp, NULL, 0, NULL, 0, 0);

        xo_free(temp.xo_stack);
        xo_buf_cleanup(src);
    }

    (void) xo_emit_hv(xop, fmt, vap);

    ssize_t len = strlen(fmt);
    if (len > 0 && fmt[len - 1] != '\n') {
        if (code > 0) {
            const char *msg = strerror(code);
            if (msg)
                xo_emit_h(xop, ": {G:strerror}{g:error/%s}", msg);
        }
        xo_emit("\n");
    }

    xo_close_marker_h(xop, "xo_emit_warn_hcv");
    xo_flush_h(xop);
}

void
xo_emit_warn_hc (xo_handle_t *xop, int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_emit_warn_hcv(xop, 1, code, fmt, vap);
    va_end(vap);
}

void
xo_emit_warn_c (int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_emit_warn_hcv(NULL, 1, code, fmt, vap);
    va_end(vap);
}

void
xo_emit_warn (const char *fmt, ...)
{
    int code = errno;
    va_list vap;

    va_start(vap, fmt);
    xo_emit_warn_hcv(NULL, 1, code, fmt, vap);
    va_end(vap);
}

void
xo_emit_warnx (const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_emit_warn_hcv(NULL, 1, -1, fmt, vap);
    va_end(vap);
}

void
xo_emit_err_v (int eval, int code, const char *fmt, va_list vap)
{
    xo_emit_warn_hcv(NULL, 0, code, fmt, vap);
    xo_finish();
    exit(eval);
}

void
xo_emit_err (int eval, const char *fmt, ...)
{
    int code = errno;
    va_list vap;
    va_start(vap, fmt);
    xo_emit_err_v(0, code, fmt, vap);
    va_end(vap);
    exit(eval);
}

void
xo_emit_errx (int eval, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_emit_err_v(0, -1, fmt, vap);
    va_end(vap);
    xo_finish();
    exit(eval);
}

void
xo_emit_errc (int eval, int code, const char *fmt, ...)
{
    va_list vap;

    va_start(vap, fmt);
    xo_emit_warn_hcv(NULL, 0, code, fmt, vap);
    va_end(vap);
    xo_finish();
    exit(eval);
}

/*
 * Get the opaque private pointer for an xo handle
 */
void *
xo_get_private (xo_handle_t *xop)
{
    xop = xo_default(xop);
    return xop->xo_private;
}

/*
 * Set the opaque private pointer for an xo handle.
 */
void
xo_set_private (xo_handle_t *xop, void *opaque)
{
    xop = xo_default(xop);
    xop->xo_private = opaque;
}

/*
 * Get the encoder function
 */
xo_encoder_func_t
xo_get_encoder (xo_handle_t *xop)
{
    xop = xo_default(xop);
    return xop->xo_encoder;
}

/*
 * Record an encoder callback function in an xo handle.
 */
void
xo_set_encoder (xo_handle_t *xop, xo_encoder_func_t encoder)
{
    xop = xo_default(xop);

    xop->xo_style = XO_STYLE_ENCODER;
    xop->xo_encoder = encoder;
}

/*
 * The xo(1) utility needs to be able to open and close lists and
 * instances, but since it's called without "state", we cannot
 * rely on the state transitions (in xo_transition) to DTRT, so
 * we have a mechanism for external parties to "force" transitions
 * that would otherwise be impossible.  This is not a general
 * mechanism, and is really tailored only for xo(1).
 */
void
xo_explicit_transition (xo_handle_t *xop, xo_state_t new_state,
                        const char *name, xo_xof_flags_t flags)
{
    xo_xsf_flags_t xsf_flags;

    xop = xo_default(xop);

    switch (new_state) {

    case XSS_OPEN_LIST:
        xo_do_open_list(xop, flags, name);
        break;

    case XSS_OPEN_INSTANCE:
        xo_do_open_instance(xop, flags, name);
        break;

    case XSS_CLOSE_INSTANCE:
        xo_depth_change(xop, name, 1, 1, XSS_OPEN_INSTANCE,
                        xo_stack_flags(flags));
        xo_stack_set_flags(xop);
        xo_do_close_instance(xop, name);
        break;

    case XSS_CLOSE_LIST:
        xsf_flags = XOF_ISSET(xop, XOF_NOT_FIRST) ? XSF_NOT_FIRST : 0;

        xo_depth_change(xop, name, 1, 1, XSS_OPEN_LIST,
                        XSF_LIST | xsf_flags | xo_stack_flags(flags));
        xo_do_close_list(xop, name);
        break;
    }
}