.\" # .\" # Copyright (c) 2014, Juniper Networks, Inc. .\" # All rights reserved. .\" # This SOFTWARE is licensed under the LICENSE provided in the .\" # ../Copyright file. By downloading, installing, copying, or .\" # using the SOFTWARE, you agree to be bound by the terms of that .\" # LICENSE. .\" # Phil Shafer, July 2014 .\" .Dd December 4, 2014 .Dt LIBXO 3 .Os .Sh NAME .Nm xo_format .Nd content of format descriptors for xo_emit .Sh DESCRIPTION .Pp .Nm libxo uses format strings to control the rendering of data into various output styles, including .Em text , .Em XML , .EM JSON , and .Em HTML . Each format string contains a set of zero or more .Dq field descriptions , which describe independent data fields. Each field description contains a set of .Dq modifiers , a .Dq content string , and zero, one, or two .Dq format descriptors . The modifiers tell .Nm libxo what the field is and how to treat it, while the format descriptors are formatting instructions using .Xr printf 3 Ns -style format strings, telling .Nm libxo how to format the field. The field description is placed inside a set of braces, with a colon .Ql ( \&: ) after the modifiers and a slash .Ql ( \&/ ) before each format descriptors. Text may be intermixed with field descriptions within the format string. .Pp The field description is given as follows: .Bd -literal -offset indent '{' [ role | modifier ]* ':' [ content ] [ '/' field-format [ '/' encoding-format ]] '}' .Ed .Pp The role describes the function of the field, while the modifiers enable optional behaviors. The contents, field-format, and encoding-format are used in varying ways, based on the role. These are described in the following sections. .Pp In the following example, three field descriptors appear. The first is a padding field containing three spaces of padding, the second is a label ("In stock"), and the third is a value field ("in-stock"). The in-stock field has a "%u" format that will parse the next argument passed to the .Xr xo_emit 3 , function as an unsigned integer. .Bd -literal -offset indent xo_emit("{P: }{Lwc:In stock}{:in-stock/%u}\\n", 65); .Ed .Pp This single line of code can generate text ("In stock: 65\\n"), XML ("65"), JSON ('"in-stock": 6'), or HTML (too lengthy to be listed here). .Ss Modifier Roles Modifiers are optional, and indicate the role and formatting of the content. The roles are listed below; only one role is permitted: .Pp .Bl -column "M" "Name12341234" .It Sy "M Name Description" .It D "decoration " "Field is non-text (e.g. colon, comma)" .It E "error " "Field is an error message" .It L "label " "Field is text that prefixes a value" .It N "note " "Field is text that follows a value" .It P "padding " "Field is spaces needed for vertical alignment" .It T "title " "Field is a title value for headings" .It U "units " "Field is the units for the previous value field" .It V "value " "Field is the name of field (the default)" .It W "warning " "Field is a warning message" .It \&[ "start anchor" "Begin a section of anchored variable-width text" .It \&] "stop anchor " "End a section of anchored variable-width text" .El .Pp .Ss The Decoration Role ({D:}) Decorations are typically punctuation marks such as colons, semi-colons, and commas used to decorate the text and make it simpler for human readers. By marking these distinctly, HTML usage scenarios can use CSS to direct their display parameters. .Bd -literal -offset indent xo_emit("{D:((}{:name}{D:))}\\n", name); .Ed .Ss The Label Role ({L:}) Labels are text that appears before a value. .Bd -literal -offset indent xo_emit("{Lwc:Cost}{:cost/%u}\\n", cost); .Ed .Ss The Note Role ({N:}) Notes are text that appears after a value. .Bd -literal -offset indent xo_emit("{:cost/%u} {N:per year}\\n", cost); .Ed .Ss The Padding Role ({P:}) Padding represents whitespace used before and between fields. The padding content can be either static, when placed directly within the field descriptor, or a printf-style format descriptor can be used, if preceded by a slash ("/"): .Bd -literal -offset indent xo_emit("{P: }{Lwc:Cost}{:cost/%u}\\n", cost); xo_emit("{P:/30s}{Lwc:Cost}{:cost/%u}\\n", "", cost); .Ed .Ss The Title Role ({T:}) Titles are heading or column headers that are meant to be displayed to the user. The title can be either static, when placed directly within the field descriptor, or a printf-style format descriptor can be used, if preceded by a slash ("/"): .Bd -literal -offset indent xo_emit("{T:Interface Statistics}\\n"); xo_emit("{T:/%20.20s}{T:/%6.6s}\\n", "Item Name", "Cost"); .Ed .Ss The Units Role ({U:}) Units are the dimension by which values are measured, such as degrees, miles, bytes, and decibels. The units field carries this information for the previous value field. .Bd -literal -offset indent xo_emit("{Lwc:Distance}{:distance/%u}{Uw:miles}\\n", miles); .Ed .Pp Note that the sense of the 'w' modifier is reversed for units; a blank is added before the contents, rather than after it. .Pp When the .Dv XOF_UNITS flag is set, units are rendered in XML as the .Dq units attribute: .Bd -literal -offset indent 50 .Ed .Pp Units can also be rendered in HTML as the "data-units" attribute: .Bd -literal -offset indent
50
.Ed .Ss The Value Role ({V:} and {:}) The value role is used to represent the a data value that is interesting for the non-display output styles (XML and JSON). Value is the default role; if no other role designation is given, the field is a value. The field name must appear within the field descriptor, followed by one or two format descriptors. The first format descriptor is used for display styles (TEXT and HTML), while the second one is used for encoding styles (XML and JSON). If no second format is given, the encoding format defaults to the first format, with any minimum width removed. If no first format is given, both format descriptors default to "%s". .Bd -literal -offset indent xo_emit("{:length/%02u}x{:width/%02u}x{:height/%02u}\\n", length, width, height); xo_emit("{:author} wrote \"{:poem}\" in {:year/%4d}\\n, author, poem, year); .Ed .Ss The Anchor Modifiers ({[:} and {]:}) The anchor roles allow a set of strings by be padded as a group, but still be visible to .Xr xo_emit 3 as distinct fields. Either the start or stop anchor can give a field width and it can be either directly in the descriptor or passed as an argument. Any fields between the start and stop anchor are padded to meet the minimum width given. .Pp To give a width directly, encode it as the content of the anchor tag: .Bd -literal -offset indent xo_emit("({[:10}{:min/%d}/{:max/%d}{]:})\\n", min, max); .Ed .Pp To pass a width as an argument, use "%d" as the format, which must appear after the "/". Note that only "%d" is supported for widths. Using any other value could ruin your day. .Bd -literal -offset indent xo_emit("({[:/%d}{:min/%d}/{:max/%d}{]:})\\n", width, min, max); .Ed .Pp If the width is negative, padding will be added on the right, suitable for left justification. Otherwise the padding will be added to the left of the fields between the start and stop anchors, suitable for right justification. If the width is zero, nothing happens. If the number of columns of output between the start and stop anchors is less than the absolute value of the given width, nothing happens. .Pp Widths over 8k are considered probable errors and not supported. If .Dv XOF_WARN is set, a warning will be generated. .Ss Modifier Flags The modifiers can also include the following flags, which modify the content emitted for some output styles: .Pp .Bl -column M "Name12341234" .It Sy M "Name Description" .It c "colon " "A colon ("":"") is appended after the label" .It d "display " "Only emit field for display styles (text/HTML)" .It e "encoding " "Only emit for encoding styles (XML/JSON)" .It k "key " "Field is a key, suitable for XPath predicates" .It n "no-quotes " "Do not quote the field when using JSON style" .It q "quotes " "Quote the field when using JSON style" .It w "white space " "A blank ("" "") is appended after the label" .El .Pp For example, the modifier string "Lwc" means the field has a label role (text that describes the next field) and should be followed by a colon ('c') and a space ('w'). The modifier string "Vkq" means the field has a value role, that it is a key for the current instance, and that the value should be quoted when encoded for JSON. .Ss The Colon Modifier ({c:}) The colon modifier appends a single colon to the data value: .Bd -literal -offset indent EXAMPLE: xo_emit("{Lc:Name}{:name}\\n", "phil"); TEXT: Name:phil .Ed .Pp The colon modifier is only used for the TEXT and HTML output styles. It is commonly combined with the space modifier ('{w:}'). It is purely a convenience feature. .Ss The Display Modifier ({d:}) The display modifier indicated the field should only be generated for the display output styles, TEXT and HTML. .Bd -literal -offset indent EXAMPLE: xo_emit("{Lcw:Name}{d:name} {:id/%d}\\n", "phil", 1); TEXT: Name: phil 1 XML: 1 .Ed .Pp The display modifier is the opposite of the encoding modifier, and they are often used to give to distinct views of the underlying data. .Ss The Encoding Modifier ({e:}) The display modifier indicated the field should only be generated for the display output styles, TEXT and HTML. .Bd -literal -offset indent EXAMPLE: xo_emit("{Lcw:Name}{:name} {e:id/%d}\\n", "phil", 1); TEXT: Name: phil XML: phil1 .Ed .Pp The encoding modifier is the opposite of the display modifier, and they are often used to give to distinct views of the underlying data. .Ss The Key Modifier ({k:}) The key modifier is used to indicate that a particular field helps uniquely identify an instance of list data. .Bd -literal -offset indent EXAMPLE: xo_open_list("user"); for (i = 0; i < num_users; i++) { xo_open_instance("user"); xo_emit("User {k:name} has {:count} tickets\\n", user[i].u_name, user[i].u_tickets); xo_close_instance("user"); } xo_close_list("user"); .Ed .Pp Currently the key modifier is only used when generating XPath values for the HTML output style when .Dv XOF_XPATH is set, but other uses are likely in the near future. .Ss The Leaf-List Modifier ({l:}) The leaf-list modifier is used to distinguish lists where each instance consists of only a single value. In XML, these are rendered as single elements, where JSON renders them as arrays. .Bd -literal -offset indent EXAMPLE: xo_open_list("user"); for (i = 0; i < num_users; i++) { xo_emit("Member {l:name}\n", user[i].u_name); } xo_close_list("user"); XML: phil pallavi JSON: "user": [ "phil", "pallavi" ] .Ed .Ss The No-Quotes Modifier ({n:}) The no-quotes modifier (and its twin, the 'quotes' modifier) affect the quoting of values in the JSON output style. JSON uses quotes for string values, but no quotes for numeric, boolean, and null data. .Xr xo_emit 3 applies a simple heuristic to determine whether quotes are needed, but often this needs to be controlled by the caller. .Bd -literal -offset indent EXAMPLE: const char *bool = is_true ? "true" : "false"; xo_emit("{n:fancy/%s}", bool); JSON: "fancy": true .Ed .Ss The Quotes Modifier ({q:}) The quotes modifier (and its twin, the 'no-quotes' modifier) affect the quoting of values in the JSON output style. JSON uses quotes for string values, but no quotes for numeric, boolean, and null data. .Xr xo_emit 3 applies a simple heuristic to determine whether quotes are needed, but often this needs to be controlled by the caller. .Bd -literal -offset indent EXAMPLE: xo_emit("{q:time/%d}", 2014); JSON: "year": "2014" .Ed .Ss The White Space Modifier ({w:}) The white space modifier appends a single space to the data value: .Bd -literal -offset indent EXAMPLE: xo_emit("{Lw:Name}{:name}\\n", "phil"); TEXT: Name phil .Ed .Pp The white space modifier is only used for the TEXT and HTML output styles. It is commonly combined with the colon modifier ('{c:}'). It is purely a convenience feature. .Pp Note that the sense of the 'w' modifier is reversed for the units role ({Uw:}); a blank is added before the contents, rather than after it. .Ss Field Formatting The field format is similar to the format string for .Xr printf 3 . Its use varies based on the role of the field, but generally is used to format the field's contents. .Pp If the format string is not provided for a value field, it defaults to "%s". .Pp Note a field definition can contain zero or more printf-style .Dq directives , which are sequences that start with a '%' and end with one of following characters: "diouxXDOUeEfFgGaAcCsSp". Each directive is matched by one of more arguments to the .Xr xo_emit 3 function. .Pp The format string has the form: .Bd -literal -offset indent '%' format-modifier * format-character .Ed .Pp The format- modifier can be: .Bl -bullet .It a '#' character, indicating the output value should be prefixed with '0x', typically to indicate a base 16 (hex) value. .It a minus sign ('-'), indicating the output value should be padded on the right instead of the left. .It a leading zero ('0') indicating the output value should be padded on the left with zeroes instead of spaces (' '). .It one or more digits ('0' - '9') indicating the minimum width of the argument. If the width in columns of the output value is less than the minimum width, the value will be padded to reach the minimum. .It a period followed by one or more digits indicating the maximum number of bytes which will be examined for a string argument, or the maximum width for a non-string argument. When handling ASCII strings this functions as the field width but for multi-byte characters, a single character may be composed of multiple bytes. .Xr xo_emit 3 will never dereference memory beyond the given number of bytes. .It a second period followed by one or more digits indicating the maximum width for a string argument. This modifier cannot be given for non-string arguments. .It one or more 'h' characters, indicating shorter input data. .It one or more 'l' characters, indicating longer input data. .It a 'z' character, indicating a 'size_t' argument. .It a 't' character, indicating a 'ptrdiff_t' argument. .It a ' ' character, indicating a space should be emitted before positive numbers. .It a '+' character, indicating sign should emitted before any number. .El .Pp Note that 'q', 'D', 'O', and 'U' are considered deprecated and will be removed eventually. .Pp The format character is described in the following table: .Pp .Bl -column C "Argument Type12" .It Sy "C Argument Type Format" .It d "int " "base 10 (decimal)" .It i "int " "base 10 (decimal)" .It o "int " "base 8 (octal)" .It u "unsigned " "base 10 (decimal)" .It x "unsigned " "base 16 (hex)" .It X "unsigned long " "base 16 (hex)" .It D "long " "base 10 (decimal)" .It O "unsigned long " "base 8 (octal)" .It U "unsigned long " "base 10 (decimal)" .It e "double " "[-]d.ddde+-dd" .It E "double " "[-]d.dddE+-dd" .It f "double " "[-]ddd.ddd" .It F "double " "[-]ddd.ddd" .It g "double " "as 'e' or 'f'" .It G "double " "as 'E' or 'F'" .It a "double " "[-]0xh.hhhp[+-]d" .It A "double " "[-]0Xh.hhhp[+-]d" .It c "unsigned char " "a character" .It C "wint_t " "a character" .It s "char * " "a UTF-8 string" .It S "wchar_t * " "a unicode/WCS string" .It p "void * " "'%#lx'" .El .Pp The 'h' and 'l' modifiers affect the size and treatment of the argument: .Bl -column "Mod" "d, i " "o, u, x, X " .It Sy "Mod" "d, i " "o, u, x, X" .It "hh " "signed char " "unsigned char" .It "h " "short " "unsigned short" .It "l " "long " "unsigned long" .It "ll " "long long " "unsigned long long" .It "j " "intmax_t " "uintmax_t" .It "t " "ptrdiff_t " "ptrdiff_t" .It "z " "size_t " "size_t" .It "q " "quad_t " "u_quad_t" .El .Pp .Ss UTF-8 and Locale Strings All strings for .Nm libxo must be UTF-8. .Nm libxo will handle turning them into locale-based strings for display to the user. .Pp For strings, the 'h' and 'l' modifiers affect the interpretation of the bytes pointed to argument. The default '%s' string is a 'char *' pointer to a string encoded as UTF-8. Since UTF-8 is compatible with .Em ASCII data, a normal 7-bit .Em ASCII string can be used. '%ls' expects a 'wchar_t *' pointer to a wide-character string, encoded as 32-bit Unicode values. '%hs' expects a 'char *' pointer to a multi-byte string encoded with the current locale, as given by the .Ev LC_CTYPE , .Ev LANG , or .Ev LC_ALL environment variables. The first of this list of variables is used and if none of the variables are set, the locale defaults to .Em UTF-8 . .Pp .Nm libxo will convert these arguments as needed to either UTF-8 (for XML, JSON, and HTML styles) or locale-based strings for display in text style. .Bd -literal -offset indent xo_emit("All strings are utf-8 content {:tag/%ls}", L"except for wide strings"); .Ed .Pp "%S" is equivalent to "%ls". .Pp For example, a function is passed a locale-base name, a hat size, and a time value. The hat size is formatted in a UTF-8 (ASCII) string, and the time value is formatted into a wchar_t string. .Bd -literal -offset indent void print_order (const char *name, int size, struct tm *timep) { char buf[32]; const char *size_val = "unknown"; if (size > 0) snprintf(buf, sizeof(buf), "%d", size); size_val = buf; } wchar_t when[32]; wcsftime(when, sizeof(when), L"%d%b%y", timep); xo_emit("The hat for {:name/%hs} is {:size/%s}.\\n", name, size_val); xo_emit("It was ordered on {:order-time/%ls}.\\n", when); } .Ed .Pp It is important to note that .Xr xo_emit 3 will perform the conversion required to make appropriate output. Text style output uses the current locale (as described above), while XML, JSON, and HTML use UTF-8. .Pp UTF-8 and locale-encoded strings can use multiple bytes to encode one column of data. The traditional "precision'" (aka "max-width") value for "%s" printf formatting becomes overloaded since it specifies both the number of bytes that can be safely referenced and the maximum number of columns to emit. .Xr xo_emit 3 uses the precision as the former, and adds a third value for specifying the maximum number of columns. .Pp In this example, the name field is printed with a minimum of 3 columns and a maximum of 6. Up to ten bytes are in used in filling those columns. .Bd -literal -offset indent xo_emit("{:name/%3.10.6s}", name); .Ed .Ss Characters Outside of Field Definitions Characters in the format string that are not part of a field definition are copied to the output for the TEXT style, and are ignored for the JSON and XML styles. For HTML, these characters are placed in a
with class "text". .Bd -literal -offset indent EXAMPLE: xo_emit("The hat is {:size/%s}.\\n", size_val); TEXT: The hat is extra small. XML: extra small JSON: "size": "extra small" HTML:
The hat is
extra small
.
.Ed .Ss "%n" is Not Supported .Nm libxo does not support the '%n' directive. It is a bad idea and we just do not do it. .Ss The Encoding Format (eformat) The "eformat" string is the format string used when encoding the field for JSON and XML. If not provided, it defaults to the primary format with any minimum width removed. If the primary is not given, both default to "%s". .Sh EXAMPLE In this example, the value for the number of items in stock is emitted: .Bd -literal -offset indent xo_emit("{P: }{Lwc:In stock}{:in-stock/%u}\\n", instock); .Ed .Pp This call will generate the following output: .Bd -literal -offset indent TEXT: In stock: 144 XML: 144 JSON: "in-stock": 144, HTML:
In stock
:
144
.Ed .Pp Clearly HTML wins the verbosity award, and this output does not include .Dv XOF_XPATH or .Dv XOF_INFO data, which would expand the penultimate line to: .Bd -literal -offset indent
144
.Ed .Sh WHAT MAKES A GOOD FIELD NAME? To make useful, consistent field names, follow these guidelines: .Pp .Ss Use lower case, even for TLAs Lower case is more civilized. Even TLAs should be lower case to avoid scenarios where the differences between "XPath" and "Xpath" drive your users crazy. Using "xpath" is simpler and better. .Ss Use hyphens, not underscores Use of hyphens is traditional in XML, and the .Dv XOF_UNDERSCORES flag can be used to generate underscores in JSON, if desired. But the raw field name should use hyphens. .Ss Use full words Do not abbreviate especially when the abbreviation is not obvious or not widely used. Use "data-size", not "dsz" or "dsize". Use "interface" instead of "ifname", "if-name", "iface", "if", or "intf". .Ss Use - Using the form - or -- helps in making consistent, useful names, avoiding the situation where one app uses "sent-packet" and another "packets-sent" and another "packets-we-have-sent". The can be dropped when it is obvious, as can obvious words in the classification. Use "receive-after-window-packets" instead of "received-packets-of-data-after-window". .Ss Reuse existing field names Nothing is worse than writing expressions like: .Bd -literal -offset indent if ($src1/process[pid == $pid]/name == $src2/proc-table/proc/p[process-id == $pid]/proc-name) { ... } .Ed .Pp Find someone else who is expressing similar data and follow their fields and hierarchy. Remember the quote is not .Dq Consistency is the hobgoblin of little minds but .Dq A foolish consistency is the hobgoblin of little minds . .Ss Think about your users Have empathy for your users, choosing clear and useful fields that contain clear and useful data. You may need to augment the display content with .Xr xo_attr 3 calls or "{e:}" fields to make the data useful. .Ss Do not use an arbitrary number postfix What does "errors2" mean? No one will know. "errors-after-restart" would be a better choice. Think of your users, and think of the future. If you make "errors2", the next guy will happily make "errors3" and before you know it, someone will be asking what is the difference between errors37 and errors63. .Ss Be consistent, uniform, unsurprising, and predictable Think of your field vocabulary as an API. You want it useful, expressive, meaningful, direct, and obvious. You want the client application's programmer to move between without the need to understand a variety of opinions on how fields are named. They should see the system as a single cohesive whole, not a sack of cats. .Pp Field names constitute the means by which client programmers interact with our system. By choosing wise names now, you are making their lives better. .Pp After using .Xr xolint 1 to find errors in your field descriptors, use .Dq "xolint -V" to spell check your field names and to detect different names for the same data. .Dq dropped-short and .Dq dropped-too-short are both reasonable names, but using them both will lead users to ask the difference between the two fields. If there is no difference, use only one of the field names. If there is a difference, change the names to make that difference more obvious. .Sh ADDITIONAL DOCUMENTATION Complete documentation can be found on github: .Bd -literal -offset indent http://juniper.github.io/libxo/libxo-manual.html .Ed .Pp .Nm libxo lives on github as: .Bd -literal -offset indent https://github.com/Juniper/libxo .Ed .Pp The latest release of .Nm libxo is available at: .Bd -literal -offset indent https://github.com/Juniper/libxo/releases .Ed .Sh SEE ALSO .Xr xolint 1 , .Xr xo_emit 3 .Sh HISTORY The .Nm libxo library was added in .Fx 11.0 . .Sh AUTHOR Phil Shafer