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32 .Nd functions for reading streaming archives
34 Streaming Archive Library (libarchive, -larchive)
38 These functions provide a complete API for reading streaming archives.
39 The general process is to first create the
41 object, set options, initialize the reader, iterate over the archive
42 headers and associated data, then close the archive and release all
45 .Ss Create archive object
47 .Xr archive_read_new 3 .
49 To read an archive, you must first obtain an initialized
52 .Fn archive_read_new .
54 .Ss Enable filters and formats
56 .Xr archive_read_filter 3
58 .Xr archive_read_format 3 .
60 You can then modify this object for the desired operations with the
62 .Fn archive_read_set_XXX
64 .Fn archive_read_support_XXX
66 In particular, you will need to invoke appropriate
67 .Fn archive_read_support_XXX
68 functions to enable the corresponding compression and format
70 Note that these latter functions perform two distinct operations:
71 they cause the corresponding support code to be linked into your
72 program, and they enable the corresponding auto-detect code.
73 Unless you have specific constraints, you will generally want
75 .Fn archive_read_support_filter_all
77 .Fn archive_read_support_format_all
78 to enable auto-detect for all formats and compression types
79 currently supported by the library.
83 .Xr archive_read_set_options 3 .
87 .Xr archive_read_open 3 .
89 Once you have prepared the
93 to actually open the archive and prepare it for reading.
94 There are several variants of this function;
95 the most basic expects you to provide pointers to several
96 functions that can provide blocks of bytes from the archive.
97 There are convenience forms that allow you to
98 specify a filename, file descriptor,
100 object, or a block of memory from which to read the archive data.
101 Note that the core library makes no assumptions about the
102 size of the blocks read;
103 callback functions are free to read whatever block size is
104 most appropriate for the medium.
108 .Xr archive_read_header 3 ,
109 .Xr archive_read_data 3
111 .Xr archive_read_extract 3 .
113 Each archive entry consists of a header followed by a certain
115 You can obtain the next header with
116 .Fn archive_read_next_header ,
117 which returns a pointer to an
118 .Tn struct archive_entry
119 structure with information about the current archive element.
120 If the entry is a regular file, then the header will be followed
123 .Fn archive_read_data
124 (which works much like the
127 to read this data from the archive, or
128 .Fn archive_read_data_block
129 which provides a slightly more efficient interface.
130 You may prefer to use the higher-level
131 .Fn archive_read_data_skip ,
132 which reads and discards the data for this entry,
133 .Fn archive_read_data_to_file ,
134 which copies the data to the provided file descriptor, or
135 .Fn archive_read_extract ,
136 which recreates the specified entry on disk and copies data
138 In particular, note that
139 .Fn archive_read_extract
141 .Tn struct archive_entry
142 structure that you provide it, which may differ from the
143 entry just read from the archive.
144 In particular, many applications will want to override the
145 pathname, file permissions, or ownership.
147 .Ss Release resources
149 .Xr archive_read_free 3 .
151 Once you have finished reading data from the archive, you
153 .Fn archive_read_close
154 to close the archive, then call
155 .Fn archive_read_free
156 to release all resources, including all memory allocated by the library.
159 The following illustrates basic usage of the library.
161 the callback functions are simply wrappers around the standard
167 .Bd -literal -offset indent
169 list_archive(const char *name)
171 struct mydata *mydata;
173 struct archive_entry *entry;
175 mydata = malloc(sizeof(struct mydata));
176 a = archive_read_new();
178 archive_read_support_filter_all(a);
179 archive_read_support_format_all(a);
180 archive_read_open(a, mydata, myopen, myread, myclose);
181 while (archive_read_next_header(a, &entry) == ARCHIVE_OK) {
182 printf("%s\en",archive_entry_pathname(entry));
183 archive_read_data_skip(a);
185 archive_read_free(a);
190 myread(struct archive *a, void *client_data, const void **buff)
192 struct mydata *mydata = client_data;
194 *buff = mydata->buff;
195 return (read(mydata->fd, mydata->buff, 10240));
199 myopen(struct archive *a, void *client_data)
201 struct mydata *mydata = client_data;
203 mydata->fd = open(mydata->name, O_RDONLY);
204 return (mydata->fd >= 0 ? ARCHIVE_OK : ARCHIVE_FATAL);
208 myclose(struct archive *a, void *client_data)
210 struct mydata *mydata = client_data;
221 .Xr archive_read_new 3 ,
222 .Xr archive_read_data 3 ,
223 .Xr archive_read_extract 3 ,
224 .Xr archive_read_filter 3 ,
225 .Xr archive_read_format 3 ,
226 .Xr archive_read_header 3 ,
227 .Xr archive_read_open 3 ,
228 .Xr archive_read_set_options 3 ,
234 library first appeared in
240 library was written by
241 .An Tim Kientzle Aq kientzle@acm.org .
243 Many traditional archiver programs treat
244 empty files as valid empty archives.
245 For example, many implementations of
247 allow you to append entries to an empty file.
248 Of course, it is impossible to determine the format of an empty file
249 by inspecting the contents, so this library treats empty files as