1ARCHIVE_READ(3) BSD Library Functions Manual ARCHIVE_READ(3)
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4 archive_read — functions for reading streaming archives
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7 Streaming Archive Library (libarchive, -larchive)
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10 #include <archive.h>
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13 These functions provide a complete API for reading streaming archives.
14 The general process is to first create the struct archive object, set
15 options, initialize the reader, iterate over the archive headers and
16 associated data, then close the archive and release all resources.
17 Create archive object
19 See archive_read_new(3).
20 To read an archive, you must first obtain an initialized struct archive
22 object from archive_read_new().
23 Enable filters and formats
25 See archive_read_filter(3) and archive_read_format(3).
26 You can then modify this object for the desired operations with the vari‐
28 ous archive_read_set_XXX() and archive_read_support_XXX() functions. In
29 particular, you will need to invoke appropriate
30 archive_read_support_XXX() functions to enable the corresponding compres‐
31 sion and format support. Note that these latter functions perform two
32 distinct operations: they cause the corresponding support code to be
33 linked into your program, and they enable the corresponding auto-detect
34 code. Unless you have specific constraints, you will generally want to
35 invoke archive_read_support_filter_all() and
36 archive_read_support_format_all() to enable auto-detect for all formats
37 and compression types currently supported by the library.
38 Set options
40 See archive_read_set_options(3).
41 Open archive
43 See archive_read_open(3).
44 Once you have prepared the struct archive object, you call
46 archive_read_open() to actually open the archive and prepare it for read‐
47 ing. There are several variants of this function; the most basic expects
48 you to provide pointers to several functions that can provide blocks of
49 bytes from the archive. There are convenience forms that allow you to
50 specify a filename, file descriptor, FILE * object, or a block of memory
51 from which to read the archive data. Note that the core library makes no
52 assumptions about the size of the blocks read; callback functions are
53 free to read whatever block size is most appropriate for the medium.
54 Consume archive
56 See archive_read_header(3), archive_read_data(3) and
57 archive_read_extract(3).
58 Each archive entry consists of a header followed by a certain amount of
60 data. You can obtain the next header with archive_read_next_header(),
61 which returns a pointer to an struct archive_entry structure with infor‐
62 mation about the current archive element. If the entry is a regular
63 file, then the header will be followed by the file data. You can use
64 archive_read_data() (which works much like the read(2) system call) to
65 read this data from the archive, or archive_read_data_block() which pro‐
66 vides a slightly more efficient interface. You may prefer to use the
67 higher-level archive_read_data_skip(), which reads and discards the data
68 for this entry, archive_read_data_into_fd(), which copies the data to the
69 provided file descriptor, or archive_read_extract(), which recreates the
70 specified entry on disk and copies data from the archive. In particular,
71 note that archive_read_extract() uses the struct archive_entry structure
72 that you provide it, which may differ from the entry just read from the
73 archive. In particular, many applications will want to override the
74 pathname, file permissions, or ownership.
75 Release resources
77 See archive_read_free(3).
78 Once you have finished reading data from the archive, you should call
80 archive_read_close() to close the archive, then call archive_read_free()
81 to release all resources, including all memory allocated by the library.
82
84 The following illustrates basic usage of the library. In this example,
85 the callback functions are simply wrappers around the standard open(2),
86 read(2), and close(2) system calls.
87 void
89 list_archive(const char *name)
90 {
91 struct mydata *mydata;
92 struct archive *a;
93 struct archive_entry *entry;
94 mydata = malloc(sizeof(struct mydata));
96 a = archive_read_new();
97 mydata->name = name;
98 archive_read_support_filter_all(a);
99 archive_read_support_format_all(a);
100 archive_read_open(a, mydata, myopen, myread, myclose);
101 while (archive_read_next_header(a, &entry) == ARCHIVE_OK) {
102 printf("%s\n",archive_entry_pathname(entry));
103 archive_read_data_skip(a);
104 }
105 archive_read_free(a);
106 free(mydata);
107 }
108 la_ssize_t
110 myread(struct archive *a, void *client_data, const void **buff)
111 {
112 struct mydata *mydata = client_data;
113 *buff = mydata->buff;
115 return (read(mydata->fd, mydata->buff, 10240));
116 }
117 int
119 myopen(struct archive *a, void *client_data)
120 {
121 struct mydata *mydata = client_data;
122 mydata->fd = open(mydata->name, O_RDONLY);
124 return (mydata->fd >= 0 ? ARCHIVE_OK : ARCHIVE_FATAL);
125 }
126 int
128 myclose(struct archive *a, void *client_data)
129 {
130 struct mydata *mydata = client_data;
131 if (mydata->fd > 0)
133 close(mydata->fd);
134 return (ARCHIVE_OK);
135 }
136
138 tar(1), libarchive(3), archive_read_new(3), archive_read_data(3),
139 archive_read_extract(3), archive_read_filter(3), archive_read_format(3),
140 archive_read_header(3), archive_read_open(3),
141 archive_read_set_options(3), archive_util(3), tar(5)
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144 The libarchive library first appeared in FreeBSD 5.3.
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147 The libarchive library was written by Tim Kientzle <kientzle@acm.org>.
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150 Many traditional archiver programs treat empty files as valid empty ar‐
151 chives. For example, many implementations of tar(1) allow you to append
152 entries to an empty file. Of course, it is impossible to determine the
153 format of an empty file by inspecting the contents, so this library
154 treats empty files as having a special “empty” format.
155BSD February 2, 2012 BSD