1 ///////////////////////////////////////////////////////////////////////////////
3 /// \file 02_decompress.c
4 /// \brief Decompress .xz files to stdout
6 /// Usage: ./02_decompress INPUT_FILES... > OUTFILE
8 /// Example: ./02_decompress foo.xz bar.xz > foobar
10 // Author: Lasse Collin
12 // This file has been put into the public domain.
13 // You can do whatever you want with this file.
15 ///////////////////////////////////////////////////////////////////////////////
26 init_decoder(lzma_stream
*strm
)
28 // Initialize a .xz decoder. The decoder supports a memory usage limit
29 // and a set of flags.
31 // The memory usage of the decompressor depends on the settings used
32 // to compress a .xz file. It can vary from less than a megabyte to
33 // a few gigabytes, but in practice (at least for now) it rarely
34 // exceeds 65 MiB because that's how much memory is required to
35 // decompress files created with "xz -9". Settings requiring more
36 // memory take extra effort to use and don't (at least for now)
37 // provide significantly better compression in most cases.
39 // Memory usage limit is useful if it is important that the
40 // decompressor won't consume gigabytes of memory. The need
41 // for limiting depends on the application. In this example,
42 // no memory usage limiting is used. This is done by setting
43 // the limit to UINT64_MAX.
45 // The .xz format allows concatenating compressed files as is:
47 // echo foo | xz > foobar.xz
48 // echo bar | xz >> foobar.xz
50 // When decompressing normal standalone .xz files, LZMA_CONCATENATED
51 // should always be used to support decompression of concatenated
52 // .xz files. If LZMA_CONCATENATED isn't used, the decoder will stop
53 // after the first .xz stream. This can be useful when .xz data has
54 // been embedded inside another file format.
56 // Flags other than LZMA_CONCATENATED are supported too, and can
57 // be combined with bitwise-or. See lzma/container.h
58 // (src/liblzma/api/lzma/container.h in the source package or e.g.
59 // /usr/include/lzma/container.h depending on the install prefix)
61 lzma_ret ret
= lzma_stream_decoder(
62 strm
, UINT64_MAX
, LZMA_CONCATENATED
);
64 // Return successfully if the initialization went fine.
68 // Something went wrong. The possible errors are documented in
69 // lzma/container.h (src/liblzma/api/lzma/container.h in the source
70 // package or e.g. /usr/include/lzma/container.h depending on the
73 // Note that LZMA_MEMLIMIT_ERROR is never possible here. If you
74 // specify a very tiny limit, the error will be delayed until
75 // the first headers have been parsed by a call to lzma_code().
79 msg
= "Memory allocation failed";
82 case LZMA_OPTIONS_ERROR
:
83 msg
= "Unsupported decompressor flags";
87 // This is most likely LZMA_PROG_ERROR indicating a bug in
88 // this program or in liblzma. It is inconvenient to have a
89 // separate error message for errors that should be impossible
90 // to occur, but knowing the error code is important for
91 // debugging. That's why it is good to print the error code
92 // at least when there is no good error message to show.
93 msg
= "Unknown error, possibly a bug";
97 fprintf(stderr
, "Error initializing the decoder: %s (error code %u)\n",
104 decompress(lzma_stream
*strm
, const char *inname
, FILE *infile
, FILE *outfile
)
106 // When LZMA_CONCATENATED flag was used when initializing the decoder,
107 // we need to tell lzma_code() when there will be no more input.
108 // This is done by setting action to LZMA_FINISH instead of LZMA_RUN
109 // in the same way as it is done when encoding.
111 // When LZMA_CONCATENATED isn't used, there is no need to use
112 // LZMA_FINISH to tell when all the input has been read, but it
113 // is still OK to use it if you want. When LZMA_CONCATENATED isn't
114 // used, the decoder will stop after the first .xz stream. In that
115 // case some unused data may be left in strm->next_in.
116 lzma_action action
= LZMA_RUN
;
118 uint8_t inbuf
[BUFSIZ
];
119 uint8_t outbuf
[BUFSIZ
];
121 strm
->next_in
= NULL
;
123 strm
->next_out
= outbuf
;
124 strm
->avail_out
= sizeof(outbuf
);
127 if (strm
->avail_in
== 0 && !feof(infile
)) {
128 strm
->next_in
= inbuf
;
129 strm
->avail_in
= fread(inbuf
, 1, sizeof(inbuf
),
132 if (ferror(infile
)) {
133 fprintf(stderr
, "%s: Read error: %s\n",
134 inname
, strerror(errno
));
138 // Once the end of the input file has been reached,
139 // we need to tell lzma_code() that no more input
140 // will be coming. As said before, this isn't required
141 // if the LZMA_CONATENATED flag isn't used when
142 // initializing the decoder.
144 action
= LZMA_FINISH
;
147 lzma_ret ret
= lzma_code(strm
, action
);
149 if (strm
->avail_out
== 0 || ret
== LZMA_STREAM_END
) {
150 size_t write_size
= sizeof(outbuf
) - strm
->avail_out
;
152 if (fwrite(outbuf
, 1, write_size
, outfile
)
154 fprintf(stderr
, "Write error: %s\n",
159 strm
->next_out
= outbuf
;
160 strm
->avail_out
= sizeof(outbuf
);
163 if (ret
!= LZMA_OK
) {
164 // Once everything has been decoded successfully, the
165 // return value of lzma_code() will be LZMA_STREAM_END.
167 // It is important to check for LZMA_STREAM_END. Do not
168 // assume that getting ret != LZMA_OK would mean that
169 // everything has gone well or that when you aren't
170 // getting more output it must have successfully
171 // decoded everything.
172 if (ret
== LZMA_STREAM_END
)
175 // It's not LZMA_OK nor LZMA_STREAM_END,
176 // so it must be an error code. See lzma/base.h
177 // (src/liblzma/api/lzma/base.h in the source package
178 // or e.g. /usr/include/lzma/base.h depending on the
179 // install prefix) for the list and documentation of
180 // possible values. Many values listen in lzma_ret
181 // enumeration aren't possible in this example, but
182 // can be made possible by enabling memory usage limit
183 // or adding flags to the decoder initialization.
187 msg
= "Memory allocation failed";
190 case LZMA_FORMAT_ERROR
:
191 // .xz magic bytes weren't found.
192 msg
= "The input is not in the .xz format";
195 case LZMA_OPTIONS_ERROR
:
196 // For example, the headers specify a filter
197 // that isn't supported by this liblzma
198 // version (or it hasn't been enabled when
199 // building liblzma, but no-one sane does
200 // that unless building liblzma for an
201 // embedded system). Upgrading to a newer
202 // liblzma might help.
204 // Note that it is unlikely that the file has
205 // accidentally became corrupt if you get this
206 // error. The integrity of the .xz headers is
207 // always verified with a CRC32, so
208 // unintentionally corrupt files can be
209 // distinguished from unsupported files.
210 msg
= "Unsupported compression options";
213 case LZMA_DATA_ERROR
:
214 msg
= "Compressed file is corrupt";
218 // Typically this error means that a valid
219 // file has got truncated, but it might also
220 // be a damaged part in the file that makes
221 // the decoder think the file is truncated.
222 // If you prefer, you can use the same error
223 // message for this as for LZMA_DATA_ERROR.
224 msg
= "Compressed file is truncated or "
229 // This is most likely LZMA_PROG_ERROR.
230 msg
= "Unknown error, possibly a bug";
234 fprintf(stderr
, "%s: Decoder error: "
235 "%s (error code %u)\n",
244 main(int argc
, char **argv
)
247 fprintf(stderr
, "Usage: %s FILES...\n", argv
[0]);
251 lzma_stream strm
= LZMA_STREAM_INIT
;
255 // Try to decompress all files.
256 for (int i
= 1; i
< argc
; ++i
) {
257 if (!init_decoder(&strm
)) {
258 // Decoder initialization failed. There's no point
259 // to retry it so we need to exit.
264 FILE *infile
= fopen(argv
[i
], "rb");
266 if (infile
== NULL
) {
267 fprintf(stderr
, "%s: Error opening the "
269 argv
[i
], strerror(errno
));
272 success
&= decompress(&strm
, argv
[i
], infile
, stdout
);
277 // Free the memory allocated for the decoder. This only needs to be
278 // done after the last file.
281 if (fclose(stdout
)) {
282 fprintf(stderr
, "Write error: %s\n", strerror(errno
));
286 return success
? EXIT_SUCCESS
: EXIT_FAILURE
;