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+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file 02_decompress.c
+/// \brief Decompress .xz files to stdout
+///
+/// Usage: ./02_decompress INPUT_FILES... > OUTFILE
+///
+/// Example: ./02_decompress foo.xz bar.xz > foobar
+//
+// Author: Lasse Collin
+//
+// This file has been put into the public domain.
+// You can do whatever you want with this file.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <lzma.h>
+
+
+static bool
+init_decoder(lzma_stream *strm)
+{
+ // Initialize a .xz decoder. The decoder supports a memory usage limit
+ // and a set of flags.
+ //
+ // The memory usage of the decompressor depends on the settings used
+ // to compress a .xz file. It can vary from less than a megabyte to
+ // a few gigabytes, but in practice (at least for now) it rarely
+ // exceeds 65 MiB because that's how much memory is required to
+ // decompress files created with "xz -9". Settings requiring more
+ // memory take extra effort to use and don't (at least for now)
+ // provide significantly better compression in most cases.
+ //
+ // Memory usage limit is useful if it is important that the
+ // decompressor won't consume gigabytes of memory. The need
+ // for limiting depends on the application. In this example,
+ // no memory usage limiting is used. This is done by setting
+ // the limit to UINT64_MAX.
+ //
+ // The .xz format allows concatenating compressed files as is:
+ //
+ // echo foo | xz > foobar.xz
+ // echo bar | xz >> foobar.xz
+ //
+ // When decompressing normal standalone .xz files, LZMA_CONCATENATED
+ // should always be used to support decompression of concatenated
+ // .xz files. If LZMA_CONCATENATED isn't used, the decoder will stop
+ // after the first .xz stream. This can be useful when .xz data has
+ // been embedded inside another file format.
+ //
+ // Flags other than LZMA_CONCATENATED are supported too, and can
+ // be combined with bitwise-or. See lzma/container.h
+ // (src/liblzma/api/lzma/container.h in the source package or e.g.
+ // /usr/include/lzma/container.h depending on the install prefix)
+ // for details.
+ lzma_ret ret = lzma_stream_decoder(
+ strm, UINT64_MAX, LZMA_CONCATENATED);
+
+ // Return successfully if the initialization went fine.
+ if (ret == LZMA_OK)
+ return true;
+
+ // Something went wrong. The possible errors are documented in
+ // lzma/container.h (src/liblzma/api/lzma/container.h in the source
+ // package or e.g. /usr/include/lzma/container.h depending on the
+ // install prefix).
+ //
+ // Note that LZMA_MEMLIMIT_ERROR is never possible here. If you
+ // specify a very tiny limit, the error will be delayed until
+ // the first headers have been parsed by a call to lzma_code().
+ const char *msg;
+ switch (ret) {
+ case LZMA_MEM_ERROR:
+ msg = "Memory allocation failed";
+ break;
+
+ case LZMA_OPTIONS_ERROR:
+ msg = "Unsupported decompressor flags";
+ break;
+
+ default:
+ // This is most likely LZMA_PROG_ERROR indicating a bug in
+ // this program or in liblzma. It is inconvenient to have a
+ // separate error message for errors that should be impossible
+ // to occur, but knowing the error code is important for
+ // debugging. That's why it is good to print the error code
+ // at least when there is no good error message to show.
+ msg = "Unknown error, possibly a bug";
+ break;
+ }
+
+ fprintf(stderr, "Error initializing the decoder: %s (error code %u)\n",
+ msg, ret);
+ return false;
+}
+
+
+static bool
+decompress(lzma_stream *strm, const char *inname, FILE *infile, FILE *outfile)
+{
+ // When LZMA_CONCATENATED flag was used when initializing the decoder,
+ // we need to tell lzma_code() when there will be no more input.
+ // This is done by setting action to LZMA_FINISH instead of LZMA_RUN
+ // in the same way as it is done when encoding.
+ //
+ // When LZMA_CONCATENATED isn't used, there is no need to use
+ // LZMA_FINISH to tell when all the input has been read, but it
+ // is still OK to use it if you want. When LZMA_CONCATENATED isn't
+ // used, the decoder will stop after the first .xz stream. In that
+ // case some unused data may be left in strm->next_in.
+ lzma_action action = LZMA_RUN;
+
+ uint8_t inbuf[BUFSIZ];
+ uint8_t outbuf[BUFSIZ];
+
+ strm->next_in = NULL;
+ strm->avail_in = 0;
+ strm->next_out = outbuf;
+ strm->avail_out = sizeof(outbuf);
+
+ while (true) {
+ if (strm->avail_in == 0 && !feof(infile)) {
+ strm->next_in = inbuf;
+ strm->avail_in = fread(inbuf, 1, sizeof(inbuf),
+ infile);
+
+ if (ferror(infile)) {
+ fprintf(stderr, "%s: Read error: %s\n",
+ inname, strerror(errno));
+ return false;
+ }
+
+ // Once the end of the input file has been reached,
+ // we need to tell lzma_code() that no more input
+ // will be coming. As said before, this isn't required
+ // if the LZMA_CONCATENATED flag isn't used when
+ // initializing the decoder.
+ if (feof(infile))
+ action = LZMA_FINISH;
+ }
+
+ lzma_ret ret = lzma_code(strm, action);
+
+ if (strm->avail_out == 0 || ret == LZMA_STREAM_END) {
+ size_t write_size = sizeof(outbuf) - strm->avail_out;
+
+ if (fwrite(outbuf, 1, write_size, outfile)
+ != write_size) {
+ fprintf(stderr, "Write error: %s\n",
+ strerror(errno));
+ return false;
+ }
+
+ strm->next_out = outbuf;
+ strm->avail_out = sizeof(outbuf);
+ }
+
+ if (ret != LZMA_OK) {
+ // Once everything has been decoded successfully, the
+ // return value of lzma_code() will be LZMA_STREAM_END.
+ //
+ // It is important to check for LZMA_STREAM_END. Do not
+ // assume that getting ret != LZMA_OK would mean that
+ // everything has gone well or that when you aren't
+ // getting more output it must have successfully
+ // decoded everything.
+ if (ret == LZMA_STREAM_END)
+ return true;
+
+ // It's not LZMA_OK nor LZMA_STREAM_END,
+ // so it must be an error code. See lzma/base.h
+ // (src/liblzma/api/lzma/base.h in the source package
+ // or e.g. /usr/include/lzma/base.h depending on the
+ // install prefix) for the list and documentation of
+ // possible values. Many values listen in lzma_ret
+ // enumeration aren't possible in this example, but
+ // can be made possible by enabling memory usage limit
+ // or adding flags to the decoder initialization.
+ const char *msg;
+ switch (ret) {
+ case LZMA_MEM_ERROR:
+ msg = "Memory allocation failed";
+ break;
+
+ case LZMA_FORMAT_ERROR:
+ // .xz magic bytes weren't found.
+ msg = "The input is not in the .xz format";
+ break;
+
+ case LZMA_OPTIONS_ERROR:
+ // For example, the headers specify a filter
+ // that isn't supported by this liblzma
+ // version (or it hasn't been enabled when
+ // building liblzma, but no-one sane does
+ // that unless building liblzma for an
+ // embedded system). Upgrading to a newer
+ // liblzma might help.
+ //
+ // Note that it is unlikely that the file has
+ // accidentally became corrupt if you get this
+ // error. The integrity of the .xz headers is
+ // always verified with a CRC32, so
+ // unintentionally corrupt files can be
+ // distinguished from unsupported files.
+ msg = "Unsupported compression options";
+ break;
+
+ case LZMA_DATA_ERROR:
+ msg = "Compressed file is corrupt";
+ break;
+
+ case LZMA_BUF_ERROR:
+ // Typically this error means that a valid
+ // file has got truncated, but it might also
+ // be a damaged part in the file that makes
+ // the decoder think the file is truncated.
+ // If you prefer, you can use the same error
+ // message for this as for LZMA_DATA_ERROR.
+ msg = "Compressed file is truncated or "
+ "otherwise corrupt";
+ break;
+
+ default:
+ // This is most likely LZMA_PROG_ERROR.
+ msg = "Unknown error, possibly a bug";
+ break;
+ }
+
+ fprintf(stderr, "%s: Decoder error: "
+ "%s (error code %u)\n",
+ inname, msg, ret);
+ return false;
+ }
+ }
+}
+
+
+extern int
+main(int argc, char **argv)
+{
+ if (argc <= 1) {
+ fprintf(stderr, "Usage: %s FILES...\n", argv[0]);
+ return EXIT_FAILURE;
+ }
+
+ lzma_stream strm = LZMA_STREAM_INIT;
+
+ bool success = true;
+
+ // Try to decompress all files.
+ for (int i = 1; i < argc; ++i) {
+ if (!init_decoder(&strm)) {
+ // Decoder initialization failed. There's no point
+ // to retry it so we need to exit.
+ success = false;
+ break;
+ }
+
+ FILE *infile = fopen(argv[i], "rb");
+
+ if (infile == NULL) {
+ fprintf(stderr, "%s: Error opening the "
+ "input file: %s\n",
+ argv[i], strerror(errno));
+ success = false;
+ } else {
+ success &= decompress(&strm, argv[i], infile, stdout);
+ fclose(infile);
+ }
+ }
+
+ // Free the memory allocated for the decoder. This only needs to be
+ // done after the last file.
+ lzma_end(&strm);
+
+ if (fclose(stdout)) {
+ fprintf(stderr, "Write error: %s\n", strerror(errno));
+ success = false;
+ }
+
+ return success ? EXIT_SUCCESS : EXIT_FAILURE;
+}
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