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Docs: Add new example programs.

Browse source 
These have more comments than the old examples and
human-readable error messages. More tutorial-like examples
are needed but these are a start.
This commit is contained in:
Lasse Collin 2012-06-14 10:52:33 +03:00
parent 1bd2c2c553
commit 3a0c5378ab
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liblzma example programs
========================
Introduction
The examples are written so that the same comments aren't
repeated (much) in later files.
On POSIX systems, the examples should build by just typing "make".
The examples that use stdin or stdout don't set stdin and stdout
to binary mode. On systems where it matters (e.g. Windows) it is
possible that the examples won't work without modification.
List of examples
01_compress_easy.c Multi-call compression using
a compression preset
02_decompress.c Multi-call decompression
03_compress_custom.c Like 01_compress_easy.c but using
a custom filter chain
(x86 BCJ + LZMA2)

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///////////////////////////////////////////////////////////////////////////////
//
/// \file 01_compress_easy.c
/// \brief Compress from stdin to stdout in multi-call mode
///
/// Usage: ./01_compress_easy PRESET < INFILE > OUTFILE
///
/// Example: ./01_compress_easy 6 < foo > foo.xz
//
// 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 void
show_usage_and_exit(const char *argv0)
{
fprintf(stderr, "Usage: %s PRESET < INFILE > OUTFILE\n"
"PRESET is a number 0-9 and can optionally be "
"by `e' to indicate extreme preset\n",
argv0);
exit(EXIT_FAILURE);
}
static uint32_t
get_preset(int argc, char **argv)
{
// One argument whose first char must be 0-9.
if (argc != 2 || argv[1][0] < '0' || argv[1][0] > '9')
show_usage_and_exit(argv[0]);
// Calculate the preste level 0-9.
uint32_t preset = argv[1][0] - '0';
// If there is a second char, it must be 'e'. It will set
// the LZMA_PRESET_EXTREME flag.
if (argv[1][1] != '\0') {
if (argv[1][1] != 'e' || argv[1][2] != '\0')
show_usage_and_exit(argv[0]);
preset |= LZMA_PRESET_EXTREME;
}
return preset;
}
static bool
init_encoder(lzma_stream *strm, uint32_t preset)
{
// Initialize the encoder using a preset. Set the integrity to check
// to CRC64, which is the default in the xz command line tool. If
// the .xz file needs to be decompressed with XZ Embedded, use
// LZMA_CHECK_CRC32 instead.
lzma_ret ret = lzma_easy_encoder(strm, preset, LZMA_CHECK_CRC64);
// 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).
const char *msg;
switch (ret) {
case LZMA_MEM_ERROR:
msg = "Memory allocation failed";
break;
case LZMA_OPTIONS_ERROR:
msg = "Specified preset is not supported";
break;
case LZMA_UNSUPPORTED_CHECK:
msg = "Specified integrity check is not supported";
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 encoder: %s (error code %u)\n",
msg, ret);
return false;
}
static bool
compress(lzma_stream *strm, FILE *infile, FILE *outfile)
{
// This will be LZMA_RUN until the end of the input file is reached.
// This tells lzma_code() when there will be no more input.
lzma_action action = LZMA_RUN;
// Buffers to temporarily hold uncompressed input
// and compressed output.
uint8_t inbuf[BUFSIZ];
uint8_t outbuf[BUFSIZ];
// Initialize the input and output pointers. Initializing next_in
// and avail_in isn't really necessary when we are going to encode
// just one file since LZMA_STREAM_INIT takes care of initializing
// those already. But it doesn't hurt much and it will be needed
// if encoding more than one file like we will in 02_decompress.c.
//
// While we don't care about strm->total_in or strm->total_out in this
// example, it is worth noting that initializing the encoder will
// always reset total_in and total_out to zero. But the encoder
// initialization doesn't touch next_in, avail_in, next_out, or
// avail_out.
strm->next_in = NULL;
strm->avail_in = 0;
strm->next_out = outbuf;
strm->avail_out = sizeof(outbuf);
// Loop until the file has been successfully compressed or until
// an error occurs.
while (true) {
// Fill the input buffer if it is empty.
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, "Read error: %s\n",
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 and that it should finish the
// encoding.
if (feof(infile))
action = LZMA_FINISH;
}
// Tell liblzma do the actual encoding.
//
// This reads up to strm->avail_in bytes of input starting
// from strm->next_in. avail_in will be decremented and
// next_in incremented by an equal amount to match the
// number of input bytes consumed.
//
// Up to strm->avail_out bytes of compressed output will be
// written starting from strm->next_out. avail_out and next_out
// will be incremented by an equal amount to match the number
// of output bytes written.
//
// The encoder has to do internal buffering, which means that
// it may take quite a bit of input before the same data is
// available in compressed form in the output buffer.
lzma_ret ret = lzma_code(strm, action);
// If the output buffer is full or if the compression finished
// successfully, write the data from the output bufffer to
// the output file.
if (strm->avail_out == 0 || ret == LZMA_STREAM_END) {
// When lzma_code() has returned LZMA_STREAM_END,
// the output buffer is likely to be only partially
// full. Calculate how much new data there is to
// be written to the output file.
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;
}
// Reset next_out and avail_out.
strm->next_out = outbuf;
strm->avail_out = sizeof(outbuf);
}
// Normally the return value of lzma_code() will be LZMA_OK
// until everything has been encoded.
if (ret != LZMA_OK) {
// Once everything has been encoded 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.
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. Most values listen in lzma_ret
// enumeration aren't possible in this example.
const char *msg;
switch (ret) {
case LZMA_MEM_ERROR:
msg = "Memory allocation failed";
break;
case LZMA_DATA_ERROR:
// This error is returned if the compressed
// or uncompressed size get near 8 EiB
// (2^63 bytes) because that's where the .xz
// file format size limits currently are.
// That is, the possibility of this error
// is mostly theoretical unless you are doing
// something very unusual.
//
// Note that strm->total_in and strm->total_out
// have nothing to do with this error. Changing
// those variables won't increase or decrease
// the chance of getting this error.
msg = "File size limits exceeded";
break;
default:
// This is most likely LZMA_PROG_ERROR, but
// if this program is buggy (or liblzma has
// a bug), it may be e.g. LZMA_BUF_ERROR or
// LZMA_OPTIONS_ERROR too.
//
// 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, "Encoder error: %s (error code %u)\n",
msg, ret);
return false;
}
}
}
extern int
main(int argc, char **argv)
{
// Get the preset number from the command line.
uint32_t preset = get_preset(argc, argv);
// Initialize a lzma_stream structure. When it is allocated on stack,
// it is simplest to use LZMA_STREAM_INIT macro like below. When it
// is allocated on heap, using memset(strmptr, 0, sizeof(*strmptr))
// works (as long as NULL pointers are represented with zero bits
// as they are on practically all computers today).
lzma_stream strm = LZMA_STREAM_INIT;
// Initialize the encoder. If it succeeds, compress from
// stdin to stdout.
bool success = init_encoder(&strm, preset);
if (success)
success = compress(&strm, stdin, stdout);
// Free the memory allocated for the encoder. If we were encoding
// multiple files, this would only need to be done after the last
// file. See 02_decompress.c for handling of multiple files.
//
// It is OK to call lzma_end() multiple times or when it hasn't been
// actually used except initialized with LZMA_STREAM_INIT.
lzma_end(&strm);
// Close stdout to catch possible write errors that can occur
// when pending data is flushed from the stdio buffers.
if (fclose(stdout)) {
fprintf(stderr, "Write error: %s\n", strerror(errno));
success = false;
}
return success ? EXIT_SUCCESS : EXIT_FAILURE;
}

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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_CONATENATED 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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///////////////////////////////////////////////////////////////////////////////
//
/// \file 03_compress_custom.c
/// \brief Compress in multi-call mode using x86 BCJ and LZMA2
///
/// Usage: ./03_compress_custom < INFILE > OUTFILE
///
/// Example: ./03_compress_custom < foo > foo.xz
//
// 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_encoder(lzma_stream *strm)
{
// Use the default preset (6) for LZMA2.
//
// The lzma_options_lzma structure and the lzma_lzma_preset() function
// are declared in lzma/lzma.h (src/liblzma/api/lzma/lzma.h in the
// source package or e.g. /usr/include/lzma/lzma.h depending on
// the install prefix).
lzma_options_lzma opt_lzma2;
if (lzma_lzma_preset(&opt_lzma2, LZMA_PRESET_DEFAULT)) {
// It should never fail because the default preset
// (and presets 0-9 optionally with LZMA_PRESET_EXTREME)
// are supported by all stable liblzma versions.
//
// (The encoder initialization later in this function may
// still fail due to unsupported preset *if* the features
// required by the preset have been disabled at build time,
// but no-one does such things except on embedded systems.)
fprintf(stderr, "Unsupported preset, possibly a bug\n");
return false;
}
// Now we could customize the LZMA2 options if we wanted. For example,
// we could set the the dictionary size (opt_lzma2.dict_size) to
// something else than the default (8 MiB) of the default preset.
// See lzma/lzma.h for details of all LZMA2 options.
//
// The x86 BCJ filter will try to modify the x86 instruction stream so
// that LZMA2 can compress it better. The x86 BCJ filter doesn't need
// any options so it will be set to NULL below.
//
// Construct the filter chain. The uncompressed data goes first to
// the first filter in the array, in this case the x86 BCJ filter.
// The array is always terminated by setting .id = LZMA_VLI_UNKNOWN.
//
// See lzma/filter.h for more information about the lzma_filter
// structure.
lzma_filter filters[] = {
{ .id = LZMA_FILTER_X86, .options = NULL },
{ .id = LZMA_FILTER_LZMA2, .options = &opt_lzma2 },
{ .id = LZMA_VLI_UNKNOWN, .options = NULL },
};
// Initialize the encoder using the custom filter chain.
lzma_ret ret = lzma_stream_encoder(strm, filters, LZMA_CHECK_CRC64);
if (ret == LZMA_OK)
return true;
const char *msg;
switch (ret) {
case LZMA_MEM_ERROR:
msg = "Memory allocation failed";
break;
case LZMA_OPTIONS_ERROR:
// We are no longer using a plain preset so this error
// message has been edited accordingly compared to
// 01_compress_easy.c.
msg = "Specified filter chain is not supported";
break;
case LZMA_UNSUPPORTED_CHECK:
msg = "Specified integrity check is not supported";
break;
default:
msg = "Unknown error, possibly a bug";
break;
}
fprintf(stderr, "Error initializing the encoder: %s (error code %u)\n",
msg, ret);
return false;
}
// This function is identical to the one in 01_compress_easy.c.
static bool
compress(lzma_stream *strm, FILE *infile, FILE *outfile)
{
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, "Read error: %s\n",
strerror(errno));
return false;
}
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) {
if (ret == LZMA_STREAM_END)
return true;
const char *msg;
switch (ret) {
case LZMA_MEM_ERROR:
msg = "Memory allocation failed";
break;
case LZMA_DATA_ERROR:
msg = "File size limits exceeded";
break;
default:
msg = "Unknown error, possibly a bug";
break;
}
fprintf(stderr, "Encoder error: %s (error code %u)\n",
msg, ret);
return false;
}
}
}
extern int
main(void)
{
lzma_stream strm = LZMA_STREAM_INIT;
bool success = init_encoder(&strm);
if (success)
success = compress(&strm, stdin, stdout);
lzma_end(&strm);
if (fclose(stdout)) {
fprintf(stderr, "Write error: %s\n", strerror(errno));
success = false;
}
return success ? EXIT_SUCCESS : EXIT_FAILURE;
}

23
doc/examples/Makefile Normal file
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@ -0,0 +1,23 @@
#
# Author: Lasse Collin
#
# This file has been put into the public domain.
# You can do whatever you want with this file.
#
CC = c99
CFLAGS = -g
LDFLAGS = -llzma
PROGS = \
01_compress_easy \
02_decompress \
03_compress_custom
all: $(PROGS)
.c:
$(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
clean:
-rm -f $(PROGS)