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DEFINITIONS
This source file includes following definitions.
- show_usage_and_exit
- get_preset
- init_encoder
- compress
- main
///////////////////////////////////////////////////////////////////////////////
//
/// \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 "
"followed 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;
}