root/doc/examples/03_compress_custom.c

DEFINITIONS

1. init_encoder
2. compress
3. main

///////////////////////////////////////////////////////////////////////////////
//
/// \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;
}