03_compress_custom.c

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//
//
//  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/lzma12.h (src/liblzma/api/lzma/lzma12.h in the
    // source package or e.g. /usr/include/lzma/lzma12.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/lzma12.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;
}