01_compress_easy.c File Reference

Compress from stdin to stdout in multi-call mode. More...

#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <lzma.h>

Go to the source code of this file.

Functions
static void	show_usage_and_exit (const char *argv0)
static uint32_t	get_preset (int argc, char **argv)
static bool	init_encoder (lzma_stream *strm, uint32_t preset)
static bool	compress (lzma_stream *strm, FILE *infile, FILE *outfile)
int	main (int argc, char **argv)

Detailed Description

Compress from stdin to stdout in multi-call mode.

Usage: ./01_compress_easy PRESET < INFILE > OUTFILE

Example: ./01_compress_easy 6 < foo > foo.xz

Definition in file 01_compress_easy.c.

Function Documentation

compress()

static bool compress ( lzma_stream *  strm, FILE *  infile, FILE *  outfile  )

static

Definition at line 108 of file 01_compress_easy.c.

{
    // 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;
        }
    }
}

References test-lz4-speed::action, lzma_stream::avail_in, lzma_stream::avail_out, if(), inbuf, LZMA_DATA_ERROR, LZMA_FINISH, LZMA_MEM_ERROR, LZMA_OK, LZMA_RUN, LZMA_STREAM_END, msg, lzma_stream::next_in, lzma_stream::next_out, NULL, outbuf, outfile, and strm.

Referenced by main().

get_preset()

static uint32_t get_preset ( int  argc, char **  argv  )

static

Definition at line 37 of file 01_compress_easy.c.

{
    // 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;
}

References argv, LZMA_PRESET_EXTREME, preset, and show_usage_and_exit().

Referenced by main().

init_encoder()

static bool init_encoder ( lzma_stream *  strm, uint32_t  preset  )

static

Definition at line 60 of file 01_compress_easy.c.

{
    // 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;
}

References LZMA_CHECK_CRC64, LZMA_MEM_ERROR, LZMA_OK, LZMA_OPTIONS_ERROR, LZMA_UNSUPPORTED_CHECK, msg, preset, and strm.

Referenced by main().

main()

int main	(	int	argc,
		char **	argv
	)

Definition at line 263 of file 01_compress_easy.c.

{
    // 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;
}

References argv, compress(), get_preset(), init_encoder(), LZMA_STREAM_INIT, preset, and strm.

show_usage_and_exit()

static void show_usage_and_exit ( const char *  argv0 )

static

Definition at line 26 of file 01_compress_easy.c.

{
    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);
}

References test-lz4-list::exit.

Referenced by get_preset().