Docs: Language fix to 01_compress_easy.c.

[xz/debian.git] / doc / examples / 01_compress_easy.c

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