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Diffstat (limited to 'doc/examples/01_compress_easy.c')
| -rw-r--r-- | doc/examples/01_compress_easy.c | 297 |
1 files changed, 297 insertions, 0 deletions
diff --git a/doc/examples/01_compress_easy.c b/doc/examples/01_compress_easy.c new file mode 100644 index 00000000..f79cade1 --- /dev/null +++ b/doc/examples/01_compress_easy.c @@ -0,0 +1,297 @@ +/////////////////////////////////////////////////////////////////////////////// +// +/// \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 " + "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; +} |