path: root/doc/examples/01_compress_easy.c

// SPDX-License-Identifier: 0BSD

///////////////////////////////////////////////////////////////////////////////
//
/// \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
//
///////////////////////////////////////////////////////////////////////////////

#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 buffer 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;
}