Docs: Add new example programs.

These have more comments than the old examples and
human-readable error messages. More tutorial-like examples
are needed but these are a start.

1 files changed, 193 insertions, 0 deletions

diff --git a/doc/examples/03_compress_custom.c b/doc/examples/03_compress_custom.c
new file mode 100644
index 00000000..51abbb17
--- /dev/null
+++ b/doc/examples/03_compress_custom.c
@@ -0,0 +1,193 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+/// \file       03_compress_custom.c
+/// \brief      Compress in multi-call mode using x86 BCJ and LZMA2
+///
+/// Usage:      ./03_compress_custom < INFILE > OUTFILE
+///
+/// Example:    ./03_compress_custom < 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 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/lzma.h (src/liblzma/api/lzma/lzma.h in the
+	// source package or e.g. /usr/include/lzma/lzma.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/lzma.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;
+}