liblzma: Add LZMA_FILTER_LZMA1EXT to support LZMA1 without end marker.

Some file formats need support for LZMA1 streams that don't use
the end of payload marker (EOPM) alias end of stream (EOS) marker.
So far liblzma API has supported decompressing such streams via
lzma_alone_decoder() when .lzma header specifies a known
uncompressed size. Encoding support hasn't been available in the API.

Instead of adding a new LZMA1-only API for this purpose, this commit
adds a new filter ID for use with raw encoder and decoder. The main
benefit of this approach is that then also filter chains are possible,
for example, if someone wants to implement support for .7z files that
use the x86 BCJ filter with LZMA1 (not BCJ2 as that isn't supported
in liblzma).

1 files changed, 25 insertions, 1 deletions

diff --git a/src/liblzma/lzma/lzma_decoder.c b/src/liblzma/lzma/lzma_decoder.c
index 550963d1..26c148a9 100644
--- a/src/liblzma/lzma/lzma_decoder.c
+++ b/src/liblzma/lzma/lzma_decoder.c
@@ -1018,11 +1018,35 @@ lzma_decoder_init(lzma_lz_decoder *lz, const lzma_allocator *allocator,
 	if (!is_lclppb_valid(options))
 		return LZMA_PROG_ERROR;
 
+	lzma_vli uncomp_size = LZMA_VLI_UNKNOWN;
+	bool allow_eopm = true;
+
+	if (id == LZMA_FILTER_LZMA1EXT) {
+		const lzma_options_lzma *opt = options;
+
+		// Only one flag is supported.
+		if (opt->ext_flags & ~LZMA_LZMA1EXT_ALLOW_EOPM)
+			return LZMA_OPTIONS_ERROR;
+
+		// FIXME? Using lzma_vli instead of uint64_t is weird because
+		// this has nothing to do with .xz headers and variable-length
+		// integer encoding. On the other hand, using LZMA_VLI_UNKNOWN
+		// instead of UINT64_MAX is clearer when unknown size is
+		// meant. A problem with using lzma_vli is that now we
+		// allow > LZMA_VLI_MAX which is fine in this file but
+		// it's still confusing. Note that alone_decoder.c also
+		// allows > LZMA_VLI_MAX when setting uncompressed size.
+		uncomp_size = opt->ext_size_low
+				+ ((uint64_t)(opt->ext_size_high) << 32);
+		allow_eopm = (opt->ext_flags & LZMA_LZMA1EXT_ALLOW_EOPM) != 0
+				|| uncomp_size == LZMA_VLI_UNKNOWN;
+	}
+
 	return_if_error(lzma_lzma_decoder_create(
 			lz, allocator, options, lz_options));
 
 	lzma_decoder_reset(lz->coder, options);
-	lzma_decoder_uncompressed(lz->coder, LZMA_VLI_UNKNOWN, true);
+	lzma_decoder_uncompressed(lz->coder, uncomp_size, allow_eopm);
 
 	return LZMA_OK;
 }