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, 35 insertions, 5 deletions

diff --git a/src/liblzma/lzma/lzma_encoder.c b/src/liblzma/lzma/lzma_encoder.c
index e2dbbc03..dc62f44f 100644
--- a/src/liblzma/lzma/lzma_encoder.c
+++ b/src/liblzma/lzma/lzma_encoder.c
@@ -416,7 +416,7 @@ lzma_lzma_encode(lzma_lzma1_encoder *restrict coder, lzma_mf *restrict mf,
 	//
 	// Plain LZMA streams without EOPM aren't supported except when
 	// output size limiting is enabled.
-	if (limit == UINT32_MAX && coder->out_limit == 0)
+	if (coder->use_eopm)
 		encode_eopm(coder, (uint32_t)(coder->uncomp_size));
 
 	// Flush the remaining bytes from the range encoder.
@@ -462,6 +462,7 @@ lzma_lzma_set_out_limit(
 	lzma_lzma1_encoder *coder = coder_ptr;
 	coder->out_limit = out_limit;
 	coder->uncomp_size_ptr = uncomp_size;
+	coder->use_eopm = false;
 	return LZMA_OK;
 }
 
@@ -599,10 +600,13 @@ lzma_lzma_encoder_reset(lzma_lzma1_encoder *coder,
 
 
 extern lzma_ret
-lzma_lzma_encoder_create(void **coder_ptr,
-		const lzma_allocator *allocator,
-		const lzma_options_lzma *options, lzma_lz_options *lz_options)
+lzma_lzma_encoder_create(void **coder_ptr, const lzma_allocator *allocator,
+		lzma_vli id, const lzma_options_lzma *options,
+		lzma_lz_options *lz_options)
 {
+	assert(id == LZMA_FILTER_LZMA1 || id == LZMA_FILTER_LZMA1EXT
+			|| id == LZMA_FILTER_LZMA2);
+
 	// Allocate lzma_lzma1_encoder if it wasn't already allocated.
 	if (*coder_ptr == NULL) {
 		*coder_ptr = lzma_alloc(sizeof(lzma_lzma1_encoder), allocator);
@@ -672,6 +676,32 @@ lzma_lzma_encoder_create(void **coder_ptr,
 	// Output size limitting is disabled by default.
 	coder->out_limit = 0;
 
+	// Determine if end marker is wanted:
+	//   - It is never used with LZMA2.
+	//   - It is always used with LZMA_FILTER_LZMA1 (unless
+	//     lzma_lzma_set_out_limit() is called later).
+	//   - LZMA_FILTER_LZMA1EXT has a flag for it in the options.
+	coder->use_eopm = (id == LZMA_FILTER_LZMA1);
+	if (id == LZMA_FILTER_LZMA1EXT) {
+		// Check if unsupported flags are present.
+		if (options->ext_flags & ~LZMA_LZMA1EXT_ALLOW_EOPM)
+			return LZMA_OPTIONS_ERROR;
+
+		coder->use_eopm = (options->ext_flags
+				& LZMA_LZMA1EXT_ALLOW_EOPM) != 0;
+
+		// TODO? As long as there are no filters that change the size
+		// of the data, it is enough to look at lzma_stream.total_in
+		// after encoding has been finished to know the uncompressed
+		// size of the LZMA1 stream. But in the future there could be
+		// filters that change the size of the data and then total_in
+		// doesn't work as the LZMA1 stream size might be different
+		// due to another filter in the chain. The problem is simple
+		// to solve: Add another flag to ext_flags and then set
+		// coder->uncomp_size_ptr to the address stored in
+		// lzma_options_lzma.reserved_ptr2 (or _ptr1).
+	}
+
 	set_lz_options(lz_options, options);
 
 	return lzma_lzma_encoder_reset(coder, options);
@@ -685,7 +715,7 @@ lzma_encoder_init(lzma_lz_encoder *lz, const lzma_allocator *allocator,
 	lz->code = &lzma_encode;
 	lz->set_out_limit = &lzma_lzma_set_out_limit;
 	return lzma_lzma_encoder_create(
-			&lz->coder, allocator, options, lz_options);
+			&lz->coder, allocator, id, options, lz_options);
 }