liblzma: Add rough support for output-size-limited encoding in LZMA1.

With this it is possible to encode LZMA1 data without EOPM so that
the encoder will encode as much input as it can without exceeding
the specified output size limit. The resulting LZMA1 stream will
be a normal LZMA1 stream without EOPM. The actual uncompressed size
will be available to the caller via the uncomp_size pointer.

One missing thing is that the LZMA layer doesn't inform the LZ layer
when the encoding is finished and thus the LZ may read more input
when it won't be used. However, this doesn't matter if encoding is
done with a single call (which is the planned use case for now).
For proper multi-call encoding this should be improved.

This commit only adds the functionality for internal use.
Nothing uses it yet.

2 files changed, 20 insertions, 0 deletions

diff --git a/src/liblzma/lz/lz_encoder.c b/src/liblzma/lz/lz_encoder.c
index 9a74b7c4..08a8afe3 100644
--- a/src/liblzma/lz/lz_encoder.c
+++ b/src/liblzma/lz/lz_encoder.c
@@ -521,6 +521,21 @@ lz_encoder_update(void *coder_ptr, const lzma_allocator *allocator,
 }
 
 
+static lzma_ret
+lz_encoder_set_out_limit(void *coder_ptr, uint64_t *uncomp_size,
+		uint64_t out_limit)
+{
+	lzma_coder *coder = coder_ptr;
+
+	// This is supported only if there are no other filters chained.
+	if (coder->next.code == NULL && coder->lz.set_out_limit != NULL)
+		return coder->lz.set_out_limit(
+				coder->lz.coder, uncomp_size, out_limit);
+
+	return LZMA_OPTIONS_ERROR;
+}
+
+
 extern lzma_ret
 lzma_lz_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 		const lzma_filter_info *filters,
@@ -544,6 +559,7 @@ lzma_lz_encoder_init(lzma_next_coder *next, const lzma_allocator *allocator,
 		next->code = &lz_encode;
 		next->end = &lz_encoder_end;
 		next->update = &lz_encoder_update;
+		next->set_out_limit = &lz_encoder_set_out_limit;
 
 		coder->lz.coder = NULL;
 		coder->lz.code = NULL;
diff --git a/src/liblzma/lz/lz_encoder.h b/src/liblzma/lz/lz_encoder.h
index 426dcd8a..e249beba 100644
--- a/src/liblzma/lz/lz_encoder.h
+++ b/src/liblzma/lz/lz_encoder.h
@@ -204,6 +204,10 @@ typedef struct {
 	/// Update the options in the middle of the encoding.
 	lzma_ret (*options_update)(void *coder, const lzma_filter *filter);
 
+	/// Set maximum allowed output size
+	lzma_ret (*set_out_limit)(void *coder, uint64_t *uncomp_size,
+			uint64_t out_limit);
+
 } lzma_lz_encoder;