Made lzma_extra pointers const in lzma_options_stream.

src/liblzma/api/lzma/stream.h

@@ -111,7 +111,7 @@ typedef struct {
 	/**
 	 * \brief       Extra information in the Header Metadata Block
 	 */
-	lzma_extra *header;
+	const lzma_extra *header;
 
 	/**
 	 * \brief       Extra information in the Footer Metadata Block
@@ -119,7 +119,7 @@ typedef struct {
 	 * It is enough to set this pointer any time before calling
 	 * lzma_code() with LZMA_FINISH as the second argument.
 	 */
-	lzma_extra *footer;
+	const lzma_extra *footer;
 
 } lzma_options_stream;
 

src/liblzma/common/stream_encoder_multi.c

@@ -220,7 +220,11 @@ stream_encode(lzma_coder *coder, lzma_allocator *allocator,
 			.uncompressed_size = coder->stream_options
 					->uncompressed_size,
 			.index = NULL,
-			.extra = coder->stream_options->header,
+			// Metadata encoder doesn't modify this, but since
+			// the lzma_extra structure is used also when decoding
+			// Metadata, the pointer is not const, and we need
+			// to cast the constness away in the encoder.
+			.extra = (lzma_extra *)(coder->stream_options->header),
 		};
 
 		return_if_error(metadata_encoder_init(coder, allocator,
@@ -238,7 +242,7 @@ stream_encode(lzma_coder *coder, lzma_allocator *allocator,
 			.total_size = LZMA_VLI_VALUE_UNKNOWN,
 			.uncompressed_size = LZMA_VLI_VALUE_UNKNOWN,
 			.index = lzma_info_index_get(coder->info, false),
-			.extra = coder->stream_options->footer,
+			.extra = (lzma_extra *)(coder->stream_options->footer),
 		};
 
 		return_if_error(metadata_encoder_init(coder, allocator,