liblzma: Add support for LZMA_IGNORE_CHECK.

src/liblzma/api/lzma/container.h

@@ -473,6 +473,30 @@ extern LZMA_API(lzma_ret) lzma_stream_buffer_encode(
 #define LZMA_TELL_ANY_CHECK             UINT32_C(0x04)
 
 
+/**
+ * This flag makes lzma_code() not calculate and verify the integrity check
+ * of the compressed data in .xz files. This means that invalid integrity
+ * check values won't be detected and LZMA_DATA_ERROR won't be returned in
+ * such cases.
+ *
+ * This flag only affects the checks of the compressed data itself; the CRC32
+ * values in the .xz headers will still be verified normally.
+ *
+ * Don't use this flag unless you know what you are doing. Possible reasons
+ * to use this flag:
+ *
+ *   - Trying to recover data from a corrupt .xz file.
+ *
+ *   - Speeding up decompression, which matters mostly with SHA-256
+ *     or with files that have compressed extremely well. It's recommended
+ *     to not use this flag for this purpose unless the file integrity is
+ *     verified externally in some other way.
+ *
+ * Support for this flag was added in liblzma 5.1.4beta.
+ */
+#define LZMA_IGNORE_CHECK               UINT32_C(0x10)
+
+
 /**
  * This flag enables decoding of concatenated files with file formats that
  * allow concatenating compressed files as is. From the formats currently

src/liblzma/common/common.h

@@ -75,6 +75,7 @@
 	( LZMA_TELL_NO_CHECK \
 	| LZMA_TELL_UNSUPPORTED_CHECK \
 	| LZMA_TELL_ANY_CHECK \
+	| LZMA_IGNORE_CHECK \
 	| LZMA_CONCATENATED )
 
 

src/liblzma/common/stream_decoder.c

@@ -57,6 +57,10 @@ struct lzma_coder_s {
 	/// If true, LZMA_GET_CHECK is returned after decoding Stream Header.
 	bool tell_any_check;
 
+	/// If true, we will tell the Block decoder to skip calculating
+	/// and verifying the integrity check.
+	bool ignore_check;
+
 	/// If true, we will decode concatenated Streams that possibly have
 	/// Stream Padding between or after them. LZMA_STREAM_END is returned
 	/// once the application isn't giving us any new input, and we aren't
@@ -182,8 +186,8 @@ stream_decode(lzma_coder *coder, const lzma_allocator *allocator,
 
 		coder->pos = 0;
 
-		// Version 0 is currently the only possible version.
+		// Version 1 is needed to support the .ignore_check option.
-		coder->block_options.version = 0;
+		coder->block_options.version = 1;
 
 		// Set up a buffer to hold the filter chain. Block Header
 		// decoder will initialize all members of this array so
@@ -195,6 +199,11 @@ stream_decode(lzma_coder *coder, const lzma_allocator *allocator,
 		return_if_error(lzma_block_header_decode(&coder->block_options,
 				allocator, coder->buffer));
 
+		// If LZMA_IGNORE_CHECK was used, this flag needs to be set.
+		// It has to be set after lzma_block_header_decode() because
+		// it always resets this to false.
+		coder->block_options.ignore_check = coder->ignore_check;
+
 		// Check the memory usage limit.
 		const uint64_t memusage = lzma_raw_decoder_memusage(filters);
 		lzma_ret ret;
@@ -433,6 +442,7 @@ lzma_stream_decoder_init(
 	next->coder->tell_unsupported_check
 			= (flags & LZMA_TELL_UNSUPPORTED_CHECK) != 0;
 	next->coder->tell_any_check = (flags & LZMA_TELL_ANY_CHECK) != 0;
+	next->coder->ignore_check = (flags & LZMA_IGNORE_CHECK) != 0;
 	next->coder->concatenated = (flags & LZMA_CONCATENATED) != 0;
 	next->coder->first_stream = true;