xz: Add --ignore-check.

src/xz/args.c

@@ -22,6 +22,7 @@ bool opt_stdout = false;
 bool opt_force = false;
 bool opt_keep_original = false;
 bool opt_robot = false;
+bool opt_ignore_check = false;
 
 // We don't modify or free() this, but we need to assign it in some
 // non-const pointers.
@@ -141,6 +142,7 @@ parse_real(args_info *args, int argc, char **argv)
 		OPT_INFO_MEMORY,
 		OPT_ROBOT,
 		OPT_FLUSH_TIMEOUT,
+		OPT_IGNORE_CHECK,
 	};
 
 	static const char short_opts[]
@@ -169,6 +171,7 @@ parse_real(args_info *args, int argc, char **argv)
 		// Basic compression settings
 		{ "format",       required_argument, NULL,  'F' },
 		{ "check",        required_argument, NULL,  'C' },
+		{ "ignore-check", no_argument,       NULL,  OPT_IGNORE_CHECK },
 		{ "block-size",   required_argument, NULL,  OPT_BLOCK_SIZE },
 		{ "block-list",  required_argument, NULL,  OPT_BLOCK_LIST },
 		{ "memlimit-compress",   required_argument, NULL, OPT_MEM_COMPRESS },
@@ -438,6 +441,10 @@ parse_real(args_info *args, int argc, char **argv)
 			break;
 		}
 
+		case OPT_IGNORE_CHECK:
+			opt_ignore_check = true;
+			break;
+
 		case OPT_BLOCK_SIZE:
 			opt_block_size = str_to_uint64("block-size", optarg,
 					0, LZMA_VLI_MAX);

src/xz/args.h

@@ -36,6 +36,7 @@ extern bool opt_force;
 extern bool opt_keep_original;
 // extern bool opt_recursive;
 extern bool opt_robot;
+extern bool opt_ignore_check;
 
 extern const char stdin_filename[];
 

src/xz/coder.c

@@ -450,7 +450,15 @@ coder_init(file_pair *pair)
 			break;
 		}
 	} else {
-		uint32_t flags = LZMA_TELL_UNSUPPORTED_CHECK;
+		uint32_t flags = 0;
+
+		// It seems silly to warn about unsupported check if the
+		// check won't be verified anyway due to --ignore-check.
+		if (opt_ignore_check)
+			flags |= LZMA_IGNORE_CHECK;
+		else
+			flags |= LZMA_TELL_UNSUPPORTED_CHECK;
+
 		if (!opt_single_stream)
 			flags |= LZMA_CONCATENATED;
 

src/xz/message.c

@@ -1122,6 +1122,8 @@ message_help(bool long_help)
 "                      `auto' (default), `xz', `lzma', and `raw'\n"
 "  -C, --check=CHECK   integrity check type: `none' (use with caution),\n"
 "                      `crc32', `crc64' (default), or `sha256'"));
+		puts(_(
+"      --ignore-check  don't verify the integrity check when decompressing"));
 	}
 
 	puts(_(

src/xz/xz.1

@@ -609,6 +609,25 @@ Integrity of the
 headers is always verified with CRC32.
 It is not possible to change or disable it.
 .TP
+.B \-\-ignore\-check
+Don't verify the integrity check of the compressed data when decompressing.
+The CRC32 values in the
+.B .xz
+headers will still be verified normally.
+.IP ""
+.B "Do not use this option unless you know what you are doing."
+Possible reasons to use this option:
+.RS
+.IP \(bu 3
+Trying to recover data from a corrupt .xz file.
+.IP \(bu 3
+Speeding up decompression.
+This matters mostly with SHA-256 or
+with files that have compressed extremely well.
+It's recommended to not use this option for this purpose
+unless the file integrity is verified externally in some other way.
+.RE
+.TP
 .BR \-0 " ... " \-9
 Select a compression preset level.
 The default is