Improved the Stream Flags handling API.

1 files changed, 80 insertions, 4 deletions

diff --git a/src/liblzma/api/lzma/stream_flags.h b/src/liblzma/api/lzma/stream_flags.h
index 80c5f00f..bb080ac7 100644
--- a/src/liblzma/api/lzma/stream_flags.h
+++ b/src/liblzma/api/lzma/stream_flags.h
@@ -36,8 +36,37 @@
  */
 typedef struct {
 	/**
+	 * \brief       Stream Flags format version
+	 *
+	 * To prevent API and ABI breakages if new features are needed in
+	 * Stream Header or Stream Footer, a version number is used to
+	 * indicate which fields in this structure are in use. For now,
+	 * version must always be zero. With non-zero version, the
+	 * lzma_stream_header_encode() and lzma_stream_footer_encode()
+	 * will return LZMA_HEADER_ERROR.
+	 *
+	 * lzma_stream_header_decode() and lzma_stream_footer_decode()
+	 * will always set this to the lowest value that supports all the
+	 * features indicated by the Stream Flags field. The application
+	 * must check that the version number set by the decoding functions
+	 * is supported by the application. Otherwise it is possible that
+	 * the application will decode the Stream incorrectly.
+	 */
+	uint32_t version;
+
+	/**
 	 * Backward Size must be a multiple of four bytes. In this Stream
 	 * format version Backward Size is the size of the Index field.
+	 *
+	 * Backward Size isn't actually part of the Stream Flags field, but
+	 * it is convenient to include in this structure anyway. Backward
+	 * Size is present only in the Stream Footer. There is no need to
+	 * initialize backward_size when encoding Stream Header.
+	 *
+	 * lzma_stream_header_decode() always sets backward_size to
+	 * LZMA_VLI_VALUE_UNKNOWN so that it is convenient to use
+	 * lzma_stream_flags_compare() when both Stream Header and Stream
+	 * Footer have been decoded.
 	 */
 	lzma_vli backward_size;
 #	define LZMA_BACKWARD_SIZE_MIN 4
@@ -48,6 +77,34 @@ typedef struct {
 	 */
 	lzma_check check;
 
+	/**
+	 * Reserved space to allow possible future extensions without
+	 * breaking the ABI. You should not touch these, because the
+	 * names of these variables may change.
+	 *
+	 * (We will never be able to use all of these since Stream Flags
+	 * is just two bytes plus Backward Size of four bytes. But it's
+	 * nice to have the proper types when they are needed.)
+	 */
+	lzma_reserved_enum reserved_enum1;
+	lzma_reserved_enum reserved_enum2;
+	lzma_reserved_enum reserved_enum3;
+	lzma_reserved_enum reserved_enum4;
+	lzma_reserved_enum reserved_enum5;
+	lzma_reserved_enum reserved_enum6;
+	lzma_bool reserved_bool1;
+	lzma_bool reserved_bool2;
+	lzma_bool reserved_bool3;
+	lzma_bool reserved_bool4;
+	lzma_bool reserved_bool5;
+	lzma_bool reserved_bool6;
+	lzma_bool reserved_bool7;
+	lzma_bool reserved_bool8;
+	uint32_t reserved_int1;
+	uint32_t reserved_int2;
+	uint32_t reserved_int3;
+	uint32_t reserved_int4;
+
 } lzma_stream_flags;
 
 
@@ -61,6 +118,8 @@ typedef struct {
  *                          need to be initialized.
  *
  * \return      - LZMA_OK: Encoding was successful.
+ *              - LZMA_HEADER_ERROR: options->version is not supported by
+ *                this liblzma version.
  *              - LZMA_PROG_ERROR: Invalid options.
  */
 extern lzma_ret lzma_stream_header_encode(
@@ -76,6 +135,8 @@ extern lzma_ret lzma_stream_header_encode(
  * \param       options     Stream Footer options to be encoded.
  *
  * \return      - LZMA_OK: Encoding was successful.
+ *              - LZMA_HEADER_ERROR: options->version is not supported by
+ *                this liblzma version.
  *              - LZMA_PROG_ERROR: Invalid options.
  */
 extern lzma_ret lzma_stream_footer_encode(
@@ -92,7 +153,7 @@ extern lzma_ret lzma_stream_footer_encode(
  *
  * options->index_size is always set to LZMA_VLI_VALUE_UNKNOWN. This is to
  * help comparing Stream Flags from Stream Header and Stream Footer with
- * lzma_stream_flags_equal().
+ * lzma_stream_flags_compare().
  *
  * \return      - LZMA_OK: Decoding was successful.
  *              - LZMA_FORMAT_ERROR: Magic bytes don't match, thus the given
@@ -121,6 +182,13 @@ extern lzma_ret lzma_stream_header_decode(
  *                is corrupt.
  *              - LZMA_HEADER_ERROR: Unsupported options are present
  *                in the footer.
+ *
+ * \note        If Stream Header was already decoded successfully, but
+ *              decoding Stream Footer returns LZMA_FORMAT_ERROR, the
+ *              application should probably report some other error message
+ *              than "unsupported file format", since the file more likely is
+ *              corrupt (possibly truncated). Stream decoder in liblzma uses
+ *              LZMA_DATA_ERROR in this situation.
  */
 extern lzma_ret lzma_stream_footer_decode(
 		lzma_stream_flags *options, const uint8_t *in)
@@ -130,10 +198,18 @@ extern lzma_ret lzma_stream_footer_decode(
 /**
  * \brief       Compare two lzma_stream_flags structures
  *
- * index_size values are compared only if both are not LZMA_VLI_VALUE_UNKNOWN.
+ * backward_size values are compared only if both are not
+ * LZMA_VLI_VALUE_UNKNOWN.
  *
- * \return      true if both structures are considered equal; false otherwise.
+ * \return      - LZMA_OK: Both are equal. If either had backward_size set
+ *                to LZMA_VLI_VALUE_UNKNOWN, backward_size values were not
+ *                compared or validated.
+ *              - LZMA_DATA_ERROR: The structures differ.
+ *              - LZMA_HEADER_ERROR: version in either structure is greater
+ *                than the maximum supported version (currently zero).
+ *              - LZMA_PROG_ERROR: Invalid value, e.g. invalid check or
+ *                backward_size.
  */
-extern lzma_bool lzma_stream_flags_equal(
+extern lzma_ret lzma_stream_flags_compare(
 		const lzma_stream_flags *a, const lzma_stream_flags *b)
 		lzma_attr_pure;