Refactor decoder library

- Move common defines to dec/webpi.h
 - Regularize naming and parameters of various "CheckAndSkip" functions.
   Also they return VP8StatusCode for clarity.
 - Move WebP header/chunk parsing functions to webpi.h
 - Fix a bug in static function GetFeatures()

Change-Id: Ibc3da4ba210d860551724dc40741959750d66b89

src/dec/webpi.h

@@ -58,15 +58,74 @@ struct WebPDecParams {
 void WebPResetDecParams(WebPDecParams* const params);
 
 //------------------------------------------------------------------------------
-// Misc utils
+// Header parsing helpers
 
-// Validates the RIFF container (if detected) and skip over it.
-// If a RIFF container is detected, returns 0 for invalid header. Else return 1.
+#define TAG_SIZE 4
+#define CHUNK_HEADER_SIZE 8
+#define RIFF_HEADER_SIZE 12
+#define VP8X_CHUNK_SIZE 12
+#define TILE_CHUNK_SIZE 8
+#define FRAME_CHUNK_SIZE 20
+#define LOOP_CHUNK_SIZE 4
+#define VP8_FRAME_HEADER_SIZE 10  // Size of the frame header within VP8 data.
+
+// Validates the RIFF container (if detected) and skips over it.
+// If a RIFF container is detected,
+// Returns VP8_STATUS_BITSTREAM_ERROR for invalid header, and
+//         VP8_STATUS_OK otherwise.
 // In case there are not enough bytes (partial RIFF container), return 0 for
 // riff_size. Else return the riff_size extracted from the header.
-uint32_t WebPCheckAndSkipRIFFHeader(const uint8_t** data_ptr,
-                                    uint32_t* data_size_ptr,
-                                    uint32_t* riff_size_ptr);
+VP8StatusCode WebPParseRIFF(const uint8_t** data, uint32_t* data_size,
+                            uint32_t* riff_size);
+
+// Validates the VP8X Header and skips over it.
+// Returns VP8_STATUS_BITSTREAM_ERROR for invalid VP8X header,
+//         VP8_STATUS_NOT_ENOUGH_DATA in case of insufficient data, and
+//         VP8_STATUS_OK otherwise.
+// If a VP8 chunk is found, bytes_skipped is set to the total number of bytes
+// that are skipped; also Width, Height & Flags are set to the corresponding
+// fields extracted from the VP8X chunk.
+VP8StatusCode WebPParseVP8X(const uint8_t** data, uint32_t* data_size,
+                            uint32_t* bytes_skipped,
+                            int* width, int* height, uint32_t* flags);
+
+// Skips to the next VP8 chunk header in the data given the size of the RIFF
+// chunk 'riff_size'.
+// Returns VP8_STATUS_BITSTREAM_ERROR if any invalid chunk size is encountered,
+//         VP8_STATUS_NOT_ENOUGH_DATA in case of insufficient data, and
+//         VP8_STATUS_OK otherwise.
+// If a VP8 chunk is found, bytes_skipped is set to the total number of bytes
+// that are skipped.
+VP8StatusCode WebPParseOptionalChunks(const uint8_t** data, uint32_t* data_size,
+                                      uint32_t riff_size,
+                                      uint32_t* bytes_skipped);
+
+// Validates the VP8 Header ("VP8 nnnn") and skips over it.
+// Returns VP8_STATUS_BITSTREAM_ERROR for invalid (vp8_chunk_size greater than
+//         riff_size) VP8 header,
+//         VP8_STATUS_NOT_ENOUGH_DATA in case of insufficient data, and
+//         VP8_STATUS_OK otherwise.
+// If a VP8 chunk is found, bytes_skipped is set to the total number of bytes
+// that are skipped and vp8_chunk_size is set to the corresponding size
+// extracted from the VP8 chunk header.
+// For a partial VP8 chunk, vp8_chunk_size is set to 0.
+VP8StatusCode WebPParseVP8Header(const uint8_t** data, uint32_t* data_size,
+                                 uint32_t riff_size, uint32_t* bytes_skipped,
+                                 uint32_t* vp8_chunk_size);
+
+// Skips over all valid chunks prior to the first VP8 frame header.
+// Returns VP8_STATUS_OK on success,
+//         VP8_STATUS_BITSTREAM_ERROR if an invalid header/chunk is found, and
+//         VP8_STATUS_NOT_ENOUGH_DATA if case of insufficient data.
+// Also, data, data_size, vp8_size & bytes_skipped are updated appropriately
+// on success, where
+// vp8_size is the size of VP8 chunk data (extracted from VP8 chunk header) and
+// bytes_skipped is set to the total number of bytes that are skipped.
+VP8StatusCode WebPParseHeaders(const uint8_t** data, uint32_t* data_size,
+                               uint32_t* vp8_size, uint32_t* bytes_skipped);
+
+//------------------------------------------------------------------------------
+// Misc utils
 
 // Initializes VP8Io with custom setup, io and teardown functions. The default
 // hooks will use the supplied 'params' as io->opaque handle.