reorganize chunk-parsing code

make room for future VP8X extensions

Change-Id: Ic78217c26f142403b733740b17980aa81602f83d

src/dec/vp8i.h

@@ -286,6 +286,20 @@ struct VP8Decoder {
 // in vp8.c
 int VP8SetError(VP8Decoder* const dec,
                 VP8StatusCode error, const char * const msg);
+
+// Validates the VP8 Header and skip over it.
+// Returns 0 for invalid (chunk_size greater than riff_size) VP8 header.
+// Else return 1.
+// is_vp8_chunk is set to:
+//   0, in case data bytes don't correspond to VP8 chunk.
+//   1, in case data bytes correspond to VP8 chunk.
+//   -1, in case not enough bytes (partial VP8 chunk) are passed.
+// chunk_size is set to the chunk size extracted from the VP8 chunk header. For
+// partial VP8 chunk, chunk_size is set to 0.
+int VP8CheckAndSkipHeader(const uint8_t** data_ptr, uint32_t* data_size_ptr,
+                          int* is_vp8_chunk, uint32_t* chunk_size,
+                          uint32_t riff_size);
+
 // Validates the VP8 data-header and retrieve basic header information viz width
 // and height. Returns 0 in case of formatting error. *width/*height/*has_alpha
 // can be passed NULL.
@@ -294,6 +308,17 @@ int VP8GetInfo(const uint8_t* data,
                uint32_t chunk_size,   // total data size expect in the chunk
                int *width, int *height, int *has_alpha);
 
+// Validates the VP8X Header and skip over it.
+// Returns 0 for invalid VP8X header. Else return 1.
+// is_vp8x_chunk is set to:
+//   0, in case data bytes doesn't correspond to VP8X chunk.
+//   1, in case data bytes correspond to VP8X chunk.
+//   -1, in case not enough bytes (partial VP8X chunk) are passed.
+// Width, Height & Flags are set to the corresponding fields extracted from the
+// VP8X chunk.
+int VP8XGetInfo(const uint8_t** data_ptr, uint32_t* data_size_ptr,
+                int* is_vp8x_chunk, int* width, int* height, uint32_t* flags);
+
 // in tree.c
 void VP8ResetProba(VP8Proba* const proba);
 void VP8ParseProba(VP8BitReader* const br, VP8Decoder* const dec);