Merge pull request #109 from Juliapixel/main

Ignore reserved bits in chunks

Author: kornelski

src/decoder.rs

@@ -43,11 +43,18 @@ quick_error! {
             display("Invalid Chunk header: {err:x?}")
         }
 
+        #[allow(deprecated)]
+        #[deprecated]
         /// Some bits were invalid
         ReservedBitSet {
             display("Reserved bits set")
         }
 
+        /// The ALPH chunk preprocessing info flag was invalid
+        InvalidAlphaPreprocessing {
+            display("Alpha chunk preprocessing flag invalid")
+        }
+
         /// Invalid compression method
         InvalidCompressionMethod {
             display("Invalid compression method")
@@ -721,10 +728,6 @@ impl<R: BufRead + Seek> WebPDecoder<R> {
         }
         let duration = extended::read_3_bytes(&mut self.r)?;
         let frame_info = self.r.read_u8()?;
-        let reserved = frame_info & 0b11111100;
-        if reserved != 0 {
-            return Err(DecodingError::ReservedBitSet);
-        }
         let use_alpha_blending = frame_info & 0b00000010 == 0;
         let dispose = frame_info & 0b00000001 != 0;
 

src/extended.rs

@@ -238,19 +238,14 @@ pub(crate) fn read_extended_header<R: Read>(
 ) -> Result<WebPExtendedInfo, DecodingError> {
     let chunk_flags = reader.read_u8()?;
 
-    let reserved_first = chunk_flags & 0b11000000;
     let icc_profile = chunk_flags & 0b00100000 != 0;
     let alpha = chunk_flags & 0b00010000 != 0;
     let exif_metadata = chunk_flags & 0b00001000 != 0;
     let xmp_metadata = chunk_flags & 0b00000100 != 0;
     let animation = chunk_flags & 0b00000010 != 0;
-    let reserved_second = chunk_flags & 0b00000001;
 
-    let reserved_third = read_3_bytes(reader)?;
-
-    if reserved_first != 0 || reserved_second != 0 || reserved_third != 0 {
-        return Err(DecodingError::ReservedBitSet);
-    }
+    // reserved bytes are ignored
+    let _reserved_bytes = read_3_bytes(reader)?;
 
     let canvas_width = read_3_bytes(reader)? + 1;
     let canvas_height = read_3_bytes(reader)? + 1;
@@ -304,19 +299,14 @@ pub(crate) fn read_alpha_chunk<R: BufRead>(
 ) -> Result<AlphaChunk, DecodingError> {
     let info_byte = reader.read_u8()?;
 
-    let reserved = info_byte & 0b11000000;
     let preprocessing = (info_byte & 0b00110000) >> 4;
     let filtering = (info_byte & 0b00001100) >> 2;
     let compression = info_byte & 0b00000011;
 
-    if reserved != 0 {
-        return Err(DecodingError::ReservedBitSet);
-    }
-
     let preprocessing = match preprocessing {
         0 => false,
         1 => true,
-        _ => return Err(DecodingError::ReservedBitSet),
+        _ => return Err(DecodingError::InvalidAlphaPreprocessing),
     };
 
     let filtering_method = match filtering {