Implement exif_metadata for TIFF

src/codecs/tiff.rs

@@ -30,6 +30,7 @@ where
     dimensions: (u32, u32),
     color_type: ColorType,
     original_color_type: ExtendedColorType,
+    start_pos: u64,
 
     // We only use an Option here so we can call with_limits on the decoder without moving.
     inner: Option<Decoder<R>>,
@@ -40,7 +41,8 @@ where
     R: BufRead + Seek,
 {
     /// Create a new `TiffDecoder`.
-    pub fn new(r: R) -> Result<TiffDecoder<R>, ImageError> {
+    pub fn new(mut r: R) -> Result<TiffDecoder<R>, ImageError> {
+        let start_pos = r.stream_position()?;
         let mut inner = Decoder::new(r).map_err(ImageError::from_tiff_decode)?;
 
         let dimensions = inner.dimensions().map_err(ImageError::from_tiff_decode)?;
@@ -115,6 +117,7 @@ where
             dimensions,
             color_type,
             original_color_type,
+            start_pos,
             inner: Some(inner),
         })
     }
@@ -266,6 +269,27 @@ impl<R: BufRead + Seek> ImageDecoder for TiffDecoder<R> {
         }
     }
 
+    fn exif_metadata(&mut self) -> ImageResult<Option<Vec<u8>>> {
+        let Some(decoder) = &mut self.inner else {
+            return Ok(None);
+        };
+
+        // Get access to the inner reader and remember the current position.
+        let reader = decoder.inner();
+        let last_pos = reader.stream_position()?;
+
+        // TIFF uses the same structure as EXIF, so we can just use the file itself
+        // as the source of decoding EXIF.
+        reader.seek(io::SeekFrom::Start(self.start_pos))?;
+        let mut result = Vec::new();
+        reader.read_to_end(&mut result)?;
+
+        // Restore the previous position.
+        reader.seek(io::SeekFrom::Start(last_pos))?;
+
+        Ok(Some(result))
+    }
+
     fn xmp_metadata(&mut self) -> ImageResult<Option<Vec<u8>>> {
         let Some(decoder) = &mut self.inner else {
             return Ok(None);

tests/metadata.rs

@@ -22,6 +22,8 @@ const EXPECTED_WEBP_TIFF_METADATA: &str = "<?xpacket begin='\u{feff}' id='W5M0Mp
 
 const XMP_TIFF_PATH: &str = "tests/images/tiff/testsuite/l1_xmp.tiff";
 
+const EXIF_TIFF_PATH: &str = "tests/images/tiff/testsuite/l1.tiff";
+
 #[test]
 #[cfg(feature = "png")]
 fn test_read_xmp_png() -> Result<(), image::ImageError> {
@@ -64,3 +66,17 @@ fn test_read_xmp_tiff() -> Result<(), image::ImageError> {
 
     Ok(())
 }
+
+#[test]
+#[cfg(feature = "tiff")]
+fn test_read_exif_tiff() -> Result<(), image::ImageError> {
+    let img_path = PathBuf::from_str(EXIF_TIFF_PATH).unwrap();
+
+    let data = fs::read(img_path)?;
+    let mut tiff_decoder = TiffDecoder::new(std::io::Cursor::new(&data))?;
+    let metadata = tiff_decoder.exif_metadata()?;
+    assert!(metadata.is_some());
+    assert_eq!(data, metadata.unwrap());
+
+    Ok(())
+}