Add support for extracting Exif data

Author: fseegraeber

src/decoder.rs

@@ -75,6 +75,8 @@ pub struct Decoder<R> {
 
     icc_markers: Vec<IccChunk>,
 
+    exif_data: Option<Vec<u8>>,
+
     // Used for progressive JPEGs.
     coefficients: Vec<Vec<i16>>,
     // Bitmask of which coefficients has been completely decoded.
@@ -95,6 +97,7 @@ impl<R: Read> Decoder<R> {
             is_jfif: false,
             is_mjpeg: false,
             icc_markers: Vec::new(),
+            exif_data: None,
             coefficients: Vec::new(),
             coefficients_finished: [0; MAX_COMPONENTS],
         }
@@ -124,6 +127,13 @@ impl<R: Read> Decoder<R> {
         }
     }
 
+    /// Returns raw exif data, starting at the TIFF header, if the image contains any.
+    ///
+    /// The returned value will be `None` until a call to `decode` has returned `Ok`.    
+    pub fn exif_data(&self) -> Option<Vec<u8>> {
+        self.exif_data.as_ref().map(|v| v.clone())
+    }
+
     /// Returns the embeded icc profile if the image contains one.
     pub fn icc_profile(&self) -> Option<Vec<u8>> {
         let mut marker_present: [Option<&IccChunk>; 256] = [None; 256];
@@ -374,6 +384,7 @@ impl<R: Read> Decoder<R> {
                             },
                             AppData::Avi1 => self.is_mjpeg = true,
                             AppData::Icc(icc) => self.icc_markers.push(icc),
+                            AppData::Exif(data) => self.exif_data = Some(data),
                         }
                     }
                 },

src/parser.rs

@@ -71,6 +71,7 @@ pub enum AppData {
     Jfif,
     Avi1,
     Icc(IccChunk),
+    Exif(Vec<u8>),
 }
 
 // http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
@@ -562,6 +563,23 @@ pub fn parse_app<R: Read>(reader: &mut R, marker: Marker) -> Result<Option<AppDa
                 }
             }
         }
+        // Exif Data
+        APP(1) => {
+            if length >= 6 {
+                let mut buffer = [0u8; 6];
+                reader.read_exact(&mut buffer)?;
+                bytes_read = buffer.len();            
+            
+            // https://web.archive.org/web/20190624045241if_/http://www.cipa.jp:80/std/documents/e/DC-008-Translation-2019-E.pdf
+            // 4.5.4 Basic Structure of JPEG Compressed Data
+            if &buffer == b"Exif\x00\x00" {
+                let mut data = vec![0; length - bytes_read];                
+                reader.read_exact(&mut data)?;
+                bytes_read += data.len();
+                result = Some(AppData::Exif(data));
+                }
+            }
+        }
         APP(2) => {
             if length > 14 {
                 let mut buffer = [0u8; 14];

tests/lib.rs

@@ -42,3 +42,18 @@ fn read_icc_profile() {
     // "acsp" is a mandatory string in ICC profile headers.
     assert_eq!(&profile[36..40], b"acsp");
 }
+
+#[test]
+fn read_exif_data() {
+    let path = Path::new("tests")
+        .join("reftest")
+        .join("images")
+        .join("ycck.jpg");
+
+    let mut decoder = jpeg::Decoder::new(File::open(&path).unwrap());
+    decoder.decode().unwrap();
+
+    let exif_data = decoder.exif_data().unwrap();
+    // exif data start as a TIFF header
+    assert_eq!(&exif_data[0..8], b"\x49\x49\x2A\x00\x08\x00\x00\x00");
+}