Test and polish encoding extra directories

src/encoder/mod.rs

@@ -250,11 +250,20 @@ pub struct DirectoryEncoder<'a, W: 'a + Write + Seek, K: TiffKind> {
 
 /// The offset of an encoded directory in the file.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
-pub struct DirectoryOffset {
-    /// The start of the directory, as a Tiff value.
-    pub offset: IfdPointer,
+pub struct DirectoryOffset<K: TiffKind> {
+    /// The start of the directory as a Tiff value.
+    ///
+    /// This is a bit of a wart in the strongly typed design of the encoder. The value _type_ must
+    /// itself know how to be represented in the Tiff file but that may differ based on endianess
+    /// as well as the offset size (`u32` or BigTIFF's `u64`). Thankfully we're allowed to
+    /// represent offsets with `LONG` or `IFD` in the usual case.
+    pub offset: K::OffsetType,
+    /// The start of the directory as a pure offset.
+    pub pointer: IfdPointer,
     /// The offset of its sequence link field, in our private representation.
     ifd_chain: NonZeroU64,
+    /// The kind of Tiff file the offset is for.
+    kind: PhantomData<K>,
 }
 
 impl<'a, W: 'a + Write + Seek, K: TiffKind> DirectoryEncoder<'a, W, K> {
@@ -315,7 +324,7 @@ impl<'a, W: 'a + Write + Seek, K: TiffKind> DirectoryEncoder<'a, W, K> {
     /// file. The encoder writes its own offset into the parent's field when [`Self::finish`] is
     /// called or it is dropped. This redefines the parent. An offset representation of the parent
     /// must be acquired by finishing it with [`Self::finish_with_offsets`].
-    pub fn set_parent(&mut self, offset: &DirectoryOffset) {
+    pub fn set_parent(&mut self, offset: &DirectoryOffset<K>) {
         self.chained_ifd_pos = Some(offset.ifd_chain);
     }
 
@@ -325,7 +334,7 @@ impl<'a, W: 'a + Write + Seek, K: TiffKind> DirectoryEncoder<'a, W, K> {
         Ok(())
     }
 
-    pub fn finish_with_offsets(mut self) -> TiffResult<DirectoryOffset> {
+    pub fn finish_with_offsets(mut self) -> TiffResult<DirectoryOffset<K>> {
         self.finish_internal()
     }
 
@@ -393,13 +402,18 @@ impl<'a, W: 'a + Write + Seek, K: TiffKind> DirectoryEncoder<'a, W, K> {
         self.writer.last_written()
     }
 
-    fn finish_internal(&mut self) -> TiffResult<DirectoryOffset> {
+    fn finish_internal(&mut self) -> TiffResult<DirectoryOffset<K>> {
         let ifd_pointer = self.write_directory()?;
+        let offset = K::convert_offset(ifd_pointer)?;
 
         if let Some(prior) = self.chained_ifd_pos {
             let curr_pos = self.writer.offset();
 
             self.writer.goto_offset(prior.get())?;
+            // Note how we are not writing the `offset` type itself here as doing so would need to
+            // go through the `TiffValue` trait—the type is not constrained by much. But for the
+            // trait we need a `TiffWriter` which comes with a bunch of additional state such as
+            // compressor etc. that we have no need for.
             K::write_offset(self.writer, ifd_pointer)?;
 
             self.writer.goto_offset(curr_pos)?;
@@ -417,8 +431,10 @@ impl<'a, W: 'a + Write + Seek, K: TiffKind> DirectoryEncoder<'a, W, K> {
         self.dropped = true;
 
         Ok(DirectoryOffset {
-            offset: IfdPointer(ifd_pointer),
+            pointer: IfdPointer(ifd_pointer),
+            offset,
             ifd_chain,
+            kind: PhantomData,
         })
     }
 }
@@ -695,7 +711,7 @@ impl<'a, W: 'a + Write + Seek, T: ColorType, K: TiffKind> ImageEncoder<'a, W, T,
         Ok(())
     }
 
-    fn finish_internal(&mut self) -> TiffResult<DirectoryOffset> {
+    fn finish_internal(&mut self) -> TiffResult<DirectoryOffset<K>> {
         self.encoder
             .write_tag(Tag::StripOffsets, K::convert_slice(&self.strip_offsets))?;
         self.encoder.write_tag(

tests/encode_images.rs

@@ -626,3 +626,59 @@ fn test_rows_per_strip() {
         }
     }
 }
+
+#[test]
+fn test_auxiliary_directory() {
+    const ARTIST: &str = "Auxiliary-tiff";
+
+    let mut data = Cursor::new(Vec::new());
+    let mut tiff = TiffEncoder::new(&mut data).unwrap();
+
+    {
+        let mut image_encoder = tiff.new_image::<colortype::Gray8>(1, 1).unwrap();
+        image_encoder.write_strip(&[1]).unwrap();
+    }
+
+    let exif = {
+        let mut extra = tiff.extra_directory().unwrap();
+        extra.write_tag(Tag::Artist, ARTIST).unwrap();
+        extra.finish_with_offsets().unwrap()
+    };
+
+    {
+        let mut image_encoder = tiff.new_image::<colortype::Gray8>(2, 1).unwrap();
+        image_encoder.write_strip(&[1, 2]).unwrap();
+        let encoder = image_encoder.encoder();
+        encoder.write_tag(Tag::ExifDirectory, exif.offset).unwrap();
+    }
+
+    drop(tiff);
+
+    data.set_position(0);
+    let mut decoder = Decoder::new(&mut data).unwrap();
+
+    {
+        assert_eq!(decoder.dimensions().unwrap(), (1, 1));
+        let _ = decoder.read_image().unwrap();
+    }
+
+    {
+        decoder.next_image().unwrap();
+        assert_eq!(decoder.dimensions().unwrap(), (2, 1));
+        let _ = decoder.read_image().unwrap();
+
+        let exif_location = decoder
+            .get_tag(Tag::ExifDirectory)
+            .expect("second directory missing Exif")
+            .into_ifd_pointer()
+            .expect("exif directory is not an IFD pointer");
+
+        let exif = decoder.read_directory(exif_location).unwrap();
+
+        let artist = decoder
+            .read_directory_tags(&exif)
+            .get_tag_ascii_string(Tag::Artist)
+            .expect("EXIF directory missing artist tag");
+        assert_eq!(artist, ARTIST);
+    }
+}