Fewer copies when writing metadata

Author: Shnatsel

src/encoder.rs

@@ -354,12 +354,20 @@ impl<W: JfifWrite> Encoder<W> {
     ///
     /// Returns an error if the segment number is invalid or data exceeds the allowed size
     pub fn add_app_segment(&mut self, segment_nr: u8, data: &[u8]) -> Result<(), EncodingError> {
+        self.add_app_segment_internal(segment_nr, data.to_vec())
+    }
+
+    fn add_app_segment_internal(
+        &mut self,
+        segment_nr: u8,
+        data: Vec<u8>,
+    ) -> Result<(), EncodingError> {
         if segment_nr == 0 || segment_nr > 15 {
             Err(EncodingError::InvalidAppSegment(segment_nr))
         } else if data.len() > 65533 {
             Err(EncodingError::AppSegmentTooLarge(data.len()))
         } else {
-            self.app_segments.push((segment_nr, data.to_vec()));
+            self.app_segments.push((segment_nr, data));
             Ok(())
         }
     }
@@ -385,16 +393,14 @@ impl<W: JfifWrite> Encoder<W> {
             return Err(EncodingError::IccTooLarge(data.len()));
         }
 
-        let mut chunk_data = Vec::with_capacity(MAX_CHUNK_LENGTH);
-
         for (i, data) in data.chunks(MAX_CHUNK_LENGTH).enumerate() {
-            chunk_data.clear();
+            let mut chunk_data = Vec::with_capacity(MAX_CHUNK_LENGTH);
             chunk_data.extend_from_slice(MARKER);
             chunk_data.push(i as u8 + 1);
             chunk_data.push(num_chunks as u8);
             chunk_data.extend_from_slice(data);
 
-            self.add_app_segment(2, &chunk_data)?;
+            self.add_app_segment_internal(2, chunk_data)?;
         }
 
         Ok(())