Recompress fdATs

src/lib.rs

@@ -389,7 +389,7 @@ impl RawImage {
     /// Create an optimized png from the raw image data using the options provided
     pub fn create_optimized_png(&self, opts: &Options) -> PngResult<Vec<u8>> {
         let deadline = Arc::new(Deadline::new(opts.timeout));
-        let mut png = optimize_raw(self.png.clone(), opts, deadline, None)
+        let mut png = optimize_raw(self.png.clone(), opts, deadline.clone(), None)
             .ok_or_else(|| PngError::new("Failed to optimize input data"))?;
 
         // Process aux chunks
@@ -399,7 +399,7 @@ impl RawImage {
             .filter(|c| opts.strip.keep(&c.name))
             .cloned()
             .collect();
-        postprocess_chunks(&mut png, opts, &self.png.ihdr);
+        postprocess_chunks(&mut png, opts, deadline, &self.png.ihdr);
 
         Ok(png.output())
     }
@@ -583,12 +583,12 @@ fn optimize_png(
     } else {
         Some(png.estimated_output_size())
     };
-    if let Some(new_png) = optimize_raw(raw.clone(), &opts, deadline, max_size) {
+    if let Some(new_png) = optimize_raw(raw.clone(), &opts, deadline.clone(), max_size) {
         png.raw = new_png.raw;
         png.idat_data = new_png.idat_data;
     }
 
-    postprocess_chunks(png, &opts, &raw.ihdr);
+    postprocess_chunks(png, &opts, deadline, &raw.ihdr);
 
     let output = png.output();
 
@@ -860,7 +860,12 @@ fn report_format(prefix: &str, png: &PngImage) {
 }
 
 /// Perform cleanup of certain chunks from the `PngData` object, after optimization has been completed
-fn postprocess_chunks(png: &mut PngData, opts: &Options, orig_ihdr: &IhdrData) {
+fn postprocess_chunks(
+    png: &mut PngData,
+    opts: &Options,
+    deadline: Arc<Deadline>,
+    orig_ihdr: &IhdrData,
+) {
     if let Some(iccp_idx) = png.aux_chunks.iter().position(|c| &c.name == b"iCCP") {
         // See if we can replace an iCCP chunk with an sRGB chunk
         let may_replace_iccp = opts.strip != StripChunks::None && opts.strip.keep(b"sRGB");
@@ -913,6 +918,38 @@ fn postprocess_chunks(png: &mut PngData, opts: &Options, orig_ihdr: &IhdrData) {
             !invalid
         });
     }
+
+    // Find fdAT chunks and attempt to recompress them
+    // Note if there are multiple fdATs per frame then decompression will fail and nothing will change
+    let mut fdat: Vec<_> = png
+        .aux_chunks
+        .iter_mut()
+        .filter(|c| &c.name == b"fdAT")
+        .collect();
+    if !fdat.is_empty() {
+        let buffer_size = orig_ihdr.raw_data_size();
+        fdat.par_iter_mut()
+            .with_max_len(1)
+            .enumerate()
+            .for_each(|(i, c)| {
+                if deadline.passed() || c.data.len() <= 4 {
+                    return;
+                }
+                if let Ok(mut data) = deflate::inflate(&c.data[4..], buffer_size).and_then(|data| {
+                    let max_size = AtomicMin::new(Some(c.data.len() - 5));
+                    opts.deflate.deflate(&data, &max_size)
+                }) {
+                    debug!(
+                        "Recompressed fdAT #{:<2}: {} ({} bytes decrease)",
+                        i,
+                        c.data.len(),
+                        c.data.len() - 4 - data.len()
+                    );
+                    c.data.truncate(4);
+                    c.data.append(&mut data);
+                }
+            })
+    }
 }
 
 /// Check if an image was already optimized prior to oxipng's operations