Progressive images now render incomplete coefficients

Progressive jpegs have multiple passes on their spectral coefficients.
This library currently waits for all coefficients to have been
read in by the various segments before it sends the coefficient data
to the DCT engine.

However, some images have (perhaps incorrectly) incomplete passes on
the coefficient data, where eg. a component might only have spectral
coefficients 0 through 5 sent due to perhaps an improperly written
encoder. In these scenarios this library would yield the error, 'not
all components have data' instead of a more forgiving approach.

This change adds a final pass over the components when in a progressive
frame. The pass checks all components to determine if any have missing
coefficients (ie. haven't been processed yet), and if this is the case
it will send the components to the DCT engine to be processed, and then
collected. This way, the library is more forgiving to incomplete
spectral information present in certain progressive files.

Added new crashtest image:
* missing-sos: Image with a SOF but no SOS marker. Expected behavior is to
    yield the 'not all components have data' error

Added new reftest images:
* progressive-incomplete: Progressive image with only the DC component.
    Expected behavior should now be to render a white square.
* progressive-missing-dc: Progressive image with only the first AC
    component. Expected behavior should be render a horizontal gradient.

Author: quilan1

src/decoder.rs

@@ -410,6 +410,46 @@ impl<R: Read> Decoder<R> {
         }
 
         let frame = self.frame.as_ref().unwrap();
+
+        // If we're decoding a progressive jpeg and a component is unfinished, render what we've got
+        if frame.coding_process == CodingProcess::DctProgressive && self.coefficients.len() == frame.components.len() {
+            for (i, component) in frame.components.iter().enumerate() {
+                // Only dealing with unfinished components
+                if self.coefficients_finished[i] == !0 {
+                    continue;
+                }
+
+                let quantization_table = match self.quantization_tables[component.quantization_table_index].clone() {
+                    Some(quantization_table) => quantization_table,
+                    None => continue,
+                };
+
+                // Get the worker prepared
+                if worker.is_none() {
+                    worker = Some(PlatformWorker::new()?);
+                }
+                let worker = worker.as_mut().unwrap();
+                let row_data = RowData {
+                    index: i,
+                    component: component.clone(),
+                    quantization_table,
+                };
+                worker.start(row_data)?;
+
+                // Send the rows over to the worker and collect the result
+                let coefficients_per_mcu_row = usize::from(component.block_size.width) * usize::from(component.vertical_sampling_factor) * 64;
+                for mcu_y in 0..frame.mcu_size.height {
+                    let row_coefficients = {
+                        let offset = usize::from(mcu_y) * coefficients_per_mcu_row;
+                        self.coefficients[i][offset .. offset + coefficients_per_mcu_row].to_vec()
+                    };
+
+                    worker.append_row((i, row_coefficients))?;
+                }
+                planes[i] = worker.get_result(i)?;
+            }
+        }
+
         compute_image(&frame.components, planes, frame.output_size, self.is_jfif, self.color_transform)
     }
 

tests/crashtest/images/README.md

@@ -6,3 +6,4 @@ dc-predictor-overflow.jpg | Found by Wim Looman (@Nemo157) while fuzzing
 derive-huffman-codes-overflow.jpg | Found by Pascal Hertleif (@killercup) while fuzzing
 missing-sof.jpg           | Found by Corey Farwell (@frewsxcv) when fuzz testing
 extraneous-bytes-after-sos.jpg | Scan from brother DSmobile 920DW provided by Filip Lundborg (@filipl)
+missing-sos.jpg           | Generated in GIMP and manually edited by John Reynolds (@quilan1)

tests/crashtest/images/missing-sos.jpg

@@ -10,3 +10,6 @@ mjpeg.jpg         | https://bugzilla.mozilla.org/show_bug.cgi?id=963907
 restarts.jpg      | `mozilla/jpg-size-33x33.jpg` with added restart markers.
 rgb.jpg           | Created from `ycck.jpg` using <code>convert ycck.jpg tga:- &#124; cjpeg -rgb -outfile rgb.jpg</code>
 ycck.jpg          | https://en.wikipedia.org/wiki/File:Channel_digital_image_CMYK_color.jpg
+non-interleaved-mcu.jpg | Generated in GIMP by John Reynolds (@quilan1)
+progressive-missing-ac.jpg | Generated in GIMP and manually edited by John Reynolds (@quilan1)
+progressive-missing-dc.jpg | Generated in GIMP and manually edited by John Reynolds (@quilan1)