Return null when gif frame cannot be decoded.

More work toward #212.

library/src/androidTest/java/com/bumptech/glide/load/resource/gif/GifFrameResourceDecoderTest.java

@@ -12,6 +12,7 @@ import org.robolectric.RobolectricTestRunner;
 import java.io.IOException;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
@@ -38,4 +39,11 @@ public class GifFrameResourceDecoderTest {
 
         assertEquals(expected, resourceDecoder.decode(gifDecoder, 100, 100).get());
     }
+
+    @Test
+    public void testReturnsNullIfGifDecoderReturnsNullFrame() {
+        when(gifDecoder.getNextFrame()).thenReturn(null);
+
+        assertNull(resourceDecoder.decode(gifDecoder, 100, 100));
+    }
 }

library/src/androidTest/java/com/bumptech/glide/load/resource/gif/GifResourceDecoderTest.java

@@ -99,7 +99,6 @@ public class GifResourceDecoderTest {
         verify(parserPool).release(eq(parser));
     }
 
-
     @Test
     public void testSetsPreferredConfigOnDecoderBeforeDecoding() {
         when(gifHeader.getNumFrames()).thenReturn(1);
@@ -148,6 +147,26 @@ public class GifResourceDecoderTest {
         verify(decoderPool).release(eq(gifDecoder));
     }
 
+    @Test
+    public void testReturnsNullIfGifDecoderFailsToDecodeFirstFrame() {
+        when(gifHeader.getNumFrames()).thenReturn(1);
+        when(gifHeader.getStatus()).thenReturn(GifDecoder.STATUS_OK);
+        when(gifDecoder.getNextFrame()).thenReturn(null);
+
+        assertNull(decoder.decode(new ByteArrayInputStream(new byte[0]), 100, 100));
+    }
+
+    @Test
+    public void testReturnsGifDecoderToPoolWhenGifDecoderReturnsNullFirstFrame() {
+        when(gifHeader.getNumFrames()).thenReturn(1);
+        when(gifHeader.getStatus()).thenReturn(GifDecoder.STATUS_OK);
+        when(gifDecoder.getNextFrame()).thenReturn(null);
+
+        decoder.decode(new ByteArrayInputStream(new byte[0]), 100, 100);
+
+        verify(decoderPool).release(eq(gifDecoder));
+    }
+
     @Test
     public void testCanObtainNonNullDecoderFromPool() {
         GifDecoder.BitmapProvider provider = mock(GifDecoder.BitmapProvider.class);

library/src/main/java/com/bumptech/glide/load/resource/gif/GifFrameResourceDecoder.java

@@ -17,7 +17,11 @@ class GifFrameResourceDecoder implements ResourceDecoder<GifDecoder, Bitmap> {
     @Override
     public Resource<Bitmap> decode(GifDecoder source, int width, int height) {
         Bitmap bitmap = source.getNextFrame();
-        return new BitmapResource(bitmap, bitmapPool);
+        if (bitmap == null) {
+            return null;
+        } else {
+            return new BitmapResource(bitmap, bitmapPool);
+        }
     }
 
     @Override

library/src/main/java/com/bumptech/glide/load/resource/gif/GifResourceDecoder.java

@@ -85,6 +85,10 @@ public class GifResourceDecoder implements ResourceDecoder<InputStream, GifDrawa
         }
 
         Bitmap firstFrame = decodeFirstFrame(decoder, header, data);
+        if (firstFrame == null) {
+            return null;
+        }
+
         Transformation<Bitmap> unitTransformation = UnitTransformation.get();
 
         GifDrawable gifDrawable = new GifDrawable(context, provider, bitmapPool, unitTransformation, width, height,

third_party/gif_decoder/src/main/java/com/bumptech/glide/gifdecoder/GifDecoder.java

@@ -250,9 +250,15 @@ public class GifDecoder {
      */
     public Bitmap getNextFrame() {
         if (header.frameCount <= 0 || framePointer < 0) {
+            if (Log.isLoggable(TAG, Log.DEBUG)) {
+                Log.d(TAG, "unable to decode frame, frameCount=" + header.frameCount + " framePointer=" + framePointer);
+            }
             status = STATUS_FORMAT_ERROR;
         }
         if (status == STATUS_FORMAT_ERROR || status == STATUS_OPEN_ERROR) {
+            if (Log.isLoggable(TAG, Log.DEBUG)) {
+                Log.d(TAG, "Unable to decode frame, status=" + status);
+            }
             return null;
         }
         status = STATUS_OK;
@@ -276,7 +282,9 @@ public class GifDecoder {
             act[frame.transIndex] = 0;
         }
         if (act == null) {
-            Log.w(TAG, "No Valid Color Table");
+            if (Log.isLoggable(TAG, Log.DEBUG)) {
+                Log.d(TAG, "No Valid Color Table");
+            }
             // No color table defined.
             status = STATUS_FORMAT_ERROR;
             return null;