Handle zero-length encoded images gracefully during deserialization

src/core/SkPictureData.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include <new>
+#include "SkImageGenerator.h"
 #include "SkPictureData.h"
 #include "SkPictureRecord.h"
 #include "SkReadBuffer.h"
 #include "SkTextBlob.h"
 #include "SkTypeface.h"
 #include "SkWriteBuffer.h"
 
 #if SK_SUPPORT_GPU
 #include "GrContext.h"
 #endif
@@ skipping 408 matching lines @@
             }
             if (!buffer.isValid()) {
                 return false;
             }
             SkDEBUGCODE(haveBuffer = true;)
         } break;
     }
     return true;    // success
 }
 
+namespace {
+
+// This generator intentionally should always fail on all attempts to get its pixels,

[scroggo, 2015/09/04 18:48:20]

FWIW, we used to show deserialize such failed encodes as red bitmaps, to show
something went wrong. Not sure whether that's something we should be doing.

+// simulating a bad or empty codec stream.
+class EmptyImageGenerator final : public SkImageGenerator {
+public:
+    EmptyImageGenerator(const SkImageInfo& info) : INHERITED(info) { }
+
+private:
+    typedef SkImageGenerator INHERITED;
+};
+
+} // anonymous namespace
+
 static const SkImage* create_image_from_buffer(SkReadBuffer& buffer) {
     int width = buffer.read32();
     int height = buffer.read32();
     if (width <= 0 || height <= 0) {    // SkImage never has a zero dimension
         buffer.validate(false);
         return nullptr;
     }
 
     SkAutoTUnref<SkData> encoded(buffer.readByteArrayAsData());
+    if (encoded->size() == 0) {
+        // The image could not be encoded at serialization time - return an empty placeholder.
+        return SkImage::NewFromGenerator(
+            new EmptyImageGenerator(SkImageInfo::MakeN32Premul(width, height)));
+    }
+
     int originX = buffer.read32();
     int originY = buffer.read32();
-    if (0 == encoded->size() || originX < 0 || originY < 0) {
+    if (originX < 0 || originY < 0) {
         buffer.validate(false);
         return nullptr;
     }
 
     const SkIRect subset = SkIRect::MakeXYWH(originX, originY, width, height);
     return SkImage::NewFromEncoded(encoded, &subset);
 }
 
 // Need a shallow wrapper to return const SkPicture* to match the other factories,
 // as SkPicture::CreateFromBuffer() returns SkPicture*
@@ skipping 176 matching lines @@
     }
 }
 
 bool SkPictureData::suitableForLayerOptimization() const {
     return fContentInfo.numLayers() > 0;
 }
 #endif
 ///////////////////////////////////////////////////////////////////////////////