MHTML generation: safely serialize image documents

third_party/WebKit/Source/web/WebFrameSerializer.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 276 matching lines @@
   TRACE_EVENT_BEGIN0("page-serialization",
                      "WebFrameSerializer::generateMHTMLParts serializing");
   Deque<SerializedResource> resources;
   {
     SCOPED_BLINK_UMA_HISTOGRAM_TIMER(
         "PageSerialization.MhtmlGeneration.SerializationTime.SingleFrame");
     MHTMLFrameSerializerDelegate coreDelegate(*webDelegate);
     FrameSerializer serializer(resources, coreDelegate);
     serializer.serializeFrame(*frame);
   }
+
+  // There was an error serializing the frame (e.g. of an image resource).
+  if (resources.isEmpty())
+    return WebThreadSafeData();

[carlosk, 2017/01/06 23:26:36]

To keep tracing logic consistent this should be moved after the TRACE_EVENT_END1
below.

[Charlie Harrison, 2017/01/07 02:31:25]

Good catch, will fix this in a follow up.

+
   TRACE_EVENT_END1("page-serialization",
                    "WebFrameSerializer::generateMHTMLParts serializing",
                    "resource count",
                    static_cast<unsigned long long>(resources.size()));
 
   // Encode serialized resources as MHTML.
   RefPtr<RawData> output = RawData::create();
   {
-    DCHECK(!resources.isEmpty());
     SCOPED_BLINK_UMA_HISTOGRAM_TIMER(
         "PageSerialization.MhtmlGeneration.EncodingTime.SingleFrame");
     // Frame is the 1st resource (see FrameSerializer::serializeFrame doc
     // comment). Frames get a Content-ID header.
     MHTMLArchive::generateMHTMLPart(
         boundary, webDelegate->getContentID(webFrame), encodingPolicy,
         resources.takeFirst(), *output->mutableData());
     while (!resources.isEmpty()) {
       TRACE_EVENT0("page-serialization",
                    "WebFrameSerializer::generateMHTMLParts encoding");
@@ skipping 43 matching lines @@
     const WebString& baseTarget) {
   // TODO(yosin) We should call |FrameSerializer::baseTagDeclarationOf()|.
   if (baseTarget.isEmpty())
     return String("<base href=\".\">");
   String baseString = "<base href=\".\" target=\"" +
                       static_cast<const String&>(baseTarget) + "\">";
   return baseString;
 }
 
 }  // namespace blink