Bug 1092996 - MSE/WebM: limit size read to what is available. r=kinetik

dom/media/AbstractMediaDecoder.h

@@ -127,6 +127,10 @@ public:
   // Called from HTMLMediaElement when owner document activity changes
   virtual void SetElementVisibility(bool aIsVisible) {}
 
+  // Called by some MediaDecoderReader to determine if we can rely
+  // on the resource length to limit reads.
+  virtual bool HasInitializationData() { return false; }
+
   // Stack based class to assist in notifying the frame statistics of
   // parsed and decoded frames. Use inside video demux & decode functions
   // to ensure all parsed and decoded frames are reported on all return paths.

dom/media/mediasource/SourceBufferDecoder.cpp

@@ -119,6 +119,12 @@ SourceBufferDecoder::UpdatePlaybackPosition(int64_t aTime)
   MSE_DEBUG("SourceBufferDecoder(%p)::UpdatePlaybackPosition UNIMPLEMENTED", this);
 }
 
+bool
+SourceBufferDecoder::HasInitializationData()
+{
+  return true;
+}
+
 void
 SourceBufferDecoder::OnReadMetadataCompleted()
 {

dom/media/mediasource/SourceBufferDecoder.h

@@ -60,6 +60,7 @@ public:
   virtual void SetMediaSeekable(bool aMediaSeekable) MOZ_FINAL MOZ_OVERRIDE;
   virtual void UpdateEstimatedMediaDuration(int64_t aDuration) MOZ_FINAL MOZ_OVERRIDE;
   virtual void UpdatePlaybackPosition(int64_t aTime) MOZ_FINAL MOZ_OVERRIDE;
+  virtual bool HasInitializationData() MOZ_FINAL MOZ_OVERRIDE;
 
   // SourceBufferResource specific interface below.
 

dom/media/webm/WebMReader.cpp

@@ -287,7 +287,8 @@ nsresult WebMReader::ReadMetadata(MediaInfo* aInfo,
   io.seek = webm_seek;
   io.tell = webm_tell;
   io.userdata = mDecoder;
-  int64_t maxOffset = -1;
+  int64_t maxOffset = mDecoder->HasInitializationData() ?
+    mDecoder->GetResource()->GetLength() : -1;
   int r = nestegg_init(&mContext, io, &webm_log, maxOffset);
   if (r == -1) {
     return NS_ERROR_FAILURE;