Support nullable buffer for AudioBufferSourceNode.

Source/modules/webaudio/AudioBufferSourceNode.cpp

 /*
  * Copyright (C) 2010, 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:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 40 matching lines @@
 const double MaxRate = 1024;
 
 PassRefPtr<AudioBufferSourceNode> AudioBufferSourceNode::create(AudioContext* context, float sampleRate)
 {
     return adoptRef(new AudioBufferSourceNode(context, sampleRate));
 }
 
 AudioBufferSourceNode::AudioBufferSourceNode(AudioContext* context, float sampleRate)
     : AudioScheduledSourceNode(context, sampleRate)
     , m_buffer(nullptr)
+    , m_nullableBuffer(nullptr)
     , m_isLooping(false)
     , m_loopStart(0)
     , m_loopEnd(0)
     , m_virtualReadIndex(0)
     , m_isGrain(false)
     , m_grainOffset(0.0)
     , m_grainDuration(DefaultGrainDuration)
     , m_lastGain(1.0)
     , m_pannerNode(0)
 {
@@ skipping 78 matching lines @@
     if (!loop()) {
         // If we're not looping, then stop playing when we get to the end.
 
         if (framesToProcess > 0) {
             // We're not looping and we've reached the end of the sample data, but we still need to provide more output,
             // so generate silence for the remaining.
             for (unsigned i = 0; i < numberOfChannels(); ++i)
                 memset(m_destinationChannels[i] + index, 0, sizeof(float) * framesToProcess);
         }
 
-        finish();
+        // If buffer was set to null, it sould keep to render slience to ready rendering with proper buffer with setBuffer().
+        if (m_buffer != m_nullableBuffer)
+            finish();
+
         return true;
     }
     return false;
 }
 
 bool AudioBufferSourceNode::renderFromBuffer(AudioBus* bus, unsigned destinationFrameOffset, size_t numberOfFrames)
 {
     ASSERT(context()->isAudioThread());
 
     // Basic sanity checking
@@ skipping 157 matching lines @@
 
     m_virtualReadIndex = virtualReadIndex;
 
     return true;
 }
 
 
 void AudioBufferSourceNode::setBuffer(AudioBuffer* buffer, ExceptionState& exceptionState)
 {
     ASSERT(isMainThread());
-    // FIXME: It does not look like we should throw if the buffer is null as
-    // the attribute is nullable in the specification.
+
+    // If a buffer is null, it is one channel of silence according to specification.
     if (!buffer) {
-        exceptionState.throwTypeError("buffer cannot be null");
-        return;
+        // Set mono channel, default frame = 512 and destination's sampleRate.
+        if (!m_nullableBuffer)
+            m_nullableBuffer = context()->createBuffer(1, 512, context()->sampleRate(), exceptionState);
+
+        if (!m_nullableBuffer) {
+            exceptionState.throwTypeError("failed creation of nullable buffer");
+            return;
+        }
+
+        buffer = m_nullableBuffer.get();
     }
 
     // The context must be locked since changing the buffer can re-configure the number of channels that are output.
     AudioContext::AutoLocker contextLocker(context());
 
     // This synchronizes with process().
     MutexLocker processLocker(m_processLock);
 
     if (buffer) {
         // Do any necesssary re-configuration to the buffer's number of channels.
@@ skipping 151 matching lines @@
 void AudioBufferSourceNode::finish()
 {
     clearPannerNode();
     ASSERT(!m_pannerNode);
     AudioScheduledSourceNode::finish();
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)