Make AudioBufferSourceNode.buffer setter conforming

third_party/WebKit/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 54 matching lines @@
       playback_rate_(playback_rate),
       detune_(detune),
       is_looping_(false),
       did_set_looping_(false),
       loop_start_(0),
       loop_end_(0),
       virtual_read_index_(0),
       is_grain_(false),
       grain_offset_(0.0),
       grain_duration_(kDefaultGrainDuration),
-      min_playback_rate_(1.0) {
+      min_playback_rate_(1.0),
+      buffer_has_been_set_(false) {
   // Default to mono. A call to setBuffer() will set the number of output
   // channels to that of the buffer.
   AddOutput(1);
 
   Initialize();
 }
 
 PassRefPtr<AudioBufferSourceHandler> AudioBufferSourceHandler::Create(
     AudioNode& node,
     float sample_rate,
@@ skipping 295 matching lines @@
 
   virtual_read_index_ = virtual_read_index;
 
   return true;
 }
 
 void AudioBufferSourceHandler::SetBuffer(AudioBuffer* buffer,
                                          ExceptionState& exception_state) {
   DCHECK(IsMainThread());
 
-  if (buffer_) {
-    exception_state.ThrowDOMException(
-        kInvalidStateError,
-        "Cannot set buffer after it has been already been set");
+  if (buffer && buffer_has_been_set_) {
+    exception_state.ThrowDOMException(kInvalidStateError,
+                                      "Cannot set buffer to non-null after it "
+                                      "has been already been set to a non-null "
+                                      "buffer");

[hongchan, 2017/07/28 18:45:32]

I am not so sure about the term "a non-null buffer". Is it a proper expression?
When you create a AudioBuffer, it cannot be a |null|. So it is always non-null.

[Raymond Toy, 2017/07/28 19:16:55]

This is the absn.buffer attribute, so you can set it to random things, including
null.  Should I rephrase the message?

     return;
   }
 
   // The context must be locked since changing the buffer can re-configure the
   // number of channels that are output.
   BaseAudioContext::AutoLocker context_locker(Context());
 
   // This synchronizes with process().
   MutexLocker process_locker(process_lock_);
 
   if (buffer) {
+    buffer_has_been_set_ = true;
+
     // Do any necesssary re-configuration to the buffer's number of channels.
     unsigned number_of_channels = buffer->numberOfChannels();
 
     // This should not be possible since AudioBuffers can't be created with too
     // many channels either.
     if (number_of_channels > BaseAudioContext::MaxNumberOfChannels()) {
       exception_state.ThrowDOMException(
           kNotSupportedError,
           ExceptionMessages::IndexOutsideRange(
               "number of input channels", number_of_channels, 1u,
@@ skipping 347 matching lines @@
 
 void AudioBufferSourceNode::start(double when,
                                   double grain_offset,
                                   double grain_duration,
                                   ExceptionState& exception_state) {
   GetAudioBufferSourceHandler().Start(when, grain_offset, grain_duration,
                                       exception_state);
 }
 
 }  // namespace blink