Corrected access of null pointer in audioproc_f

webrtc/modules/audio_processing/test/aec_dump_based_simulator.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 212 matching lines @@
   dump_input_file_ = OpenFile(settings_.aec_dump_input_filename->c_str(), "rb");
 
   if (settings_.artificial_nearend_filename) {
     std::unique_ptr<WavReader> artificial_nearend_file(
         new WavReader(settings_.artificial_nearend_filename->c_str()));
 
     RTC_CHECK_EQ(1, artificial_nearend_file->num_channels())
         << "Only mono files for the artificial nearend are supported, "
            "reverted to not using the artificial nearend file";
 
+    const int sample_rate_hz = artificial_nearend_file->sample_rate();
     artificial_nearend_buffer_reader_.reset(
         new ChannelBufferWavReader(std::move(artificial_nearend_file)));
     artificial_nearend_buf_.reset(new ChannelBuffer<float>(
-        rtc::CheckedDivExact(artificial_nearend_file->sample_rate(),
-                             kChunksPerSecond),
-        1));
+        rtc::CheckedDivExact(sample_rate_hz, kChunksPerSecond), 1));

[ivoc, 2016/12/14 10:26:41]

Maybe I'm missing something, but to me it looks like this statement is exactly
the same (minus formatting) as before the change. How does this prevent access
of a nullptr?

[peah-webrtc, 2016/12/14 10:33:40]

I think what happens is that the pointer artificial_nearend_file is lost  in the
std::move() operation on row 235, which in turn makes the call to
artificial_nearend_file->sample_rate() access an invalid pointer.

But please correct me if I'm wrong in that and that something else was wrong.
The former code fails when I run it, and the new code does not fail.

[ivoc, 2016/12/14 10:37:06]

Ah right, that's a good point. It's easy to forget the effect of std::move (I
guess that's why it was missed in the initial CL).

   }
 
   webrtc::audioproc::Event event_msg;
   int num_forward_chunks_processed = 0;
   const float kOneBykChunksPerSecond =
       1.f / AudioProcessingSimulator::kChunksPerSecond;
   while (ReadMessageFromFile(dump_input_file_, &event_msg)) {
     switch (event_msg.type()) {
       case webrtc::audioproc::Event::INIT:
         RTC_CHECK(event_msg.has_init());
@@ skipping 326 matching lines @@
 }
 
 void AecDumpBasedSimulator::HandleMessage(
     const webrtc::audioproc::ReverseStream& msg) {
   PrepareReverseProcessStreamCall(msg);
   ProcessReverseStream(interface_used_ == InterfaceType::kFixedInterface);
 }
 
 }  // namespace test
 }  // namespace webrtc