Use CopyOnWriteBuffer instead of Buffer to avoid unnecessary copies.

webrtc/base/copyonwritebuffer.h

Index: webrtc/base/copyonwritebuffer.h
diff --git a/webrtc/base/copyonwritebuffer.h b/webrtc/base/copyonwritebuffer.h
index 17f2710f3ecbd404646268d4af9a003d7c2e5465..895f449f77a3349afa1cba6042fb3914ab0c4ae2 100644
--- a/webrtc/base/copyonwritebuffer.h
+++ b/webrtc/base/copyonwritebuffer.h
@@ -42,7 +42,9 @@ class CopyOnWriteBuffer {
   template <typename T, typename internal::ByteType<T>::t = 0>
   CopyOnWriteBuffer(const T* data, size_t size, size_t capacity)
       : CopyOnWriteBuffer(size, capacity) {
-    std::memcpy(buffer_->data(), data, size);
+    if (size > 0) {
+      std::memcpy(buffer_->data(), data, size);
+    }

[kwiberg-webrtc, 2016/03/14 11:53:49]

The reason for having the conditional is clearer if you write the (equivalent)
if (buffer_) instead.

[joachim, 2016/03/17 20:27:21]

Done.

   }
 
   // Construct a buffer from the contents of an array.
@@ -128,9 +130,9 @@ class CopyOnWriteBuffer {
   template <typename T, typename internal::ByteType<T>::t = 0>
   void SetData(const T* data, size_t size) {
     RTC_DCHECK(IsConsistent());
-    if (!buffer_ || !buffer_->HasOneRef()) {
-      buffer_ = new RefCountedObject<Buffer>(data, size, size);
-    } else {
+    if (size && (!buffer_ || !buffer_->HasOneRef())) {
+      buffer_ = new RefCountedObject<Buffer>(data, size);
+    } else if (buffer_) {
       buffer_->SetData(data, size);
     }
     RTC_DCHECK(IsConsistent());

[kwiberg-webrtc, 2016/03/14 11:53:49]

Hmm. This is still wrong: if size == 0 and !buffer_->HasOneRef(), you'll modify
the shared buffer. I think it should be something like

if (!buffer_ || !buffer_->HasOneRef()) {
  buffer_ = size > 0 ? new RefCountedObject<Buffer>(data, size)
                     : nullptr;
} else {
  buffer_->SetData(data, size);
}

[joachim, 2016/03/17 20:27:21]

Thanks. Changed and added a test.