Make peeking before the head of OffsetByteQueue a hard error.

media/mp4/offset_byte_queue.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "media/mp4/offset_byte_queue.h"
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 
 namespace media {
@@ skipping 19 matching lines @@
   *size = size_;
 }
 
 void OffsetByteQueue::Pop(int count) {
   queue_.Pop(count);
   head_ += count;
   Sync();
 }
 
 void OffsetByteQueue::PeekAt(int64 offset, const uint8** buf, int* size) {
+  DCHECK(offset >= head());

[acolwell GONE FROM CHROMIUM, 2012/07/30 20:49:04]

Is this a result of a coding error, or can unexpected or corrupt files trigger
this? If it is the former then I'm fine with the DCHECK. If it is the later then
I'd prefer the original code since this situation should allow us to signal an
error w/o crashing.

[strobe_, 2012/07/31 18:34:38]

As of now, it can only be the result of a programming error. (Formerly, it could
have been the result of a corrupt file, but recent changes eliminate that.)

   if (offset < head() || offset >= tail()) {
     *buf = NULL;
     *size = 0;
     return;
   }
   *buf = &buf_[offset - head()];
   *size = tail() - offset;
 }
 
 bool OffsetByteQueue::Trim(int64 max_offset) {
   if (max_offset < head_) return true;
   if (max_offset > tail()) {
     Pop(size_);
     return false;
   }
   Pop(max_offset - head_);
   return true;
 }
 
 void OffsetByteQueue::Sync() {
   queue_.Peek(&buf_, &size_);
 }
 
 }  // namespace media