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// Copyright (c) 2011 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 "base/compiler_specific.h"
#include "base/memory/scoped_ptr.h"
#include "net/tools/balsa/buffer_interface.h"
namespace net {
// The ring buffer is a circular buffer, that is, reads or writes may wrap
// around the end of the linear memory contained by the class (and back to
// the beginning). This is a good choice when you want to use a fixed amount
// of buffering and don't want to be moving memory around a lot.
// What is the penalty for using this over a normal, linear buffer?
// Reading all the data may take two operations, and
// writing all the data may take two operations.
// In the proxy, this class is used as a fixed size buffer between
// clients and servers (so that the memory size is constrained).
class RingBuffer : public BufferInterface {
explicit RingBuffer(int buffer_size);
virtual ~RingBuffer();
// Resize the buffer to the size specified here. If the buffer_size passed
// in here is smaller than the amount of data in the buffer, then the oldest
// data will be dropped, but all other data will be saved.
// This means: If the buffer size is increasing, all data that was resident
// in the buffer prior to this call will be resident after this call.
void Resize(int buffer_size);
// The following functions all override pure virtual functions
// in BufferInterface. See buffer_interface.h for a description
// of what they do if the function isn't documented here.
virtual int ReadableBytes() const OVERRIDE;
virtual int BufferSize() const OVERRIDE;
virtual int BytesFree() const OVERRIDE;
virtual bool Empty() const OVERRIDE;
virtual bool Full() const OVERRIDE;
// returns the number of characters written.
// appends up-to-'size' bytes to the ringbuffer.
virtual int Write(const char* bytes, int size) OVERRIDE;
// Stores a pointer into the ring buffer in *ptr, and stores the number of
// characters which are allowed to be written in *size.
// If there are no writable bytes available, then *size will contain 0.
virtual void GetWritablePtr(char** ptr, int* size) const OVERRIDE;
// Stores a pointer into the ring buffer in *ptr, and stores the number of
// characters which are allowed to be read in *size.
// If there are no readable bytes available, then *size will contain 0.
virtual void GetReadablePtr(char** ptr, int* size) const OVERRIDE;
// Returns the number of bytes read into 'bytes'.
virtual int Read(char* bytes, int size) OVERRIDE;
// Removes all data from the ring buffer.
virtual void Clear() OVERRIDE;
// Reserves contiguous writable empty space in the buffer of size bytes.
// Since the point of this class is to have a fixed size buffer, be careful
// not to inadvertently resize the buffer using Reserve(). If the reserve
// size is <= BytesFree(), it is guaranteed that the buffer size will not
// change.
// This can be an expensive operation, it may new a buffer copy all existing
// data and delete the old data. Even if the existing buffer does not need
// to be resized, unread data may still need to be non-destructively copied
// to consolidate fragmented free space. If the size requested is less than
// or equal to BytesFree(), it is guaranteed that the buffer size will not
// change.
virtual bool Reserve(int size) OVERRIDE;
// Removes the oldest 'amount_to_advance' characters.
// If amount_to_consume > ReadableBytes(), this performs a Clear() instead.
virtual void AdvanceReadablePtr(int amount_to_advance) OVERRIDE;
// Moves the internal pointers around such that the amount of data specified
// here is expected to already be resident (as if it was Written).
virtual void AdvanceWritablePtr(int amount_to_advance) OVERRIDE;
int read_idx() const { return read_idx_; }
int write_idx() const { return write_idx_; }
int bytes_used() const { return bytes_used_; }
int buffer_size() const { return buffer_size_; }
const char* buffer() const { return buffer_.get(); }
int set_read_idx(int idx) { return read_idx_ = idx; }
int set_write_idx(int idx) { return write_idx_ = idx; }
scoped_ptr<char[]> buffer_;
int buffer_size_;
int bytes_used_;
int read_idx_;
int write_idx_;
RingBuffer(const RingBuffer&);
void operator=(const RingBuffer&);
} // namespace net