LengthPrefixMessageFramer.cs

// Copyright (c) 2012, Event Store LLP
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// 
// Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
// Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
// Neither the name of the Event Store LLP nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// 
using System;
using System.Collections.Generic;
using EventStore.Common.Utils;

namespace EventStore.Transport.Tcp.Framing
{

    /// <summary>
    /// Uses length-prefixed framing to encode outgoing messages and decode
    /// incoming messages, using internal state and raising a callback once 
    /// full message arrives.
    /// </summary>
    public class LengthPrefixMessageFramer : IMessageFramer
    {
        public const int HeaderLength = sizeof(Int32);
        
        private byte[] _messageBuffer;
        private int _bufferIndex = 0;
        private Action<ArraySegment<byte>> _receivedHandler;
        private readonly int _maxPackageSize;

        private int _headerBytes = 0;
        private int _packageLength = 0;

        /// <summary>
        /// Initializes a new instance of the <see cref="LengthPrefixMessageFramer"/> class.
        /// </summary>
        public LengthPrefixMessageFramer(int maxPackageSize = 64*1024*1024)
        {
            Ensure.Positive(maxPackageSize, "maxPackageSize");
            _maxPackageSize = maxPackageSize;
        }

        public void Reset()
        {
            _messageBuffer = null;
            _headerBytes = 0;
            _packageLength = 0;
            _bufferIndex = 0;
        }

        public void UnFrameData(IEnumerable<ArraySegment<byte>> data)
        {
            if (data == null) 
                throw new ArgumentNullException("data");

            foreach (ArraySegment<byte> buffer in data)
            {
                Parse(buffer);
            }
        }

        public void UnFrameData(ArraySegment<byte> data)
        {
            Parse(data);
        }
        /// <summary>
        /// Parses a stream chunking based on length-prefixed framing. 
        /// Calls are re-entrant and hold state internally. Once full message arrives,
        /// callback is raised (it is registered via <see cref="RegisterMessageArrivedCallback"/>
        /// </summary>
        /// <param name="bytes">A byte array of data to append</param>
        private void Parse(ArraySegment<byte> bytes)
        {
            byte[] data = bytes.Array;
            for (int i = bytes.Offset; i < bytes.Offset + bytes.Count; i++)
            {
                if (_headerBytes < HeaderLength)
                {
                    _packageLength |= (data[i] << (_headerBytes*8)); // little-endian order
                    ++_headerBytes;
                    if (_headerBytes == HeaderLength)
                    {
                        if (_packageLength <= 0 || _packageLength > _maxPackageSize)
                            throw new PackageFramingException(string.Format("Package size is out of bounds: {0} (max: {1}).", _packageLength, _maxPackageSize));

                        _messageBuffer = new byte[_packageLength];
                    }
                } 
                else
                {
                    int copyCnt = Math.Min(bytes.Count + bytes.Offset - i, _packageLength - _bufferIndex);
                    Buffer.BlockCopy(bytes.Array, i, _messageBuffer, _bufferIndex, copyCnt);
                    _bufferIndex += copyCnt;
                    i += copyCnt - 1;

                    if (_bufferIndex == _packageLength)
                    {
                        if (_receivedHandler != null)
                            _receivedHandler(new ArraySegment<byte>(_messageBuffer, 0, _bufferIndex));
                        _messageBuffer = null;
                        _headerBytes = 0;
                        _packageLength = 0;
                        _bufferIndex = 0;
                    }
                }
            }
        }

        public IEnumerable<ArraySegment<byte>> FrameData(ArraySegment<byte> data)
        {
            var length = data.Count;

            yield return new ArraySegment<byte>(
                new[] { (byte) length, (byte) (length >> 8), (byte) (length >> 16), (byte) (length >> 24) });
            yield return data;
        }

        public void RegisterMessageArrivedCallback(Action<ArraySegment<byte>> handler)
        {
            if (handler == null) 
                throw new ArgumentNullException("handler");

            _receivedHandler = handler;
        }
    }
}