本文及程序不是介绍WCF怎么用，而是研究如何在WCF通信时的通道两端自动进行数据压缩和解压缩，从而增加分布式数据传输速度。
而且，这个过程是完全透明的，用户及编程人员根本不需要知道它的存在，相当于HOOK在两端的一个组件。可以使用中网络带宽较小
的网络环境中。当WCF在两个实体间通讯的时候，便自动创建一个信息通道转接通讯，这个消息包含数据请求和相应。WCF使用特殊的
编码器将请求和响应数据转换成一系列的字节。
我所带的项目里遇到大文件分布式传输问题，经过分析考虑采用WCF通道压缩技术来解决此问题。执行这样的编码是需要传输大文件（XML格式）由一台机器到另一台机器传输，而连接有速度限制。经过查看了一些国外英文网站，发现我不用写一个特殊的函数边压缩和边解压，而是配置传输通道可以做到这一点，这种方式压缩可重复使用的任何契约。我发现自己编写的消息编码器是最简单的方式来实现功能，真正的问题是如何编写信息编码器，在MSDN上没有找到任何关于此应用的实例。消息契约编码器的想法是Hook连接两端发送和接收信息的渠道。程序是采用Microsoft Visual Studio 2008 WCF设计。
图1 WCF消息通道编码过程时序图
发送方：代码中加入方法，该方法及其参数的序列化成SOAP消息，消息编码序列化的信息将成为一个字节数组，字节数组发送传输层。
接收方：传输层接收字节数组，消息编码器并行化字节数组到一条消息，该方法及其参数并行化到一个SOAP消息，方法是被监听的。 当加入压缩信息编码器，该方法要求有一点改变：发送方：代码中加入方法，该方法及其参数的序列化成SOAP消息，消息契约编码让其内在的信息编码序列的信息成为一个字节数组，消息契约编码压缩的字节数组第二个字节数组，字节数组发送传输层。
接收方：传输层接收字节数组，消息契约编码的字节数组解压到第二字节数组，消息契约编码让其内在的信息编码化的第二个字节数组消息，该方法及其参并行化到SOAP消息，方法是被监听的。
这个消息契约编码分为几个类：
CompactMessageEncoder //这个类提供了信息编码实施。
CompactMessageEncoderFactory //这个类是负责提供契约信息编码实例。
CompactMessageEncodingBindingElement //这个类负责通道的协议约束规范。
CompactMessageEncodingElement //这个类使信息编码通过增加应用程序配置文件。
图2 消息通道编码器静态类图
压缩方法：契约消息编码器是使用gzip压缩的NET Framework范围内执行的，是调用System.IO.Compression.GZipStream名字空间类中。
加入引用CompactMessageEncoder.dll，修改app.config文件引用，应用程序必须要在客户端和服务器端。
压缩缓冲代码：
private static ArraySegment<byte> CompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager, int messageOffset)
{
// Create a memory stream for the final message
MemoryStream memoryStream = new MemoryStream();
// Copy the bytes that should not be compressed into the stream
memoryStream.Write(buffer.Array, 0, messageOffset);
// Compress the message into the stream
using (GZipStream gzStream = new GZipStream(memoryStream, CompressionMode.Compress, true))
{
gzStream.Write(buffer.Array, messageOffset, buffer.Count);
}
// Convert the stream into a bytes array
byte[] compressedBytes = memoryStream.ToArray();
// Allocate a new buffer to hold the new bytes array
byte[] bufferedBytes = bufferManager.TakeBuffer(compressedBytes.Length);
// Copy the compressed data into the allocated buffer
Array.Copy(compressedBytes, 0, bufferedBytes, 0, compressedBytes.Length);
// Release the original buffer we got as an argument
bufferManager.ReturnBuffer(buffer.Array);
// Create a new ArraySegment that points to the new message buffer
ArraySegment<byte> byteArray = new ArraySegment<byte>(bufferedBytes, messageOffset, compressedBytes.Length - messageOffset);
return byteArray;
}
{
// Create a memory stream for the final message
MemoryStream memoryStream = new MemoryStream();
// Copy the bytes that should not be compressed into the stream
memoryStream.Write(buffer.Array, 0, messageOffset);
// Compress the message into the stream
using (GZipStream gzStream = new GZipStream(memoryStream, CompressionMode.Compress, true))
{
gzStream.Write(buffer.Array, messageOffset, buffer.Count);
}
// Convert the stream into a bytes array
byte[] compressedBytes = memoryStream.ToArray();
// Allocate a new buffer to hold the new bytes array
byte[] bufferedBytes = bufferManager.TakeBuffer(compressedBytes.Length);
// Copy the compressed data into the allocated buffer
Array.Copy(compressedBytes, 0, bufferedBytes, 0, compressedBytes.Length);
// Release the original buffer we got as an argument
bufferManager.ReturnBuffer(buffer.Array);
// Create a new ArraySegment that points to the new message buffer
ArraySegment<byte> byteArray = new ArraySegment<byte>(bufferedBytes, messageOffset, compressedBytes.Length - messageOffset);
return byteArray;
}
解压缓冲代码：
Code
private static ArraySegment<byte> DecompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager)
{
// Create a new memory stream, and copy into it the buffer to decompress
MemoryStream memoryStream = new MemoryStream(buffer.Array, buffer.Offset, buffer.Count);
// Create a memory stream to store the decompressed data
MemoryStream decompressedStream = new MemoryStream();
// The totalRead stores the number of decompressed bytes
int totalRead = 0;
int blockSize = 1024;
// Allocate a temporary buffer to use with the decompression
byte[] tempBuffer = bufferManager.TakeBuffer(blockSize);
// Uncompress the compressed data
using (GZipStream gzStream = new GZipStream(memoryStream, CompressionMode.Decompress))
{
while (true)
{
// Read from the compressed data stream
int bytesRead = gzStream.Read(tempBuffer, 0, blockSize);
if (bytesRead == 0)
break;
// Write to the decompressed data stream
decompressedStream.Write(tempBuffer, 0, bytesRead);
totalRead += bytesRead;
}
}
// Release the temporary buffer
bufferManager.ReturnBuffer(tempBuffer);
// Convert the decompressed data stream into bytes array
byte[] decompressedBytes = decompressedStream.ToArray();
// Allocate a new buffer to store the message
byte[] bufferManagerBuffer = bufferManager.TakeBuffer(decompressedBytes.Length + buffer.Offset);
// Copy the bytes that comes before the compressed message in the buffer argument
Array.Copy(buffer.Array, 0, bufferManagerBuffer, 0, buffer.Offset);
// Copy the decompressed data
Array.Copy(decompressedBytes, 0, bufferManagerBuffer, buffer.Offset, decompressedBytes.Length);
// Create a new ArraySegment that points to the new message buffer
ArraySegment<byte> byteArray = new ArraySegment<byte>(bufferManagerBuffer, buffer.Offset, decompressedBytes.Length);
// Release the original message buffer
bufferManager.ReturnBuffer(buffer.Array);
return byteArray;
}
private static ArraySegment<byte> DecompressBuffer(ArraySegment<byte> buffer, BufferManager bufferManager)
{
// Create a new memory stream, and copy into it the buffer to decompress
MemoryStream memoryStream = new MemoryStream(buffer.Array, buffer.Offset, buffer.Count);
// Create a memory stream to store the decompressed data
MemoryStream decompressedStream = new MemoryStream();
// The totalRead stores the number of decompressed bytes
int totalRead = 0;
int blockSize = 1024;
// Allocate a temporary buffer to use with the decompression
byte[] tempBuffer = bufferManager.TakeBuffer(blockSize);
// Uncompress the compressed data
using (GZipStream gzStream = new GZipStream(memoryStream, CompressionMode.Decompress))
{
while (true)
{
// Read from the compressed data stream
int bytesRead = gzStream.Read(tempBuffer, 0, blockSize);
if (bytesRead == 0)
break;
// Write to the decompressed data stream
decompressedStream.Write(tempBuffer, 0, bytesRead);
totalRead += bytesRead;
}
}
// Release the temporary buffer
bufferManager.ReturnBuffer(tempBuffer);
// Convert the decompressed data stream into bytes array
byte[] decompressedBytes = decompressedStream.ToArray();
// Allocate a new buffer to store the message
byte[] bufferManagerBuffer = bufferManager.TakeBuffer(decompressedBytes.Length + buffer.Offset);
// Copy the bytes that comes before the compressed message in the buffer argument
Array.Copy(buffer.Array, 0, bufferManagerBuffer, 0, buffer.Offset);
// Copy the decompressed data
Array.Copy(decompressedBytes, 0, bufferManagerBuffer, buffer.Offset, decompressedBytes.Length);
// Create a new ArraySegment that points to the new message buffer
ArraySegment<byte> byteArray = new ArraySegment<byte>(bufferManagerBuffer, buffer.Offset, decompressedBytes.Length);
// Release the original message buffer
bufferManager.ReturnBuffer(buffer.Array);
return byteArray;
}
改变服务端配置
加入消息契约编码器之前app.config的实例：
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.serviceModel>
<services>
<service name="Server.MyService">
<endpoint
address="net.tcp://localhost:1234/MyService"
binding="netTcpBinding"
contract="Server.IMyService" />
</service>
</services>
</system.serviceModel>
</configuration>
<configuration>
<system.serviceModel>
<services>
<service name="Server.MyService">
<endpoint
address="net.tcp://localhost:1234/MyService"
binding="netTcpBinding"
contract="Server.IMyService" />
</service>
</services>
</system.serviceModel>
</configuration>
加入消息契约编码器后app.config的例子：
Code
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.serviceModel>
<services>
<service name="Server.MyService">
<!-- Set the binding of the endpoint to customBinding -->
<endpoint
address="net.tcp://localhost:1234/MyService"
binding="customBinding"
contract="Server.IMyService" />
</service>
</services>
<!-- Defines a new customBinding that contains the compactMessageEncoding -->
<bindings>
<customBinding>
<binding name="compactBinding">
<compactMessageEncoding>
<!-- Defines the inner message encoder as binary encoder -->
<binaryMessageEncoding />
</compactMessageEncoding>
<tcpTransport />
</binding>
</customBinding>
</bindings>
<!-- Adds the extension dll so the WCF can find the compactMessageEncoding -->
<extensions>
<bindingElementExtensions>
<add name="compactMessageEncoding" type="Amib.WCF.CompactMessageEncodingElement, CompactMessageEncoder, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
</bindingElementExtensions>
</extensions>
</system.serviceModel>
</configuration>
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<system.serviceModel>
<services>
<service name="Server.MyService">
<!-- Set the binding of the endpoint to customBinding -->
<endpoint
address="net.tcp://localhost:1234/MyService"
binding="customBinding"
contract="Server.IMyService" />
</service>
</services>
<!-- Defines a new customBinding that contains the compactMessageEncoding -->
<bindings>
<customBinding>
<binding name="compactBinding">
<compactMessageEncoding>
<!-- Defines the inner message encoder as binary encoder -->
<binaryMessageEncoding />
</compactMessageEncoding>
<tcpTransport />
</binding>
</customBinding>
</bindings>
<!-- Adds the extension dll so the WCF can find the compactMessageEncoding -->
<extensions>
<bindingElementExtensions>
<add name="compactMessageEncoding" type="Amib.WCF.CompactMessageEncodingElement, CompactMessageEncoder, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" />
</bindingElementExtensions>
</extensions>
</system.serviceModel>
</configuration>
客户端配置变化
加入消息契约编码器之前app.config的实例：
加入消息契约编码器后app.config的例子：
这种压缩方法，消息堵塞的几率很小。使用CompactMessageEncoder在同一台机器运行客户端和服务器上可能会降低效率。