本文及程序不是介紹WCF怎麼用，而是研究如何在WCF通信時的通道兩端自動進行數據壓縮和解壓縮，從而增加分佈式數據傳輸速度。
而且，這個過程是完全透明的，用戶及編程人員根本不需要知道它的存在，相當於HOOK在兩端的一個組件。可以使用中網絡帶寬較小
的網絡環境中。當WCF在兩個實體間通訊的時候，便自動創建一個信息通道轉接通訊，這個消息包含數據請求和相應。WCF使用特殊的
編碼器將請求和響應數據轉換成一系列的字節。
我所帶的項目裏遇到大文件分佈式傳輸問題，經過分析考慮採用WCF通道壓縮技術來解決此問題。執行這樣的編碼是需要傳輸大文件（XML格式）由一臺機器到另一臺機器傳輸，而連接有速度限制。經過查看了一些國外英文網站，發現我不用寫一個特殊的函數邊壓縮和邊解壓，而是配置傳輸通道可以做到這一點，這種方式壓縮可重複使用的任何契約。我發現自己編寫的消息編碼器是最簡單的方式來實現功能，真正的問題是如何編寫信息編碼器，在MSDN上沒有找到任何關於此應用的實例。消息契約編碼器的想法是Hook連接兩端發送和接收信息的渠道。程序是採用Microsoft Visual Studio 2008 WCF設計。
圖1 WCF消息通道編碼過程時序圖
發送方：代碼中加入方法，該方法及其參數的序列化成SOAP消息，消息編碼序列化的信息將成爲一個字節數組，字節數組發送傳輸層。
接收方：傳輸層接收字節數組，消息編碼器並行化字節數組到一條消息，該方法及其參數並行化到一個SOAP消息，方法是被監聽的。 當加入壓縮信息編碼器，該方法要求有一點改變：發送方：代碼中加入方法，該方法及其參數的序列化成SOAP消息，消息契約編碼讓其內在的信息編碼序列的信息成爲一個字節數組，消息契約編碼壓縮的字節數組第二個字節數組，字節數組發送傳輸層。
接收方：傳輸層接收字節數組，消息契約編碼的字節數組解壓到第二字節數組，消息契約編碼讓其內在的信息編碼化的第二個字節數組消息，該方法及其參並行化到SOAP消息，方法是被監聽的。
這個消息契約編碼分爲幾個類：
CompactMessageEncoder //這個類提供了信息編碼實施。
CompactMessageEncoderFactory //這個類是負責提供契約信息編碼實例。
CompactMessageEncodingBindingElement //這個類負責通道的協議約束規範。
CompactMessageEncodingElement //這個類使信息編碼通過增加應用程序配置文件。
圖2 消息通道編碼器靜態類圖
壓縮方法：契約消息編碼器是使用gzip壓縮的NET Framework範圍內執行的，是調用System.IO.Compression.GZipStream名字空間類中。
加入引用CompactMessageEncoder.dll，修改app.config文件引用，應用程序必須要在客戶端和服務器端。
壓縮緩衝代碼：
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;
}
解壓緩衝代碼：
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;
}
改變服務端配置
加入消息契約編碼器之前app.config的實例：
<?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>
加入消息契約編碼器後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>
客戶端配置變化
加入消息契約編碼器之前app.config的實例：
Code
加入消息契約編碼器後app.config的例子：
Code這種壓縮方法，消息堵塞的機率很小。使用CompactMessageEncoder在同一臺機器運行客戶端和服務器上可能會降低效率。