对于WCF应用来说，传输前压缩请求消息和回复消息，不但可以降低网络流量，也可以提高网络传输的性能
一、消息压缩方案
二、用于数据压缩与解压缩组件
三、用于消息压缩与解压的组件
四、用于对请求/回复消息压缩和解压缩的组件
五、将CompressionMessageFormatter用于WCF运行时框架的操作行为
六、查看结构压缩后的消息
七、扩展
一、消息压缩方案
消息压缩在WCF中的实现其实很简单，我们只需要在消息（请求消息/回复消息）被序列化之后，发送之前进行压缩；在接收之后，反序列化之前进行解压缩即可。针对压缩/解压缩使用的时机，有三种典型的解决方案。通过自定义MessageEncoder和MessageEncodingBindingElement 来完成。
1.将编码后的字节流压缩传输
2.创建用于压缩和解压缩的信道
3. 自定义MessageFormatter实现序列化后的压缩和法序列化前的解压缩
这里要介绍的解决方案3。
二、用于数据压缩与解压缩组件
我们支持两种方式的压缩，Dflate和GZip。两种不同的压缩算法通过如下定义的CompressionAlgorithm枚举表示。
1 public enum CompressionAlgorithm2 {3 GZip,4 Deflate5 }
而如下定义的DataCompressor负责基于上述两种压缩算法实际上的压缩和解压缩工作。
1 internal class DataCompressor 2 { 3 public static byte[] Compress(byte[] decompressedData, CompressionAlgorithm algorithm) 4 { 5 using (MemoryStream stream = new MemoryStream()) 6 { 7 if (algorithm == CompressionAlgorithm.Deflate) 8 { 9 GZipStream stream2 = new GZipStream(stream, CompressionMode.Compress, true);10 stream2.Write(decompressedData, 0, decompressedData.Length);11 stream2.Close();12 }13 else14 {15 DeflateStream stream3 = new DeflateStream(stream, CompressionMode.Compress, true);16 stream3.Write(decompressedData, 0, decompressedData.Length);17 stream3.Close();18 }19 return stream.ToArray();20 }21 }22 23 public static byte[] Decompress(byte[] compressedData, CompressionAlgorithm algorithm)24 {25 using (MemoryStream stream = new MemoryStream(compressedData))26 {27 if (algorithm == CompressionAlgorithm.Deflate)28 {29 using (GZipStream stream2 = new GZipStream(stream, CompressionMode.Decompress))30 {31 return LoadToBuffer(stream2);32 }33 }34 else35 {36 using (DeflateStream stream3 = new DeflateStream(stream, CompressionMode.Decompress))37 {38 return LoadToBuffer(stream3);39 }40 }41 }42 }43 44 private static byte[] LoadToBuffer(Stream stream)45 {46 using (MemoryStream stream2 = new MemoryStream())47 {48 int num;49 byte[] buffer = new byte[0x400];50 while ((num = stream.Read(buffer, 0, buffer.Length)) > 0)51 {52 stream2.Write(buffer, 0, num);53 }54 return stream2.ToArray();55 }56 }57 }
三、用于消息压缩与解压的组件
而针对消息的压缩和解压缩通过如下一个MessageCompressor来完成。具体来说，我们通过上面定义的DataCompressor对消息的主体部分内容进行压缩，并将压缩后的内容存放到一个预定义的 元素中（名称和命名空间分别为CompressedBody和http://www.yswenli.net/comporession/），同时添加相应的MessageHeader表示消息经过了压缩，以及采用的压缩算法。对于解压缩，则是通过消息是否具有相应的MessageHeader判断该消息是否经过压缩，如果是则根据相应的算法对其进行解压缩。
具体的实现如下：
1 public class MessageCompressor 2 { 3 public MessageCompressor(CompressionAlgorithm algorithm) 4 { 5 this.Algorithm = algorithm; 6 } 7 public Message CompressMessage(Message sourceMessage) 8 { 9 byte[] buffer;10 using ( DictionaryReader reader1 = sourceMessage.GetReaderAtBodyContents())11 {12 buffer = Encoding.UTF8.GetBytes(reader1.ReadOuter ());13 }14 if (buffer.Length == 0)15 {16 Message emptyMessage = Message.CreateMessage(sourceMessage.Version, (string)null);17 sourceMessage.Headers.CopyHeadersFrom(sourceMessage);18 sourceMessage.Properties.CopyProperties(sourceMessage.Properties);19 emptyMessage.Close();20 return emptyMessage;21 }22 byte[] compressedData = DataCompressor.Compress(buffer, this.Algorithm);23 string copressedBody = CompressionUtil.CreateCompressedBody(compressedData);24 TextReader reader = new TextReader(new StringReader(copressedBody), new Na ble());25 Message message2 = Message.CreateMessage(sourceMessage.Version, null, ( Reader)reader);26 message2.Headers.CopyHeadersFrom(sourceMessage);27 message2.Properties.CopyProperties(sourceMessage.Properties);28 message2.AddCompressionHeader(this.Algorithm);29 sourceMessage.Close();30 return message2;31 }32 33 public Message DecompressMessage(Message sourceMessage)34 {35 if (!sourceMessage.IsCompressed())36 {37 return sourceMessage;38 }39 CompressionAlgorithm algorithm = sourceMessage.GetCompressionAlgorithm();40 sourceMessage.RemoveCompressionHeader();41 byte[] compressedBody = sourceMessage.GetCompressedBody();42 byte[] decompressedBody = DataCompressor.Decompress(compressedBody, algorithm);43 string newMessage = Encoding.UTF8.GetString(decompressedBody);44 TextReader reader2 = new TextReader(new StringReader(newMessage ));45 Message newMessage = Message.CreateMessage(sourceMessage.Version, null, reader2);46 newMessage.Headers.CopyHeadersFrom(sourceMessage);47 newMessage.Properties.CopyProperties(sourceMessage.Properties);48 return newMessage;49 }50 public CompressionAlgorithm Algorithm { get; private set; }51 }
下面是针对Message类型而定义了一些扩展方法和辅助方法。
1 public static class CompressionUtil 2 { 3 public const string CompressionMessageHeader = "Compression"; 4 public const string CompressionMessageBody = "CompressedBody"; 5 public const string Namespace = "http://www.yswenli.net/compression"; 6 7 public static bool IsCompressed(this Message message) 8 { 9 return message.Headers.FindHeader(CompressionMessageHeader, Namespace) > -1;10 }11 12 public static void AddCompressionHeader(this Message message, CompressionAlgorithm algorithm)13 {14 message.Headers.Add(MessageHeader.CreateHeader(CompressionMessageHeader, Namespace, string.Format("algorithm = "{0}"", algorithm)));15 }16 17 public static void RemoveCompressionHeader(this Message message)18 {19 message.Headers.RemoveAll(CompressionMessageHeader, Namespace);20 }21 22 public static CompressionAlgorithm GetCompressionAlgorithm(this Message message)23 {24 if (message.IsCompressed())25 {26 var algorithm = message.Headers.GetHeader<string>(CompressionMessageHeader, Namespace);27 algorithm = algorithm.Replace("algorithm =", string.Empty).Replace(""", string.Empty).Trim();28 if (algorithm == CompressionAlgorithm.Deflate.ToString())29 {30 return CompressionAlgorithm.Deflate;31 }32 33 if (algorithm == CompressionAlgorithm.GZip.ToString())34 {35 return CompressionAlgorithm.GZip;36 }37 throw new InvalidOperationException("Invalid compression algrorithm!");38 }39 throw new InvalidOperationException("Message is not compressed!");40 }41 42 public static byte[] GetCompressedBody(this Message message)43 {44 byte[] buffer;45 using ( Reader reader1 = message.GetReaderAtBodyContents())46 {47 buffer = Convert.From 64String(reader1.ReadElementString(CompressionMessageBody, Namespace));48 }49 return buffer;50 }51 52 public static string CreateCompressedBody(byte[] content)53 {54 StringWriter output = new StringWriter();55 using ( Writer writer2 = Writer.Create(output))56 {57 writer2.WriteStartElement(CompressionMessageBody, Namespace);58 writer2.Write 64(content, 0, content.Length);59 writer2.WriteEndElement();60 }61 return output.ToString();62 }63 }
四、用于对请求/回复消息压缩和解压缩的组件
消息的序列化和反序列化最终是通过MessageFormatter来完成的。具体来说，客户端通过ClientMessageFormatter实现对请求消息的序列化和对回复消息的序列化，而服务端通过DispatchMessageFormatter实现对请求消息的反序列化和对回复消息的序列化。
在默认的情况下，WCF选用的MessageFormatter为DataContractSerializerOperationFormatter，它采用DataContractSerializer进行实际的序列化和法序列化操作。我们自定义的MessageFormatter实际上是对DataContractSerializerOperationFormatter的封装，我们依然使用它来完成序列化和反序列化工作，额外实现序列化后的压缩和法序列化前的解压缩。
因为DataContractSerializerOperationFormatter是一个internal类型，我们只有通过反射的方式来创建它。如下的代码片断为用于进行消息压缩与解压缩的自定义MessageFormatter，即CompressionMessageFormatter的定义。
1 public class CompressionMessageFormatter : IDispatchMessageFormatter, IClientMessageFormatter 2 { 3 private const string DataContractSerializerOperationFormatterTypeName = "System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter, System.ServiceModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"; 4 5 public IDispatchMessageFormatter InnerDispatchMessageFormatter { get; private set; } 6 public IClientMessageFormatter InnerClientMessageFormatter { get; private set; } 7 public MessageCompressor MessageCompressor { get; private set; } 8 9 public CompressionMessageFormatter(CompressionAlgorithm algorithm, OperationDe ion de ion, DataContractFormatAttribute dataContractFormatAttribute, DataContractSerializerOperationBehavior serializerFactory)10 {11 this.MessageCompressor = new MessageCompressor(algorithm);12 Type innerFormatterType = Type.GetType(DataContractSerializerOperationFormatterTypeName);13 var innerFormatter = Activator.CreateInstance(innerFormatterType, de ion, dataContractFormatAttribute, serializerFactory);14 this.InnerClientMessageFormatter = innerFormatter as IClientMessageFormatter;15 this.InnerDispatchMessageFormatter = innerFormatter as IDispatchMessageFormatter;16 }17 18 public void DeserializeRequest(Message message, [] parameters)19 {20 message = this.MessageCompressor.DecompressMessage(message);21 this.InnerDispatchMessageFormatter.DeserializeRequest(message, parameters);22 }23 24 public Message SerializeReply(MessageVersion messageVersion, [] parameters, result)25 {26 var message = this.InnerDispatchMessageFormatter.SerializeReply(messageVersion, parameters, result);27 return this.MessageCompressor.CompressMessage(message);28 }29 30 public DeserializeReply(Message message, [] parameters)31 {32 message = this.MessageCompressor.DecompressMessage(message);33 return this.InnerClientMessageFormatter.DeserializeReply(message, parameters);34 }35 36 public Message SerializeRequest(MessageVersion messageVersion, [] parameters)37 {38 var message = this.InnerClientMessageFormatter.SerializeRequest(messageVersion, parameters);39 return this.MessageCompressor.CompressMessage(message);40 }41 }
五、将CompressionMessageFormatter用于WCF运行时框架的操作行为
ClientMessageFormatter和DispatchMessageFormatter实际上属于ClientOperation和DispatchOperation的组件。我们可以通过如下一个自定义的操作行为CompressionOperationBehaviorAttribute将其应用到相应的操作上。
1 [AttributeUsage(AttributeTargets.Method)] 2 public class CompressionOperationBehaviorAttribute : Attribute, IOperationBehavior 3 { 4 public CompressionAlgorithm Algorithm { get; set; } 5 6 public void AddBindingParameters(OperationDe ion operationDe ion, BindingParameterCollection bindingParameters) { } 7 8 public void ApplyClientBehavior(OperationDe ion operationDe ion, ClientOperation clientOperation) 9 {10 clientOperation.SerializeRequest = true;11 clientOperation.DeserializeReply = true;12 var dataContractFormatAttribute = operationDe ion.SyncMethod.GetCustomAttributes(typeof(DataContractFormatAttribute), true).FirstOrDefault() as DataContractFormatAttribute;13 if (null == dataContractFormatAttribute)14 {15 dataContractFormatAttribute = new DataContractFormatAttribute();16 }17 18 var dataContractSerializerOperationBehavior = operationDe ion.Behaviors.Find<DataContractSerializerOperationBehavior>();19 clientOperation.Formatter = new CompressionMessageFormatter(this.Algorithm, operationDe ion, dataContractFormatAttribute, dataContractSerializerOperationBehavior);20 }21 22 public void ApplyDispatchBehavior(OperationDe ion operationDe ion, DispatchOperation dispatchOperation)23 {24 dispatchOperation.SerializeReply = true;25 dispatchOperation.DeserializeRequest = true;26 var dataContractFormatAttribute = operationDe ion.SyncMethod.GetCustomAttributes(typeof(DataContractFormatAttribute), true).FirstOrDefault() as DataContractFormatAttribute;27 if (null == dataContractFormatAttribute)28 {29 dataContractFormatAttribute = new DataContractFormatAttribute();30 }31 var dataContractSerializerOperationBehavior = operationDe ion.Behaviors.Find<DataContractSerializerOperationBehavior>();32 dispatchOperation.Formatter = new CompressionMessageFormatter(this.Algorithm, operationDe ion, dataContractFormatAttribute, dataContractSerializerOperationBehavior);33 }34 35 public void Validate(OperationDe ion operationDe ion) { }36 }
六、查看结构压缩后的消息
为了验证应用了CompressionOperationBehaviorAttribute特性的操作方法对应的消息是否经过了压缩，我们可以通过一个简单的例子来检验。我们采用常用的计算服务的例子，下面是服务契约和服务类型的定义。我们上面定义的CompressionOperationBehaviorAttribute应用到服务契约的Add操作上。
1 [ServiceContract(Namespace = "http://www.yswenli.net/")] 2 public interface ICalculator 3 { 4 [OperationContract] 5 [CompressionOperationBehavior] 6 double Add(double x, double y); 7 } 8 public class CalculatorService : ICalculator 9 {10 public double Add(double x, double y)11 {12 return x + y;13 }14 }
我们采用BasicHttpBinding作为终结点的绑定类型（具体的配置请查看源代码），下面是通过Fiddler获取的消息的内容，它们的主体部分都经过了基于压缩的编码。
1 <s:Envelope ns:s="http://schemas. soap.org/soap/envelope/">2 <s:Header>3 <Compression ns="http://www.yswenli.net/compression">algorithm = "GZip"</Compression>4 </s:Header>5 <s:Body>6 <CompressedBody ns="http://www.yswenli.net/compression">7L0HYBx ... CQAA//8=</CompressedBody>7 </s:Body>8 </s:Envelope>
回复消息
1 <s:Envelope ns:s="http://schemas. soap.org/soap/envelope/">2 <s:Header>3 <Compression ns="http://www.yswenli.net/compression">algorithm = "GZip"</Compression>4 </s:Header>5 <s:Body>6 <CompressedBody ns="http://www.yswenli.net/compression">7L0H...PAAAA//8=</CompressedBody>7 </s:Body>8 </s:Envelope>
七、扩展
如果不想使微软自带的序列化或者因为某些原因（emoji字符异常等）可以使用自定义的IDispatchMessageInspector。由于CompressionMessageFormatter使用基于DataContractSerializer序列化器的DataContractSerializerOperationFormatter进行消息的序列化和发序列化工作，而DataContractSerializer仅仅是WCF用于序列化的一种默认的选择（WCF还可以采用传统的 Seriaizer）；为了让CompressionMessageFormatter能够使用其他序列化器，可以对于进行相应的修正。
转载请标明本文来源：http://www.cnblogs.com/yswenli/p/6670081.html
更多内容欢迎我的的github：https://github.com/yswenli
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