通过WCF扩展实现消息压缩
对于需要进行大规模数据传输的WCF应用来说，对于请求消息和回复消息进行传输前的压缩，不但可以降低网络流量，也可以提高网络传输的性能。由于WCF的扩展性，我们可以采用不同的方式实现对消息的压缩，本文提供一种比较简单的实现方式。[源代码从这里下载]一、三种可行的消息压缩方案
二、DataCompressor——用于数据压缩与解压缩组件
三、MessageCompressor——用于消息压缩与解压的组件
四、CompressionMessageFormatter——用于对请求/回复消息压缩和解压缩的组件
五、CompressionOperationBehaviorAttribute——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、补充说明
一、三种可行的消息压缩方案
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，我们具有三种典型的解决方案。
[*]通过自定义MessageEncoder和MessageEncodingBindingElement 来完成。具体的实现，可以参阅张玉彬的文章《WCF进阶:将编码后的字节流压缩传输》和MSDN的文章《Custom Message Encoder: Compression Encoder》。
[*]直接创建用于压缩和解压缩的信道，在CodePlex中具有这么一个WCF Extensions；
[*]自定义MessageFormatter实现序列化后的压缩和法序列化前的解压缩，这就是我们今天将要介绍的解决方案。
二、DataCompressor——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: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">public enum CompressionAlgorithm 2: { 3: GZip, 4: </s:Header></s:Header>Deflate 5: }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: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">internal class DataCompressor 2: { 3: public static byte[] Compress(byte[] decompressedData, CompressionAlgorithm algorithm) 4: </s:Header></s:Header>{ 5: <s:Body><s:Body> using (MemoryStream stream = new MemoryStream()) 6: { 7: </s:Body></s:Body> if (algorithm == CompressionAlgorithm.Deflate) 8: </s:Envelope></s:Envelope> { 9: GZipStream stream2 = new GZipStream(stream, CompressionMode.Compress, true); 10: stream2.Write(decompressedData, 0, decompressedData.Length); 11: stream2.Close(); 12: } 13: else 14: { 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: else 35: { 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; 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、MessageCompressor——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XML元素中（名称和命名空间分别为CompressedBody和http://www.artech.com/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: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">public class MessageCompressor 2:{ 3: public MessageCompressor(CompressionAlgorithm algorithm) 4: </s:Header></s:Header> { 5: <s:Body><s:Body> this.Algorithm = algorithm; 6: } 7: </s:Body></s:Body> public Message CompressMessage(Message sourceMessage) 8: </s:Envelope></s:Envelope> { 9: byte[] buffer; 10: using (XmlDictionaryReader reader1 = sourceMessage.GetReaderAtBodyContents()) 11: { 12: buffer = Encoding.UTF8.GetBytes(reader1.ReadOuterXml()); 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: XmlTextReader reader = new XmlTextReader(new StringReader(copressedBody), new NameTable()); 25: Message message2 = Message.CreateMessage(sourceMessage.Version, null, (XmlReader)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 newMessageXml = Encoding.UTF8.GetString(decompressedBody); 44: XmlTextReader reader2 = new XmlTextReader(new StringReader(newMessageXml)); 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: 51: public CompressionAlgorithm Algorithm { get; private set; } 52:}下面是针对Message类型而定义了一些扩展方法和辅助方法。
1: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">public static class CompressionUtil 2: { 3: public const string CompressionMessageHeader = "Compression"; 4: </s:Header></s:Header>public const string CompressionMessageBody = "CompressedBody"; 5: <s:Body><s:Body>public const string Namespace = "http://www.artech.com/compression"; 6: 7: </s:Body></s:Body>public static bool IsCompressed(this Message message) 8: </s:Envelope></s:Envelope> { 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 (XmlReader reader1 = message.GetReaderAtBodyContents()) 46: { 47: buffer = Convert.FromBase64String(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 (XmlWriter writer2 = XmlWriter.Create(output)) 56: { 57: writer2.WriteStartElement(CompressionMessageBody, Namespace); 58: writer2.WriteBase64(content, 0, content.Length); 59: writer2.WriteEndElement(); 60: } 61: return output.ToString(); 62: } 63: }四、CompressionMessageFormatter——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: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">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: <s:Body><s:Body>public IDispatchMessageFormatter InnerDispatchMessageFormatter { get; private set; } 6: public IClientMessageFormatter InnerClientMessageFormatter { get; private set; } 7: </s:Body></s:Body>public MessageCompressor MessageCompressor { get; private set; } 8: 9: public CompressionMessageFormatter(CompressionAlgorithm algorithm, OperationDescription description, DataContractFormatAttribute dataContractFormatAttribute, DataContractSerializerOperationBehavior serializerFactory) 10: { 11: this.MessageCompressor = new MessageCompressor(algorithm); 12: Type innerFormatterType = Type.GetType(DataContractSerializerOperationFormatterTypeName); 13: var innerFormatter = Activator.CreateInstance(innerFormatterType, description, dataContractFormatAttribute, serializerFactory); 14: this.InnerClientMessageFormatter = innerFormatter as IClientMessageFormatter; 15: this.InnerDispatchMessageFormatter = innerFormatter as IDispatchMessageFormatter; 16: } 17: 18: public void DeserializeRequest(Message message, object[] parameters) 19: { 20: message = this.MessageCompressor.DecompressMessage(message); 21: this.InnerDispatchMessageFormatter.DeserializeRequest(message, parameters); 22: } 23: 24: public Message SerializeReply(MessageVersion messageVersion, object[] parameters, object result) 25: { 26: var message = this.InnerDispatchMessageFormatter.SerializeReply(messageVersion, parameters, result); 27: return this.MessageCompressor.CompressMessage(message); 28: } 29: 30: public object DeserializeReply(Message message, object[] parameters) 31: { 32: message = this.MessageCompressor.DecompressMessage(message); 33: return this.InnerClientMessageFormatter.DeserializeReply(message, parameters); 34: } 35: 36: public Message SerializeRequest(MessageVersion messageVersion, object[] parameters) 37: { 38: var message = this.InnerClientMessageFormatter.SerializeRequest(messageVersion, parameters); 39: return this.MessageCompressor.CompressMessage(message); 40: } 41: }五、CompressionOperationBehaviorAttribute——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: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"> 2: public class CompressionOperationBehaviorAttribute: Attribute, IOperationBehavior 3: { 4: </s:Header></s:Header>public CompressionAlgorithm Algorithm { get; set; } 5: 6: public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters) { } 7: 8: </s:Envelope></s:Envelope> public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation) 9: { 10: clientOperation.SerializeRequest = true; 11: clientOperation.DeserializeReply = true; 12: var dataContractFormatAttribute = operationDescription.SyncMethod.GetCustomAttributes(typeof(DataContractFormatAttribute), true).FirstOrDefault() as DataContractFormatAttribute; 13: if (null == dataContractFormatAttribute) 14: { 15: dataContractFormatAttribute = new DataContractFormatAttribute(); 16: } 17: 18: var dataContractSerializerOperationBehavior = operationDescription.Behaviors.Find<DataContractSerializerOperationBehavior>(); 19: clientOperation.Formatter = new CompressionMessageFormatter(this.Algorithm, operationDescription, dataContractFormatAttribute, dataContractSerializerOperationBehavior); 20: } 21: 22: public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation) 23: { 24: dispatchOperation.SerializeReply = true; 25: dispatchOperation.DeserializeRequest = true; 26: var dataContractFormatAttribute = operationDescription.SyncMethod.GetCustomAttributes(typeof(DataContractFormatAttribute), true).FirstOrDefault() as DataContractFormatAttribute; 27: if (null == dataContractFormatAttribute) 28: { 29: dataContractFormatAttribute = new DataContractFormatAttribute(); 30: } 31: var dataContractSerializerOperationBehavior = operationDescription.Behaviors.Find<DataContractSerializerOperationBehavior>(); 32: dispatchOperation.Formatter = new CompressionMessageFormatter(this.Algorithm, operationDescription, dataContractFormatAttribute, dataContractSerializerOperationBehavior); 33: } 34: 35: public void Validate(OperationDescription operationDescription) { } 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: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"> 2: public interface ICalculator 3: { 4: </s:Header></s:Header> 5: <s:Body><s:Body> 6: double Add(double x, double y); 7: } 8: </s:Envelope></s:Envelope>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 xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"> 2: <s:Header><s:Header> 3: <Compression xmlns="http://www.artech.com/compression">algorithm = "GZip"</Compression> 4: </s:Header></s:Header> 5: <s:Body><s:Body> 6: <CompressedBody xmlns="http://www.artech.com/compression">7L0HYBx ... CQAA//8=</CompressedBody> 7: </s:Body></s:Body> 8: </s:Envelope></s:Envelope>回复消息
1: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"> 2: <s:Header><s:Header> 3: <Compression xmlns="http://www.artech.com/compression">algorithm = "GZip"</Compression> 4: </s:Header></s:Header> 5: <s:Body><s:Body> 6: <CompressedBody xmlns="http://www.artech.com/compression">7L0H...PAAAA//8=</CompressedBody> 7: </s:Body></s:Body> 8: </s:Envelope></s:Envelope>七、补充说明
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XmlSeriaizer）。为了让CompressionMessageFormatter能够使用其他序列化器，你可以对于进行相应的修正。
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