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
复制代码 - 4: </s:Header></s:Header> Deflate
复制代码 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
复制代码 - 3: public static byte[] Compress(byte[] decompressedData, CompressionAlgorithm algorithm)
复制代码 - 4: </s:Header></s:Header> {
复制代码 - 5: <s:Body><s:Body> using (MemoryStream stream = new MemoryStream())
复制代码 - 7: </s:Body></s:Body> if (algorithm == CompressionAlgorithm.Deflate)
复制代码 - 8: </s:Envelope></s:Envelope> {
复制代码 - 9: GZipStream stream2 = new GZipStream(stream, CompressionMode.Compress, true);
复制代码 - 10: stream2.Write(decompressedData, 0, decompressedData.Length);
复制代码 - 15: DeflateStream stream3 = new DeflateStream(stream, CompressionMode.Compress, true);
复制代码 - 16: stream3.Write(decompressedData, 0, decompressedData.Length);
复制代码 - 19: return stream.ToArray();
复制代码 - 23: public static byte[] Decompress(byte[] compressedData, CompressionAlgorithm algorithm)
复制代码 - 25: using (MemoryStream stream = new MemoryStream(compressedData))
复制代码 - 27: if (algorithm == CompressionAlgorithm.Deflate)
复制代码 - 29: using (GZipStream stream2 = new GZipStream(stream, CompressionMode.Decompress))
复制代码 - 31: return LoadToBuffer(stream2);
复制代码 - 36: using (DeflateStream stream3 = new DeflateStream(stream, CompressionMode.Decompress))
复制代码 - 38: return LoadToBuffer(stream3);
复制代码 - 44: private static byte[] LoadToBuffer(Stream stream)
复制代码 - 46: using (MemoryStream stream2 = new MemoryStream())
复制代码 - 49: byte[] buffer = new byte[0x400];
复制代码 - 50: while ((num = stream.Read(buffer, 0, buffer.Length)) > 0)
复制代码 - 52: stream2.Write(buffer, 0, num);
复制代码 - 54: return stream2.ToArray();
复制代码 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
复制代码 - 3: public MessageCompressor(CompressionAlgorithm algorithm)
复制代码 - 4: </s:Header></s:Header> {
复制代码 - 5: <s:Body><s:Body> this.Algorithm = algorithm;
复制代码 - 7: </s:Body></s:Body> public Message CompressMessage(Message sourceMessage)
复制代码 - 8: </s:Envelope></s:Envelope> {
复制代码 - 10: using (XmlDictionaryReader reader1 = sourceMessage.GetReaderAtBodyContents())
复制代码 - 12: buffer = Encoding.UTF8.GetBytes(reader1.ReadOuterXml());
复制代码 - 14: if (buffer.Length == 0)
复制代码 - 16: Message emptyMessage = Message.CreateMessage(sourceMessage.Version, (string)null);
复制代码 - 17: sourceMessage.Headers.CopyHeadersFrom(sourceMessage);
复制代码 - 18: sourceMessage.Properties.CopyProperties(sourceMessage.Properties);
复制代码 - 19: emptyMessage.Close();
复制代码 - 22: byte[] compressedData = DataCompressor.Compress(buffer, this.Algorithm);
复制代码 - 23: string copressedBody = CompressionUtil.CreateCompressedBody(compressedData);
复制代码 - 24: XmlTextReader reader = new XmlTextReader(new StringReader(copressedBody), new NameTable());
复制代码 - 25: Message message2 = Message.CreateMessage(sourceMessage.Version, null, (XmlReader)reader);
复制代码 - 26: message2.Headers.CopyHeadersFrom(sourceMessage);
复制代码 - 27: message2.Properties.CopyProperties(sourceMessage.Properties);
复制代码 - 28: message2.AddCompressionHeader(this.Algorithm);
复制代码 - 29: sourceMessage.Close();
复制代码 - 33: public Message DecompressMessage(Message sourceMessage)
复制代码 - 35: if (!sourceMessage.IsCompressed())
复制代码 - 37: return sourceMessage;
复制代码 - 39: CompressionAlgorithm algorithm = sourceMessage.GetCompressionAlgorithm();
复制代码 - 40: sourceMessage.RemoveCompressionHeader();
复制代码 - 41: byte[] compressedBody = sourceMessage.GetCompressedBody();
复制代码 - 42: byte[] decompressedBody = DataCompressor.Decompress(compressedBody, algorithm);
复制代码 - 43: string newMessageXml = Encoding.UTF8.GetString(decompressedBody);
复制代码 - 44: XmlTextReader reader2 = new XmlTextReader(new StringReader(newMessageXml));
复制代码 - 45: Message newMessage = Message.CreateMessage(sourceMessage.Version, null, reader2);
复制代码 - 46: newMessage.Headers.CopyHeadersFrom(sourceMessage);
复制代码 - 47: newMessage.Properties.CopyProperties(sourceMessage.Properties);
复制代码 - 51: public CompressionAlgorithm Algorithm { get; private set; }
复制代码 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
复制代码 - 3: public const string CompressionMessageHeader = "Compression";
复制代码 - 4: </s:Header></s:Header> public const string CompressionMessageBody = "CompressedBody";
复制代码 - 5: <s:Body><s:Body> public const string Namespace = "http://www.artech.com/compression";
复制代码 - 7: </s:Body></s:Body> public static bool IsCompressed(this Message message)
复制代码 - 8: </s:Envelope></s:Envelope> {
复制代码 - 9: return message.Headers.FindHeader(CompressionMessageHeader, Namespace) > -1;
复制代码 - 12: public static void AddCompressionHeader(this Message message, CompressionAlgorithm algorithm)
复制代码 - 14: message.Headers.Add(MessageHeader.CreateHeader(CompressionMessageHeader, Namespace, string.Format("algorithm = "{0}"",algorithm)));
复制代码 - 17: public static void RemoveCompressionHeader(this Message message)
复制代码 - 19: message.Headers.RemoveAll(CompressionMessageHeader, Namespace);
复制代码 - 22: public static CompressionAlgorithm GetCompressionAlgorithm(this Message message)
复制代码 - 24: if (message.IsCompressed())
复制代码 - 26: var algorithm = message.Headers.GetHeader<string>(CompressionMessageHeader, Namespace);
复制代码 - 27: algorithm = algorithm.Replace("algorithm =", string.Empty).Replace(""", string.Empty).Trim();
复制代码 - 28: if (algorithm == CompressionAlgorithm.Deflate.ToString())
复制代码 - 30: return CompressionAlgorithm.Deflate;
复制代码 - 33: if (algorithm == CompressionAlgorithm.GZip.ToString())
复制代码 - 35: return CompressionAlgorithm.GZip;
复制代码 - 37: throw new InvalidOperationException("Invalid compression algrorithm!");
复制代码 - 39: throw new InvalidOperationException("Message is not compressed!");
复制代码 - 42: public static byte[] GetCompressedBody(this Message message)
复制代码 - 45: using (XmlReader reader1 = message.GetReaderAtBodyContents())
复制代码 - 47: buffer = Convert.FromBase64String(reader1.ReadElementString(CompressionMessageBody, Namespace));
复制代码 - 52: public static string CreateCompressedBody(byte[] content)
复制代码 - 54: StringWriter output = new StringWriter();
复制代码 - 55: using (XmlWriter writer2 = XmlWriter.Create(output))
复制代码 - 57: writer2.WriteStartElement(CompressionMessageBody, Namespace);
复制代码 - 58: writer2.WriteBase64(content, 0, content.Length);
复制代码 - 59: writer2.WriteEndElement();
复制代码 - 61: return output.ToString();
复制代码 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
复制代码 - 3: private const string DataContractSerializerOperationFormatterTypeName = "System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter, System.ServiceModel, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089";
复制代码 - 5: <s:Body><s:Body> public IDispatchMessageFormatter InnerDispatchMessageFormatter { get; private set; }
复制代码 - 6: public IClientMessageFormatter InnerClientMessageFormatter { get; private set; }
复制代码 - 7: </s:Body></s:Body> public MessageCompressor MessageCompressor { get; private set; }
复制代码 - 9: public CompressionMessageFormatter(CompressionAlgorithm algorithm, OperationDescription description, DataContractFormatAttribute dataContractFormatAttribute, DataContractSerializerOperationBehavior serializerFactory)
复制代码 - 11: this.MessageCompressor = new MessageCompressor(algorithm);
复制代码 - 12: Type innerFormatterType = Type.GetType(DataContractSerializerOperationFormatterTypeName);
复制代码 - 13: var innerFormatter = Activator.CreateInstance(innerFormatterType, description, dataContractFormatAttribute, serializerFactory);
复制代码 - 14: this.InnerClientMessageFormatter = innerFormatter as IClientMessageFormatter;
复制代码 - 15: this.InnerDispatchMessageFormatter = innerFormatter as IDispatchMessageFormatter;
复制代码 - 18: public void DeserializeRequest(Message message, object[] parameters)
复制代码 - 20: message = this.MessageCompressor.DecompressMessage(message);
复制代码 - 21: this.InnerDispatchMessageFormatter.DeserializeRequest(message, parameters);
复制代码 - 24: public Message SerializeReply(MessageVersion messageVersion, object[] parameters, object result)
复制代码 - 26: var message = this.InnerDispatchMessageFormatter.SerializeReply(messageVersion, parameters, result);
复制代码 - 27: return this.MessageCompressor.CompressMessage(message);
复制代码 - 30: public object DeserializeReply(Message message, object[] parameters)
复制代码 - 32: message = this.MessageCompressor.DecompressMessage(message);
复制代码 - 33: return this.InnerClientMessageFormatter.DeserializeReply(message, parameters);
复制代码 - 36: public Message SerializeRequest(MessageVersion messageVersion, object[] parameters)
复制代码 - 38: var message = this.InnerClientMessageFormatter.SerializeRequest(messageVersion, parameters);
复制代码 - 39: return this.MessageCompressor.CompressMessage(message);
复制代码 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/">[AttributeUsage( AttributeTargets.Method)]
复制代码 - 2: public class CompressionOperationBehaviorAttribute: Attribute, IOperationBehavior
复制代码 - 4: </s:Header></s:Header> public CompressionAlgorithm Algorithm { get; set; }
复制代码 - 6: public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters) { }
复制代码 - 8: </s:Envelope></s:Envelope> public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation)
复制代码 - 10: clientOperation.SerializeRequest = true;
复制代码 - 11: clientOperation.DeserializeReply = true;
复制代码 - 12: var dataContractFormatAttribute = operationDescription.SyncMethod.GetCustomAttributes(typeof(DataContractFormatAttribute), true).FirstOrDefault() as DataContractFormatAttribute;
复制代码 - 13: if (null == dataContractFormatAttribute)
复制代码 - 15: dataContractFormatAttribute = new DataContractFormatAttribute();
复制代码 - 18: var dataContractSerializerOperationBehavior = operationDescription.Behaviors.Find<DataContractSerializerOperationBehavior>();
复制代码 - 19: clientOperation.Formatter = new CompressionMessageFormatter(this.Algorithm, operationDescription, dataContractFormatAttribute, dataContractSerializerOperationBehavior);
复制代码 - 22: public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
复制代码 - 24: dispatchOperation.SerializeReply = true;
复制代码 - 25: dispatchOperation.DeserializeRequest = true;
复制代码 - 26: var dataContractFormatAttribute = operationDescription.SyncMethod.GetCustomAttributes(typeof(DataContractFormatAttribute), true).FirstOrDefault() as DataContractFormatAttribute;
复制代码 - 27: if (null == dataContractFormatAttribute)
复制代码 - 29: dataContractFormatAttribute = new DataContractFormatAttribute();
复制代码 - 31: var dataContractSerializerOperationBehavior = operationDescription.Behaviors.Find<DataContractSerializerOperationBehavior>();
复制代码 - 32: dispatchOperation.Formatter = new CompressionMessageFormatter(this.Algorithm, operationDescription, dataContractFormatAttribute, dataContractSerializerOperationBehavior);
复制代码 - 35: public void Validate(OperationDescription operationDescription) { }
复制代码 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/">[ServiceContract(Namespace= "http://www.artech.com/")]
复制代码 - 2: public interface ICalculator
复制代码 - 4: </s:Header></s:Header> [OperationContract]
复制代码 - 5: <s:Body><s:Body> [CompressionOperationBehavior]
复制代码 - 6: double Add(double x, double y);
复制代码 - 8: </s:Envelope></s:Envelope>public class CalculatorService : ICalculator
复制代码 - 10: public double Add(double x, double y)
复制代码 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/">
复制代码 - 3: <Compression xmlns="http://www.artech.com/compression">algorithm = "GZip"</Compression>
复制代码 - 4: </s:Header></s:Header>
复制代码 - 6: <CompressedBody xmlns="http://www.artech.com/compression">7L0HYBx ... CQAA//8=</CompressedBody>
复制代码 - 8: </s:Envelope></s:Envelope>
复制代码 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/">
复制代码 - 3: <Compression xmlns="http://www.artech.com/compression">algorithm = "GZip"</Compression>
复制代码 - 4: </s:Header></s:Header>
复制代码 - 6: <CompressedBody xmlns="http://www.artech.com/compression">7L0H...PAAAA//8=</CompressedBody>
复制代码 - 8: </s:Envelope></s:Envelope>
复制代码 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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