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
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
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。
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 CompressionAlgorithm
2: {
3: GZip,
4: 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: 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: 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[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、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: 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 (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: public static class CompressionUtil
2: {
3: public const string CompressionMessageHeader = "Compression";
4: public const string CompressionMessageBody = "CompressedBody";
5: public const string Namespace = "http://www.artech.com/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 (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: 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, 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: [AttributeUsage( AttributeTargets.Method)]
2: public class CompressionOperationBehaviorAttribute: Attribute, IOperationBehavior
3: {
4: public CompressionAlgorithm Algorithm { get; set; }
5:
6: public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters) { }
7:
8: 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: [ServiceContract(Namespace= "http://www.artech.com/")]
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 xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
2: <s:Header>
3: <Compression xmlns="http://www.artech.com/compression">algorithm = "GZip"</Compression>
4: </s:Header>
5: <s:Body>
6: <CompressedBody xmlns="http://www.artech.com/compression">7L0HYBx ... CQAA//8=</CompressedBody>
7: </s:Body>
8: </s:Envelope>
回复消息
1: <s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
2: <s:Header>
3: <Compression xmlns="http://www.artech.com/compression">algorithm = "GZip"</Compression>
4: </s:Header>
5: <s:Body>
6: <CompressedBody xmlns="http://www.artech.com/compression">7L0H...PAAAA//8=</CompressedBody>
7: </s:Body>
8: </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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