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 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、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.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 (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 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 (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、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、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.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 xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"> 2 <s:Header> 3 <Compression xmlns="http://www.yswenli.net/compression">algorithm = "GZip"</Compression> 4 </s:Header> 5 <s:Body> 6 <CompressedBody xmlns="http://www.yswenli.net/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.yswenli.net/compression">algorithm = "GZip"</Compression> 4 </s:Header> 5 <s:Body> 6 <CompressedBody xmlns="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XmlSeriaizer）；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。
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时间： 2024-10-29 19:05:45