對于WCF應用來說，傳輸前壓縮請求消息和回複消息，不但可以降低網絡流量，也可以提高網絡傳輸的性能
一、消息壓縮方案
二、用于資料壓縮與解壓縮元件
三、用于消息壓縮與解壓的元件
四、用于對請求/回複消息壓縮和解壓縮的元件
五、将CompressionMessageFormatter用于WCF運作時架構的操作行為
六、檢視結構壓縮後的消息
七、擴充
一、消息壓縮方案
消息壓縮在WCF中的實作其實很簡單，我們隻需要在消息（請求消息/回複消息）被序列化之後，發送之前進行壓縮；在接收之後，反序列化之前進行解壓縮即可。針對壓縮/解壓縮使用的時機，有三種典型的解決方案。通過自定義MessageEncoder和MessageEncodingBindingElement 來完成。
1.将編碼後的位元組流壓縮傳輸
2.建立用于壓縮和解壓縮的信道
3. 自定義MessageFormatter實作序列化後的壓縮和法序列化前的解壓縮
這裡要介紹的解決方案3。
二、用于資料壓縮與解壓縮元件
我們支援兩種方式的壓縮，Dflate和GZip。兩種不同的壓縮算法通過如下定義的CompressionAlgorithm枚舉表示。
1 public enum CompressionAlgorithm
2 {
3 GZip,
4 Deflate
5 } 而如下定義的DataCompressor負責基于上述兩種壓縮算法實際上的壓縮和解壓縮工作。
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、用于消息壓縮與解壓的元件
而針對消息的壓縮和解壓縮通過如下一個MessageCompressor來完成。具體來說，我們通過上面定義的DataCompressor對消息的主體部分内容進行壓縮，并将壓縮後的内容存放到一個預定義的XML元素中（名稱和命名空間分别為CompressedBody和http://www.yswenli.net/comporession/），同時添加相應的MessageHeader表示消息經過了壓縮，以及采用的壓縮算法。對于解壓縮，則是通過消息是否具有相應的MessageHeader判斷該消息是否經過壓縮，如果是則根據相應的算法對其進行解壓縮。
具體的實作如下：
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 } 下面是針對Message類型而定義了一些擴充方法和輔助方法。
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、用于對請求/回複消息壓縮和解壓縮的元件
消息的序列化和反序列化最終是通過MessageFormatter來完成的。具體來說，用戶端通過ClientMessageFormatter實作對請求消息的序列化和對回複消息的序列化，而服務端通過DispatchMessageFormatter實作對請求消息的反序列化和對回複消息的序列化。
在預設的情況下，WCF選用的MessageFormatter為DataContractSerializerOperationFormatter，它采用DataContractSerializer進行實際的序列化和法序列化操作。我們自定義的MessageFormatter實際上是對DataContractSerializerOperationFormatter的封裝，我們依然使用它來完成序列化和反序列化工作，額外實作序列化後的壓縮和法序列化前的解壓縮。
因為DataContractSerializerOperationFormatter是一個internal類型，我們隻有通過反射的方式來建立它。如下的代碼片斷為用于進行消息壓縮與解壓縮的自定義MessageFormatter，即CompressionMessageFormatter的定義。
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運作時架構的操作行為
ClientMessageFormatter和DispatchMessageFormatter實際上屬于ClientOperation和DispatchOperation的元件。我們可以通過如下一個自定義的操作行為CompressionOperationBehaviorAttribute将其應用到相應的操作上。
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、檢視結構壓縮後的消息
為了驗證應用了CompressionOperationBehaviorAttribute特性的操作方法對應的消息是否經過了壓縮，我們可以通過一個簡單的例子來檢驗。我們采用常用的計算服務的例子，下面是服務契約和服務類型的定義。我們上面定義的CompressionOperationBehaviorAttribute應用到服務契約的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 } 我們采用BasicHttpBinding作為終結點的綁定類型（具體的配置請檢視源代碼），下面是通過Fiddler擷取的消息的内容，它們的主體部分都經過了基于壓縮的編碼。
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> 回複消息
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> 如果不想使微軟自帶的序列化或者因為某些原因（emoji字元異常等）可以使用自定義的
IDispatchMessageInspector。由于CompressionMessageFormatter使用基于DataContractSerializer序列化器的DataContractSerializerOperationFormatter進行消息的序列化和發序列化工作，而DataContractSerializer僅僅是WCF用于序列化的一種預設的選擇（WCF還可以采用傳統的XmlSeriaizer）；為了讓CompressionMessageFormatter能夠使用其他序列化器，可以對于進行相應的修正。
轉載請标明本文來源： http://www.cnblogs.com/yswenli/p/6670081.html 更多内容歡迎我的的github： https://github.com/yswenli 如果發現本文有什麼問題和任何建議，也随時歡迎交流~
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