Soap扩展调用顺序原理分析

Soap扩展调用顺序原理分析

最近学习了一下WebService的Soap扩展开发，在学习时我发现最大的问题是不同优先级的SoapExtension的调用顺序以及chainStream方法的用途，我们知道SoapMessage具有一个Stream属性，那么为什么我们不能在SoapExtension的ProcessMessage中直接操作这个Stream呢，例如你的代码可能会是这个样子：

publicoverridevoidProcessMessage(SoapMessagemessage)

??????? {

??????????? switch (message.Stage)

??????????? {

??????????????? //序列化之后压缩这个流

??????????????? caseSoapMessageStage.AfterSerialize:

??????????????????? message.Stream = CompressStream(message.Stream);

??????????????????? break;

?

??????????????? //反序列化之前解压缩这个流

??????????????? caseSoapMessageStage.BeforeDeserialize:

??????????????????? message.Stream = DeCompressStream(message.Stream);

??????????????????? break;

??????????????? default:

??????????????????? break;

??????????? }

??????? }

??????? ///<summary>

??????? ///压缩输入流，返回压缩后的新流。

??????? ///</summary>

??????? ///<param name="inputStream">输入流，该流将被压缩</param>

??????? ///<returns>返回压缩后的新流。</returns>

??????? privateStreamCompressStream(StreaminputStream)

??????? {

??????????? //simulate code here

??????????? returnnewMemoryStream();

??????? }

??????? ///<summary>

??????? ///解压缩输入流，返回解压后的新流。

??????? ///</summary>

??????? ///<param name="compressedStream">被压缩的输入流</param>

??????? ///<returns>返回解压后的新流。</returns>

??????? privateStreamDeCompressStream(StreamcompressedStream)

??????? {

??????????? //simulate code here

??????????? returnnewMemoryStream();

??????? }

我非常希望这段代码能够正确执行，但是在WebService调用时，在第一个CompressStream就无法通过，因为其为空。看了下面我的解释可能您能找到答案。

继续之前请首先记住如下几个结论：

1、SOAP扩展是在SoapMessage (SoapClientMessage和SoapServerMessage类型)传输过程中对其SOAP消息处理过程的拦截器，其可以在SoapMessage的四个阶段进行拦截并且插入代码，这四个阶段分别是BeforeSerialize"AfterSerialize"BeforeDeserialize和AfterDeserialize。

2、?在整个WebService访问过程中，ChainStream一共执行四次，在客户端执行两次，在服务器端执行两次。ChainStream的调用是按照Soap扩展的高优先级到低优先级的调用顺序依次调用的。

3、?每次SoapMessage的Stage状态发生改变时都会调用SoapExtension的ProcessMessage。所以这个函数一共执行8次。其中需要特别注意的是，不同优先级的Soap扩展在Soap消息传输的不同阶段其调用顺序是不一样的，具体可以分为两个阶段：即Serialize阶段，其调用是按照Soap扩展的优先级从低到高执行的，在Deserialize阶段，其调用是按照Soap扩展优先级从高到低执行的。

从下面这段代码我们就可以看出ProcessMessage调用顺序：

internalvoidRunExtensions(SoapExtension[] extensions,bool throwOnException)

{??

// extensions已经按照优先级由高到底排好序

??? if (extensions != null)

??? {?? ?
//在BeforeDeSerialize或者AfterDeSerialize阶段按照由高到低的优先级顺序执行

??????? if ((this.stage & (SoapMessageStage.AfterDeserialize | SoapMessageStage.BeforeDeserialize)) != ((SoapMessageStage) 0))

??????? {

??????????? for (int i = 0; i < extensions.Length; i++)

??????????? {

??????????????? extensions[i].ProcessMessage(this);

??????????????? if ((this.Exception != null) && throwOnException)

??????????????? {

??????????????????? throw this.Exception;

??????????????? }

??????????? }

??????? }

??????? else

??????? {???

???????????????????????????????? ?//在BeforeSerialize或者AfterSerialize阶段按照由低到高的优先级顺序执行

??????????? for (int j = extensions.Length - 1; j >= 0; j--)

??????????? {

??????????????? extensions[j].ProcessMessage(this);

??????????????? if ((this.Exception != null) && throwOnException)

??????????????? {

??????????????????? throw this.Exception;

??????????????? }

??????????? }

??????? }

??? }

}

4、SoapExtension的优先级越高，其越接近网络，即其越接近网络传输层数据。

5、WebService调用过程基本可以分为两个阶段：1、从客户端发出请求到服务器端接受请求的过程刚好就是ProcessMessage执行的四个阶段，2、从服务器端发出响应到客户端接受响应其也是执行ProcessMessage的四个阶段状态，其执行chainStream和SoapExtension执行顺序和1完全一样，只不过在第一步中传输的是SoapClientMessage,而第二步中传输的是SoapServerMessage。

6、我们知道SoapExtension的Priority属性为0，其优先级越高，如果我们现在有两个SoapExtension，分别是CompressExtension(用于压缩和解压缩)和CryptoExtension(用于加密和解密)，我们现在希望其执行顺序是这样的，在客户端发出请求时，首先压缩然后加密（这样可能获得较高性能）。我们知道在客户端发出请求时ProcessMessage的执行是先从低优先级执行的，所以我们将CryptoExtension的优先级设置为高于CompressExtension的优先级即可。

我们来看一下客户端通过WebService代理发出请求的具体执行流程。

1.????? 客户端创建代理实例，进行必要初始化，如设置SoapHeader;

2.????? 客户端通过代理实例调用Web方法;

3.????? 代理实例调用基类SoapHttpClientProtocol的Invoke方法，将Web方法作为字符串传递进去；

4.????? SoapHttpClientProtocol 根据Url获取WebRequest；

5.????? SoapHttpClientProtocol 根据本地代理配置文件或者特性利用反射生成本地?SoapReflectedExtension对象，并且对其进行排序，该对象即SoapExtension的反射形式类，其主要作用是动态生成SoapExtension对象，并且调用其GetInitializer（第一次调用）和Initialize方法，主要是为了满足性能需求；

6.????? 创建SoapClientMessage实例，并且设置其Stream和SoapExtensionStream为一个空的SoapExtensionStream的实例；

7.????? 按照优先级顺序调用SoapExtension的ChainStream方法；并且将第六步的SoapExtensionStream传递进去；并将ChainStream的返回值设置为SoapMessage的Stream属性。这样最低优先级的SoapExtension的ChainStream返回值和SoapMessage的Message属性为同一个对象；

8.????? 设置SoapMessage的Stage为BeforeSerialize，按照由低到高的优先级顺序调用SoapExtension的ProcessMessage方法；

9.????? 设置Soap标头信息；

10.?获取WebRequest的RequestStream对象，如果当前SoapExtensionStream不为空则将该Stream绑定给SoapExtensionStream的InnerStream对象，这样就使得最高优先级的SoapExtension可以引用该Stream.否则直接将SoapMessage的Stream设置为RequestStream。

11.?序列化Soap调用的参数，并且将其写入SoapMessage的Stream属性中。

12.?设置SoapMessage的Stage为AfterSerialize，按照由低到高的优先级顺序调用SoapExtension的ProcessMessage方法；这里需要特别留意：由于在第7步中的最低优先级SoapExtension的Stream已经被第11步写入数据，所以在该步中第一个调用的SoapExtension的_newStream(_workStream)就具有了原始SOAP的消息流。

这就是我们在扩展SoapExtension时为啥在调用AfterSerialize之后_newStream中具有数据的原因。

13.?在SoapExtension扩展时的BeforeDeserialize阶段，由于ChainStream和ProcessMessage都是按照由高到低的顺序执行的，所以我们可以知道最接近网络的SoapExtension首先传入的是一个网络流(NetworkStream)，所以我们在ChainStream中保存的_oldStream就是该网络流。

14.?在服务器端其执行步骤和客户端执行步骤基本完全一样，只不过在传输过程中是SoapServerMessage。

这是一个MSDN的实例，请注意其中的注释语句。

usingSystem;

usingSystem.Collections.Generic;

usingSystem.Text;

usingSystem.IO;

usingSystem.Web;

usingSystem.Web.Services;

usingSystem.Web.Services.Protocols;

namespaceSoapExtensionLib

{

??? ///<summary>

??? ///跟踪soap请求和响应。

///</summary>

publicclassTraceExtension:SoapExtension

??? {

??????? privateStream_newStream;//可以传给低扩展的流

??????? privateStream_oldStream;//优先级高的扩展传递进来的流

??????? privatestring_fileName;//日志文件路径

??????? publicoverrideStreamChainStream(Streamstream)

??????? {

??????????? _oldStream = stream;

??????????? _newStream = newMemoryStream();

??????????? return_newStream;

??????? }

??????? publicoverridevoidProcessMessage(SoapMessagemessage)

??????? {

??????????? switch (message.Stage)

??????????? {

??????????????? caseSoapMessageStage.BeforeSerialize:

??????????????????? break;

??????????????? caseSoapMessageStage.AfterSerialize:

??????????????????? WriteOutput(message);

??????????????????? break;

??????????????? caseSoapMessageStage.BeforeDeserialize:

??????????????????? WriteInput(message);

??????????????????? break;

??????????????? caseSoapMessageStage.AfterDeserialize:

??????????????????? break;

??????????? }

??????? }

??????? privatevoidWriteOutput(SoapMessagemessage)

??????? {

??????????? //这里是准备向网络传输的，即客户端发出请求和服务器端发出响应时发生的。

??????????? //在这两个阶段ChainStream调用顺序和ProcessMessage相反，所以可以肯定_newStream

??????????? //一定不为空，而_oldStream为空。

??????????? _newStream.Position = 0;

??????????? FileStreamfs = newFileStream(_fileName,FileMode.Append,FileAccess.Write);

??????????? StreamWriterwriter = newStreamWriter(fs);

??????????? writer.WriteLine("date time:" + DateTime.Now.ToString());

??????????? writer.Flush();

??????????? CopyStream(_newStream,fs);

??????????? writer.Close();

??????????? //这里非常重要，因为需要将低优先级低的扩展逐级向上复制给高优先级的扩展

??????????? _newStream.Position = 0;

??????????? CopyStream(_newStream,_oldStream);

??????? }

??????? privatevoidWriteInput(SoapMessagemessage)

??????? {

??????????? //这里是从网络传输进来的，即服务器端接受请求和客户端接受响应时发生的。

??????????? //在这两个阶段ChainStream调用顺序和ProcessMessage相同，所以可以肯定_oldStream

??????????? //一定不为空，而_newStream为空。

??????????? CopyStream(_oldStream,_newStream);

??????????? FileStreamfs = newFileStream(_fileName,FileAccess.Write);

??????????? StreamWriterwriter = newStreamWriter(fs);

??????????? writer.WriteLine("date time:" + DateTime.Now.ToString());

??????????? writer.Flush();

??????????? _newStream.Position = 0;

??????????? CopyStream(_newStream,fs);

??????????? writer.Close();

??????????? _newStream.Position = 0;

??????? }

??????? privatevoidCopyStream(Streamfrom,Streamto)

??????? {

??????????? TextReaderreader = newStreamReader(from);

??????????? TextWriterwriter = newStreamWriter(to);

??????????? writer.WriteLine(reader.ReadToEnd());

??????????? writer.Flush();

??????? }

??????? publicoverrideobjectGetInitializer(TypeserviceType)

??????? {

??????????? return"c:""" + serviceType.FullName + ".log";

??????? }

??????? publicoverrideobjectGetInitializer(LogicalMethodInfomethodInfo,SoapExtensionAttributeattribute)

??????? {

??????????? return ((TraceExtensionAttribute)attribute).FileName;

??????? }

??????? publicoverridevoidInitialize(objectinitializer)

??????? {

??????????? _fileName = (string)initializer;

??????? }

??? }

}

我们以一个压缩SOAP消息的扩展为例结束本专题。

首先定义一个SoapExtension的扩展类CompressExtension

usingSystem;

usingSystem.Collections.Generic;

usingSystem.Text;

usingSystem.IO;

usingSystem.Web;

usingSystem.Web.Services;

usingSystem.Web.Services.Protocols;

usingICSharpCode.SharpZipLib.Core;

usingICSharpCode.SharpZipLib.Zip;

namespaceSoapExtensionLib

{

??? ///<summary>

??? ///提供压缩和解压缩的Soap扩展。

??? ///</summary>

??? publicclassCompressExtension:SoapExtension

??? {

??????? privateStream_workStream;

??????? privateStream_oldStream;

??????? privateint_compressLevel;

??????? privatestaticreadonlyint_DEFAULTLEVEL=9;

??????? publicoverrideStreamChainStream(Streamstream)

??????? {

??????????? _oldStream = stream;

??????????? _workStream = newMemoryStream();

??????????? return_workStream;

??????? }

??????? publicoverrideobjectGetInitializer(TypeserviceType)

??????? {

??????????? return_DEFAULTLEVEL;

??????? }

??????? publicoverrideobjectGetInitializer(LogicalMethodInfomethodInfo,SoapExtensionAttributeattribute)

??????? {

??????????? return ((CompressExtensionAttribute)attribute).CompressLevel;

??????? }

??????? publicoverridevoidInitialize(objectinitializer)

??????? {

??????????? _compressLevel = (int)initializer;

??????? }

??????? publicoverridevoidProcessMessage(SoapMessagemessage)

??????? {

??????????? switch (message.Stage)

??????????? {

??????????????? caseSoapMessageStage.AfterSerialize:

??????????????????? CompressStream();

??????????????????? break;

??????????????? caseSoapMessageStage.BeforeDeserialize:

??????????????????? DeCompressStream();

??????????????????? break;

??????????????? default:

??????????????????? break;

??????????? }

??????? }

??????? privatevoidCompressStream()

??????? {

??????????? //利用zip算法将_workStream压缩到_oldStream中，

??????????? //_oldStream将传递给高优先级的SoapExtension进行处理。

??????????? _workStream.Position = 0;

??????????? ZipOutputStreamzipStream = newZipOutputStream(_oldStream);

??????????? zipStream.SetLevel(_compressLevel);

??????????? byte[] buffer = newbyte[4096];

??????????? ZipEntryentry = newZipEntry("compress");

??????????? zipStream.PutNextEntry(entry);

??????????? StreamUtils.Copy(_workStream,zipStream,buffer);

??????????? zipStream.Finish();

??????? }

??????? privatevoidDeCompressStream()

??????? {

??????????? //利用zip算法将_oldStream解压缩到_workStream中。

??????????? //_workStream将传输给低优先级的SoapExtension进行处理。

??????????? ZipInputStreamzipStream = newZipInputStream(_oldStream);

??????????? ZipEntrytheEntry = null;

??????????? byte[] buffer = newbyte[4096];

??????????? while ((theEntry = zipStream.GetNextEntry()) != null)

??????????? {

??????????????? intreadByt = 0;

??????????????? do{

??????????????????? readByt = zipStream.Read(buffer,buffer.Length);

??????????????????? _workStream.Write(buffer,readByt);

??????????????? }

??????????????? while (readByt > 0);

??????????? }

??????????? _workStream.Position = 0;

??????? }

??? }

}

再定义一个特性：

usingSystem;

usingSystem.Collections.Generic;

usingSystem.Text;

usingSystem.IO;

usingSystem.Web;

usingSystem.Web.Services;

usingSystem.Web.Services.Protocols;

namespaceSoapExtensionLib

{

??? [AttributeUsage(AttributeTargets.Method)]

??? publicclassCompressExtensionAttribute:SoapExtensionAttribute

??? {

??????? privateint_priority;

??????? privateint_level;

??????? publicCompressExtensionAttribute()

??????? {

??????????? _level = 9;

??????????? _priority = 0;

??????? }

??????? publicoverrideTypeExtensionType

??????? {

??????????? get { returntypeof(CompressExtension); }

??????? }

??????? publicintCompressLevel

??????? {

??????????? get { return_level; }

??????????? set { _level = value; }

??????? }

??????? publicoverrideintPriority

??????? {

??????????? get

??????????? {

??????????????? return_priority;

??????????? }

??????????? set

??????????? {

??????????????? _priority = value;

??????????? }

??????? }

??? }

}

下面是这个测试的WebService

usingSystem;

usingSystem.Web;

usingSystem.Web.Services;

usingSystem.Web.Services.Protocols;

usingSoapExtensionLib;

[WebService(Namespace = "http://tempuri.org/")]

[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]

publicclassService : System.Web.Services.WebService

{

??? publicService () {

??????? //如果使用设计的组件，请取消注释以下行

??????? //InitializeComponent();

??? }

??? [WebMethod]

??? [SoapExtensionLib.CompressExtension(CompressLevel = 9)]

??? publicstringHelloWorld() {

??????? return"Hello World";

??? }

??? [WebMethod]

??? [SoapExtensionLib.CompressExtension(CompressLevel=9)]

??? publicstringCaculateString()

??? {

??????? return"Zhang xuebao";

??? }

}