qr code dll vb net EXTENDING .NET REMOTING in Visual Basic .NET

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CHAPTER 13 EXTENDING .NET REMOTING
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To work around this issue, you can create a custom sink that will be used between the client-side binary formatter and the client-side transport channel. This sink can intercept the response message and check its content-type header. If the header is application/octet-stream , then the message contains a real binary message and the sink will just forward it. Otherwise, the sink will read the complete error message in text format and forward a matching exception to the call chain. To implement this, let me first show you the TcpTrace output for an incorrect message in Figure 13-9 and the (incorrect) resulting exception message in Figure 13-10.
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Figure 13-9. This response message results in an incorrect exception.
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Figure 13-10. The incorrect exception information
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The custom sink I am going to show you will intercept the preceding message and turn it into a more reasonable exception. This sink s process message method will first forward the call onto the next sink in the chain (so that it is transferred to the server) and will then inspect the response stream. To inspect the stream, it uses a method, GetExceptionIfNecessary(), which I ll show you in just in a minute.
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CHAPTER 13 EXTENDING .NET REMOTING
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This method returns either null, if everything is OK, or an exception with a more meaningful error message. If an exception is returned, ProcessMessage() will simply throw the exception. public void ProcessMessage(IMessage msg, ITransportHeaders requestHeaders, Stream requestStream, out ITransportHeaders responseHeaders, out Stream responseStream) { _next.ProcessMessage(msg, requestHeaders, requestStream, out responseHeaders, out responseStream); Exception ex = GetExceptionIfNecessary(ref responseHeaders, ref responseStream); if (ex!=null) throw ex; } The method for examining the content of the response stream first looks at the Content-Type header. If this header has the value application/octet-stream , it is not modified and the method does not return an exception. Otherwise, it reads the complete response text and creates a new Exception object, setting its description to the text that has been received from the server. This method can look like this: private Exception GetExceptionIfNecessary( ref ITransportHeaders headers, ref Stream stream) { int chunksize=0x400; MemoryStream ms = new MemoryStream(); string ct = headers["Content-Type"] as String; if (ct==null || ct != "application/octet-stream") { byte[] buf = new byte[chunksize]; StringBuilder bld = new StringBuilder(); for (int size = stream.Read(buf, 0, chunksize); size > 0; size = stream.Read(buf, 0, chunksize)) { bld.Append(Encoding.ASCII.GetString(buf, 0, size)); } return new RemotingException(bld.ToString()); } return null; } Additionally, you will need to implement AsyncProcessRequest() and AsyncProcessResponse() to provide a similar behavior. public void AsyncProcessRequest(IClientChannelSinkStack sinkStack, IMessage msg,
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CHAPTER 13 EXTENDING .NET REMOTING
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ITransportHeaders headers, Stream stream) { sinkStack.Push(this,null); _next.AsyncProcessRequest( sinkStack, msg, headers, stream); } public void AsyncProcessResponse( IClientResponseChannelSinkStack sinkStack, object state, ITransportHeaders headers, Stream stream) { Exception ex = GetExceptionIfNecessary(ref headers, ref stream); if (ex!=null) { sinkStack.DispatchException(ex); } else { sinkStack.AsyncProcessResponse(headers, stream); } } After creating the complete sink and an appropriate sink provider, you can use it in your client-side configuration file like this: <configuration> <system.runtime.remoting> <application> <channels> <channel ref="http"> <clientProviders> <formatter ref="binary" /> <provider type="HttpErrorInterceptor.InterceptorSinkProvider, HttpErrorInterceptor" /> </clientProviders> </channel> </channels> <!-- client entries removed --> </application> </system.runtime.remoting> </configuration>
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Note You can find the complete source code for this sink (and, of course, for any other sample contained
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in this book) at the book s source-code download page at http://www.apress.com.
CHAPTER 13 EXTENDING .NET REMOTING
After you apply this configuration file and run the same client-side command that initially resulted in the incorrect exception, you will now receive the information shown in Figure 13-11. This information correctly reflects the source of the problem.
Figure 13-11. The corrected exception information
Using a Custom Proxy
In the previous parts of this chapter, you read about the possible ways you can extend the .NET Remoting framework using additional custom message sinks. There is another option for changing the default behavior of the remoting system: custom proxy objects. Figure 13-12 shows you the default proxy configuration.
TransparentProxy
RemotingProxy [RealProxy]
_identity
Identity
_channelSink
First sink in chain [IMessageSink]
Figure 13-12. The default combination of proxy objects
You can change this by replacing RemotingProxy with a custom proxy that inherits from RealProxy.
Note You ll normally miss the opportunity to use configuration files in this case. To work around this issue,
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