C# extending SoapExtension -

问题:

Background: I'm trying to write a simple SoapExtension class to log inbound/outbound Soap messages from an asmx web service. Following this article on msdn, I have been able to get things working. However I'd really like to understand why/how it's working rather than just copy & pasting code.

The question: What I'm stuggling to grasp specifically is the handling of the IO streams in the example. All other articles I've read on the web handle the streams in an identical way... first getting a reference to the original stream, creating an in memory "working" stream, and then swapping the contents as necessary.

First question is, what is meant by "stream chaining" in this context? My understaning of streams is that writing to any stream will automatically write to the 'inner' streams in a pipeline. If that's the case, why is it necessary to manually copy contents from one stream to another?

Second question is, in the examples Copy method they're creating a StreamReader and StreamWriter each time, without disposing them - is this not putting extra pressure on the GC? Doesn't seem like something you'd want on a high traffic web service... I tried wrapping both in using statements, but disposing the reader/writer also closed the stream which led to more serious errors. .NET 4 has new Stream.CopyTo(Stream) methods, but what would be a better approach for .NET 3.5?

回答1:

Well, by chaining streams you can basically have different streams that do different things, in a chained sequence. For instance, you can have one stream that compresses the data, and then another stream that encrypts the data (or the opposite if we are moving in the other direction).

As for ChainStream itself, well... There are lots of things to say about this one. I really recommend this article called Inside of Chainstream, which is extremely in-depth and also covers most of the questions you have.

回答2:

The chaining is done in the framework. You get the original stream and return the stream where you put your modified result. The framework will chain this new stream into any other extensions.

It is implemented this way because the chaining works "backwards". Normally you add new functionality on top of streams but in this case you want to deal with the information fed into the original stream.

Calling close on stream is the same as Dispose.