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Ethereal-dev: [Ethereal-dev] Dissector for an open connection

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From: Bob Bell <bbell@xxxxxxxxxxxxxxxxxxxxx>
Date: Fri, 4 Jun 2004 16:32:27 -0400
I'm planning on writing a dissector for an internal application-level protocol used here at work. However, with this protocol TCP connections are made and help for long periods of time (basically, until they are broken). Multiple separate requests can be sent of each of these connections. I'm thinking that it will be tricky to discover the start of stop of a request. It would be disappointing to be limited to only dissecting the connections that Ethereal can see form.

This might be viewed as the equivalent, say, of a *really* long held HTTP/1.1 connection. One might try to scan for the start of a particular request by looking for the pattern: "<COMMAND> <PATH> HTTP/1.1\n((.+)\n)*(Host: .*)\n((.+)\n)*\n". However, that's obviously no guarantee. After guessing that a particular group of bytes was the start of an HTTP/1.1 request, one might later discover that it was in fact the content of a web page describing a request, inside a <pre></pre> or <code></code> block. This is just an example, and there may be flaws with it, but I hope it conveys the gist of what I'm trying to say.

Is there any documentation describing how one might go about doing this, or might there be an existing dissector that solves this problem that I could use as a model for my dissector? Thanks! I admit I haven't gotten my feet too wet with writing a dissector yet, but I thought I'd get this squared away first.

--
Bob Bell <bbell@xxxxxxxxxxxxxxxxxxxxx>