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From Andrej van der Zee <>
Subject Re: Apache log modules
Date Sun, 28 Nov 2010 23:56:50 GMT
Hi Sorin,

Thanks for your reply.

> request_rec->connection->id is a long int that is unique. It is built
> from the process_id and thread_id of the apache thread that serves the
> request.

Will this be unique for MPM worker across control processes / worker threads?

> However, a client may open several connections to the server
> during the same transaction, so I guess this does not help you much.

My assumption is that both client and server have KeepAlive enabled.
In that case, should there "generally" not be just one connection

> There's a module called unique_id. It creates a string that is stored
> in the req->subprocess_env and can be logged with "%{UNIQUE_ID}e". It
> encodes the request timestamp, the connection->id, the _server_ IP and
> a random number. It does not encode the client IP or port. However, if
> you combine it with the client-IP and client port that you can log as
> well in the same log line, you could, probably, extract what you want
> after some log-postprocessing.

So I can decode the unique ID and extract the connection ID from it? I
guess so...

> Different clients behind a NAT router will use different ports.
> However, based solely on ports, you won't be able to distinguish
> between two different clients on one hand or one client that makes
> several connections on the other hand. A method that is used by some
> of my colleagues in order to distinguish between different clients
> (but I don't know much about it, so I can't tell you more) is to
> analyse the TCP header of the packet in order to extract the TCP
> sequence numbers.

That sounds interesting but as far as I can see this information is
not available in the application layer. Hard to imagine, but are there
any tricks to get this information in Apache modules? Or are your
colleagues using sniffers such as tcpdump?

Thank you,

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