Re: ncat: using UDP with --chat

[David Fifield <david () bamsoftware com>]

On Tue, Oct 13, 2009 at 07:08:32PM +0200, clemens fischer wrote:
> it said:
>
>   $ ncat -u -l 9999 --chat
>   Ncat: UDP mode does not support connection brokering.
>   If this feature is important to you, write nmap-dev () insecure org with a
>   description of how you intend to use it, as an aid to deciding how UDP
>   connection brokering should work. QUITTING.
>
> My idea is to use UDP chat mode as a kind of emergency IPC mechanism
> together with "--allow" between cooperating processes on machines
> without eg. posix mesage queues.
>
> Connecting clients would tag their messages themselves, like:
>
>   $ echo "temperature1: 33C" | ncat -u localhost 9999
>
> Other clients would see and evaluate the entire line and respond in
> a similiar way.

Cool, thanks for the note. One of the problems we've had in defining
connection brokering for UDP is knowing which clients to relay data to.
When the Ncat broker receives the "temperature1: 33C" message, where
does it send it? Presumably it should be sent to all interested
processes, but the broker has to know about those somehow.

One idea we've had is to consider any host that has ever sent UDP data
to the broker to be a "connected" client, perhaps with timeouts for
inactive hosts. This would require each participating process to "sign
in" by sending a message, to make the broker aware of them.

Is that something that would work for you? It would help if you would
sketch more of the IPC architecture. You've shown how the clients will
send to each other; what do they do to receive?

David Fifield

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