Re: [lwip-users] bug #2240 - UDP pcb connect behaviour

[Leon Woestenberg]

Hello,

> Yes, I beleive that's correct.  My change to udp.c for this
> assumes connectionless behaviour, so now I'm going to
> advertise my stupidity... Isn't that the way UDP should work?
>

UDP is connectionless in the sense that it merely tries to send
datagrams to a certain address without any attempts to keep
a communication channel open with that address.

An UDP protocol control block (think of a simple socket) can
send and receive datagrams to/from any host during operation,
unlike a TCP connection.

A UDP PCB can however, assume a connected state, where
the remote address is used to send datagrams to, and to accept
only datagrams from that address.

This kind of UDP PCB is referred to as a "connected" PCB (or
socket) which might introduce the confusion, as the UDP
communication protocol is still "connection-less".

> Assuming there are cases where accept() and connect() are
> used with UDP, then maybe a real fix would be to have some
> kind of flag field in the pcb that allows udp_input() to
> determine if it is a connection or connectionless bind.
>
There is no such thing, and AFAIK nothing needs to be fixed.
(unless netcon_*() has a bug).

Regards,

Leon.

>
>
> Leon Woestenberg wrote:
> >
> > Ed Suller submitted this bug report. (Thanks Ed.)
> >
> > >A UDP server appears to "lock on" to the IP address of
> > >he first client that communicates with it. After the first
> > >client transaction, no other client (different IP) can
> > >communcate with that server. Assuming that it is agreed
> > >by all that this is a bug, I have what I think is a
> > >fix for this and will submit a patch.
> >
> > This behaviour corresponds with accept() or connect(), where the socket
> > connects with the
> > remote IP address and remote UDP port address. Ed's fix probably
implements
> > recvfrom() behaviour,
> > where the socket stays unconnected to a remote address.
> >
> > None of both is wrong, but we should make both available and especially
well
> > documented.
> >
> > Regards, Leon.
> >
> > _______________________________________________
> > lwip-users mailing list
> > address@hidden
> > http://mail.nongnu.org/mailman/listinfo/lwip-users


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