[Haskell-cafe] Re: Coming up with a better API for Network.Socket.recv

Johan Tibell johan.tibell at gmail.com
Fri Feb 27 04:09:46 EST 2009

2009/2/27 Brandon S. Allbery KF8NH <allbery at ece.cmu.edu>:
> On 2009 Feb 26, at 23:41, Achim Schneider wrote:
>> "Brandon S. Allbery KF8NH" <allbery at ece.cmu.edu> wrote:
>>> On 2009 Feb 26, at 16:45, Johan Tibell wrote:
>>> Anyway, the reason recv doesn't return 0 is that if you have a
>>> datagram socket, a zero-length recv is valid and doesn't mean EOF.
>> My man page says a retval of 0 means that "the peer has performed an
>> orderly shutdown", which, in the UDP case, means that it has send a
>> complete datagram... no mention of EOF. A true EOF in the sense of "no
>> more data will be received" would mean unbinding the socket.
> Right.  Just have to realize that a zero-length datagram packet is possible
> and even meaningful, so 0 isn't available as an EOF flag.

If this is the case then the Network.Socket module is broken when used
for UDP as it throw an exception on receiving a valid message.

> Anyway, the POSIX spec indicates the EOF condition as return -1 with errno
> == ECONNRESET; this should not be taken as anything but the limited
> expressiveness of a C-based API.  We should map this return to Nothing.

I'm not sure I agree. I think using exceptions in this case is fine as
loosing the connection is indeed an exceptional condition and the best
thing a program can do in this case is probably to abort processing of
the disconnected client.



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