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

2009/2/27 Brandon S. Allbery KF8NH :

On 2009 Feb 26, at 23:41, Achim Schneider wrote:

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"Brandon S. Allbery KF8NH" wrote:

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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. Cheers, Johan