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

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

"Brandon S. Allbery KF8NH" wrote:

...

On 2009 Feb 26, at 16:45, Johan Tibell wrote:

...

definition of `recv` would look like. My current thinking is that it would mimic what C/Python/Java does and return a zero length ByteString when EOF is reached.

Ew. Isn't this what Maybe is for?

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. 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. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH