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

On Fri, Feb 27, 2009 at 12:03 AM, Bryan O'Sullivan wrote:

On Thu, Feb 26, 2009 at 1:45 PM, Johan Tibell wrote:

...

I find it quite inconvenient to use the `recv` function in Network.Socket as it throws an exception when reaching EOF and there's no way to check whether EOF has been reached before calling `recv`.

I agree, the current behaviour is quite unfortunate. In fact, I'm pretty sure I added an entry point named recv_ to network-bytestring to work around precisely this problem.

Yes, that's indeed the reason we added it. My current thinking is that we'd drop `recv` from network-bytestring in favor of `recv_`. I've checked how many libraries on Hackage depend on network-bytestring and there are few enough that we could make such a change. It's a bit unfortunate that these libraries have an open dependency on network-bytestring (e.g. network-bytestring >= 0.1.1.2). I will contact the maintainers of those libraries before making a new release.

There's another problem with the network APIs: they mirror the BSD socket API too faithfully, and provide insufficient type safety. You can try to send on an unconnected socket, and to bind a socket that's already connected, both of which should be statically forbidden. The APIs for datagram-oriented networking ought to be distinct from the stream-oriented variety, I think, even if the underlying C-level calls end up being substantially the same.

Really, the big thing that's missing here is enough application of elbow grease from someone who's got a good eye for design and doesn't mind all the slog involved. I think that if someone published a network-alt package (much like the one that was published a few years ago) and tooted their horn vigorously enough, we could put the existing network package out to pasture in fairly short order.

I would be interested in trying to create a better API. However, I'm not sure what it would look like. The design space is pretty big. * How can we provide the static guarantees we want? Perhaps with some kind of lightweight monadic regions but if so which definition should we use i.e. can a region return a Socket to the parent region or not? This has implications on how easy the API is to understand. * Should we use enumerators or not? Can they be added as a convenience layer on top of type safe low-level layer? Cheers, Johan