net/server: improve error for truthy handler and type :datagram

[ifreund]

Since it is invalid to call accept on a datagram socket, net/server always errors if handler is truthy and type is :datagram.

Tweak the implementation to give a better error message in this case.

References: #1614

[sogaiu]

Thanks for the PR!

If type is nil, net/listen behaves as if type is :stream, right?

Do we want to handle things a bit differently in the case for type being nil and handler is not nil?

Right now it looks to me like the case form might just skip doing anything with handler if type is nil:

(case type
  :stream (if handler
            (ev/go (fn [] (net/accept-loop s handler))))
  :datagram (if handler
              (error "handler not supported for :datagram servers")))

May be we can use (default type :stream) or something earlier in the code? Although I suppose that relies on net/listen's current behavior...may be that's not a problem.

[ifreund]

Good catch @sogaiu! I think the (default type :stream) approach is fine. It doesn't even really rely on the behavior of net/listen to function as documented, the only downside is that it could become inconsistent with net/listen if the default type there is changed. That doesn't seem likely to ever happen though in my humble opinion :)

[ifreund]

The newest revision avoids using default and also avoids binding a socket at all if the arguments are invalid.

[sogaiu]

Just a quick note.

Don't know if it would be an improvement, but perhaps an alternative to this expression:

    (if (and (= type :datagram) handler)
      (error "handler not supported for :datagram servers"))

might be to use assert?

Will think on it a bit more.

[ifreund]

I think I do like the assert a bit more, perhaps this is finally the final version of this patch :)

[sogaiu]

LGTM

[pepe]

LGTM