Accept a FD instead of a port number.

[noteed]

It would be nice to be able to start the server on an existing file descriptor instead of having it opening one based on a port number. This can be usefull e.g. with Circus: Circus will manage the port (and call listen on it) and fork the server, allowing it to accept on the FD shared between possibly multiple snap workers.

[pheaver]

i am very interested in this, too.

[gregorycollins]

The new snap server will support this.

[bos]

Also interested.

[teh]

Me, too, because I want to set some non-portable flags when opening the socket such as SOCK_CLOEXEC or setFdOption (fromIntegral $ fdSocket socket) CloseOnExec True.

[gregorycollins]

@teh we already support that: https://hackage.haskell.org/package/snap-server-0.9.4.6/docs/Snap-Http-Server-Config.html#v:getStartupHook

[teh]

Apologies for missing that - thank you!