Read server socket until `WouldBlock`

Using the `-n` feature of @Aaron1011's excellent client I was able to
find and fix a nagging bug.

Post conversion from the hand-rolled event loop to a `mio` based one,
the server would intermittently fail to respond to client requests.

The server's UDP socket is edge-triggered and the `mio` docs clearly
state that [operations must be performed until `WouldBlock`](https://carllerche.github.io/mio/mio/struct.Poll.html#edge-triggered-and-level-triggered)
otherwise `poll` might not return subsequent events.

Fix is to loop inside the MESSAGE token match until `recv_from`
returns `WouldBlock`.

The resulting code is excessively nested; a cleanup will follow.

0 files changed, 0 insertions, 0 deletions