A pong waits no longer than the read's deadline

[sepehr-safari]

Closes #118.

A ping was answered with a write that had no bound. A relay that sent pings and had stopped reading filled the socket, so the pong waited for room that never came while holding the connection's write lock. That held the read past any deadline, and any other write on the connection behind it.

With a deadline, the pong is now skipped when another write holds the lock, or when the socket has no room before the deadline. The room check is a poll for writability on IoStream that writes nothing, the same shape as the read deadline's peek. A pong frame is far below the kernel's low-water mark, so a socket that reports room takes it whole. Skipping is harmless: a peer that is not reading would not read it, and RFC 6455 lets an endpoint answer only the latest of several pings. With no deadline, a ping is answered as before.

Tests

• with a deadline, a pong is skipped rather than waited on when the peer has no room: a stream with no room; the read returns the next message and nothing is written. Without the room check it fails.
• with a deadline, a pong is skipped rather than queued behind another write: the write lock held by someone else; same expectation. Without the lock check the test hangs on the held lock.
• with a deadline and room to write, a ping is still answered.

All 217 tests pass.

Release

The last commit bumps the version to 0.14.7.