If do_read() returns with EWOULDBLOCK, we must ensure that we actually have
processed the full length header before checking the zero-initialized buffer
length.
While we currently have no need for messages larger than 65KB, we should design
the protocol to be future-proof, as we plan to keep at least to lowest protocol
layer stable.
To avoid any allocation issues, we currently keep the message size limit at
512KB.
Uses separate locks for socket read and write operations. While holding the
socket reader lock, a different thread can still claim the socket write lock.
This allows to asynchronously send event messages while holding the read
lock.
Martin Willi