net.http: Send entire HTTP request header as one write When opportunistic writes are enabled this reduces the number of syscalls and TCP packets sent on the wire. Experiments with TCP Fast Open made this even more obvious. That table trick probably wasn't as efficient. Lua generates bytecode for a table with zero array slots and space for two entries in the hash part, plus code to set [2] and [4]. I didn't verify but I suspect it would have had to resize the table when setting [1] and [3], although probably only once. Concatenating the strings directly in Lua is easier to read and involves no extra table or function call.

net.server_epoll: Immediately attempt to read from newly accepted connections This may speed up client-first protocols (e.g. XMPP, HTTP and TLS) when the first client data already arrived by the time we accept() it. If LuaSocket supported TCP_DEFER_ACCEPT we could use that to further increase the chance that there's already data to handle. In case no data has arrived, no harm should be done, :onreadable would simply set the read timeout and we'll get back to it once there is something to handle.

net.server_epoll: Separate handling of new incoming and outgoing connections The :init method is more suited for new outgoing connections, which is why it uses the connect_timeout setting. Depending on whether a newly accepted connection is to a Direct TLS port or not, it should be handled differently, and was already. The :starttls method sets up timeouts on its own, so the one set in :init was not needed. Newly accepted plain TCP connections don't need a write timeout set, a read timeout is enough.

net.server_epoll: Ensure timeout after closing This should make sure that if there's data left to be written when closing a connection, there's also a timeout so that it doesn't wait forever.

core.loggingmanager: Disable pretty printing when not connected to a tty Things can behave unexpectedly when fed ANSI escape codes.

util.pposix: Bind isatty(3) Useful for disabling certain behavior, ANSI colors etc when not connected to a terminal.

util.prosodyctl.check: Normalize away trailing dot in some messages too

util.prosodyctl.check: Normalize potential to form without trailing '.' In some cases you might end up with both 'xmpp.example.com' and 'xmpp.example.com.', which are the same thing so no point in doing the same checks twice.

util.prosodyctl.check: Point out if A/AAAA exists despite disabled IPvX Clients would try to connect and receive an error or timeout, increasing the time it takes to establish a connection. Probably not what you want. If you really want IPv6 or IPv4 disabled, best remove the A or AAAA record.

util.prosodyctl.check: Warn if both use_ipv4 and use_ipv6 are set to false Why would you do this?!