Switch from gen_tcp to the socket NIF API - #9
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Use socket:accept/recv/send/close throughout the acceptor and
connection loop. The raw SO_REUSEPORT options are replaced with the
portable {socket, reuseport} option and the listener's send_timeout
behaviour is emulated with socket:send/3 plus close-on-error.
Accepted sockets have {otp, select_read} enabled: every successful
recv re-arms the read select inside the same NIF call, so the steady
state is one $socket message plus one recv per request instead of
recv/EAGAIN/select/recv. Keep-alive throughput improves ~7%
(107.5k -> 115.1k req/s, 64 connections, M2 Pro). Connection-per-
request drops ~6% on stock OTP because socket:close finalizes on a
dirty scheduler; a fix is pending upstream.
select_read requires OTP 27.3, so the CI matrix drops 25 and 26.
Dialyzer is skipped on 27 since its socket specs predate select_read.
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Summary
Ports the acceptor and connection loop from gen_tcp to the socket NIF API.
{socket, reuseport}option.send_timeout/send_timeout_closebehaviour is emulated withsocket:send/3and close-on-error.{otp, select_read}: each successful recv re-arms the read select inside the same NIF call, so the steady state is one$socketmessage plus one recv per request instead of recv/EAGAIN/select/recv.Benchmarks (M2 Pro, 64 connections, empty 200 handler):
{otp, select_read}was added in OTP 27.3, so the CI matrix drops 25 and 26. Dialyzer is skipped on 27 because its socket specs predate select_read (compile/xref/eunit still run there).