Set TCP_NODELAY and SO_KEEPALIVE on all S7 sockets#677
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Eliminates 100-150ms per-exchange latency caused by Nagle's algorithm interacting with TCP delayed ACKs. S7 is a request/response protocol that sends complete PDUs per sendall() call, so Nagle only adds delay. TCP_NODELAY is set on all client-initiated sockets (snap7/connection.py, which is also used by s7/connection.py via ISOTCPConnection) and on all accepted sockets in snap7/server, snap7/partner, and s7/_s7commplus_server. SO_KEEPALIVE is also enabled to detect dead connections during idle periods. Closes #673 https://claude.ai/code/session_01CkAzrsFA7oZHZL7h2JEavb
Without explicit timing parameters, SO_KEEPALIVE uses the OS default of ~2 hours idle before the first probe fires (Linux: tcp_keepalive_time=7200), making it practically useless for PLC connections. Sets TCP_KEEPIDLE=60, TCP_KEEPINTVL=10, TCP_KEEPCNT=3 on platforms that support them (Linux, macOS 10.15+), reducing dead-connection detection to ~90s of idle. Windows keeps OS defaults, which are already more aggressive than Linux defaults. https://claude.ai/code/session_01CkAzrsFA7oZHZL7h2JEavb
The Quick Start previously showed s7.Client as the recommended API, but pip install python-snap7 delivers v3.0 which only has the snap7 package. A user following the README would get an ImportError. - Quick Start now shows only the stable snap7 API (v3.0) - Renamed "Version 3.1 (unreleased)" to "Version 4.0 (unreleased)" - Added an explicit rst note block warning that 4.0 is not yet on PyPI - Moved the s7.Client example and s7CommPlus description into the 4.0 section https://claude.ai/code/session_01CkAzrsFA7oZHZL7h2JEavb
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
TCP_NODELAYon all sockets (client, server, partner, S7CommPlus server) to eliminate 100-150ms Nagle's algorithm delaySO_KEEPALIVEon all sockets to detect dead connections during idle periods_tcp_connect) and accepted connections (server/partneraccept())Closes #673. Based on feedback from real PLC testing in #668.
Test plan
tests/test_connection.py🤖 Generated with Claude Code