Joseph Doherty
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793c787315
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Phase 3 PR 53 -- Transport reconnect-on-drop + SO_KEEPALIVE for DL205 no-keepalive quirk. AutomationDirect H2-ECOM100 does NOT send TCP keepalives per docs/v2/dl205.md behavioral-oddities section -- any NAT/firewall device between the gateway and the PLC can silently close an idle socket after 2-5 minutes of inactivity. The PLC itself never notices and the first SendAsync after the drop would previously surface as IOException / EndOfStreamException / SocketException to the caller even though the PLC is perfectly healthy. PR 53 makes ModbusTcpTransport survive mid-session socket drops: SendAsync wraps the previous body as SendOnceAsync; on the first attempt, if the failure is a socket-layer error (IOException, SocketException, EndOfStreamException, ObjectDisposedException) AND autoReconnect is enabled (default true), the transport tears down the dead socket, calls ConnectAsync to re-establish, and resends the PDU exactly once. Deliberately single-retry -- further failures propagate so the driver health surface reflects the real state, no masking a dead PLC. Protocol-layer failures (e.g. ModbusException with exception code 02) are specifically NOT caught by the reconnect path -- they would just come back with the same exception code after the reconnect, so retrying is wasted wire time. Socket-level vs protocol-level is a discriminator inside IsSocketLevelFailure. Also enables SO_KEEPALIVE on the TcpClient with aggressive timing: TcpKeepAliveTime=30s, TcpKeepAliveInterval=10s, TcpKeepAliveRetryCount=3. Total time-to-detect-dead-socket = 30 + 10*3 = 60s, vs the Windows default 2-hour idle + 9 retries = 2h40min. Best-effort: older OSes that don't expose the fine-grained keepalive knobs silently skip them (catch {}). New ModbusDriverOptions.AutoReconnect bool (default true) threads through to the default transport factory in ModbusDriver -- callers wanting the old 'fail loud on drop' behavior can set AutoReconnect=false, or use a custom transportFactory that ignores the option. Unit tests: ModbusTcpReconnectTests boots a FlakeyModbusServer in-process (real TcpListener on loopback) that serves one valid FC03 response then forcibly shuts down the socket. Transport_recovers_from_mid_session_drop_and_retries_successfully issues two consecutive SendAsync calls and asserts both return valid PDUs -- the second must trigger the reconnect path transparently. Transport_without_AutoReconnect_propagates_drop_to_caller asserts the legacy behavior when the opt-out is taken. Validates real socket semantics rather than mocked exceptions. 142/142 Modbus.Tests pass (113 prior + 2 mapper + 2 reconnect + 25 accumulated across PRs 45-52); 11/11 DL205 integration tests still pass with MODBUS_SIM_PROFILE=dl205 -- no regression from the transport change.
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2026-04-18 22:32:13 -04:00 |
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