The R2-01 live gate (S7_1500ConnectTimeoutOutageTests, docker-pause blackhole)
surfaced a real gap the offline fakes couldn't: S7.Net's ReadTimeout/WriteTimeout
map to the TcpClient's ReceiveTimeout/SendTimeout, which govern only SYNCHRONOUS
socket calls — the async read/write paths S7.Net uses ignore them. On an
established-but-frozen peer (frozen PLC / firewall DROP / cable pulled mid-flow,
TCP session still open) a read blocked until the OS TCP stack gave up (minutes),
silently wedging the poll loop: no Bad tick, no reconnect. STAB-14 fixed only the
CONNECT leg (EnsureConnectedAsync CancelAfter); this is its READ-leg sibling.
- New S7OperationDeadline: bounds every data-plane wire op with a wall-clock
ceiling (= _options.Timeout), surfacing an overrun as TimeoutException. Applied
in S7PlcAdapter to Read/ReadBytes/Write/WriteBytes/ReadStatus. OpenAsync is left
to EnsureConnectedAsync's own CancelAfter (not double-bounded).
- IsS7ConnectionFatal now classifies TimeoutException fatal → handle marked dead →
next EnsureConnectedAsync reopens (connect-timeout fix takes over from there).
- Tests: 5 S7OperationDeadline unit tests (deadline / token-honouring / caller-
cancel-passthrough / resultless), 1 driver-reaction test (read TimeoutException
→ reopen). Driver.S7.Tests 260/260.
- Live gate S7_1500ConnectTimeoutOutageTests now GREEN against the real snap7 sim
(8s: baseline Good -> pause blackhole -> Bad tick -> unpause -> recovered Good).
The S7 Plc was opened once in InitializeAsync and never re-opened: a transient
PLC reboot / network blip permanently killed the driver until redeploy. Introduce
an IS7Plc / IS7PlcFactory seam (mirrors TwinCAT's ITwinCATClientFactory) and a lazy
EnsureConnectedAsync that disposes a dead handle and re-opens a fresh connection on
the next data call. Reads/writes mark the handle dead on a connection-fatal fault
(socket drop / ErrorCode.ConnectionError) but NOT on a data-address error; the probe
loop routes through EnsureConnectedAsync as a backstop.
The seam also closes the S7 TEST-1 gap — the reconnect state machine is now unit-
testable without a live PLC (S7.Net.Plc is sealed with no in-process fake).
Verification:
- 4 deterministic unit guards (fatal→reopen, data-error→no-reopen, raw socket→reopen,
reopen-fail→degrade-then-recover); full S7 unit suite 234/234 green.
- LIVE end-to-end proof against real python-snap7 (S7_1500ReconnectTests, double-gated
on sim reachability + S7_RECONNECT_BOUNCE_CMD): bounced the container, driver observed
the outage and resumed Good reads with NO redeploy. Baseline smoke 3/3 still green.
Joseph Doherty