lmxopcua/docs/drivers/TestConnectProbes.md

Test-Connect Probes — Protocol Handshakes

Each driver's Test-Connect button in the AdminUI runs a probe against the form's current config (never the persisted row, never the live driver actor). Before Phase 5 (shipped 2026-06-16) every probe was a bare TCP ConnectAsync — a live-but-rejecting device showed a healthy green tick, and the operator only discovered the truth when the driver faulted at deploy. Phase 5 replaced each TCP-only probe with a real protocol handshake so a reachable-but-wrong or actively-rejecting endpoint now reads RED.

The IDriverProbe / DriverProbeResult contract and DI registration are unchanged. Probes run in a transient actor with a timeout clamp of 1–60 s and must not mutate any state.

For the AdminUI probe flow (button → AdminOperationsActor → transient probe actor), see docs/plans/2026-05-28-adminui-driver-pages-design.md §4.

---

Result contract

All probes return a consistent DriverProbeResult(bool Ok, string? Message, TimeSpan? Latency). The message templates below are uniform across all 8 drivers:

Outcome	Ok	Message template
TCP connect fails	false	"Connect failed: {SocketErrorCode}"
TCP ok + handshake ok	true	driver-specific descriptive string (see table below)
TCP ok but handshake rejected	false	"Reachable at {host}:{port} but {proto} handshake failed: {detail}"
Timeout	false	"Probe timed out after {n}s."

The third row is the key new behavior: a reachable device that answers on the port but rejects the protocol-level handshake now surfaces a false result with a human-readable explanation rather than a false-green TCP-open tick.

---

Per-driver handshake

Driver	Handshake	Ok message	Dev-rig target
Modbus	FC03 (Read Holding Registers, qty 1 @ addr 0) via ModbusTcpTransport. A Modbus exception PDU still proves a real Modbus device → Ok. A non-MBAP reply → handshake fail.	"Modbus FC03 OK"	10.100.0.35:5020 (Modbus sim)
OpcUaClient	DiscoveryClient.GetEndpointsAsync — no session, no app-cert, no auth. ≥ 1 endpoint → Ok. A non-OPC-UA TCP server throws or times out → handshake fail.	"OPC UA: N endpoint(s)"	opc.tcp://10.100.0.35:50000 (opc-plc)
S7	Plc.OpenAsync (COTP CR/CC + S7 setup-communication), check IsConnected, then Close. Wrong rack/slot or a non-S7 server causes OpenAsync to throw → handshake fail.	"S7 connected (CPU …)"	10.100.0.35:1102 (python-snap7 sim)
AbCip	libplctag Tag InitializeAsync (EIP session + CIP Forward Open). A CIP-level error such as tag-not-found still proves the controller answered CIP → Ok. A session/ForwardOpen/connect error → handshake fail.	"CIP session OK"	10.100.0.35:44818 (CIP sim)
AbLegacy	Same libplctag InitializeAsync handshake as AbCip, PCCC protocol family.	"CIP session OK" (PCCC family)	Deferred — no PLC5/SLC sim
TwinCAT	AdsClient.Connect + ReadStateAsync. See degrade semantics below.	"ADS state: {state}"	Deferred — no ADS target
FOCAS	cnc_allclibhndl3 via a direct DllImport("fwlib32") in the probe. See degrade semantics below.	"FOCAS handle OK"	Deferred — no CNC + FWLIB
Galaxy	gRPC unary call to GalaxyRepository.TestConnection on the configured mxaccessgw endpoint. See auth-rejection rule below.	"gateway gRPC OK"	http://10.100.0.48:5120 (mxaccessgw)
Heidenhain	LSV2 A_LG INSPECT (password resolved from its secret:/env: reference) + R_VR, through the same read-only allowlist as the driver; a refusal or malformed version record → fail. No logout — the socket close ends the session.	"LSV2 INSPECT session OK at host:port: <model> NC <version>"	Deferred — no LSV2 control; simulator-proven
MQTT	One MQTT CONNECT (no SUBSCRIBE, no publish) under a -probe--suffixed client id, then disconnect. A rejected CONNACK is a returned result code, not an exception — MQTTnet 5 does not throw — so the probe inspects ResultCode and reuses the driver's own DescribeConnackRejection, making the button and the running driver word a rejection identically.	"MQTT CONNECT OK"	10.100.0.35:8883 (Mosquitto TLS+auth fixture)

Historian.Wonderware had a TCP Hello→HelloAck handshake probe before Phase 5, but the Wonderware historian backend (and its driver-type / probe) has since been retired — the historian backend is now the external HistorianGateway (a gRPC client package, not a probed IDriver). See Historian.Wonderware.md (retired stub) and ../Historian.md.

---

Degrade semantics

Three drivers have environmental constraints that can prevent the handshake from running on certain hosts. The degradation principle is: the probe must never produce a result worse than today's TCP-only probe. A genuine protocol rejection from a reachable device is a correct RED; an inability to run the handshake at all (no FWLIB, no managed router) degrades to the existing TCP-reachability message — still a green tick but annotated.

TwinCAT degrade

Where the handshake is available:

• AdsClient.Connect(netId, port) + ReadStateAsync → Ok=true, "ADS state: {state}" (Run / Config / Stop).
• An ADS route-table rejection from a reachable ADS router is a true RED: "Reachable at {host}:{port} but ADS handshake failed: {detail} — check the target's ADS route table authorizes this host". This is the correct result: the driver would also be unable to function without an authorized route.

Where the handshake is unavailable (headless server, no TwinCAT runtime, the managed AMS router cannot start):

• Probe degrades to TCP-reachability: Ok=true, "(ADS handshake unavailable on this host — TCP reachability only)".

FOCAS degrade

On a Windows host with the FANUC FWLIB shared library present:

• cnc_allclibhndl3 is called via a direct DllImport("fwlib32") declared in the probe (the production Wire.WireFocasClient is a pure-managed FOCAS/2 TCP client, not an FWLIB P/Invoke, so the probe carries its own native binding). A successful handle allocation → Ok=true, "FOCAS handle OK".
• A CNC-level rejection → handshake fail.

On dev, Linux, or macOS (no native FWLIB — UnimplementedFocasClientFactory gates the driver):

• DllNotFoundException / NotSupportedException is caught and the probe degrades to TCP-reachability: Ok=true, "(FOCAS handshake unavailable on this host — FWLIB absent, TCP reachability only)".

Galaxy auth-rejection rule

The probe builds the gRPC channel from the form's config and issues one lightweight unary call. It does not resolve secretref: secrets — the key string in the transient config (possibly empty or unresolved) is used as-is.

• Unavailable / transport failure → Ok=false (gateway is down or unreachable).
• Unauthenticated / PermissionDenied → Ok=true, "gateway reachable & speaking gRPC (auth not checked)" — an auth rejection proves a live mxaccessgw gRPC server. This is the correct result: the driver's own session-layer will handle auth; the probe is testing reachability only.

The mxaccessgw client surfaces a rejected key as a typed MxGatewayAuthenticationException / MxGatewayAuthorizationException, not a raw RpcException — the probe catches both and maps them to the reachable result above. (Live verification on 10.100.0.48:5120 with no key returns MxGatewayAuthenticationException("Missing or invalid API key.") → Ok=true.)

Config note: UseTls must match the endpoint scheme — UseTls:false for an http:// (h2c) gateway, UseTls:true for https://. A mismatch fails the client's own validation (the same constraint the Galaxy driver enforces).

---

Live-verify scope

Driver	Live-verify status	Notes
Modbus	Verified	Dev-rig sim 10.100.0.35:5020; green vs sim, RED vs wrong port / non-Modbus server, timeout vs black-hole IP
OpcUaClient	Verified	opc-plc 10.100.0.35:50000; same three-scenario matrix
S7	Verified	python-snap7 10.100.0.35:1102
AbCip	Verified	CIP sim 10.100.0.35:44818
Galaxy	Verified	mxaccessgw 10.100.0.48:5120; Unauthenticated reply counts as Ok
MQTT	Verified	Mosquitto 10.100.0.35:8883; live suite covers TLS+auth Ok, foreign-CA rejection, and wrong-password rejection surfacing rather than reporting healthy
AbLegacy	Deferred	No PLC5/SLC sim; unit-proven + code path identical to AbCip
TwinCAT	Deferred	No ADS target; unit-proven + degrade guard tested
FOCAS	Deferred	No CNC + FWLIB on dev host; degrade guard is the CI-observable path
Heidenhain	Deferred	No LSV2 control; probe path shared with the simulator-tested driver (#803)

---

Implementation references

• Phase 5 design: docs/plans/2026-06-16-stillpending-phase-5-probes-design.md
• Parent roadmap: docs/plans/2026-06-15-stillpending-backlog-design.md §Phase 5
• AdminUI probe flow: docs/plans/2026-05-28-adminui-driver-pages-design.md §4
• Per-driver probe implementations: src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.<Type>/<Type>DriverProbe.cs
• IDriverProbe contract: src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IDriverProbe.cs
• Probe dispatch + timeout clamp: src/Server/ZB.MOM.WW.OtOpcUa.Host/Actors/AdminOperationsActor.cs (around line 284)