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Joseph Doherty 6c6800e513 Merge hw4-udtwrite (#592/#611)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

# Conflicts:
#	docs/drivers/AbCip.md

2026-10-09 04:32:03 -04:00

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ab_server test fixture

Coverage map + gap inventory for the AB CIP integration fixture backed by libplctag's ab_server simulator.

TL;DR: ab_server is a connectivity + atomic-read smoke harness for the AB CIP driver. It does not benchmark UDTs, alarms, or any family-specific quirk. UDT / alarm / quirk behavior is verified only by unit tests with FakeAbCipTagRuntime.

What the fixture is

Binary: ab_server — a C program from the upstream libplctag/libplctag repository (MIT license). It is not part of this repo's source tree; Docker/Dockerfile clones libplctag at a pinned tag and builds the ab_server CMake target in a multi-stage build.
Launcher: Docker (only supported path). Docker/Dockerfile multi-stage-builds ab_server from source by cloning libplctag at a pinned tag + copies the binary into a slim runtime image. Docker/docker-compose.yml has per-family services (controllogix / compactlogix / micro800 / guardlogix); all bind :44818.
Lifecycle: AbServerFixture TCP-probes 10.100.0.35:44818 (the shared Docker host) at collection init + records a skip reason when unreachable. Tests skip via [AbServerFact] / [AbServerTheory] which check the same probe.
Profiles: KnownProfiles.{ControlLogix, CompactLogix, Micro800, GuardLogix} in AbServerProfile.cs — thin Family + ComposeProfile + Notes records; the compose file is the canonical source of truth for which tags get seeded + which --plc mode the simulator boots in.
Tests: one smoke, AbCipReadSmokeTests.Driver_reads_seeded_DInt_from_ab_server, parametrized over all four profiles via [AbServerTheory] + [MemberData].
Endpoint override: AB_SERVER_ENDPOINT=host:port points the fixture at a real PLC instead of the local container.

Per-transport suites and capture recipe

Every integration test in AbCip.IntegrationTests now runs once per transport (TransportMatrix: Libplctag and Native). Run one compose profile at a time and name it with AB_SERVER_COMPOSE_PROFILE (all profiles bind :44818, so set it to the running profile; unset, only the default controllogix rows run — ab_server does not self-identify its --plc mode, so crossing every family at one container failed the non-matching rows instead of skipping them, #594). NativeLeaseReleaseSoakTests is the ab_server soak of the background lease release (AB_LEASE_SOAK_CYCLES, default 100; read-only, skips without the fixture, #593). On the 2026-10-07 run native passed everything libplctag passed on all seven profiles; on micro800 libplctag failed on the empty-path defect described in AbCip.md and native passed. That defect is now fixed: a re-run of the micro800 smoke test passes on both transports. Evidence: native-ab-transport-gate-results.

Write-capable tests (the Logix Emulate ALMD test, and AbCipUdtMemberWriteTests — #611 discovered-member writes, both transports, against the UdtSeg.* member tags of the controllogix profile) require AB_SERVER_ALLOW_WRITES=1 and refuse while AB_DIFF_ENDPOINT is set.
Differential harness (AbCip.IntegrationTests/Differential, LiveIntegration) compares libplctag and native on browse, template and read parity against one endpoint. It is read-only by construction, aborts on the first connection failure, never retries, and caps the native phase at one Forward Open. Env: AB_DIFF_ENDPOINT, AB_DIFF_PATH, AB_DIFF_FAMILY, AB_DIFF_TAGS, AB_DIFF_MAX_TAGS (at most 500), AB_DIFF_MAX_TEMPLATES, AB_DIFF_PACE_MS (default 20), AB_DIFF_COUNT_OPENS. Always run with --filter "FullyQualifiedName~Differential" and AB_SERVER_ENDPOINT=127.0.0.1:1.
ab_server serves no UDTs, so template parity is vacuous there. Docker patch 0003 serves a UDT member path from a flat tag named by that dotted path (UdtSeg.ID, UdtSeg.Sub.Code, UdtSeg.Points[2]) — the wire of a member read/write, not a structure — and accepts the pad byte libplctag adds to a 1-byte write, which stock ab_server refused (0x03) for every libplctag BOOL/SINT write. Two blind spots follow (see the Docker README §0003): a +1-byte over-write of an odd-sized tag is no longer caught, and a malformed single segment "UdtSeg.ID" resolves where a real Logix would refuse it. Native writes remain simulator-only.
Golden-frame capture: scripts/ab-capture/capture.sh (capture client in scripts/ab-capture/client); fixtures live in tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Ab.Transport.Tests/Captures/ with a README.

What it actually covers

Read path: driver → libplctag → CIP-over-EtherNet/IP → simulator → back.
Atomic Logix types per seed: DINT, REAL, BOOL, SINT, STRING.
One DINT[16] array tag (ControlLogix profile only).
--plc controllogix and --plc compactlogix mode dispatch.
The skip-on-missing-binary behavior (AbServerFactAttribute) so a fresh clone without the simulator stays green.

What it does NOT cover

Each gap below is either stated explicitly in the profile's Notes field or inferable from the seed-tag set + smoke-test surface.

1. UDTs / CIP Template Object (class 0x6C)

ControlLogix profile Notes: "ab_server lacks full UDT emulation."

Unverified against ab_server:

PR 6 structured read/write (AbCipStructureMember fan-out) — except the member-path wire of a write, which patch 0003 serves (AbCipUdtMemberWriteTests, #611); offsets and BIT-member semantics are not emulated
#179 Template Object shape reader (CipTemplateObjectDecoder + FetchUdtShapeAsync)
#194 whole-UDT read optimization (AbCipUdtReadPlanner + AbCipUdtMemberLayout + the ReadGroupAsync path in AbCipDriver)

Unit coverage: AbCipFetchUdtShapeTests, CipTemplateObjectDecoderTests, AbCipUdtMemberLayoutTests, AbCipUdtReadPlannerTests, AbCipDriverWholeUdtReadTests — all with golden Template-Object byte buffers

offset-keyed FakeAbCipTag values.

2. ALMD / ALMA alarm projection (#177)

Depends on the ALMD UDT shape, which ab_server cannot emulate. The OnAlarmEvent raise/clear path + ack-write semantics are not exercised end-to-end.

Unit coverage: AbCipAlarmProjectionTests — fakes feed InAlarm / Severity via ValuesByOffset + assert the emitted AlarmEventArgs.

3. Micro800 unconnected-only path

Micro800 profile Notes: "--plc=Micro800 mode (unconnected-only, empty path). Driver-side enforcement verified in the unit suite."

The compose service boots ab_server --plc=Micro800 with an empty routing path. The unconnected-session requirement (PR 11) is validated at the driver unit-test level via FakeAbCipTagRuntime; the wire-level contract (what happens when a connected-send arrives at a real Micro800 backplane) is not exercised by the simulator. Real Micro800 (2080-series) on a lab rig would be the authoritative benchmark.

4. GuardLogix safety subsystem

GuardLogix profile Notes: "ab_server doesn't emulate the safety subsystem."

Only the _S-suffix naming classifier (PR 12, SecurityClassification.ViewOnly forced on safety tags) runs. Actual safety-partition write rejection — what happens when a non-safety write lands on a real 1756-L8xS — is not exercised.

5. CompactLogix connection size and the regular-open fallback

Since T21 the CompactLogix profile defaults to a Large Forward Open (4002), matching what libplctag opens for plc=compactlogix. The old 504 default was cosmetic under libplctag, which never received it, and cost the native transport ~3× the round trips per poll. A pre-v20 CompactLogix (1769-L3x) or a bridge that refuses the Large open is handled by CipConnection's fallback (a regular open at min(size, 504) in the same throttled attempt). That fallback is pinned by unit tests against a fake target only: ab_server accepts any size, so a refusing controller is never exercised here.

6. BOOL-within-DINT read-modify-write (#181)

The AbCipDriver.WriteBitInDIntAsync RMW path + its per-parent SemaphoreSlim serialization is unit-tested only (AbCipBoolInDIntRmwTests). ab_server seeds a plain TestBOOL tag; the .N bit-within-DINT syntax that triggers the RMW path is not exercised end-to-end.

7. Capability surfaces beyond read

No smoke test for:

IWritable.WriteAsync
ITagDiscovery.DiscoverAsync (@tags walker)
ISubscribable.SubscribeAsync (poll-group engine)
IHostConnectivityProbe state transitions under wire failure
IPerCallHostResolver multi-device routing

The driver implements all of these + they have unit coverage, but the only end-to-end path ab_server validates today is atomic ReadAsync.

Logix Emulate golden-box tier

Rockwell Studio 5000 Logix Emulate sits above ab_server in fidelity + below real hardware. When an operator has Emulate running on a reachable Windows box + sets two env vars, the suite promotes several behaviours from unit-only to end-to-end wire-level coverage:

$env:AB_SERVER_PROFILE  = 'emulate'
$env:AB_SERVER_ENDPOINT = '<emulate-pc-ip>:44818'
dotnet test tests\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbCip.IntegrationTests

With AB_SERVER_PROFILE unset or abserver, the Emulate-tier classes skip cleanly + the ab_server Docker fixture runs as usual.

Gap this fixture doc calls out	ab_server	Logix Emulate	Real hardware
UDT / CIP Template Object (task #194)	no	yes	yes
ALMD alarm projection (task #177)	no	yes	yes
`@tags` Symbol Object walk with `Program:` scope	partial	yes	yes
Add-On Instructions	no	yes	yes
GuardLogix safety-partition write rejection	no	yes (Emulate 5580)	yes
CompactLogix Large-open refusal → regular-open fallback	no	yes (5370 firmware)	yes
EtherNet/IP embedded-switch behaviour	no	no	yes
Redundant chassis failover (1756-RM)	no	no	yes
Motion control timing	no	no	yes

Tests that promote to Emulate (gated on AB_SERVER_PROFILE=emulate via AbServerProfileGate.SkipUnless):

AbCipEmulateUdtReadTests.WholeUdt_read_decodes_each_member_at_its_Template_Object_offset — #194 whole-UDT optimization, verified against real Template Object bytes
AbCipEmulateAlmdTests.Real_ALMD_raise_fires_OnAlarmEvent_through_the_driver_projection — #177 ALMD projection, verified against the real ALMD instruction

Required Studio 5000 project state is documented in tests/…/AbCip.IntegrationTests/LogixProject/README.md; the .L5X export lands there once the Emulate PC is on-site + the project is authored.

Costs to accept:

Rockwell TechConnect or per-seat license — not redistributable; not CI-runnable. Each operator licenses their own Emulate install.
Windows-only + Hyper-V conflict — Emulate can't coexist with Docker Desktop's WSL 2 backend on the same OS, same way TwinCAT XAR can't (see docs/v2/dev-environment.md §Integration host).
Manual lifecycle — no docker compose up equivalent; operator opens Emulate, loads the L5X, clicks Run. The L5X in the repo keeps project state reproducible, runtime-start is human.

When to trust ab_server, when to reach for a rig

Question	ab_server	Unit tests	Logix Emulate	Lab rig
"Does the driver talk CIP at all?"	yes	-	yes	-
"Is my atomic read path wired correctly?"	yes	yes	yes	yes
"Does whole-UDT grouping work?"	no	yes	yes	yes
"Do ALMD alarms raise + clear?"	no	yes	yes	yes
"Is Micro800 unconnected-only enforced wire-side?"	partial (--plc=Micro800 boots, but wire rejection untested)	partial	yes	yes (required)
"Does GuardLogix reject non-safety writes on safety tags?"	no	no	yes (Emulate 5580)	yes
"Does CompactLogix refuse a Large Forward Open?"	no	partial	yes (5370 firmware)	yes
"Does BOOL-in-DINT RMW race against concurrent writers?"	no	yes	partial	yes (stress)
"Does EtherNet/IP embedded-switch behave correctly?"	no	no	no	yes (required)
"Does redundant-chassis failover work?"	no	no	no	yes (required)

Follow-up candidates

If integration-level UDT / alarm / quirk proof becomes a shipping gate, the options are roughly:

Logix Emulate golden-box tier (scaffolded; see the section above) — highest-fidelity path short of real hardware. Closes UDT / ALMD / AOI / optimized-DB gaps in one license + one Windows PC.
Extend ab_server upstream — the project accepts PRs + already carries a CIP framing layer that UDT emulation could plug into.
Stand up a lab rig — physical 1756-L7x / 5069-L3x / 2080-LC30 / 1756-L8xS controllers. The only path that covers safety partitions across nodes, redundant chassis, embedded-switch behaviour, and motion timing.

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