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Joseph Doherty 01f4ee6b53 Auto: abcip-3.3 — read-strategy selector (WholeUdt / MultiPacket / Auto)

Closes #237

2026-04-25 23:16:06 -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 in libplctag's src/tools/ab_server/ (libplctag/libplctag, MIT).
Launcher: Docker (only supported path). Docker/Dockerfile multi-stage-builds ab_server from source against a pinned libplctag 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 127.0.0.1:44818 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.

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.
Symbolic vs Logical addressing wall-clock (PR abcip-3.2, AbCipAddressingModeBenchTests) — both modes complete + emit timing. Emulate-tier only: ab_server does not currently honour the CIP Symbol Object class 0x6B cip_addr attribute that Logical mode sets, so on the fixture the two modes measure the same wire path. The bench scaffold asserts both complete + records timing for human inspection; the actual Symbolic-vs-Logical perf comparison requires a real ControlLogix / CompactLogix on the network. See docs/drivers/AbCip-Performance.md §"Addressing mode" for the full caveat.

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)
#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.

PR abcip-3.3 layers a per-device ReadStrategy selector on top (WholeUdt / MultiPacket / Auto, see AbCip-Performance.md §"Read strategy"). Strategy switching is planner-side: the dispatcher picks between AbCipUdtReadPlanner (whole-UDT) and AbCipMultiPacketReadPlanner (per-member, bundled per parent) per batch. The selector + per-batch Auto heuristic + family-compat fall-back + per-device dispatch counters are unit-tested only in AbCipReadStrategyTests — ab_server cannot host a 50-member UDT to exercise the sparse case the strategy is designed for, and the libplctag .NET wrapper (1.5.x) does not expose explicit Multi-Service-Packet bundling, so wire-level coverage stays Emulate-tier in AbCipEmulateMultiPacketReadTests (gated on AB_SERVER_PROFILE=emulate).

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 InFaulted / Severity via ValuesByOffset + assert the emitted AlarmEventArgs.

3. Micro800 unconnected-only path

Micro800 profile Notes: "ab_server has no --plc micro800 — falls back to controllogix emulation."

The empty routing path + unconnected-session requirement (PR 11) is unit-tested but never challenged at the CIP wire level. 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 narrow ConnectionSize cap

CompactLogix profile Notes: "ab_server lacks the narrower limit itself."

Driver-side AbCipPlcFamilyProfile caps ConnectionSize at the CompactLogix value per PR 10, but ab_server accepts whatever the client asks for — the cap's correctness is trusted from its unit test, never stressed against a simulator that rejects oversized requests.

PR abcip-3.1 layers the per-device ConnectionSize override on top (AbCipDeviceOptions.ConnectionSize, range [500..4002], see AbCip-Performance.md). Same gap — ab_server happily honours an oversized override against the CompactLogix profile, so the legacy-firmware warning + Forward Open rejection that real 5069-L1/L2/L3 parts emit are unit-tested only. Live coverage stays Emulate / rig-only (connect against a real CompactLogix L2 with ConnectionSize=1500 to confirm the Forward Open fails with CIP error 0x01/0x113).

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\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 narrow ConnectionSize enforcement	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?"	no (emulated as CLX)	partial	yes	yes (required)
"Does GuardLogix reject non-safety writes on safety tags?"	no	no	yes (Emulate 5580)	yes
"Does CompactLogix refuse oversized ConnectionSize?"	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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