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Joseph Doherty 1d3544f18e S7 integration fixture — python-snap7 server closes the wire-level coverage gap (#216 ) + per-driver fixture coverage docs for every driver in the fleet. Closes #216 . Two shipments in one PR because the docs landed as I surveyed each driver's fixture + the S7 work is the first wire-level-gap closer pulled from that survey.

S7 integration — AbCip/Modbus already have real-simulator integration suites; S7 had zero wire-level coverage despite being a Tier-A driver (all unit tests mocked IS7Client). Picked python-snap7's `snap7.server.Server` over raw Snap7 C library because `pip install` beats per-OS binary-pin maintenance, the package ships a Python __main__ shim that mirrors our existing pymodbus serve.ps1 + *.json pattern structurally, and the python-snap7 project is actively maintained. New project `tests/ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests/` with four moving parts: (a) `Snap7ServerFixture` — collection-scoped TCP probe on `localhost:1102` that sets `SkipReason` when the simulator's not running, matching the `ModbusSimulatorFixture` shape one directory over (same S7_SIM_ENDPOINT env var override convention for pointing at a real S7 CPU on port 102); (b) `PythonSnap7/` — `serve.ps1` wrapper + `server.py` shim + `s7_1500.json` seed profile + `README.md` documenting install / run / known limitations; (c) `S7_1500/S7_1500Profile.cs` — driver-side `S7DriverOptions` whose tag addresses map 1:1 to the JSON profile's seed offsets (DB1.DBW0 u16, DB1.DBW10 i16, DB1.DBD20 i32, DB1.DBD30 f32, DB1.DBX50.3 bool, DB1.DBW100 scratch); (d) `S7_1500SmokeTests` — three tests proving typed reads + write-then-read round-trip work through real S7netplus + real ISO-on-TCP + real snap7 server. Picked port 1102 default instead of S7-standard 102 because 102 is privileged on Linux + triggers Windows Firewall prompt; S7netplus 0.20 has a 5-arg `Plc(CpuType, host, port, rack, slot)` ctor that lets the driver honour `S7DriverOptions.Port`, but the existing driver code called the 4-arg overload + silently hardcoded 102. One-line driver fix (S7Driver.cs:87) threads `_options.Port` through — the S7 unit suite (58/58) still passes unchanged because every unit test uses a fake IS7Client that never sees the real ctor. Server seed-type matrix in `server.py` covers u8 / i8 / u16 / i16 / u32 / i32 / f32 / bool-with-bit / ascii (S7 STRING with max_len header). register_area takes the SrvArea enum value, not the string name — a 15-minute debug after the first test run caught that; documented inline.

Per-driver test-fixture coverage docs — eight new files in `docs/drivers/` laying out what each driver's harness actually benchmarks vs. what's trusted from field deployments. Pattern mirrors the AbServer-Test-Fixture.md doc that shipped earlier in this arc: TL;DR → What the fixture is → What it actually covers → What it does NOT cover → When-to-trust table → Follow-up candidates → Key files. Ugly truth the survey made visible: Galaxy + Modbus + (now) S7 + AB CIP have real wire-level coverage; AB Legacy / TwinCAT / FOCAS / OpcUaClient are still contract-only because their libraries ship no fake + no open-source simulator exists (AB Legacy PCCC), no public simulator exists (FOCAS), the vendor SDK has no in-process fake (TwinCAT/ADS.NET), or the test wiring just hasn't happened yet (OpcUaClient could trivially loopback against this repo's own server — flagged as #215). Each doc names the specific follow-up route: Snap7 server for S7 (done), TwinCAT 3 developer-runtime auto-restart for TwinCAT, Tier-C out-of-process Host for FOCAS, lab rigs for AB Legacy + hardware-gated bits of the others. `docs/drivers/README.md` gains a coverage-map section linking all eight. Tracking tasks #215-#222 filed for each PR-able follow-up.

Build clean (driver + integration project + docs); S7.Tests 58/58 (unchanged); S7.IntegrationTests 3/3 (new, verified end-to-end against a live python-snap7 server: `driver_reads_seeded_u16_through_real_S7comm`, `driver_reads_seeded_typed_batch`, `driver_write_then_read_round_trip_on_scratch_word`). Next fixture follow-up is #215 (OpcUaClient loopback against own server) — highest ROI of the remaining set, zero external deps.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-04-20 11:29:15 -04:00

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python-snap7 server profiles

JSON-driven seed profiles for snap7.server.Server from python-snap7 (MIT). Shape mirrors the pymodbus profiles under tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Pymodbus/ — a PowerShell launcher + per-family JSON + a Python shim that the launcher exec's.

File	What it seeds	Test category
`s7_1500.json`	DB1 (1024 bytes) with smoke values at known offsets (i16 @ DBW10, i32 @ DBD20, f32 @ DBD30, bool @ DBX50.3, scratch word @ DBW100, STRING "Hello" @ 200) + MB (256 bytes) with probe marker at MW0.	`Trait=Integration, Device=S7_1500`

Default port 1102 (non-privileged; sidesteps Windows Firewall prompt + Linux's root-required bind on port 102). The fixture (Snap7ServerFixture) defaults to localhost:1102. Override via S7_SIM_ENDPOINT to point at a real S7 CPU on port 102. The S7 driver threads _options.Port through to S7netplus's 5-arg Plc ctor, so the non-standard port works end-to-end.

Install

pip install "python-snap7>=2.0"

python-snap7 wraps the upstream snap7 C library; the install pulls platform-specific binaries automatically. Requires Python ≥ 3.10. Windows Firewall will prompt on first bind; allow Private network.

Run

Foreground (Ctrl+C to stop):

.\serve.ps1 -Profile s7_1500

Non-default port:

.\serve.ps1 -Profile s7_1500 -Port 102

Or invoke the Python shim directly:

python .\server.py .\s7_1500.json --port 1102

Run the integration tests

In a separate shell with the simulator running:

cd C:\Users\dohertj2\Desktop\lmxopcua
dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests

Tests auto-skip with a clear SkipReason when localhost:1102 isn't reachable within 2 seconds.

What's encoded in `s7_1500.json`

Address	Type	Seed	Purpose
`DB1.DBW0`	u16	`4242`	read-back probe
`DB1.DBW10`	i16	`-12345`	smoke i16 read
`DB1.DBD20`	i32	`1234567890`	smoke i32 read
`DB1.DBD30`	f32	`3.14159`	smoke f32 read (big-endian)
`DB1.DBX50.3`	bool	`true`	smoke bool read at bit 3
`DB1.DBW100`	u16	`0`	scratch for write-then-read
`DB1.STRING[200]`	S7 STRING	`"Hello"` (max 32, cur 5)	smoke string read
`MW0`	u16	`1`	`S7ProbeOptions.ProbeAddress` default

Seed types supported by server.py: u8, i8, u16, i16, u32, i32, f32, bool (with "bit": 0..7), ascii (S7 STRING type with configurable max_len).

Known limitations (python-snap7 upstream)

The snap7.server.Server docstring admits:

"Legacy S7 server implementation. Emulates a Siemens S7 PLC for testing and development purposes. [...] pure Python emulator implementation that simulates PLC behaviour for protocol compliance testing rather than full industrial-grade functionality."

What that means in practice — things this fixture does NOT cover:

S7-1500 Optimized-DB symbolic access — the real S7-1500 with TIA Portal optimization enabled uses symbolic addressing that's wire-incompatible with absolute DB addressing. Our driver targets non-optimized DBs; so does snap7's server. Rig test required to verify against an Optimized CPU.
PG / OP / S7-Basic session types — S7netplus uses OP session; the simulator accepts whatever session type is requested, unlike real CPUs that allocate session slots differently.
SCL variant-specific behaviour — e.g. S7-1200 missing certain PDU types, S7-300's older handshake, S7-400 multi-CPU racks with non-zero slot. Simulator collapses all into one generic CPU emulation.
PUT/GET-disabled-by-default — real S7-1200/1500 CPUs refuse reads when PUT/GET is off in TIA Portal hardware config; the driver maps that to BadDeviceFailure. Simulator has no such toggle + always accepts.

References

python-snap7 GitHub — source + install
snap7.server API — Server class reference
docs/drivers/S7-Test-Fixture.md — coverage map + gap inventory
docs/v2/s7.md — driver-side addressing + family notes

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