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>
This commit is contained in:
Joseph Doherty
@@ -0,0 +1,110 @@
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# python-snap7 server profiles
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JSON-driven seed profiles for `snap7.server.Server` from
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[python-snap7](https://github.com/gijzelaerr/python-snap7) (MIT). Shape
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mirrors the pymodbus profiles under
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`tests/ZB.MOM.WW.OtOpcUa.Driver.Modbus.IntegrationTests/Pymodbus/` — a
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PowerShell launcher + per-family JSON + a Python shim that the launcher
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exec's.
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| File | What it seeds | Test category |
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|---|---|---|
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| [`s7_1500.json`](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` |
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Default port **1102** (non-privileged; sidesteps Windows Firewall prompt +
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Linux's root-required bind on port 102). The fixture
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(`Snap7ServerFixture`) defaults to `localhost:1102`. Override via
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`S7_SIM_ENDPOINT` to point at a real S7 CPU on port 102. The S7 driver
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threads `_options.Port` through to S7netplus's 5-arg `Plc` ctor, so the
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non-standard port works end-to-end.
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## Install
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```powershell
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pip install "python-snap7>=2.0"
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```
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`python-snap7` wraps the upstream `snap7` C library; the install pulls
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platform-specific binaries automatically. Requires Python ≥ 3.10.
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Windows Firewall will prompt on first bind; allow Private network.
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## Run
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Foreground (Ctrl+C to stop):
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```powershell
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.\serve.ps1 -Profile s7_1500
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```
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Non-default port:
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```powershell
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.\serve.ps1 -Profile s7_1500 -Port 102
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```
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Or invoke the Python shim directly:
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```powershell
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python .\server.py .\s7_1500.json --port 1102
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```
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## Run the integration tests
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In a separate shell with the simulator running:
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```powershell
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cd C:\Users\dohertj2\Desktop\lmxopcua
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dotnet test tests\ZB.MOM.WW.OtOpcUa.Driver.S7.IntegrationTests
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```
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Tests auto-skip with a clear `SkipReason` when `localhost:1102` isn't
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reachable within 2 seconds.
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## What's encoded in `s7_1500.json`
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| Address | Type | Seed | Purpose |
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|---|---|---|---|
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| `DB1.DBW0` | u16 | `4242` | read-back probe |
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| `DB1.DBW10` | i16 | `-12345` | smoke i16 read |
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| `DB1.DBD20` | i32 | `1234567890` | smoke i32 read |
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| `DB1.DBD30` | f32 | `3.14159` | smoke f32 read (big-endian) |
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| `DB1.DBX50.3` | bool | `true` | smoke bool read at bit 3 |
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| `DB1.DBW100` | u16 | `0` | scratch for write-then-read |
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| `DB1.STRING[200]` | S7 STRING | `"Hello"` (max 32, cur 5) | smoke string read |
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| `MW0` | u16 | `1` | `S7ProbeOptions.ProbeAddress` default |
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Seed types supported by `server.py`: `u8`, `i8`, `u16`, `i16`, `u32`,
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`i32`, `f32`, `bool` (with `"bit": 0..7`), `ascii` (S7 STRING type with
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configurable `max_len`).
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## Known limitations (python-snap7 upstream)
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The `snap7.server.Server` docstring admits:
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> "Legacy S7 server implementation. Emulates a Siemens S7 PLC for testing
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> and development purposes. [...] pure Python emulator implementation that
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> simulates PLC behaviour for protocol compliance testing rather than
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> full industrial-grade functionality."
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What that means in practice — things this fixture does NOT cover:
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- **S7-1500 Optimized-DB symbolic access** — the real S7-1500 with TIA Portal
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optimization enabled uses symbolic addressing that's wire-incompatible with
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absolute DB addressing. Our driver targets non-optimized DBs; so does
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snap7's server. Rig test required to verify against an Optimized CPU.
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- **PG / OP / S7-Basic session types** — S7netplus uses OP session; the
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simulator accepts whatever session type is requested, unlike real CPUs
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that allocate session slots differently.
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- **SCL variant-specific behaviour** — e.g. S7-1200 missing certain PDU
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types, S7-300's older handshake, S7-400 multi-CPU racks with non-zero
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slot. Simulator collapses all into one generic CPU emulation.
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- **PUT/GET-disabled-by-default** — real S7-1200/1500 CPUs refuse reads
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when PUT/GET is off in TIA Portal hardware config; the driver maps that
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to `BadDeviceFailure`. Simulator has no such toggle + always accepts.
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## References
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- [python-snap7 GitHub](https://github.com/gijzelaerr/python-snap7) — source + install
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- [snap7.server API](https://python-snap7.readthedocs.io/en/latest/API/server.html) — `Server` class reference
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- [`docs/drivers/S7-Test-Fixture.md`](../../../docs/drivers/S7-Test-Fixture.md) — coverage map + gap inventory
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- [`docs/v2/s7.md`](../../../docs/v2/s7.md) — driver-side addressing + family notes
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@@ -0,0 +1,35 @@
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{
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"_description": "S7-1500 profile — single DB1 (1024 bytes) + MB (256 bytes) with well-known seeds at named offsets for the smoke + byte-order + string tests. Big-endian Siemens wire order throughout.",
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"areas": [
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{
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"area": "DB",
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"index": 1,
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"size": 1024,
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"seeds": [
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{ "_desc": "DB1.DBW0 — read-back probe, S7Driver default ProbeAddress target is MW0; this shadows it",
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"offset": 0, "type": "u16", "value": 4242 },
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{ "_desc": "DB1.DBW10 — i16 smoke value for SmokeI16 read path",
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"offset": 10, "type": "i16", "value": -12345 },
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{ "_desc": "DB1.DBD20 — i32 smoke value for SmokeI32 read path",
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"offset": 20, "type": "i32", "value": 1234567890 },
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{ "_desc": "DB1.DBD30 — f32 smoke value for SmokeF32 read path (IEEE-754 big-endian)",
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"offset": 30, "type": "f32", "value": 3.14159 },
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{ "_desc": "DB1.DBX50.3 — bool bit at byte-50 bit-3 for SmokeBool read path",
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"offset": 50, "type": "bool", "value": true, "bit": 3 },
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{ "_desc": "DB1.DBW100 — scratch for write-then-read round-trip tests; seeded 0",
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"offset": 100, "type": "u16", "value": 0 },
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{ "_desc": "DB1.STRING[200] — S7 string 'Hello' (max 32, cur 5)",
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"offset": 200, "type": "ascii", "value": "Hello", "max_len": 32 }
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]
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},
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{
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"area": "MK",
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"index": 0,
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"size": 256,
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"seeds": [
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{ "_desc": "MW0 — probe target for S7ProbeOptions.ProbeAddress default",
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"offset": 0, "type": "u16", "value": 1 }
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]
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}
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]
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}
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@@ -0,0 +1,56 @@
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<#
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.SYNOPSIS
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Launches the python-snap7 S7 server with one of the integration-test
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profiles. Foreground process — Ctrl+C to stop. Mirrors the pymodbus
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`serve.ps1` wrapper in tests\...\Modbus.IntegrationTests\Pymodbus\.
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.PARAMETER Profile
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Which profile JSON to load: currently only 's7_1500' ships. Additional
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families (S7-1200, S7-300) can drop in as new JSON files alongside.
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.PARAMETER Port
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TCP port to bind. Default 1102 (non-privileged; matches
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Snap7ServerFixture default endpoint). Pass 102 to match S7 standard —
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requires root on Linux + triggers Windows Firewall prompt.
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.EXAMPLE
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.\serve.ps1 -Profile s7_1500
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.EXAMPLE
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.\serve.ps1 -Profile s7_1500 -Port 102
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#>
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[CmdletBinding()]
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param(
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[Parameter(Mandatory)] [ValidateSet('s7_1500')] [string]$Profile,
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[int]$Port = 1102
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)
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$ErrorActionPreference = 'Stop'
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$here = $PSScriptRoot
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# python-snap7 installs the `snap7` Python package; we call via `python -m`
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# or via the server.py shim in this folder. Shim path is simpler to diagnose.
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$python = Get-Command python -ErrorAction SilentlyContinue
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if (-not $python) { $python = Get-Command py -ErrorAction SilentlyContinue }
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if (-not $python) {
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Write-Error "python not found on PATH. Install Python 3.10+ and 'pip install python-snap7'."
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exit 1
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}
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# Verify python-snap7 is installed so failures surface here, not in a
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# confusing ImportError from server.py.
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& $python.Source -c "import snap7.server" 2>$null
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if ($LASTEXITCODE -ne 0) {
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Write-Error "python-snap7 not importable. Install with: pip install 'python-snap7>=2.0'"
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exit 1
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}
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$jsonFile = Join-Path $here "$Profile.json"
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if (-not (Test-Path $jsonFile)) {
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Write-Error "Profile config not found: $jsonFile"
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exit 1
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}
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Write-Host "Starting python-snap7 server: profile=$Profile TCP=localhost:$Port"
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Write-Host "Ctrl+C to stop."
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& $python.Source (Join-Path $here "server.py") $jsonFile --port $Port
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@@ -0,0 +1,150 @@
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"""python-snap7 S7 server for integration tests.
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Reads a JSON profile from argv[1], allocates bytearrays for each declared area
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(DB / MB / EB / AB), poke-seeds values at declared offsets, then starts the
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snap7 Server on the configured port + blocks until Ctrl+C. Shape intentionally
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mirrors the pymodbus `serve.ps1 + *.json` pattern one directory over so
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someone familiar with the Modbus fixture can read this without re-learning.
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The snap7.server.Server class is the MIT-licensed S7 PLC emulator wrapped by
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python-snap7 (https://github.com/gijzelaerr/python-snap7). Its own docstring
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admits "protocol compliance testing rather than full industrial-grade
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functionality" — good enough for ISO-on-TCP wire-level round-trip but NOT
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for S7-1500 Optimized-DB symbolic access, SCL variant-specific behaviour, or
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PG/OP/S7-Basic session differentiation.
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"""
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from __future__ import annotations
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import argparse
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import ctypes
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import json
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import signal
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import sys
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import time
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from pathlib import Path
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# python-snap7 installs as `snap7` package; Server class lives under `snap7.server`.
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import snap7
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from snap7.type import SrvArea
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|
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# Map JSON area names → SrvArea enum values. PE = inputs (I/E), PA = outputs
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# (Q/A), MK = memory (M), DB = data blocks, TM = timers, CT = counters.
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AREA_MAP: dict[str, int] = {
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"PE": SrvArea.PE,
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"PA": SrvArea.PA,
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"MK": SrvArea.MK,
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"DB": SrvArea.DB,
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"TM": SrvArea.TM,
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"CT": SrvArea.CT,
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}
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def seed_buffer(buf: bytearray, seeds: list[dict]) -> None:
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"""Poke seed values into the area buffer at declared byte offsets.
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Each seed is {"offset": int, "type": str, "value": int|float|bool|str}
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where type ∈ {u8, i8, u16, i16, u32, i32, f32, bool, ascii}. Endianness is
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big-endian (Siemens wire format).
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"""
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for seed in seeds:
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off = int(seed["offset"])
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t = seed["type"]
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v = seed["value"]
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if t == "u8":
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buf[off] = int(v) & 0xFF
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elif t == "i8":
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buf[off] = int(v) & 0xFF
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elif t == "u16":
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buf[off:off + 2] = int(v).to_bytes(2, "big", signed=False)
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elif t == "i16":
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buf[off:off + 2] = int(v).to_bytes(2, "big", signed=True)
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elif t == "u32":
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buf[off:off + 4] = int(v).to_bytes(4, "big", signed=False)
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elif t == "i32":
|
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buf[off:off + 4] = int(v).to_bytes(4, "big", signed=True)
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elif t == "f32":
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import struct
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buf[off:off + 4] = struct.pack(">f", float(v))
|
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elif t == "bool":
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bit = int(seed.get("bit", 0))
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if bool(v):
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buf[off] |= (1 << bit)
|
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else:
|
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buf[off] &= ~(1 << bit) & 0xFF
|
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elif t == "ascii":
|
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# Siemens STRING type: byte 0 = max length, byte 1 = current length,
|
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# bytes 2+ = payload. Seeds supply the payload text; we fill max/cur.
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payload = str(v).encode("ascii")
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max_len = int(seed.get("max_len", 254))
|
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buf[off] = max_len
|
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buf[off + 1] = len(payload)
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buf[off + 2:off + 2 + len(payload)] = payload
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else:
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raise ValueError(f"Unknown seed type '{t}'")
|
||||
|
||||
|
||||
def main() -> int:
|
||||
parser = argparse.ArgumentParser(description="python-snap7 S7 server for integration tests")
|
||||
parser.add_argument("profile", help="Path to profile JSON")
|
||||
parser.add_argument("--port", type=int, default=1102, help="TCP port (default 1102 non-privileged)")
|
||||
args = parser.parse_args()
|
||||
|
||||
profile_path = Path(args.profile)
|
||||
if not profile_path.is_file():
|
||||
print(f"profile not found: {profile_path}", file=sys.stderr)
|
||||
return 1
|
||||
|
||||
with profile_path.open() as f:
|
||||
profile = json.load(f)
|
||||
|
||||
server = snap7.server.Server()
|
||||
# Keep bytearray refs alive for the server's lifetime — snap7 doesn't copy
|
||||
# the buffer, it takes a pointer. Letting GC collect would corrupt reads.
|
||||
buffers: list[bytearray] = []
|
||||
|
||||
for area_decl in profile.get("areas", []):
|
||||
area_name = area_decl["area"]
|
||||
if area_name not in AREA_MAP:
|
||||
print(f"unknown area '{area_name}' (expected one of {list(AREA_MAP)})", file=sys.stderr)
|
||||
return 1
|
||||
index = int(area_decl.get("index", 0)) # DB number for DB area, 0 for MK/PE/PA
|
||||
size = int(area_decl["size"])
|
||||
buf = bytearray(size)
|
||||
seed_buffer(buf, area_decl.get("seeds", []))
|
||||
buffers.append(buf)
|
||||
# register_area takes (area, index, c-array); we wrap the bytearray
|
||||
# into a ctypes char array so the native lib can take &buf[0].
|
||||
arr_type = ctypes.c_char * size
|
||||
arr = arr_type.from_buffer(buf)
|
||||
server.register_area(AREA_MAP[area_name], index, arr)
|
||||
print(f" seeded {area_name}{index} size={size} seeds={len(area_decl.get('seeds', []))}")
|
||||
|
||||
port = int(args.port)
|
||||
print(f"Starting python-snap7 server on TCP {port} (Ctrl+C to stop)")
|
||||
server.start(tcp_port=port)
|
||||
|
||||
stop = {"sig": False}
|
||||
def _handle(*_a):
|
||||
stop["sig"] = True
|
||||
signal.signal(signal.SIGINT, _handle)
|
||||
try:
|
||||
signal.signal(signal.SIGTERM, _handle)
|
||||
except Exception:
|
||||
pass # SIGTERM not on all platforms
|
||||
|
||||
try:
|
||||
while not stop["sig"]:
|
||||
time.sleep(0.25)
|
||||
finally:
|
||||
print("stopping python-snap7 server")
|
||||
try:
|
||||
server.stop()
|
||||
except Exception:
|
||||
pass
|
||||
return 0
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
sys.exit(main())
|
||||
Reference in New Issue
Block a user