# python-snap7 server profiles

JSON-driven seed profiles for `snap7.server.Server` from
[python-snap7](https://github.com/gijzelaerr/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`](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

```powershell
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):

```powershell
.\serve.ps1 -Profile s7_1500
```

Non-default port:

```powershell
.\serve.ps1 -Profile s7_1500 -Port 102
```

Or invoke the Python shim directly:

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

## Run the integration tests

In a separate shell with the simulator running:

```powershell
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](https://github.com/gijzelaerr/python-snap7) — source + install
- [snap7.server API](https://python-snap7.readthedocs.io/en/latest/API/server.html) — `Server` class reference
- [`docs/drivers/S7-Test-Fixture.md`](../../../docs/drivers/S7-Test-Fixture.md) — coverage map + gap inventory
- [`docs/v2/s7.md`](../../../docs/v2/s7.md) — driver-side addressing + family notes