# mbproxy

A .NET 10 Windows Service that sits inline as a Modbus TCP proxy in front of a fleet of AutomationDirect DirectLOGIC DL205/DL260 controllers, rewriting BCD-encoded registers bidirectionally so upstream clients can read and write them as plain integers. The proxy also offers an opt-in per-tag response cache (default OFF) for FC03/FC04 reads with bounded operator-configured staleness — see [`docs/Architecture/ResponseCache.md`](docs/Architecture/ResponseCache.md) before enabling it.

> ⚠ **32-bit BCD wire format is "two base-10000 digits in CDAB", not standard CDAB binary Int32.** A 32-bit BCD tag at address `A` decodes as `decimal = high * 10_000 + low` where `low` is the register at `A` and `high` is the register at `A+1`. Each word independently must be 0–9999. Standard Modbus clients (NModbus, FluentModbus, Wonderware DAServer) that interpret CDAB as straight binary Int32 will silently corrupt any value > 9999 on writes and read garbage on reads. Configure your client to send/receive each register as a separate base-10000 BCD digit pair, not as a single binary Int32. Full details in [`docs/Features/BcdRewriting.md`](docs/Features/BcdRewriting.md).

## Hard constraints / prerequisites

- **Windows 10 / Server 2019 or later, 64-bit.** No Linux or Docker support — the service uses `Microsoft.Extensions.Hosting.WindowsServices` and the Windows Event Log.
- **Modbus TCP backends reachable** from the proxy host on port 502 (or the port configured per PLC). The H2-ECOM100 module caps simultaneous connections at **4 per PLC** — a fifth upstream client will fail to connect.
- **Admin rights** to install the service (`install.ps1` requires elevation).
- **No COM dependency** — this is a pure .NET 10 socket-level proxy (unlike the `.NET Framework 4.8 / x86` siblings in this repo).
- **Python 3.10+** on the test machine to run the pymodbus-backed E2E simulator (not needed to run the service in production).

## Layout

```
src/Mbproxy/          Main C# project (net10.0, Microsoft.NET.Sdk.Worker)
tests/Mbproxy.Tests/  xUnit v3 test project (314 unit + 48 E2E tests)
install/              PowerShell install/uninstall scripts and config template
docs/                 Architecture, features, operations, reference, and testing docs
```

## Resource index

| Task | Go to |
|---|---|
| Architecture entry point — listener topology, request flow, per-PLC isolation | [`docs/Architecture/Overview.md`](docs/Architecture/Overview.md) |
| DL205/DL260 Modbus quirks (BCD, CDAB, octal V-memory, FC limits) | [`docs/Reference/dl205.md`](docs/Reference/dl205.md) |
| pymodbus simulator profile (register seeds for E2E tests) | [`tests/sim/dl205.json`](tests/sim/dl205.json) |
| Agent-oriented coding guide (architecture bullets, device quirks, phase context) | [`CLAUDE.md`](CLAUDE.md) |

## Detailed documentation

The `docs/` tree is organized by topic. Start with [`Architecture/Overview.md`](docs/Architecture/Overview.md) for the end-to-end picture; jump to the focused pages below when you need depth on one area.

### Architecture

- [`Architecture/Overview.md`](docs/Architecture/Overview.md) — Listener topology, request flow, per-PLC isolation.
- [`Architecture/ConnectionModel.md`](docs/Architecture/ConnectionModel.md) — Single backend connection per PLC, TxId multiplexing, request-timeout watchdog, disconnect cascade.
- [`Architecture/ReadCoalescing.md`](docs/Architecture/ReadCoalescing.md) — In-flight FC03/FC04 deduplication via `InFlightByKeyMap`.
- [`Architecture/ResponseCache.md`](docs/Architecture/ResponseCache.md) — Opt-in per-tag response cache with bounded operator-configured staleness.

### Features

- [`Features/BcdRewriting.md`](docs/Features/BcdRewriting.md) — BCD codec, CDAB word order, FC03/04/06/16 scope, partial-overlap policy.
- [`Features/HotReload.md`](docs/Features/HotReload.md) — `IOptionsMonitor`-driven config reload with per-change-kind reconcile rules.

### Operations

- [`Operations/Configuration.md`](docs/Operations/Configuration.md) — Full `appsettings.json` reference: every `Mbproxy:*` key, default, and validation rule.
- [`Operations/StatusPage.md`](docs/Operations/StatusPage.md) — Admin endpoint surface (`/`, `/status.json`) with every JSON field documented.
- [`Operations/Troubleshooting.md`](docs/Operations/Troubleshooting.md) — Diagnosis playbook keyed to log events and status counters.

### Reference

- [`Reference/LogEvents.md`](docs/Reference/LogEvents.md) — Stable `mbproxy.*` event catalog (28 events across 7 categories).

### Testing

- [`Testing/Simulator.md`](docs/Testing/Simulator.md) — pymodbus DL205 fixture, skip policy, and the load-bearing pymodbus 3.13 framer quirk.

## Build and run

**Build (Debug, multi-file — fast for iteration):**

```powershell
dotnet build Mbproxy.slnx -c Debug
```

**Publish (Release, single-file, win-x64):**

```powershell
.\install\publish.ps1 -Clean
```

Produces both flavours under `publish-out\`:

| Flavour | Path | Size | Target prerequisite |
|---|---|---|---|
| Self-contained | `publish-out\self-contained\Mbproxy.exe` | ~100 MB | None — bundles .NET 10 + ASP.NET Core runtime |
| Framework-dependent | `publish-out\framework-dependent\Mbproxy.exe` | ~1.5 MB | .NET 10 + ASP.NET Core preinstalled |

Pass `-OutputDir <path>` to publish elsewhere; omit `-Clean` to skip the wipe. The script wraps `dotnet publish src/Mbproxy/Mbproxy.csproj -c Release -r win-x64 [-p:SelfContained=false]` — run those directly if you only need one flavour.

**Run tests:**

```powershell
dotnet test Mbproxy.slnx -c Debug                    # all tests
dotnet test Mbproxy.slnx -c Debug --filter Category=Unit   # unit tests only (no Python required)
dotnet test Mbproxy.slnx -c Debug --filter Category=E2E    # E2E tests (require Python + pymodbus)
```

**Run interactively (without installing as a service):**

```powershell
cd src/Mbproxy
dotnet run --configuration Debug
```

Edit `src/Mbproxy/appsettings.json` to configure PLCs before running. The admin status page will be at `http://localhost:8080/` by default.

## Install

The `install/` directory holds the publish, install, and uninstall scripts. Quick path:

```powershell
# 1. Publish (produces publish-out\self-contained\ and publish-out\framework-dependent\)
.\install\publish.ps1 -Clean

# 2. Install (elevated PowerShell) — point at the flavour you want to deploy
.\install\install.ps1 -PublishOutput .\publish-out\self-contained -Start

# 3. Edit the config that was placed at %ProgramData%\mbproxy\appsettings.json

# 4. Verify
Invoke-WebRequest http://localhost:8080/ -UseBasicParsing
```

## Maintenance

Documentation doctrine for this repo: [`../DOCS-GUIDE.md`](../DOCS-GUIDE.md).

- This README routes to deep docs — it does not duplicate them.
- Design decisions and rationale live in the `docs/` tree (Architecture, Features, Operations, Reference, Testing).
- When the service's public surface or task→tool mapping changes, update this README and the root [`../CLAUDE.md`](../CLAUDE.md) index row.
