wwtools/mbproxy

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 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.

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
DL205/DL260 Modbus quirks (BCD, CDAB, octal V-memory, FC limits)	docs/Reference/dl205.md
pymodbus simulator profile (register seeds for E2E tests)	tests/sim/dl205.json
Agent-oriented coding guide (architecture bullets, device quirks, phase context)	CLAUDE.md

Detailed documentation

The docs/ tree is organized by topic. Start with 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 — Listener topology, request flow, per-PLC isolation.
• Architecture/ConnectionModel.md — Single backend connection per PLC, TxId multiplexing, request-timeout watchdog, disconnect cascade.
• Architecture/ReadCoalescing.md — In-flight FC03/FC04 deduplication via InFlightByKeyMap.
• Architecture/ResponseCache.md — Opt-in per-tag response cache with bounded operator-configured staleness.

Features

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

Operations

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

Reference

• Reference/LogEvents.md — Stable mbproxy.* event catalog (28 events across 7 categories).

Testing

• 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):

dotnet build Mbproxy.slnx -c Debug

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

.\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:

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):

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:

# 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.

• 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 index row.