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PROTOCOL_VERSION 5 -> 6, and one behaviour: `bridge.busy` maps to 425 Too Early in all three responders. Everything else is free, and that is the point. The key rides in the command body, which every write endpoint already passes through verbatim; `champ.boss.killed` lands in `events` and on the feed through the generic forward path with no arm of its own. No store migration — nothing gains a column. Worth naming what the dumb-forwarder property means here specifically: the sidecar makes no idempotency promise of its own. It does not dedupe, does not cache, and does not know what a key means. The guarantee is the shard's, end to end, which is the only place it can be. 425 rather than 409 because 409 is already the protocol-version gate's answer, and the two want opposite dispositions from a client: a version mismatch is a deployment fault nobody should retry, a busy shard is a retry that will succeed. Sharing a status would make the difference readable only by inspecting the body, which is how a retry loop ends up hiding a mismatched deployment. A replayed reply is an ordinary 200 — `replayed: true` is for the log. Co-Authored-By: Claude <noreply@anthropic.com>
uo-link — Rust sidecar
The Rust sidecar half of the Runic Gateway bridge. The ServUO shard dials out to this sidecar over a loopback TCP socket (newline-delimited JSON); the sidecar owns the WebSocket + REST API the website consumes, along with auth, buffering, and fan-out.
ServUO plugin (C#, net48) ──loopback TCP, newline-JSON──► Rust sidecar ──WebSocket/JSON──► website
(RunicGateway/servuo-plugins) >>> THIS REPO <<<
The shard never speaks WebSocket and exposes no port of its own — the sidecar is the only network-facing component, which is what keeps the game unreachable from the internet.
Running a shard? Don't build this
The Runic Gateway installer installs this sidecar for you — the released binary, its config, a hardened service account and the service registration — alongside the shard plugin, in one run, on Linux or Windows:
sudo ./runicgateway-installer-linux-x86_64 install
It ends by printing the base URL, WebSocket URL, protocol version and auth token to paste into Admin → Shard on your site. Guide: installer/INSTALL.md.
Installing it yourself is supported too — the release binaries on this repo's releases page are the same ones the installer fetches, and INSTALL.md Appendix A3–A4 covers placing the binary and registering the service by hand.
Everything below this line is for developing on the sidecar.
Related repos
| Repo | What |
|---|---|
this — RunicGateway/link |
The Rust sidecar (sidecar/). |
| RunicGateway/installer | The installer — deploys this sidecar and the plugin onto a shard host. The supported way to set one up. |
| RunicGateway/servuo-plugins | The C# ServUO plugin — the shard side of the bridge (overlay/, patches/, deploy.ps1, test scaffolding). |
| RunicGateway/docs | All project documentation — design docs, protocol spec, integration guide, research. |
Layout
| Path | What |
|---|---|
sidecar/ |
The Rust sidecar crate — terminates the loopback link to the shard, exposes WS + REST to the website. See sidecar/README.md. |
.gitea/workflows/pr-checks.yml |
Gates every PR into main on cargo fmt --check, cargo clippy -D warnings, and cargo test. |
.gitea/workflows/release.yml |
Builds + releases the sidecar binary (Linux + Windows) on every merge to main. |
Build & run (development)
Building from source is for working on the sidecar; a deployment gets its binary from a release, via the installer or by hand. The sidecar is a standard cargo crate:
cd sidecar
cargo build --release # binary at target/release/uo-link-sidecar
cp sidecar.toml.example sidecar.toml # then edit
cargo run --release
Deploying it by hand rather than developing on it: --config <PATH> names the config file (as does
$UOLINK_CONFIG), and --print-config prints the resolved settings — including the auth token
the website needs — as JSON, provisioning the config file on first run. That is the supported way
to read the token back; it is not meant to be scraped from the log.
uo-link-sidecar --print-config --config /etc/runicgateway/sidecar.toml
Running as a service
The same binary runs in the foreground and as a system service — there is no --service flag to
remember, because the process can tell how it was started.
- Linux/systemd supervises any foreground process, so the unit just runs the binary.
SIGTERM(whatsystemctl stopsends) andSIGINTboth unwind it cleanly; logs go to the journal. - Windows cannot. The service control manager only supervises a process that connects back to
it within ~30 seconds via
StartServiceCtrlDispatcher; a plain console program registered withsc.exe createis killed with error 1053 despite running perfectly. So on Windows the sidecar speaks that handshake: started by the SCM it runs as a service, started from a shell the connect fails withERROR_FAILED_SERVICE_CONTROLLER_CONNECTand it falls through to an ordinary foreground run. It reportsRunningonly once the shard port is bound and the store is open, and — having no console — logs touo-link-sidecar.<date>.logbeside its config, rolled daily.
Only the starting and stopping is platform-specific: src/app.rs is the entire sidecar and is
shared, while src/windows.rs and src/unix.rs do nothing but start it and tell it when to stop.
The Windows crates are declared under [target.'cfg(windows)'.dependencies], so Cargo neither
resolves nor builds them for a Linux target.
Registering the service is the installer's job; to do it by hand see INSTALL.md Appendix A4.
.gitea/workflows/release.yml cross-compiles Linux + Windows binaries and cuts a Gitea release on
every merge to main (conventional-commit versioning). See sidecar/README.md
for configuration and the wire protocol.
Before that, .gitea/workflows/pr-checks.yml runs the same gates on every pull request into main —
cargo fmt --check, cargo clippy --all-targets -- -D warnings, then cargo test --locked. Run them
locally before pushing and the PR will be green:
cd sidecar
cargo fmt # or --check to just report
cargo clippy --locked --all-targets -- -D warnings
cargo test --locked
Deployment & compatibility
The plugin (RunicGateway/servuo-plugins) and this sidecar are deployed together but built independently:
- The plugin is deployed as source into the ServUO server root and compiled by ServUO at boot — no build artifact, no CI build.
- The sidecar is a standalone Rust binary released from this repo.
The only coupling is the loopback JSON protocol (the shard dials 127.0.0.1). Compatibility is a
protocol concern, not a build-order one — keep the event/command catalog in sync across the two
repos. Canonical spec:
PLAN.md §5/§7 and
INTEGRATION.md.
Because a wedged or absent sidecar cannot stall the shard, either side can be deployed or restarted
independently.
License
Runic Gateway is free software, licensed under the GNU General Public License v3.0 or later — see LICENSE.md.
Copyright (C) 2026 Runic Gateway
This program is free software: you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation, either version 3 of the License, or (at your option) any later
version. It is distributed WITHOUT ANY WARRANTY; without even the implied
warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
Contributions are welcome — please read CONTRIBUTING.md (note the AI-usage disclosure requirement) and our Code of Conduct. Report vulnerabilities privately per SECURITY.md.