# toybox

Vats whose code is installed at runtime: each vat is a Durable Object whose app runs as a [facet](https://developers.cloudflare.com/dynamic-workers/usage/durable-object-facets/) on code loaded through workerd's Worker Loader. Think `vatAdmin.createVat(bundle)`, with a supervisor per vat.

- [supervisor.js](supervisor.js): `Vat` stores code by SHA-256 and runs the app on it; `Public` and `Admin` are the two entrypoints; `Egress` is a grant of one host.
- [switchboard.js](switchboard.js): a separate workerd process, the vats' only way out, after [Flower](https://github.com/NuxiNL/flower)'s switchboard: each of its sockets serves a Cap'n Web `Handle` with fixed labels, and `constrain(labels)` returns a narrower one.
- [labels.js](labels.js): Flower's label rule, shared by both: labels only accumulate, a missing key matches anything, and a key both sides set must agree.
- [config.capnp](config.capnp): the sockets have no addresses; whoever starts workerd hands them in, so holding a socket is the authority it grants.

| socket | reaches | what its holder can do |
|---|---|---|
| `http` | `Public` | `GET /<vat>/…`: talk to a vat's app |
| `admin` | `Admin` | `PUT /<vat>` with an ES module body: install it and (re)start the app; its storage carries over. `?egress=<labels as JSON>` grants the app egress within those labels. |

An app must export `class App extends DurableObject` (see [apps/](apps/)). Its global `fetch` always throws: nothing in a vat is ambient. A grant arrives as `env.egress`, an `Egress` with the labels in `ctx.props`. Its `fetch`, WebSocket upgrades included, goes through a switchboard handle constrained to those labels; the switchboard refuses the rest, which comes back as a 403. `env.egress.constrain(labels)` returns a narrower `Egress`. It is an object, so the app can pass it to whichever of its parts should have it.

| label | constrains |
|---|---|
| `scheme` | `http` or `https` |
| `host` | host name or address, no port |
| `port` | explicit, or the scheme's default |
| `network` | set by the switchboard socket: `public` or `local` |

The switchboard has two sockets, so two root handles: `public` (no loopback or private addresses) and `local`. toybox holds one, as an external service (`-e switchboard=unix:…`): `pnpm start` and the systemd units give it `public`; the tests give theirs `local` to reach an echo server.

## Run it

```sh
pnpm install
pnpm test         # real workerds: install, upgrade, isolation, egress grants and constrain, fetch and WebSocket out, crash and restart
pnpm switchboard  # systemd-socket-activate on ./switchboard-public.sock and ./switchboard-local.sock
pnpm start        # likewise on 127.0.0.1:8787 and ./admin.sock; state in ./state
```

Then, in a third terminal:

```sh
curl -X PUT --unix-socket admin.sock --data-binary @apps/counter-v1.js http://toybox/alice
curl localhost:8787/alice                # v1 count 1
curl -X PUT --unix-socket admin.sock --data-binary @apps/counter-v2.js http://toybox/alice
curl localhost:8787/alice                # v2 count 2

curl -g -X PUT --unix-socket admin.sock --data-binary @apps/egress-probe.js 'http://toybox/erin?egress={"host":"example.com"}'
curl 'localhost:8787/erin?url=https://example.com/'   # got: <!doctype html>…
curl 'localhost:8787/erin?url=https://example.org/'   # got: egress refused: egress to example.org not granted
```

## Under systemd

[systemd/](systemd/) has socket and service pairs for toybox and its switchboard, assuming this directory is installed at `/opt/toybox`. toybox gets no network of its own (`PrivateNetwork=yes`): only the two sockets it is handed and the switchboard's `public` socket, which only members of the `toybox` group can open. The switchboard binds its `local` socket in its own 0700 runtime directory, so no other unit holds that handle.

Neither unit has been run under the system manager yet.

`PrivateNetwork=` needs the system manager; as a `systemd-run --user` unit, systemd logs "lack privileges for network namespace, proceeding without".