dckcandClaude Opus 5.5
8d8900d84d
createVat (POST / on the admin socket) makes a vat with newUniqueId and returns its id, which addresses it only there. A vat is reachable only where it is mounted: ?mount=<labels> on each start, as ?egress= is granted; absent means none. The ingress reads a request's labels from its query string, plus a Toybox-Labels header for secret ones (a URL ends up in logs and Referers). It routes to the vat whose mount labels the request carries, every one: stricter than Flower's no-conflict match, since an ingress client holds no constrained handle and a label it omits must not match. Registration keeps Flower's rule, so a mount must conflict with every other and no request can carry two. The app keeps the whole path and sees its connection labels in Toybox-Connection-Labels. A vat from before ids lives at idFromName(name). PUT /by-name/<name> reaches it on the admin socket; it stays unreachable from outside until mounted. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
69 lines
5.5 KiB
Markdown
69 lines
5.5 KiB
Markdown
# toybox
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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. Vats have no names: creating one returns its id, which addresses it only on the admin socket. Everything else a vat can do or be reached by is granted explicitly: egress by labels it may fetch within, ingress by labels it is mounted at.
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- [supervisor.js](supervisor.js): `Vat` stores code by SHA-256 and runs the app on it; `Directory` holds the mounts; `Public` (the ingress) and `Admin` are the two entrypoints; `Egress` is an egress grant.
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- [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.
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- [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. Ingress lookup is stricter (below).
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- [config.capnp](config.capnp): the sockets have no addresses; whoever starts workerd hands them in, so holding a socket is the authority it grants.
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| socket | reaches | what its holder can do |
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|---|---|---|
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| `http` | `Public` | reach the vat mounted at labels the request carries |
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| `admin` | `Admin` | `POST /` with an ES module body: create a vat and start it; the reply is `{"vat": <id>, "hash": <code hash>}`. `PUT /<id>` with a body: upgrade it; its storage carries over. `PUT /by-name/<name>`: the same, for a vat from before ids. |
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Every start states the vat's grants, as JSON labels in query parameters; absent means none:
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- `?egress=<labels>`: what the app may fetch (below).
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- `?mount=<labels>`: where the ingress finds it. A mount must conflict with every other one (some shared key, different values), so no request can carry two mounts' labels; an overlapping mount is a 409.
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## Ingress
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A request's labels are its query parameters, plus a `Toybox-Labels` header (JSON) for secret ones. A URL ends up in logs and `Referer`s, so a secret label belongs in the header: a webkey page keeps the secret in its fragment and sends it in-band. A key given twice is a 400.
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The request reaches the vat whose mount labels it carries, every one with the same value. That is stricter than Flower's match (no conflicting key): an ingress client holds no constrained handle, so a label it omits must not match, or a secret label would protect nothing. The path is the app's own. The app sees the mount's and the request's labels together in `Toybox-Connection-Labels` (JSON), as a Flower server gets its connection labels. Responses carry `Referrer-Policy: no-referrer`.
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## Egress
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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.
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| label | constrains |
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|---|---|
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| `scheme` | `http` or `https` |
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| `host` | host name or address, no port |
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| `port` | explicit, or the scheme's default |
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| `network` | set by the switchboard socket: `public` or `local` |
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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.
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## Run it
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```sh
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pnpm install
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pnpm test # real workerds: createVat, upgrade, mounts, secret labels, egress grants and constrain, fetch and WebSocket out, crash and restart
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pnpm switchboard # systemd-socket-activate on ./switchboard-public.sock and ./switchboard-local.sock
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pnpm start # likewise on 127.0.0.1:8787 and ./admin.sock; state in ./state
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```
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Then, in a third terminal:
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```sh
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admin() { curl -sg --unix-socket admin.sock "$@"; }
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alice=$(admin -X POST --data-binary @apps/counter-v1.js 'http://toybox/?mount={"vat":"alice"}' | jq -r .vat)
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curl 'localhost:8787/?vat=alice' # v1 count 1
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admin -X PUT --data-binary @apps/counter-v2.js "http://toybox/$alice?mount={\"vat\":\"alice\"}"
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curl 'localhost:8787/?vat=alice' # v2 count 2
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admin -X POST --data-binary @apps/egress-probe.js 'http://toybox/?mount={"vat":"erin"}&egress={"host":"example.com"}'
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curl 'localhost:8787/?vat=erin&url=https://example.com/' # got: <!doctype html>…
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curl 'localhost:8787/?vat=erin&url=https://example.org/' # got: egress refused: egress to example.org not granted
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```
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## Under systemd
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[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.
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Neither unit has been run under the system manager yet.
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`PrivateNetwork=` needs the system manager; as a `systemd-run --user` unit, systemd logs "lack privileges for network namespace, proceeding without".
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