Ch. 7: Bring in the browser

Turn a browser tab into a iii worker that creates links, shows live clicks, and answers server-initiated prompts.

In this chapter the browser becomes a worker. It connects to the engine over WebSocket, calls link::create directly (no REST API Gateway), binds to the live click feed from Chapter 5 to update a counter, and registers a user::confirm_destructive_op function the server calls when a delete needs a human’s go-ahead.

Add the workers

A browser worker connects through the rbac-proxy RBAC-gated port, separate from the trusted port your local workers use. The auth worker holds the authentication logic that gates those connections. Uncomment the Ch. 7 block in worker-compose.yaml:

worker-compose.yaml

auth:
  worker: path://./auth
  env_file: ["./.env"]

The env_file gives the worker LINKLY_BROWSER_TOKEN from .env; the scaffold ships dev-token for local work. auth::browser admits a browser only when the token it receives matches, so change this value for anything beyond your machine.

If you’re continuing from the previous chapter you might still be in the channel-client folder. Make sure to cd ..!

Put a proxy in front for browsers

The engine’s port at 49134 is the trusted listener; local workers (link worker, analytics worker) connect there. The browser must not. The rbac-proxy worker opens a separate public port and reverse-proxies to the engine, authenticating every connection and gating every call it makes. Uncomment the Ch. 7 rbac-proxy container:

worker-compose.yaml

rbac-proxy:
  worker: package://rbac-proxy
  version: "1.0.6"
  config_name: rbac-proxy
  config_override:
    host: 127.0.0.1
    port: 3110
    engine_url: ws://127.0.0.1:49134
    rbac:
      auth_function_id: auth::browser
      expose_functions:
        - match("link::create")
        - match("link::request_delete")
        - match("link::click_summary")

Restart Compose so it starts the proxy:

iii trigger compose::restart

expose_functions is an allowlist of which functions a browser session can call. The browser hears about clicks through the click-streamer::click trigger type, not a function call, and reads the starting total with link::click_summary, so that query is on the list too. auth_function_id names a function rbac-proxy invokes on every connection to admit or reject it; you write that next.

Gate connections with an auth function

The auth worker owns connection gating, so the link worker stays focused on links. auth::browser runs once per browser connection: it receives the request’s headers, query_params, and ip_address, and returns the session’s permissions (allow/deny additions, arbitrary context). Throw to reject. Create auth/src/index.ts:

auth/src/index.ts

import { registerWorker } from "iii-sdk";
import { Logger } from "@iii-dev/helpers/observability";

const worker = registerWorker(process.env.III_URL ?? "ws://localhost:49134", {
  workerName: "auth",
});
const logger = new Logger();

worker.registerFunction(
  "auth::browser",
  async (input: {
    headers: Record<string, string>;
    query_params: Record<string, string[]>;
    ip_address: string;
  }) => {
    // Fail closed: no LINKLY_BROWSER_TOKEN set means no browser is admitted.
    const expected = process.env.LINKLY_BROWSER_TOKEN;
    const token = input.query_params.token?.[0];
    if (!expected || token !== expected) {
      throw new Error("unauthorized");
    }
    // Each tab sends a unique session id and registers in its own
    // `browser-<session>` namespace, so the functions two tabs register never
    // collide. Granting only that namespace key keeps a tab out of `default`.
    const session = input.query_params.session?.[0];
    if (!session) {
      throw new Error("missing session");
    }
    return {
      allow_trigger_type_registration: false,
      // The tab may listen to the live click feed and nothing else.
      allowed_trigger_types: ["click-streamer::click"],
      allow_function_registration: true,
      namespaces: {
        [`browser-${session}`]: ["ui::on_click", "user::confirm_destructive_op"],
      },
      context: { source: "browser" },
    };
  },
);

logger.info("auth worker ready");

The client sends the same token as VITE_LINKLY_TOKEN, which you set below. A real deployment would look the token up in a session store; the shape stays the same. The token travels in a query parameter because browsers cannot send custom WebSocket headers.

Each tab also sends a unique session id. The engine allows one function per id in a namespace, so two tabs both registering ui::on_click in default would collide. namespaces gives each session its own browser-<session> namespace and permits registration only there: the tab’s functions live in isolation, and it still calls link::* in default through the expose_functions allowlist. allowed_trigger_types does the same for bindings: the tab may bind the live click feed and no other trigger type.

Add a server-initiated delete

First give the link worker a link::delete that removes a link from both the database and the state cache. Add it to link/src/index.ts:

link/src/index.ts

worker.registerFunction("link::delete", async (payload: { code: string }) => {
  await worker.trigger({
    function_id: "database::execute",
    payload: { db: DB, sql: "DELETE FROM links WHERE code = ?", params: [payload.code] },
  });
  await worker.trigger({
    function_id: "state::delete",
    payload: { scope: "links", key: payload.code },
  });
  logger.info("link deleted", { code: payload.code });
  return { deleted: true };
});

Now add a wrapper that asks the connected browser first, then deletes only if the browser confirms. The server-side worker.trigger of a browser-registered function is the same primitive you’ve used between server workers, in reverse. This lets us reverse the typical pattern: instead of the browser asking the server for confirmation, the server asks the browser. Other implementations would achieve this with SSE but here it works like normal synchronous code.

link/src/index.ts

worker.registerFunction(
  "link::request_delete",
  async (payload: { code: string; session: string }) => {
    const { confirmed } = await worker.trigger<
      { code: string; action: string },
      { confirmed: boolean }
    >({
      function_id: "user::confirm_destructive_op",
      // Ask the one tab that owns this session, in its private namespace.
      namespace: `browser-${payload.session}`,
      payload: { code: payload.code, action: `delete link "${payload.code}"` },
    });
    if (!confirmed) {
      return { deleted: false };
    }
    await worker.trigger({ function_id: "link::delete", payload: { code: payload.code } });
    return { deleted: true };
  },
);

Scaffold the frontend

Initialize a Vite project

From the project root (the folder with worker-compose.yaml), create a Vite + React + TypeScript app. create-vite creates the frontend/ folder for you:

npm create vite@latest frontend -- --template react-ts --no-interactive

--no-interactive makes create-vite skip its questions: it scaffolds frontend/ with its default linter and neither installs nor starts anything, since iii-browser-sdk has to be installed first. npm may first ask “Ok to proceed?” to download create-vite; answer yes.

Now install the dependencies:

cd frontend
npm install
npm install iii-browser-sdk

iii-browser-sdk installs at 0.24.x while the backend workers pin iii-sdk 0.23.0. The two work together: each one connects to the engine, never to the other.

Then tell the app where the proxy is and which token to send. Create frontend/.env.local; Vite reads it at startup. VITE_LINKLY_TOKEN must equal LINKLY_BROWSER_TOKEN in the project’s .env, and VITE_LINKLY_PROXY_URL uses the rbac-proxy port:

frontend/.env.local

VITE_LINKLY_TOKEN=dev-token
VITE_LINKLY_PROXY_URL=ws://localhost:3110

Setup a client-side worker

Connect the SDK to our iii instance in frontend/src/iii.ts. Note how we’re using a different URL format and port, this goes back to the setup we did with rbac-proxy and RBAC.

src/iii.ts

import { registerWorker } from "iii-browser-sdk";

// Both come from frontend/.env.local.
const TOKEN = import.meta.env.VITE_LINKLY_TOKEN;
const PROXY_URL = import.meta.env.VITE_LINKLY_PROXY_URL;
if (!TOKEN || !PROXY_URL) {
  throw new Error("Set VITE_LINKLY_TOKEN and VITE_LINKLY_PROXY_URL in frontend/.env.local");
}

// A per-tab id. The tab registers its functions in `browser-<SESSION>`, so two
// open tabs never collide on `ui::on_click` or `user::confirm_destructive_op`.
export const SESSION = crypto.randomUUID();

export const worker = registerWorker(
  `${PROXY_URL}?token=${encodeURIComponent(TOKEN)}&session=${SESSION}`,
  { namespace: `browser-${SESSION}` },
);

Create the application

We’ll build src/App.tsx in pieces. You can replace the template’s src/App.tsx with the code samples below.

Add imports

First the imports and types: Click is the notification click-streamer::click delivers, and Summary is what link::click_summary returns.

src/App.tsx

import { useEffect, useState } from "react";
import { worker, SESSION } from "./iii.js";

type Click = { id: number; code: string; clicked_at: string };
type Summary = { total: number; last_id: number };

Add client-side state

Open the component and declare its state: the form fields, the newly created link, and the live click counter.

src/App.tsx

export default function App() {
  const [url, setUrl] = useState('')
  const [code, setCode] = useState('')
  const [created, setCreated] = useState<{ code: string; url: string } | null>(null)
  const [clicks, setClicks] = useState(0)
  const [latest, setLatest] = useState<Click | null>(null)

Count clicks live

Bind to the click-streamer::click trigger type from Chapter 5. The tab is a worker like any other, so it listens the same way watch.ts did: it registers a function (ui::on_click) and a trigger that routes every click to it, then reads the starting total with link::click_summary.

Two details keep the counter correct:

• Bind first, then read. A click that lands between the two is still delivered. Clicks that arrive before the read returns wait in early, and the click id tells the tab whether the total already includes them, so nothing is counted twice.
• Read again after a reconnect. Clicks sent while the tab was disconnected are not replayed, but the stored total is always current.

The cleanup unregisters everything on unmount:

src/App.tsx

useEffect(() => {
  let lastId = 0; // highest click id already counted
  let ready = false; // false until the read lands
  const early: Click[] = [];

  function apply(click: Click) {
    if (click.id <= lastId) return; // a duplicate, or already in the total
    lastId = click.id;
    setClicks((n) => n + 1);
    setLatest(click);
  }

  async function sync() {
    ready = false;
    const summary = await worker.trigger<Record<string, never>, Summary>({
      function_id: "link::click_summary",
      // This tab is in its own namespace; link::click_summary lives in `default`.
      namespace: "default",
      payload: {},
    });
    lastId = summary.last_id;
    setClicks(summary.total);
    ready = true;
    early.splice(0).forEach(apply);
  }

  const fn = worker.registerFunction("ui::on_click", async (click: Click) => {
    if (ready) apply(click);
    else early.push(click);
    return null;
  });
  const trig = worker.registerTrigger({
    type: "click-streamer::click",
    function_id: "ui::on_click",
    config: {},
    // ui::on_click lives in this tab's namespace, so the trigger resolves it
    // there. registerTrigger fills that in from the worker's namespace.
  });
  sync();
  const stopListening = worker.addConnectionStateListener((state) => {
    if (state === "connected") sync();
  });
  return () => {
    stopListening();
    trig.unregister();
    fn.unregister();
  };
}, []);

Create a function

Register the function the server calls back when it needs human confirmation. It shows a native prompt and returns the user’s decision:

This function registers and runs the exact same as other functions did in previous chapters. Except for managing auth and permissions there is no functional difference between client side and server side.

src/App.tsx

useEffect(() => {
  const fn = worker.registerFunction(
    "user::confirm_destructive_op",
    async (data: { action: string; code: string }) => {
      const confirmed = window.confirm(`Confirm: ${data.action}?`);
      return { confirmed };
    },
  );
  return () => fn.unregister();
}, []);

Create links directly, no gateways

Submit the form by calling link::create directly.

There is no fetch or REST API in the way here, the client worker in the browser works the exact same as every other worker.

src/App.tsx

async function onSubmit(e: React.FormEvent) {
  e.preventDefault();
  const link = await worker.trigger<{ url: string; code?: string }, { code: string; url: string }>({
    function_id: "link::create",
    // This tab is in its own namespace; link::create lives in `default`.
    namespace: "default",
    payload: { url, code: code || undefined },
  });
  setCreated(link);
  setUrl("");
  setCode("");
}

Create the UI

Finally, the UI: a link shortener form, the last-created link, and the live click counter.

src/App.tsx

  return (
    <main>
      <h1>Linkly</h1>

      <form onSubmit={onSubmit}>
        <label>URL <input value={url} onChange={(e) => setUrl(e.target.value)} required /></label>
        <label>Code (optional) <input value={code} onChange={(e) => setCode(e.target.value)} /></label>
        <button type="submit">Shorten</button>
      </form>

      {created && (
        <p>
          Created <code>{created.code}</code> → <code>{created.url}</code>.
        </p>
      )}

      <section>
        <h2>Live clicks: {clicks}</h2>
        {latest && (
          <p>Last: <code>{latest.code}</code> at <code>{latest.clicked_at}</code></p>
        )}
      </section>

      <footer>
        <small>This tab is session <code>{SESSION}</code>.</small>
      </footer>
    </main>
  )
}

See it work

Start the UI:

npm run dev

Open your browser, Vite typically hosts local websites at http://localhost:5173.

Shorten a link, then watch the clicks arrive in real time

Shorten a link from the form, then visit http://localhost:3111/s/<code> a few times. You’ll see the “Live clicks” counter go up in real time. Reload the tab and the counter starts from the stored total, not from zero.

Request user confirmation directly from the backend

Copy the session id the tab prints, then trigger the delete for one of your links, naming that session so the server calls back the right tab:

iii trigger link::request_delete code=<code> session=<session from the tab>

That tab shows a confirm prompt, and the server deletes only after you click OK. The session names the tab’s namespace, so the server asks exactly the browser that owns it, never another tab.

Conclusion

The client is a worker that is exactly the same as every other worker. We connected it through an RBAC-gated port (via rbac-proxy) that uses an auth function to admit it because the browser isn’t trusted like our other workers. However any other worker can be gated this same way.

Once everything is set up our client calls server functions directly, binds a trigger type for live updates, and registers functions the server calls back, all on the same iii bus as the rest of Linkly.