partyrpc

Partykit + RPC = PartyRPC Move Fast (and Break Everything). Everything is better with typesafety.

Install

pnpm i partyrpc

Usage

Terminology

• Events: what WS messages your party server expects to receive from clients
• Responses: what WS messages your party server sends back to clients

WS Events

Define your (safe) party events and responses:

// src/safe-party.ts
import * as v from "valibot";
import { createPartyRpc } from "partyrpc/server";

type UContext = { counter: number };
type PongResponse = { type: "pong"; size: number };
type LatencyResponse = { type: "latency"; id: string };
type CounterResponse = { type: "counter"; counter: number };

type PartyResponses = PongResponse | LatencyResponse | CounterResponse;

const party = createPartyRpc<PartyResponses, UContext>();

export const safeParty = party.events({
  ping: {
    schema: v.never(),
    onMessage(message, ws, room, ctx) {
      party.send(ws, { type: "pong", size: room.connections.size });
    },
  },
  latency: {
    schema: v.object({ id: v.string() }),
    onMessage(message, ws, room, ctx) {
      party.send(ws, { type: "latency", id: message.id });
    },
  },
  "add-to-counter": {
    schema: v.object({ amount: v.number() }),
    onMessage(message, ws, room, ctx) {
      ctx.counter += message.amount;
      party.send(ws, { type: "counter", counter: ctx.counter });
    },
  },
});

export type SafePartyEvents = typeof safeParty.events;
export type SafePartyResponses = typeof safeParty.responses;

Bind it to your party server:

// src/server.ts
import * as Party from "partykit/server";
import { safeParty } from "./safe-party";

// optional context
const ctx = { counter: 0 };

export default class Server implements Party.Server {
  constructor(readonly party: Party.Party) {}

  onConnect(conn: Party.Connection, ctx: Party.ConnectionContext) {
    conn.addEventListener("message", (evt) => {
      safeParty.onMessage(evt.data, conn, this.party, userCtx);
    });
  }
}

Server satisfies Party.Worker;

Finally, create your party client:

// src/client.ts
import PartySocket from "partysocket";
import { createPartyClient } from "partyrpc/client";
import { SafePartyEvents, SafePartyResponses } from "./safe-party";

const partySocket = new PartySocket({
  host: PARTYKIT_HOST,
  room: "some-room",
});
const client = createPartyClient<SafePartyEvents, SafePartyResponses>(partySocket, { debug: true });

Subscribe to typesafe responses:

// src/clients.ts

client.on("latency", (msg) => {
  // msg is typed as LatencyResponse, defined above as { type: "latency"; id: string }
});

client.on("pong", (msg) => {
  console.log("got pong", msg.size);
  // msg is typed as PongResponse, defined above as { type: "pong"; size: number }
});

client.on("counter", (msg) => {
  // msg is typed as CounterResponse, defined above as { type: "counter"; counter: number }
});

Send typesafe events:

// src/clients.ts

client.send({ type: "ping" }); // ✅
client.send({ type: "ping", id: "foo" }); // ❌ error, 'id' does not exist in type '{ type: "ping"; }'.

client.send({ type: "add-to-counter", amount: 3 }); // ✅
client.send({ type: "add-to-counter" }); // ❌ error, 'amount' is declared here.

You can also hook to typesafe events (only react atm).

• usePartyMessage is a hook that will trigger your callback whenever a message of a given type is received.
• that callback will always have the latest state of your component, thanks to a useEvent hook.
• usePartyMessage doesn't add any event listener to the socket, it really just hooks into the client's message handler

// src/clients.ts
import { createPartyHooks } from "partyrpc/react";
const { usePartyMessage, useSocketEvent } = createPartyHooks(client);

function App() {
  const [count, setCount] = useState(0);

  usePartyMessage("counter", (msg) => {
    console.log("received counter", msg);
    // msg is typed as CounterResponse, defined above as { type: "counter"; counter: number }

    console.log({ count });
    // count is always up to date, thanks to a useEvent hook
  });

  useSocketEvent("open", () => {
    console.log("socket opened");
  });

  useSocketEvent("close", () => {
    console.log("socket closed");
  });

  // ...
}

Fetch requests

You can also use partyrpc to define typesafe endpoints on your PartyKit server.

// src/safe-party.ts
import * as v from "valibot";
import { createPartyRpc } from "partyrpc/server";

type UContext = { counter: number };

const party = createPartyRpc<PartyResponses, UContext>();
export const router = party.endpoints([
  party.route({
    method: "get",
    path: "/api/counter",
    response: v.object({ counter: v.number() }),
    handler(_req, _lobby, _ctx, userCtx) {
      return { counter: userCtx.counter };
    },
  }),
  party.route({
    method: "post",
    path: "/api/counter",
    parameters: {
      body: v.object({ amount: v.number() }),
    },
    response: v.object({ counter: v.number(), added: v.number() }),
    handler(req, lobby, ctx, userCtx) {
      req.params;
      //   ^? typed as { body: { amount: number } }

      userCtx.counter += req.params.body.amount;
      // ^? typed as { counter: number }

      return { counter: userCtx.counter, added: req.params.body.amount };
    },
  }),
]);

and later used them with your own fetcher instance:

// src/client.ts
import { ofetch } from "ofetch";
import { createPartyClient } from "partyrpc/client";
import { SafePartyEvents, SafePartyResponses } from "./safe-party";

const api = createApiClient(router.endpoints, (method, url, params) =>
  ofetch(url, {
    method,
    body: params?.body as any,
    headers: params?.header as any,
    query: params?.query as any,
  }),
).setBaseUrl("http://127.0.0.1:1999");

// ...

api.post("/api/counter", { body: { amount: 4 } }).then((res) => {
  res;
  // ^? typed as { counter: number; added: number; }
  return console.log(res);
});

Caveats

• Currently only compatible with valibot, ideally it'll use typeschema at some point to allow you to use your preferred validation library.
• Currently only allow events and responses that match a { type: string } shape, ala xstate. Not sure if that will change. Maybe data will end up being wrapped in a data property, but that seems like a lot of extra typing.