WebSockets

You can use WebSockets for all or some of the communication with your server, see wsLink for how to set it up on the client.

tip

The document here outlines the specific details of using WebSockets. For general usage of subscriptions, see our subscriptions guide.

Creating a WebSocket-server

bash
yarn add ws

bash
yarn add ws

server/wsServer.ts
ts
import { applyWSSHandler } from '@trpc/server/adapters/ws';
import { WebSocketServer } from 'ws';
import { appRouter } from './routers/app';
import { createContext } from './trpc';
 
const wss = new WebSocketServer({
  port: 3001,
});
const handler = applyWSSHandler({
  wss,
  router: appRouter,
  createContext,
  // Enable heartbeat messages to keep connection open (disabled by default)
  keepAlive: {
    enabled: true,
    // server ping message interval in milliseconds
    pingMs: 30000,
    // connection is terminated if pong message is not received in this many milliseconds
    pongWaitMs: 5000,
  },
});
 
wss.on('connection', (ws) => {
  console.log(`++ Connection (${wss.clients.size})`);
  ws.once('close', () => {
    console.log(`-- Connection (${wss.clients.size})`);
  });
});
console.log('WebSocket Server listening on ws://localhost:3001');
 
process.on('SIGTERM', () => {
  console.log('SIGTERM');
  handler.broadcastReconnectNotification();
  wss.close();
});

server/wsServer.ts
ts
import { applyWSSHandler } from '@trpc/server/adapters/ws';
import { WebSocketServer } from 'ws';
import { appRouter } from './routers/app';
import { createContext } from './trpc';
 
const wss = new WebSocketServer({
  port: 3001,
});
const handler = applyWSSHandler({
  wss,
  router: appRouter,
  createContext,
  // Enable heartbeat messages to keep connection open (disabled by default)
  keepAlive: {
    enabled: true,
    // server ping message interval in milliseconds
    pingMs: 30000,
    // connection is terminated if pong message is not received in this many milliseconds
    pongWaitMs: 5000,
  },
});
 
wss.on('connection', (ws) => {
  console.log(`++ Connection (${wss.clients.size})`);
  ws.once('close', () => {
    console.log(`-- Connection (${wss.clients.size})`);
  });
});
console.log('WebSocket Server listening on ws://localhost:3001');
 
process.on('SIGTERM', () => {
  console.log('SIGTERM');
  handler.broadcastReconnectNotification();
  wss.close();
});

Setting TRPCClient to use WebSockets

tip

You can use Links to route queries and/or mutations to HTTP transport and subscriptions over WebSockets.

client.ts
tsx
import { createTRPCClient, createWSClient, wsLink } from '@trpc/client';
import type { AppRouter } from './server';
 
// create persistent WebSocket connection
const wsClient = createWSClient({
  url: `ws://localhost:3001`,
});
 
// configure TRPCClient to use WebSockets transport
const client = createTRPCClient<AppRouter>({
  links: [
    wsLink({
      client: wsClient,
    }),
  ],
});

client.ts
tsx
import { createTRPCClient, createWSClient, wsLink } from '@trpc/client';
import type { AppRouter } from './server';
 
// create persistent WebSocket connection
const wsClient = createWSClient({
  url: `ws://localhost:3001`,
});
 
// configure TRPCClient to use WebSockets transport
const client = createTRPCClient<AppRouter>({
  links: [
    wsLink({
      client: wsClient,
    }),
  ],
});

Authentication / connection params

tip

If you're doing a web application, you can ignore this section as the cookies are sent as part of the request.

In order to authenticate with WebSockets, you can define connectionParams to createWSClient. This will be sent as the first message when the client establishes a WebSocket connection.

server/context.ts
ts
import type { CreateWSSContextFnOptions } from '@trpc/server/adapters/ws';
 
export const createContext = async (opts: CreateWSSContextFnOptions) => {
  const token = opts.info.connectionParams?.token;
         
const token: string | undefined
 
  // [... authenticate]
 
  return {};
};
 
export type Context = Awaited<ReturnType<typeof createContext>>;

server/context.ts
ts
import type { CreateWSSContextFnOptions } from '@trpc/server/adapters/ws';
 
export const createContext = async (opts: CreateWSSContextFnOptions) => {
  const token = opts.info.connectionParams?.token;
         
const token: string | undefined
 
  // [... authenticate]
 
  return {};
};
 
export type Context = Awaited<ReturnType<typeof createContext>>;

client/trpc.ts
ts
import { createTRPCClient, createWSClient, wsLink } from '@trpc/client';
import type { AppRouter } from './server';
import superjson from 'superjson';
 
const wsClient = createWSClient({
  url: `ws://localhost:3000`,
 
  connectionParams: async () => {
    return {
      token: 'supersecret',
    };
  },
});
export const trpc = createTRPCClient<AppRouter>({
  links: [wsLink({ client: wsClient, transformer: superjson })],
});

client/trpc.ts
ts
import { createTRPCClient, createWSClient, wsLink } from '@trpc/client';
import type { AppRouter } from './server';
import superjson from 'superjson';
 
const wsClient = createWSClient({
  url: `ws://localhost:3000`,
 
  connectionParams: async () => {
    return {
      token: 'supersecret',
    };
  },
});
export const trpc = createTRPCClient<AppRouter>({
  links: [wsLink({ client: wsClient, transformer: superjson })],
});

Automatic tracking of id using tracked() (recommended)

If you yield an event using our tracked()-helper and include an id, the client will automatically reconnect when it gets disconnected and send the last known ID when reconnecting as part of the lastEventId-input.

You can send an initial lastEventId when initializing the subscription and it will be automatically updated as the browser receives data.

info

If you're fetching data based on the lastEventId, and capturing all events is critical, you may want to use ReadableStream's or a similar pattern as an intermediary as is done in our full-stack SSE example to prevent newly emitted events being ignored while yield'ing the original batch based on lastEventId.

ts
import EventEmitter, { on } from 'events';
import { initTRPC, tracked } from '@trpc/server';
import { z } from 'zod';
 
type Post = { id: string; title: string };
 
const t = initTRPC.create();
const publicProcedure = t.procedure;
const router = t.router;
 
const ee = new EventEmitter();
 
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z
        .object({
          // lastEventId is the last event id that the client has received
          // On the first call, it will be whatever was passed in the initial setup
          // If the client reconnects, it will be the last event id that the client received
          lastEventId: z.string().nullish(),
        })
        .optional(),
    )
    .subscription(async function* (opts) {
      if (opts.input?.lastEventId) {
        // [...] get the posts since the last event id and yield them
      }
      // listen for new events
      for await (const [data] of on(ee, 'add', {
        // Passing the AbortSignal from the request automatically cancels the event emitter when the subscription is aborted
        signal: opts.signal,
      })) {
        const post = data as Post;
        // tracking the post id ensures the client can reconnect at any time and get the latest events since this id
        yield tracked(post.id, post);
      }
    }),
});

ts
import EventEmitter, { on } from 'events';
import { initTRPC, tracked } from '@trpc/server';
import { z } from 'zod';
 
type Post = { id: string; title: string };
 
const t = initTRPC.create();
const publicProcedure = t.procedure;
const router = t.router;
 
const ee = new EventEmitter();
 
export const subRouter = router({
  onPostAdd: publicProcedure
    .input(
      z
        .object({
          // lastEventId is the last event id that the client has received
          // On the first call, it will be whatever was passed in the initial setup
          // If the client reconnects, it will be the last event id that the client received
          lastEventId: z.string().nullish(),
        })
        .optional(),
    )
    .subscription(async function* (opts) {
      if (opts.input?.lastEventId) {
        // [...] get the posts since the last event id and yield them
      }
      // listen for new events
      for await (const [data] of on(ee, 'add', {
        // Passing the AbortSignal from the request automatically cancels the event emitter when the subscription is aborted
        signal: opts.signal,
      })) {
        const post = data as Post;
        // tracking the post id ensures the client can reconnect at any time and get the latest events since this id
        yield tracked(post.id, post);
      }
    }),
});

WebSockets RPC Specification

You can read more details by drilling into the TypeScript definitions:

• /packages/server/src/unstable-core-do-not-import/rpc/envelopes.ts
• /packages/server/src/unstable-core-do-not-import/rpc/codes.ts.

query / mutation

Request

ts
interface RequestMessage {
  id: number | string;
  jsonrpc?: '2.0';
  method: 'query' | 'mutation';
  params: {
    path: string;
    input?: unknown; // <-- pass input of procedure, serialized by transformer
  };
}

ts
interface RequestMessage {
  id: number | string;
  jsonrpc?: '2.0';
  method: 'query' | 'mutation';
  params: {
    path: string;
    input?: unknown; // <-- pass input of procedure, serialized by transformer
  };
}

Response

... below, or an error.

ts
interface ResponseMessage {
  id: number | string;
  jsonrpc?: '2.0';
  result: {
    type: 'data'; // always 'data' for mutation / queries
    data: TOutput; // output from procedure
  };
}

ts
interface ResponseMessage {
  id: number | string;
  jsonrpc?: '2.0';
  result: {
    type: 'data'; // always 'data' for mutation / queries
    data: TOutput; // output from procedure
  };
}

subscription / subscription.stop

Start a subscription

ts
interface SubscriptionRequest {
  id: number | string;
  jsonrpc?: '2.0';
  method: 'subscription';
  params: {
    path: string;
    input?: unknown; // <-- pass input of procedure, serialized by transformer
  };
}

ts
interface SubscriptionRequest {
  id: number | string;
  jsonrpc?: '2.0';
  method: 'subscription';
  params: {
    path: string;
    input?: unknown; // <-- pass input of procedure, serialized by transformer
  };
}

To cancel a subscription, call subscription.stop

ts
interface SubscriptionStopRequest {
  id: number | string; // <-- id of your created subscription
  jsonrpc?: '2.0';
  method: 'subscription.stop';
}

ts
interface SubscriptionStopRequest {
  id: number | string; // <-- id of your created subscription
  jsonrpc?: '2.0';
  method: 'subscription.stop';
}

Subscription response shape

... below, or an error.

ts
interface SubscriptionResponse {
  id: number | string;
  jsonrpc?: '2.0';
  result:
    | {
        type: 'data';
        data: TData; // subscription emitted data
      }
    | {
        type: 'started'; // subscription started
      }
    | {
        type: 'stopped'; // subscription stopped
      };
}

ts
interface SubscriptionResponse {
  id: number | string;
  jsonrpc?: '2.0';
  result:
    | {
        type: 'data';
        data: TData; // subscription emitted data
      }
    | {
        type: 'started'; // subscription started
      }
    | {
        type: 'stopped'; // subscription stopped
      };
}

Connection params

If the connection is initialized with ?connectionParams=1, the first message has to be connection params.

ts
interface ConnectionParamsMessage {
  data: Record<string, string> | null;
  method: 'connectionParams';
}

ts
interface ConnectionParamsMessage {
  data: Record<string, string> | null;
  method: 'connectionParams';
}

Errors

See https://www.jsonrpc.org/specification#error_object or Error Formatting.

Notifications from Server to Client

{ id: null, type: 'reconnect' }

Tells clients to reconnect before shutting down the server. Invoked by wssHandler.broadcastReconnectNotification().