graphql-ws

What is graphql-ws?

The graphql-ws package is a lightweight and fast WebSocket server and client for GraphQL subscriptions, designed to work with the GraphQL JavaScript reference implementation. It allows you to set up a full-duplex communication channel between the client and server to facilitate real-time data exchange using the GraphQL protocol.

What are graphql-ws's main functionalities?

Creating a WebSocket server for GraphQL subscriptions

This code sample demonstrates how to create a WebSocket server that handles GraphQL subscriptions. It uses the `useServer` function from `graphql-ws` to attach the WebSocket server to an existing HTTP server.

const { createServer } = require('http');
const { execute, subscribe } = require('graphql');
const { useServer } = require('graphql-ws/lib/use/ws');
const { schema } = require('./my-graphql-schema');

const server = createServer(function weServeSocketsOnly(_, res) {
  res.writeHead(404);
  res.end();
});

const wsServer = new WebSocket.Server({
  server,
  path: '/graphql',
});

useServer({ schema, execute, subscribe }, wsServer);

server.listen(4000);

Creating a WebSocket client for GraphQL subscriptions

This code sample shows how to create a WebSocket client that can subscribe to GraphQL subscriptions. The `createClient` function from `graphql-ws` is used to establish a connection to the WebSocket server, and the `subscribe` method is used to listen for real-time data updates.

const { createClient } = require('graphql-ws');

const client = createClient({
  url: 'ws://localhost:4000/graphql',
});

client.subscribe(
  {
    query: 'subscription { somethingChanged { id } }',
    variables: {},
  },
  {
    next: data => console.log('data received:', data),
    error: err => console.error('error during subscription:', err),
    complete: () => console.log('subscription completed'),
  }
);

Other packages similar to graphql-ws

subscriptions-transport-ws

This package is another implementation of GraphQL over WebSocket protocol. It is the predecessor of graphql-ws and was developed by the Apollo team. However, it is now deprecated in favor of graphql-ws, which is more lightweight and has a simpler API.

apollo-server

Apollo Server is a community-driven, open-source GraphQL server that works with many Node.js HTTP server frameworks. Apollo Server supports subscriptions with WebSocket and integrates well with the Apollo ecosystem. It is more feature-rich but also heavier compared to graphql-ws, which is focused solely on WebSocket communication.

README

Coherent, zero-dependency, lazy, simple, GraphQL over WebSocket Protocol compliant server and client.

Getting started

Install

$ yarn add graphql-ws

Create a GraphQL schema

import { buildSchema } from 'graphql';

// Construct a schema, using GraphQL schema language
const schema = buildSchema(`
  type Query {
    hello: String
  }
  type Subscription {
    greetings: String
  }
`);

// The roots provide resolvers for each GraphQL operation
const roots = {
  query: {
    hello: () => 'Hello World!',
  },
  subscription: {
    greetings: async function* sayHiIn5Languages() {
      for (const hi of ['Hi', 'Bonjour', 'Hola', 'Ciao', 'Zdravo']) {
        yield { greetings: hi };
      }
    },
  },
};

Start the server

import https from 'https';
import { execute, subscribe } from 'graphql';
import { createServer } from 'graphql-ws';

const server = https.createServer(function weServeSocketsOnly(_, res) {
  res.writeHead(404);
  res.end();
});

createServer(
  {
    schema, // from the previous step
    roots, // from the previous step
    execute,
    subscribe,
  },
  {
    server,
    path: '/graphql',
  },
);

server.listen(443);

Use the client

import { createClient } from 'graphql-ws';

const client = createClient({
  url: 'wss://welcomer.com/graphql',
});

// query
(async () => {
  const result = await new Promise((resolve, reject) => {
    let result;
    client.subscribe(
      {
        query: '{ hello }',
      },
      {
        next: (data) => (result = data),
        error: reject,
        complete: () => resolve(result),
      },
    );
  });

  expect(result).toEqual({ hello: 'Hello World!' });
})();

// subscription
(async () => {
  const onNext = () => {
    /**/
  };

  await new Promise((resolve, reject) => {
    client.subscribe(
      {
        query: 'subscription { greetings }',
      },
      {
        next: onNext,
        error: reject,
        complete: resolve,
      },
    );
  });

  expect(onNext).toBeCalledTimes(5); // we say "Hi" in 5 languages
})();

Recipes

Client usage with Promise

import { createClient, SubscribePayload } from 'graphql-ws';

const client = createClient({
  url: 'wss://hey.there/graphql',
});

async function execute<T>(payload: SubscribePayload) {
  return new Promise((resolve, reject) => {
    let result: T;
    client.subscribe<T>(payload, {
      next: (data) => (result = data),
      error: reject,
      complete: () => resolve(result),
    });
  });
}

// use
(async () => {
  try {
    const result = await execute({
      query: '{ hello }',
    });
    // complete
    // next = result = { data: { hello: 'Hello World!' } }
  } catch (err) {
    // error
  }
})();

Client usage with Observable

import { Observable } from 'relay-runtime';
// or
import { Observable } from '@apollo/client';
// or
import { Observable } from 'rxjs';
// or
import Observable from 'zen-observable';
// or any other lib which implements Observables as per the ECMAScript proposal: https://github.com/tc39/proposal-observable

const client = createClient({
  url: 'wss://graphql.loves/observables',
});

function toObservable(operation) {
  return new Observable((observer) => client.subscribe(operation, observer));
}

const observable = toObservable({ query: `subscription { ping }` });

const subscription = observable.subscribe({
  next: (data) => {
    expect(data).toBe({ data: { ping: 'pong' } });
  },
});

// ⏱

subscription.unsubscribe();

Client usage with Relay

import {
  Network,
  Observable,
  RequestParameters,
  Variables,
} from 'relay-runtime';
import { createClient } from 'graphql-ws';

const subscriptionsClient = createClient({
  url: 'wss://i.love/graphql',
  connectionParams: () => {
    const session = getSession();
    if (!session) {
      return {};
    }
    return {
      Authorization: `Bearer ${session.token}`,
    };
  },
});

// yes, both fetch AND subscribe handled in one implementation
function fetchOrSubscribe(operation: RequestParameters, variables: Variables) {
  return Observable.create((sink) => {
    if (!operation.text) {
      return sink.error(new Error('Operation text cannot be empty'));
    }
    return subscriptionsClient.subscribe(
      {
        operationName: operation.name,
        query: operation.text,
        variables,
      },
      {
        ...sink,
        error: (err) => {
          if (err instanceof Error) {
            sink.error(err);
          } else if (err instanceof CloseEvent) {
            sink.error(
              new Error(
                `Socket closed with event ${err.code}` + err.reason
                  ? `: ${err.reason}` // reason will be available on clean closes
                  : '',
              ),
            );
          } else {
            // GraphQLError[]
            sink.error(new Error(err.map(({ message }) => message).join(', ')));
          }
        },
      },
    );
  });
}

export const network = Network.create(fetchOrSubscribe, fetchOrSubscribe);

Client usage with Apollo

import { ApolloLink, Operation, FetchResult, Observable } from '@apollo/client';
import { createClient, Config, Client } from 'graphql-ws';

class WebSocketLink extends ApolloLink {
  private client: Client;

  constructor(config: Config) {
    super();
    this.client = createClient(config);
  }

  public request(operation: Operation): Observable<FetchResult> {
    return new Observable((sink) => {
      return this.client.subscribe<FetchResult>(operation, {
        ...sink,
        error: (err) => {
          if (err instanceof Error) {
            sink.error(err);
          } else if (err instanceof CloseEvent) {
            sink.error(
              new Error(
                `Socket closed with event ${err.code}` + err.reason
                  ? `: ${err.reason}` // reason will be available on clean closes
                  : '',
              ),
            );
          } else {
            // GraphQLError[]
            sink.error(new Error(err.map(({ message }) => message).join(', ')));
          }
        },
      });
    });
  }
}

const link = new WebSocketLink({
  url: 'wss://where.is/graphql',
  connectionParams: () => {
    const session = getSession();
    if (!session) {
      return {};
    }
    return {
      Authorization: `Bearer ${session.token}`,
    };
  },
});

Client usage in Node

const WebSocket = require('ws'); // yarn add ws
const Crypto = require('crypto');
const { createClient } = require('graphql-ws');

const client = createClient({
  url: 'wss://no.browser/graphql',
  webSocketImpl: WebSocket,
  /**
   * Generates a v4 UUID to be used as the ID.
   * Reference: https://stackoverflow.com/a/2117523/709884
   */
  generateID: () =>
    ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, (c) =>
      (c ^ (Crypto.randomBytes(1)[0] & (15 >> (c / 4)))).toString(16),
    ),
});

// consider other recipes for usage inspiration

Server usage with Express GraphQL

import https from 'https';
import express from 'express';
import { graphqlHTTP } from 'express-graphql';
import { createServer } from 'graphql-ws';
import { execute, subscribe } from 'graphql';
import { schema } from 'my-graphql-schema';

// create express and middleware
const app = express();
app.use('/graphql', graphqlHTTP({ schema }));

// create a http server using express
const server = https.createServer(app);

server.listen(443, () => {
  createServer(
    {
      schema,
      execute,
      subscribe,
    },
    {
      server,
      path: '/graphql', // you can use the same path too, just use the `ws` schema
    },
  );
});

Server usage with console logging

import https from 'https';
import { execute, subscribe } from 'graphql';
import { createServer } from 'graphql-ws';

const server = https.createServer(function weServeSocketsOnly(_, res) {
  res.writeHead(404);
  res.end();
});

createServer(
  {
    schema,
    onConnect: (ctx) => {
      console.log('Connect', ctx);
    },
    onSubscribe: (ctx, msg) => {
      console.log('Subscribe', { ctx, msg });
    },
    onNext: (ctx, msg, args, result) => {
      console.debug('Next', { ctx, msg, args, result });
    },
    onError: (ctx, msg, errors) => {
      console.error('Error', { ctx, msg, errors });
    },
    onComplete: (ctx, msg) => {
      console.log('Complete', { ctx, msg });
    },
  },
  {
    server,
    path: '/graphql',
  },
);

server.listen(443);

Server usage on a multi WebSocket server

import https from 'https';
import WebSocket from 'ws';
import url from 'url';
import { execute, subscribe } from 'graphql';
import { createServer, createClient } from 'graphql-ws';
import { schema } from 'my-graphql-schema';

const server = https.createServer(function weServeSocketsOnly(_, res) {
  res.writeHead(404);
  res.end();
});

/**
 * Two websocket servers on different paths:
 * - `/wave` sends out waves
 * - `/graphql` serves graphql
 */
const waveWS = new WebSocket.Server({ noServer: true });
const graphqlWS = new WebSocket.Server({ noServer: true });

// delegate upgrade requests to relevant destinations
server.on('upgrade', (request, socket, head) => {
  const pathname = url.parse(request.url).pathname;

  if (pathname === '/wave') {
    waveWS.handleUpgrade(request, socket, head, (client) => {
      waveWS.emit('connection', client, request);
    });
  } else if (pathname === '/graphql') {
    graphqlWS.handleUpgrade(request, socket, head, (client) => {
      graphqlWS.emit('connection', client, request);
    });
  } else {
    socket.destroy();
  }
});

// wave on connect
waveWS.on('connection', (socket) => {
  socket.send('🌊');
});

// serve graphql
createServer(
  {
    schema,
    execute,
    subscribe,
  },
  graphqlWS,
);

server.listen(443);

Server usage with custom static GraphQL arguments

import { validate, execute, subscribe } from 'graphql';
import { createServer } from 'graphql-ws';
import { schema, roots, getStaticContext } from 'my-graphql';

createServer(
  {
    context: getStaticContext(),
    schema,
    roots,
    execute,
    subscribe,
  },
  {
    server,
    path: '/graphql',
  },
);

Server usage with custom dynamic GraphQL arguments and validation

import { parse, validate, execute, subscribe } from 'graphql';
import { createServer } from 'graphql-ws';
import { schema, getDynamicContext, myValidationRules } from 'my-graphql';

createServer(
  {
    execute,
    subscribe,
    onSubscribe: (ctx, msg) => {
      const args = {
        schema,
        contextValue: getDynamicContext(ctx, msg),
        operationName: msg.payload.operationName,
        document: parse(msg.payload.operationName),
        variableValues: msg.payload.variables,
      };

      // dont forget to validate when returning custom execution args!
      const errors = validate(args.schema, args.document, myValidationRules);
      if (errors.length > 0) {
        return errors; // return `GraphQLError[]` to send `ErrorMessage` and stop subscription
      }

      return args;
    },
  },
  {
    server,
    path: '/graphql',
  },
);

Server and client usage with persisted queries

// 🛸 server

import { parse, execute, subscribe } from 'graphql';
import { createServer } from 'graphql-ws';
import { schema } from 'my-graphql-schema';

// a unique GraphQL execution ID used for representing
// a query in the persisted queries store. when subscribing
// you should use the `SubscriptionPayload.query` to transmit the id
type QueryID = string;

const queriesStore: Record<QueryID, ExecutionArgs> = {
  iWantTheGreetings: {
    schema, // you may even provide different schemas in the queries store
    document: parse('subscription Greetings { greetings }'),
  },
};

createServer(
  {
    execute,
    subscribe,
    onSubscribe: (_ctx, msg) => {
      const query = queriesStore[msg.payload.query];
      if (!query) {
        // for extra security you only allow the queries from the store
        throw new Error('404: Query Not Found');
      }
      return {
        ...query,
        variableValues: msg.payload.variables, // use the variables from the client
      };
    },
  },
  {
    server,
    path: '/graphql',
  },
);

// 📺 client

import { createClient } from 'graphql-ws';

const client = createClient({
  url: 'wss://persisted.graphql/queries',
});

(async () => {
  const onNext = () => {
    /**/
  };

  await new Promise((resolve, reject) => {
    client.subscribe(
      {
        query: 'iWantTheGreetings',
      },
      {
        next: onNext,
        error: reject,
        complete: resolve,
      },
    );
  });

  expect(onNext).toBeCalledTimes(5); // greetings in 5 languages
})();

Documentation

Check the docs folder out for TypeDoc generated documentation.

How does it work?

Read about the exact transport intricacies used by the library in the GraphQL over WebSocket Protocol document.

Want to help?

File a bug, contribute with code, or improve documentation? Read up on our guidelines for contributing and drive development with yarn test --watch away!