apollo-server/packages/apollo-server-express/src/ApolloServer.ts

import * as express from 'express';
import * as corsMiddleware from 'cors';
import { json } from 'body-parser';
import { createServer, Server as HttpServer } from 'http';
import gui from 'graphql-playground-middleware-express';
import { ApolloServerBase } from 'apollo-server-core';
import * as accepts from 'accepts';

import { graphqlExpress } from './expressApollo';

export interface ServerRegistration {
  app: express.Application;
  server: ApolloServerBase<express.Request>;
  path?: string;
  subscriptions?: boolean;
  cors?: corsMiddleware.CorsOptions;
}

export const registerServer = async ({
  app,
  server,
  path,
  cors,
}: ServerRegistration) => {
  // XXX multiple paths?
  server.use({ path, getHttp: () => createServer(app) });

  app.use(path, corsMiddleware(cors), json(), (req, res, next) => {
    // make sure we check to see if graphql gui should be on
    if (!server.disableTools && req.method === 'GET') {
      //perform more expensive content-type check only if necessary
      const accept = accepts(req);
      const types = accept.types() as string[];
      const prefersHTML =
        types.find(
          (x: string) => x === 'text/html' || x === 'application/json',
        ) === 'text/html';

      if (prefersHTML) {
        return gui({
          endpoint: path,
          subscriptionsEndpoint: server.subscriptions && path,
        })(req, res, next);
      }
    }
    return graphqlExpress(server.request.bind(server))(req, res, next);
  });
};