GraphQL HTTP Server Middleware

Create a GraphQL HTTP server with any HTTP web framework that supports connect styled middleware, including Connect itself, Express and Restify.

Installation

npm install --save express-graphql

TypeScript

This module includes a TypeScriptdeclaration file to enable auto complete in compatible editors and typeinformation for TypeScript projects.

Simple Setup

Just mount express-graphql as a route handler:

const express = require('express');
const { graphqlHTTP } = require('express-graphql');

const app = express();

app.use(
  '/graphql',
  graphqlHTTP({
    schema: MyGraphQLSchema,
    graphiql: true,
  }),
);

app.listen(4000);

Setup with Restify

Use .get or .post (or both) rather than .use to configure your route handler. If you want to show GraphiQL in the browser, set graphiql: true on your .get handler.

const restify = require('restify');
const { graphqlHTTP } = require('express-graphql');

const app = restify.createServer();

app.post(
  '/graphql',
  graphqlHTTP({
    schema: MyGraphQLSchema,
    graphiql: false,
  }),
);

app.get(
  '/graphql',
  graphqlHTTP({
    schema: MyGraphQLSchema,
    graphiql: true,
  }),
);

app.listen(4000);

Setup with Subscription Support

const express = require('express');
const { graphqlHTTP } = require('express-graphql');

const typeDefs = require('./schema');
const resolvers = require('./resolvers');
const { makeExecutableSchema } = require('graphql-tools');
const schema = makeExecutableSchema({
  typeDefs: typeDefs,
  resolvers: resolvers,
});

const { execute, subscribe } = require('graphql');
const { createServer } = require('http');
const { SubscriptionServer } = require('subscriptions-transport-ws');

const PORT = 4000;

var app = express();

app.use(
  '/graphql',
  graphqlHTTP({
    schema: schema,
    graphiql: { subscriptionEndpoint: `ws://localhost:${PORT}/subscriptions` },
  }),
);

const ws = createServer(app);

ws.listen(PORT, () => {
  // Set up the WebSocket for handling GraphQL subscriptions.
  new SubscriptionServer(
    {
      execute,
      subscribe,
      schema,
    },
    {
      server: ws,
      path: '/subscriptions',
    },
  );
});

Options

The graphqlHTTP function accepts the following options:

• schema: A GraphQLSchema instance from GraphQL.js.A schema must be provided.

• graphiql: If true, presents GraphiQL when the GraphQL endpoint isloaded in a browser. We recommend that you set graphiql to true when yourapp is in development, because it's quite useful. You may or may not want itin production.Alternatively, instead of true you can pass in an options object:

  • defaultQuery: An optional GraphQL string to use when no queryis provided and no stored query exists from a previous session.If undefined is provided, GraphiQL will use its own default query.

  • headerEditorEnabled: An optional boolean which enables the header editor when true.Defaults to false.

  • subscriptionEndpoint: An optional GraphQL string contains the WebSocket server url for subscription.

  • websocketClient: An optional GraphQL string for websocket client used for subscription, v0: subscriptions-transport-ws, v1: graphql-ws. Defaults to v0 if not provided

• rootValue: A value to pass as the rootValue to the execute()function from GraphQL.js/src/execute.js.

• context: A value to pass as the contextValue to the execute()function from GraphQL.js/src/execute.js. If context is not provided, therequest object is passed as the context.

• pretty: If true, any JSON response will be pretty-printed.

• extensions: An optional function for adding additional metadata to theGraphQL response as a key-value object. The result will be added to the"extensions" field in the resulting JSON. This is often a useful place toadd development time metadata such as the runtime of a query or the amountof resources consumed. This may be an async function. The function isgiven one object as an argument: { document, variables, operationName, result, context }.

• validationRules: Optional additional validation rules that queries mustsatisfy in addition to those defined by the GraphQL spec.

• customValidateFn: An optional function which will be used to validateinstead of default validate from graphql-js.

• customExecuteFn: An optional function which will be used to executeinstead of default execute from graphql-js.

• customFormatErrorFn: An optional function which will be used to format anyerrors produced by fulfilling a GraphQL operation. If no function isprovided, GraphQL's default spec-compliant formatError function will be used.

• customParseFn: An optional function which will be used to create a documentinstead of the default parse from graphql-js.

• formatError: is deprecated and replaced by customFormatErrorFn. It will beremoved in version 1.0.0.

In addition to an object defining each option, options can also be provided asa function (or async function) which returns this options object. This functionis provided the arguments (request, response, graphQLParams) and is calledafter the request has been parsed.

The graphQLParams is provided as the object { query, variables, operationName, raw }.

app.use(
  '/graphql',
  graphqlHTTP(async (request, response, graphQLParams) => ({
    schema: MyGraphQLSchema,
    rootValue: await someFunctionToGetRootValue(request),
    graphiql: true,
  })),
);

HTTP Usage

Once installed at a path, express-graphql will accept requests withthe parameters:

• query: A string GraphQL document to be executed.

• variables: The runtime values to use for any GraphQL query variablesas a JSON object.

• operationName: If the provided query contains multiple namedoperations, this specifies which operation should be executed. If notprovided, a 400 error will be returned if the query contains multiplenamed operations.

• raw: If the graphiql option is enabled and the raw parameter isprovided, raw JSON will always be returned instead of GraphiQL even whenloaded from a browser.

GraphQL will first look for each parameter in the query string of a URL:

/graphql?query=query+getUser($id:ID){user(id:$id){name}}&variables={"id":"4"}

If not found in the query string, it will look in the POST request body.

If a previous middleware has already parsed the POST body, the request.bodyvalue will be used. Use multer or a similar middleware to add supportfor multipart/form-data content, which may be useful for GraphQL mutationsinvolving uploading files. See an example using multer.

If the POST body has not yet been parsed, express-graphql will interpret itdepending on the provided Content-Type header.

• application/json: the POST body will be parsed as a JSONobject of parameters.

• application/x-www-form-urlencoded: the POST body will beparsed as a url-encoded string of key-value pairs.

• application/graphql: the POST body will be parsed as GraphQLquery string, which provides the query parameter.

Combining with Other Express Middleware

By default, the express request is passed as the GraphQL context.Since most express middleware operates by adding extra data to therequest object, this means you can use most express middleware just by inserting it before graphqlHTTP is mounted. This covers scenarios such as authenticating the user, handling file uploads, or mounting GraphQL on a dynamic endpoint.

This example uses express-session to provide GraphQL with the currently logged-in session.

const session = require('express-session');
const { graphqlHTTP } = require('express-graphql');

const app = express();

app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 } }));

app.use(
  '/graphql',
  graphqlHTTP({
    schema: MySessionAwareGraphQLSchema,
    graphiql: true,
  }),
);

Then in your type definitions, you can access the request via the third "context" argument in your resolve function:

new GraphQLObjectType({
  name: 'MyType',
  fields: {
    myField: {
      type: GraphQLString,
      resolve(parentValue, args, request) {
        // use `request.session` here
      },
    },
  },
});

Providing Extensions

The GraphQL response allows for adding additional information in a response toa GraphQL query via a field in the response called "extensions". This is addedby providing an extensions function when using graphqlHTTP. The functionmust return a JSON-serializable Object.

When called, this is provided an argument which you can use to get informationabout the GraphQL request:

{ document, variables, operationName, result, context }

This example illustrates adding the amount of time consumed by running theprovided query, which could perhaps be used by your development tools.

const { graphqlHTTP } = require('express-graphql');

const app = express();

const extensions = ({
  document,
  variables,
  operationName,
  result,
  context,
}) => {
  return {
    runTime: Date.now() - context.startTime,
  };
};

app.use(
  '/graphql',
  graphqlHTTP((request) => {
    return {
      schema: MyGraphQLSchema,
      context: { startTime: Date.now() },
      graphiql: true,
      extensions,
    };
  }),
);

When querying this endpoint, it would include this information in the result,for example:

{
  "data": { ... },
  "extensions": {
    "runTime": 135
  }
}

Additional Validation Rules

GraphQL's validation phase checks the query to ensure that it can be successfully executed against the schema. The validationRules option allows for additional rules to be run during this phase. Rules are applied to each node in an AST representing the query using the Visitor pattern.

A validation rule is a function which returns a visitor for one or more node Types. Below is an example of a validation preventing the specific field name metadata from being queried. For more examples, see the specifiedRules in the graphql-js package.

import { GraphQLError } from 'graphql';

export function DisallowMetadataQueries(context) {
  return {
    Field(node) {
      const fieldName = node.name.value;

      if (fieldName === 'metadata') {
        context.reportError(
          new GraphQLError(
            `Validation: Requesting the field ${fieldName} is not allowed`,
          ),
        );
      }
    },
  };
}

Disabling introspection

Disabling introspection does not reflect best practices and does not necessarily make yourapplication any more secure. Nevertheless, disabling introspection is possible by utilizing theNoSchemaIntrospectionCustomRule provided by the graphql-jspackage.

import { NoSchemaIntrospectionCustomRule } from 'graphql';

app.use(
  '/graphql',
  graphqlHTTP((request) => {
    return {
      schema: MyGraphQLSchema,
      validationRules: [NoSchemaIntrospectionCustomRule],
    };
  }),
);

Other Exports

getGraphQLParams(request: Request): Promise<GraphQLParams>

Given an HTTP Request, this returns a Promise for the parameters relevant torunning a GraphQL request. This function is used internally to handle theincoming request, you may use it directly for building other similar services.

const { getGraphQLParams } = require('express-graphql');

getGraphQLParams(request).then((params) => {
  // do something...
});

Debugging Tips

During development, it's useful to get more information from errors, such asstack traces. Providing a function to customFormatErrorFn enables this:

customFormatErrorFn: (error) => ({
  message: error.message,
  locations: error.locations,
  stack: error.stack ? error.stack.split('\n') : [],
  path: error.path,
});

Experimental features

Each release of express-graphql will be accompanied by an experimental release containing support for the @defer and @stream directive proposal. We are hoping to get community feedback on these releases before the proposal is accepted into the GraphQL specification. You can use this experimental release of express-graphql by adding the following to your project's package.json file.

"express-graphql": "experimental-stream-defer",
"graphql": "experimental-stream-defer"

Community feedback on this experimental release is much appreciated and can be provided on the PR for the defer-stream branch or the GraphQL.js issue for feedback.

Contributing to this repo

This repository is managed by EasyCLA. Project participants must sign the free GraphQL Specification Membership agreement before making a contribution. You only need to do this one time, and it can be signed by individual contributors or their employers.

To initiate the signature process please open a PR against this repo. The EasyCLA bot will block the merge if we still need a membership agreement from you.

You can find detailed information here. If you have issues, please email operations@graphql.org.

If your company benefits from GraphQL and you would like to provide essential financial support for the systems and people that power our community, please also consider membership in the GraphQL Foundation.