# GraphQL HTTP Server Middleware

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Create a GraphQL HTTP server with any HTTP web framework that supports connect styled middleware, including [Connect](https://github.com/senchalabs/connect) itself, [Express](https://expressjs.com) and [Restify](http://restify.com/).

## Installation

```sh
npm install --save express-graphql
```

### TypeScript

This module includes a [TypeScript](https://www.typescriptlang.org/)
declaration file to enable auto complete in compatible editors and type
information for TypeScript projects. This module depends on 'graphql' and the Node.js
types, so install `@types/graphql` and `@types/node`:

```sh
$ npm install --save --dev @types/graphql @types/node
```

## Simple Setup

Just mount `express-graphql` as a route handler:

```js
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.

```js
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);
```

## 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 is
  loaded in a browser. We recommend that you set `graphiql` to `true` when your
  app is in development, because it's quite useful. You may or may not want it
  in production.
  Alternatively, instead of `true` you can pass in an options object:

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

- **`rootValue`**: A value to pass as the `rootValue` to the `graphql()`
  function from [`GraphQL.js/src/execute.js`](https://github.com/graphql/graphql-js/blob/master/src/execution/execute.js#L119).

- **`context`**: A value to pass as the `context` to the `graphql()`
  function from [`GraphQL.js/src/execute.js`](https://github.com/graphql/graphql-js/blob/master/src/execution/execute.js#L120). If `context` is not provided, the
  `request` 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 the
  GraphQL response as a key-value object. The result will be added to
  `"extensions"` field in the resulting JSON. This is often a useful place to
  add development time metadata such as the runtime of a query or the amount
  of resources consumed. This may be an async function. The function is
  given one object as an argument: `{ document, variables, operationName, result, context }`.

- **`validationRules`**: Optional additional validation rules queries must
  satisfy in addition to those defined by the GraphQL spec.

- **`customValidateFn`**: An optional function which will be used to validate
  instead of default `validate` from `graphql-js`.

- **`customExecuteFn`**: An optional function which will be used to execute
  instead of default `execute` from `graphql-js`.

- **`customFormatErrorFn`**: An optional function which will be used to format any
  errors produced by fulfilling a GraphQL operation. If no function is
  provided, GraphQL's default spec-compliant [`formatError`][] function will be used.

- **`customParseFn`**: An optional function which will be used to create a document
  instead of the default `parse` from `graphql-js`.

- **`formatError`**: is deprecated and replaced by `customFormatErrorFn`. It will be
  removed in version 1.0.0.

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

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

```js
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 with
the parameters:

- **`query`**: A string GraphQL document to be executed.

- **`variables`**: The runtime values to use for any GraphQL query variables
  as a JSON object.

- **`operationName`**: If the provided `query` contains multiple named
  operations, this specifies which operation should be executed. If not
  provided, a 400 error will be returned if the `query` contains multiple
  named operations.

- **`raw`**: If the `graphiql` option is enabled and the `raw` parameter is
  provided raw JSON will always be returned instead of GraphiQL even when
  loaded from a browser.

GraphQL will first look for each parameter in the URL's query-string:

```
/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.body`
value will be used. Use [`multer`][] or a similar middleware to add support
for `multipart/form-data` content, which may be useful for GraphQL mutations
involving uploading files. See an [example using multer](https://github.com/graphql/express-graphql/blob/304b24b993c8f16fffff8d23b0fa4088e690874b/src/__tests__/http-test.js#L674-L741).

If the POST body has not yet been parsed, express-graphql will interpret it
depending on the provided _Content-Type_ header.

- **`application/json`**: the POST body will be parsed as a JSON
  object of parameters.

- **`application/x-www-form-urlencoded`**: this POST body will be
  parsed as a url-encoded string of key-value pairs.

- **`application/graphql`**: The POST body will be parsed as GraphQL
  query 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 the
request 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.

```js
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:

```js
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 to
a GraphQL query via a field in the response called `"extensions"`. This is added
by providing an `extensions` function when using `graphqlHTTP`. The function
must return a JSON-serializable Object.

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

`{ document, variables, operationName, result, context }`

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

```js
const graphqlHTTP = require('express-graphql');

const app = express();

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

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:

```js
{
  "data": { ... }
  "extensions": {
    "runTime": 135
  }
}
```

## Additional Validation Rules

GraphQL's [validation phase](https://graphql.github.io/graphql-spec/#sec-Validation) 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 fieldname `metadata` from being queried. For more examples see the [`specifiedRules`](https://github.com/graphql/graphql-js/tree/master/src/validation/rules) in the [graphql-js](https://github.com/graphql/graphql-js) package.

```js
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`,
          ),
        );
      }
    },
  };
}
```

## Other Exports

**`getGraphQLParams(request: Request): Promise<GraphQLParams>`**

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

```js
const graphqlHTTP = require('express-graphql');

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

## Debugging Tips

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

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

[`graphql.js`]: https://github.com/graphql/graphql-js
[`formaterror`]: https://github.com/graphql/graphql-js/blob/master/src/error/formatError.js
[graphiql]: https://github.com/graphql/graphiql
[`multer`]: https://github.com/expressjs/multer
[`express-session`]: https://github.com/expressjs/session