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GraphQL Koa Middleware

npm version Build Status Coverage Status

Create a GraphQL HTTP server with Koa.

Port from express-graphql.

Installation

npm install --save koa-graphql

TypeScript

This module includes a TypeScript declaration file to enable auto complete in compatible editors and type information for TypeScript projects.

Simple Setup

Mount koa-graphql as a route handler:

const Koa = require('koa');
const mount = require('koa-mount');
const { graphqlHTTP } = require('koa-graphql');

const app = new Koa();

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

app.listen(4000);

Setup with Koa Router

With @koa/router:

const Koa = require('koa');
const Router = require('@koa/router');
const { graphqlHTTP } = require('koa-graphql');

const app = new Koa();
const router = new Router();

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

app.use(router.routes()).use(router.allowedMethods());

Setup with Koa v1

For Koa 1, use koa-convert to convert the middleware:

const koa = require('koa');
const mount = require('koa-mount'); // koa-mount@1.x
const convert = require('koa-convert');
const { graphqlHTTP } = require('koa-graphql');

const app = koa();

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

Setup with Subscription Support

const Koa = require('koa');
const mount = require('koa-mount');
const { graphqlHTTP } = require('koa-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;
const app = new Koa();
app.use(
  mount(
    '/graphql',
    graphqlHTTP({
      schema: schema,
      graphiql: {
        subscriptionEndpoint: `ws://localhost:${PORT}/subscriptions`,
      },
    }),
  ),
);
const ws = createServer(app.callback());
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 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.

    • 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

    • shouldPersistHeaders

    • editorTheme: By passing an object you may change the theme of GraphiQL. Details are below in the Custom GraphiQL themes section.

  • 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 context to the execute() function from graphql-js/src/execute.js. If context is not provided, the ctx 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 the "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 that 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.

  • fieldResolver

  • typeResolver

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 }.

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

HTTP Usage

Once installed at a path, koa-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 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.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.

If the POST body has not yet been parsed, koa-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: the 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 koa Middleware

By default, the koa request is passed as the GraphQL context. Since most koa middleware operates by adding extra data to the request object, this means you can use most koa 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 koa-session to provide GraphQL with the currently logged-in session.

const Koa = require('koa');
const mount = require('koa-mount');
const session = require('koa-session');
const { graphqlHTTP } = require('koa-graphql');

const app = new Koa();
app.keys = ['some secret'];
app.use(session(app));
app.use(function* (next) {
  this.session.id = 'me';
  yield next;
});

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

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

new GraphQLObjectType({
  name: 'MyType',
  fields: {
    myField: {
      type: GraphQLString,
      resolve(parentValue, args, ctx) {
        // use `ctx.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.

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

const app = new Koa();

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

app.use(
  mount(
    '/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 your application any more secure. Nevertheless, disabling introspection is possible by utilizing the NoSchemaIntrospectionCustomRule provided by the graphql-js package.

import { NoSchemaIntrospectionCustomRule } from 'graphql';

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

Custom GraphiQL Themes

To use custom GraphiQL theme you should pass to graphiql option an object with the property editorTheme. It could be a string with the name of a theme from CodeMirror

router.all(
  '/graphql',
  graphqlHTTP({
    schema: MyGraphQLSchema,
    graphiql: {
      editorTheme: 'blackboard',
    },
  }),
);

List of available CodeMirror themes

or an object with url and name properties where url should lead to your custom theme and name would be passed to the GraphiQL react element on creation as the editorTheme property

router.all(
  '/graphql',
  graphqlHTTP({
    schema: MyGraphQLSchema,
    graphiql: {
      editorTheme: {
        name: 'blackboard',
        url: 'https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.53.2/theme/erlang-dark.css',
      },
    },
  }),
);

For details see the GraphiQL spec

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

Debugging Tips

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

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

Examples

Other Relevant Projects

Please checkout awesome-graphql.

Contributing

Welcome pull requests!

License

MIT