graphql-upload

Middleware and an Upload scalar to add support for GraphQL multipart requests (file uploads via queries and mutations) to various Node.js GraphQL servers.

Setup

First, check if there are GraphQL multipart request spec server implementations (most for Node.js integrate graphql-upload) that are more suitable for your environment than a manual setup.

To install graphql-upload and the graphql peer dependency with npm, run:

npm install graphql-upload graphql

Use the graphqlUploadKoa or graphqlUploadExpress middleware just before GraphQL middleware. Alternatively, use processRequest to create custom middleware.

A schema built with separate SDL and resolvers (e.g. using makeExecutableSchema from @graphql-tools/schema) requires the Upload scalar to be setup.

Usage

Clients implementing the GraphQL multipart request spec upload files as Upload scalar query or mutation variables. Their resolver values are promises that resolve file upload details for processing and storage. Files are typically streamed into cloud storage but may also be stored in the filesystem.

See the example API and client.

Tips

• The process must have both read and write access to the directory identified by os.tmpdir().
• The device requires sufficient disk space to buffer the expected number of concurrent upload requests.
• Promisify and await file upload streams in resolvers or the server will send a response to the client before uploads are complete, causing a disconnect.
• Handle file upload promise rejection and stream errors; uploads sometimes fail due to network connectivity issues or impatient users disconnecting.
• Process multiple uploads asynchronously with Promise.all or a more flexible solution such as Promise.allSettled where an error in one does not reject them all.
• Only use createReadStream() before the resolver returns; late calls (e.g. in an unawaited async function or callback) throw an error. Existing streams can still be used after a response is sent, although there are few valid reasons for not awaiting their completion.
• Use stream.destroy() when an incomplete stream is no longer needed, or temporary files may not get cleaned up.

Architecture

The GraphQL multipart request spec allows a file to be used for multiple query or mutation variables (file deduplication), and for variables to be used in multiple places. GraphQL resolvers need to be able to manage independent file streams. As resolvers are executed asynchronously, it’s possible they will try to process files in a different order than received in the multipart request.

busboy parses multipart request streams. Once the operations and map fields have been parsed, Upload scalar values in the GraphQL operations are populated with promises, and the operations are passed down the middleware chain to GraphQL resolvers.

fs-capacitor is used to buffer file uploads to the filesystem and coordinate simultaneous reading and writing. As soon as a file upload’s contents begins streaming, its data begins buffering to the filesystem and its associated promise resolves. GraphQL resolvers can then create new streams from the buffer by calling createReadStream(). The buffer is destroyed once all streams have ended or closed and the server has responded to the request. Any remaining buffer files will be cleaned when the process exits.

Support

• Node.js: ^12.20 || >= 14.13

API

Table of contents

• class GraphQLUpload
• class Upload
  • Upload instance method reject
  • Upload instance method resolve
  • Upload instance property file
  • Upload instance property promise
• function graphqlUploadExpress
• function graphqlUploadKoa
• function processRequest
• type FileUpload
• type FileUploadCreateReadStream
• type GraphQLOperation
• type ProcessRequestFunction
• type ProcessRequestOptions

class GraphQLUpload

A GraphQL Upload scalar that can be used in a GraphQLSchema. It’s value in resolvers is a promise that resolves file upload details for processing and storage.

Examples

Ways to import.

import { GraphQLUpload } from 'graphql-upload';

import GraphQLUpload from 'graphql-upload/public/GraphQLUpload.js';

Ways to require.

const { GraphQLUpload } = require('graphql-upload');

const GraphQLUpload = require('graphql-upload/public/GraphQLUpload.js');

A schema built using makeExecutableSchema from @graphql-tools/schema.

const { makeExecutableSchema } = require('@graphql-tools/schema');
const { GraphQLUpload } = require('graphql-upload');

const schema = makeExecutableSchema({
  typeDefs: /* GraphQL */ `
    scalar Upload
  `,
  resolvers: {
    Upload: GraphQLUpload,
  },
});

A manually constructed schema with an image upload mutation.

const {
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLBoolean,
} = require('graphql');
const { GraphQLUpload } = require('graphql-upload');

const schema = new GraphQLSchema({
  mutation: new GraphQLObjectType({
    name: 'Mutation',
    fields: {
      uploadImage: {
        description: 'Uploads an image.',
        type: GraphQLBoolean,
        args: {
          image: {
            description: 'Image file.',
            type: GraphQLUpload,
          },
        },
        async resolve(parent, { image }) {
          const { filename, mimetype, createReadStream } = await image;
          const stream = createReadStream();
          // Promisify the stream and store the file, then…
          return true;
        },
      },
    },
  }),
});

---

class Upload

A file expected to be uploaded as it has been declared in the map field of a GraphQL multipart request. The processRequest function places references to an instance of this class wherever the file is expected in the GraphQL operation. The Upload scalar derives it’s value from the promise property.

Examples

Ways to import.

import { Upload } from 'graphql-upload';

import Upload from 'graphql-upload/public/Upload.js';

Ways to require.

const { Upload } = require('graphql-upload');

const Upload = require('graphql-upload/public/Upload.js');

Upload instance method reject

Rejects the upload promise with an error. This should only be utilized by processRequest.

Parameter	Type	Description
error	object	Error instance.

Upload instance method resolve

Resolves the upload promise with the file upload details. This should only be utilized by processRequest.

Parameter	Type	Description
file	FileUpload	File upload details.

Upload instance property file

The file upload details, available when the upload promise resolves. This should only be utilized by processRequest.

Type: undefined | FileUpload

Upload instance property promise

Promise that resolves file upload details. This should only be utilized by GraphQLUpload.

Type: Promise<FileUpload>

---

function graphqlUploadExpress

Creates Express middleware that processes GraphQL multipart requests using processRequest, ignoring non-multipart requests. It sets the request body to be similar to a conventional GraphQL POST request for following GraphQL middleware to consume.

Parameter	Type	Description
options	ProcessRequestOptions	Middleware options. Any ProcessRequestOptions can be used.
options.processRequest	ProcessRequestFunction? = processRequest	Used to process GraphQL multipart requests.

Returns: Function — Express middleware.

Examples

Ways to import.

import { graphqlUploadExpress } from 'graphql-upload';

import graphqlUploadExpress from 'graphql-upload/public/graphqlUploadExpress.js';

Ways to require.

const { graphqlUploadExpress } = require('graphql-upload');

const graphqlUploadExpress = require('graphql-upload/public/graphqlUploadExpress.js');

Basic express-graphql setup.

const express = require('express');
const graphqlHTTP = require('express-graphql');
const { graphqlUploadExpress } = require('graphql-upload');
const schema = require('./schema');

express()
  .use(
    '/graphql',
    graphqlUploadExpress({ maxFileSize: 10000000, maxFiles: 10 }),
    graphqlHTTP({ schema })
  )
  .listen(3000);

---

function graphqlUploadKoa

Creates Koa middleware that processes GraphQL multipart requests using processRequest, ignoring non-multipart requests. It sets the request body to be similar to a conventional GraphQL POST request for following GraphQL middleware to consume.

Parameter	Type	Description
options	ProcessRequestOptions	Middleware options. Any ProcessRequestOptions can be used.
options.processRequest	ProcessRequestFunction? = processRequest	Used to process GraphQL multipart requests.

Returns: Function — Koa middleware.

Examples

Ways to import.

import { graphqlUploadKoa } from 'graphql-upload';

import graphqlUploadKoa from 'graphql-upload/public/graphqlUploadKoa.js';

Ways to require.

const { graphqlUploadKoa } = require('graphql-upload');

const graphqlUploadKoa = require('graphql-upload/public/graphqlUploadKoa.js');

Basic graphql-api-koa setup.

const Koa = require('koa');
const bodyParser = require('koa-bodyparser');
const { errorHandler, execute } = require('graphql-api-koa');
const { graphqlUploadKoa } = require('graphql-upload');
const schema = require('./schema');

new Koa()
  .use(errorHandler())
  .use(bodyParser())
  .use(graphqlUploadKoa({ maxFileSize: 10000000, maxFiles: 10 }))
  .use(execute({ schema }))
  .listen(3000);

---

function processRequest

Processes a GraphQL multipart request. It parses the operations and map fields to create an Upload instance for each expected file upload, placing references wherever the file is expected in the GraphQL operation for the Upload scalar to derive it’s value. Errors are created with http-errors to assist in sending responses with appropriate HTTP status codes. Used in graphqlUploadExpress and graphqlUploadKoa and can be used to create custom middleware.

Type: ProcessRequestFunction

Examples

Ways to import.

import { processRequest } from 'graphql-upload';

import processRequest from 'graphql-upload/public/processRequest.js';

Ways to require.

const { processRequest } = require('graphql-upload');

const processRequest = require('graphql-upload/public/processRequest.js');

---

type FileUpload

File upload details that are only available after the file’s field in the GraphQL multipart request has begun streaming in.

Type: object

Property	Type	Description
filename	string	File name.
mimetype	string	File MIME type. Provided by the client and can’t be trusted.
encoding	string	File stream transfer encoding.
createReadStream	FileUploadCreateReadStream	Creates a Node.js readable stream of the file’s contents, for processing and storage.

---

type FileUploadCreateReadStream

Creates a Node.js readable stream of an uploading file’s contents, for processing and storage. Multiple calls create independent streams. Throws if called after all resolvers have resolved, or after an error has interrupted the request.

Type: Function

Parameter	Type	Description
options	object?	fs-capacitor ReadStreamOptions.
options.encoding	string? = null	Specify an encoding for the data chunks to be strings (without splitting multi-byte characters across chunks) instead of Node.js Buffer instances. Supported values depend on the Buffer implementation and include utf8, ucs2, utf16le, latin1, ascii, base64, or hex.
options.highWaterMark	number? = 16384	Maximum number of bytes to store in the internal buffer before ceasing to read from the underlying resource.

Returns: Readable — Node.js readable stream of the file’s contents.

See

• Node.js Readable stream constructor docs.
• Node.js stream backpressure guide.

---

type GraphQLOperation

A GraphQL operation object in a shape that can be consumed and executed by most GraphQL servers.

Type: object

Property	Type	Description
query	string	GraphQL document containing queries and fragments.
operationName	string | null?	GraphQL document operation name to execute.
variables	object | null?	GraphQL document operation variables and values map.

See

• GraphQL over HTTP spec.
• Apollo Server POST requests.

---

type ProcessRequestFunction

Processes a GraphQL multipart request.

Type: Function

Parameter	Type	Description
request	IncomingMessage	Node.js HTTP server request instance.
response	ServerResponse	Node.js HTTP server response instance.
options	ProcessRequestOptions?	Options for processing the request.

Returns: Promise<GraphQLOperation | Array<GraphQLOperation>> — GraphQL operation or batch of operations for a GraphQL server to consume (usually as the request body).

See

• processRequest.

---

type ProcessRequestOptions

Options for processing a GraphQL multipart request; mostly relating to security, performance and limits.

Type: object

Property	Type	Description
maxFieldSize	number? = 1000000	Maximum allowed non-file multipart form field size in bytes; enough for your queries.
maxFileSize	number? = Infinity	Maximum allowed file size in bytes.
maxFiles	number? = Infinity	Maximum allowed number of files.