@w3cub/electron-fetch

electron-fetch

A light-weight module that brings window.fetch to Electron's background process. Forked from node-fetch.

⚠❗️ WARNING: For now, a lot of things are broken on electron7. You can follow the github issues at https://github.com/electron/electron/labels/component%2Fnet

Motivation

Instead of implementing XMLHttpRequest over Electron's net module to run browser-specific Fetch polyfill, why not go from native net.request to fetch API directly? Hence electron-fetch, minimal code for a window.fetch compatible API on Electron's background runtime.

Why not simply use node-fetch? Well, Electron's net module does a better job than Node.js' http module at handling web proxies.

Features

• Stay consistent with window.fetch API.
• Runs on both Electron and Node.js, using either Electron's net module, or Node.js http module as backend.
• Make conscious trade-off when following whatwg fetch spec and stream spec implementation details, document known difference.
• Use native promise.
• Use native stream for body, on both request and response.
• Decode content encoding (gzip/deflate) properly, and convert string output (such as res.text() and res.json()) to UTF-8 automatically.
• Useful extensions such as timeout, redirect limit (when running on Node.js), response size limit, [explicit errors][] for troubleshooting.

Difference from client-side fetch

• See Known Differences for details.
• If you happen to use a missing feature that window.fetch offers, feel free to open an issue.
• Pull requests are welcomed too!

Difference from node-fetch

• Removed node-fetch specific options, such as compression.
• Added electron-specific option to specify the Session.
• Removed possibility to use custom Promise implementation (it's 2018, Promise is available everywhere!).
• Removed the possibility to forbid content compression (incompatible with Electron's net module, and of limited interest)
• standard-ized the code.

Install

$ npm i @w3cub/electron-fetch --save

Usage

import fetch from 'electron-fetch'
// or
// const fetch = require('electron-fetch').default

// plain text or html

fetch('https://github.com/')
	.then(res => res.text())
	.then(body => console.log(body))

// json

fetch('https://api.github.com/users/github')
	.then(res => res.json())
	.then(json => console.log(json))

// catching network error
// 3xx-5xx responses are NOT network errors, and should be handled in then()
// you only need one catch() at the end of your promise chain

fetch('http://domain.invalid/')
	.catch(err => console.error(err))

// stream
// the node.js way is to use stream when possible

fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png')
	.then(res => {
		const dest = fs.createWriteStream('./octocat.png')
		res.body.pipe(dest)
	})

// buffer
// if you prefer to cache binary data in full, use buffer()
// note that buffer() is a electron-fetch only API

import fileType from 'file-type'

fetch('https://assets-cdn.github.com/images/modules/logos_page/Octocat.png')
	.then(res => res.buffer())
	.then(buffer => fileType(buffer))
	.then(type => { /* ... */ })

// meta

fetch('https://github.com/')
	.then(res => {
		console.log(res.ok)
		console.log(res.status)
		console.log(res.statusText)
		console.log(res.headers.raw())
		console.log(res.headers.get('content-type'))
	})

// post

fetch('http://httpbin.org/post', { method: 'POST', body: 'a=1' })
	.then(res => res.json())
	.then(json => console.log(json))

// post with stream from file

import { createReadStream } from 'fs'

const stream = createReadStream('input.txt')
fetch('http://httpbin.org/post', { method: 'POST', body: stream })
	.then(res => res.json())
	.then(json => console.log(json))

// post with JSON

const body = { a: 1 }
fetch('http://httpbin.org/post', { 
	method: 'POST',
	body:    JSON.stringify(body),
	headers: { 'Content-Type': 'application/json' },
})
	.then(res => res.json())
	.then(json => console.log(json))

// post with form-data (detect multipart)

import FormData from 'form-data'

const form = new FormData()
form.append('a', 1)
fetch('http://httpbin.org/post', { method: 'POST', body: form })
	.then(res => res.json())
	.then(json => console.log(json))

// post with form-data (custom headers)
// note that getHeaders() is non-standard API

import FormData from 'form-data'

const form = new FormData()
form.append('a', 1)
fetch('http://httpbin.org/post', { method: 'POST', body: form, headers: form.getHeaders() })
	.then(res => res.json())
	.then(json => console.log(json))

// node 7+ with async function

(async function () {
	const res = await fetch('https://api.github.com/users/github')
	const json = await res.json()
	console.log(json)
})()

See test cases for more examples.

API

fetch(url[, options])

• url A string representing the URL for fetching
• options Options for the HTTP(S) request
• Returns: Promise<Response>

Perform an HTTP(S) fetch.

url should be an absolute url, such as http://example.com/. A path-relative URL (/file/under/root) or protocol-relative URL (//can-be-http-or-https.com/) will result in a rejected promise.

Options

The default values are shown after each option key.

const defaultOptions = {
	// These properties are part of the Fetch Standard
	method: 'GET',
	headers: {},        // request headers. format is the identical to that accepted by the Headers constructor (see below)
	body: null,         // request body. can be null, a string, a Buffer, a Blob, or a Node.js Readable stream
	redirect: 'follow', // (/!\ only works when running on Node.js) set to `manual` to extract redirect headers, `error` to reject redirect

	// The following properties are electron-fetch extensions
	follow: 20,         // (/!\ only works when running on Node.js) maximum redirect count. 0 to not follow redirect
	timeout: 0,         // req/res timeout in ms, it resets on redirect. 0 to disable (OS limit applies)
	size: 0,            // maximum response body size in bytes. 0 to disable
	session: session.defaultSession, // (/!\ only works when running on Electron) Electron Session object.,
	agent: null,        // (/!\ only works when useElectronNet is false) Node HTTP Agent.,
	user: undefined,    // When running on Electron behind an authenticated HTTP proxy, username to use to authenticate
	password: undefined // When running on Electron behind an authenticated HTTP proxy, password to use to authenticate
}

Default Headers

If no values are set, the following request headers will be sent automatically:

Header	Value
Accept-Encoding	gzip,deflate
Accept	*/*
Connection	close
Content-Length	(automatically calculated, if possible)
User-Agent	electron-fetch/3.0 (+https://github.com/icai/electron-fetch)

Class: Request

An HTTP(S) request containing information about URL, method, headers, and the body. This class implements the Body interface.

Due to the nature of Node.js, the following properties are not implemented at this moment:

• type
• destination
• referrer
• referrerPolicy
• mode
• credentials
• cache
• integrity
• keepalive

The following electron-fetch extension properties are provided:

• follow (/!\ only works when running on Node.js)
• counter (/!\ only works when running on Node.js)
• session (/!\ only works when running on Electron)
• agent (/!\ only works when running on Node.js)

See options for exact meaning of these extensions.

new Request(input[, options])

(spec-compliant)

• input A string representing a URL, or another Request (which will be cloned)
• options [Options][#fetch-options] for the HTTP(S) request

Constructs a new Request object. The constructor is identical to that in the browser.

In most cases, directly fetch(url, options) is simpler than creating a Request object.

Class: Response

An HTTP(S) response. This class implements the Body interface.

The following properties are not implemented in electron-fetch at this moment:

• Response.error()
• Response.redirect()
• type
• redirected
• trailer

new Response([body[, options]])

(spec-compliant)

• body A string or Readable stream
• options A ResponseInit options dictionary

Constructs a new Response object. The constructor is identical to that in the browser.

Because Node.js & Electron's background do not implement service workers (for which this class was designed), one rarely has to construct a Response directly.

Class: Headers

This class allows manipulating and iterating over a set of HTTP headers. All methods specified in the Fetch Standard are implemented.

new Headers([init])

(spec-compliant)

• init Optional argument to pre-fill the Headers object

Construct a new Headers object. init can be either null, a Headers object, an key-value map object, or any iterable object.

// Example adapted from https://fetch.spec.whatwg.org/#example-headers-class

const meta = {
  'Content-Type': 'text/xml',
  'Breaking-Bad': '<3'
}
const headers = new Headers(meta)

// The above is equivalent to
const meta = [
  [ 'Content-Type', 'text/xml' ],
  [ 'Breaking-Bad', '<3' ]
]
const headers = new Headers(meta)

// You can in fact use any iterable objects, like a Map or even another Headers
const meta = new Map()
meta.set('Content-Type', 'text/xml')
meta.set('Breaking-Bad', '<3')
const headers = new Headers(meta)
const copyOfHeaders = new Headers(headers)

Interface: Body

Body is an abstract interface with methods that are applicable to both Request and Response classes.

The following methods are not yet implemented in electron-fetch at this moment:

• formData()

body.body

(deviation from spec)

• Node.js Readable stream

The data encapsulated in the Body object. Note that while the Fetch Standard requires the property to always be a WHATWG ReadableStream, in electron-fetch it is a Node.js Readable stream.

body.bodyUsed

(spec-compliant)

• Boolean

A boolean property for if this body has been consumed. Per spec, a consumed body cannot be used again.

body.arrayBuffer()

body.blob()

body.json()

body.text()

(spec-compliant)

• Returns: Promise

Consume the body and return a promise that will resolve to one of these formats.

body.buffer()

(electron-fetch extension)

• Returns: Promise<Buffer>

Consume the body and return a promise that will resolve to a Buffer.

body.textConverted()

(electron-fetch extension)

• Returns: Promise<String>

Identical to body.text(), except instead of always converting to UTF-8, encoding sniffing will be performed and text converted to UTF-8, if possible.

Class: FetchError

(electron-fetch extension)

An operational error in the fetching process. See ERROR-HANDLING.md for more info.

Request cancellation with AbortSignal

You may cancel requests with AbortController. A suggested implementation is abort-controller.

An example of timing out a request after 150ms could be achieved as the following:

const fetch = require('@w3cub/electron-fetch');
const AbortController = require('abort-controller');

const controller = new AbortController();
const timeout = setTimeout(() => {
	controller.abort();
}, 150);

fetch('https://example.com', {signal: controller.signal})
	.then(res => res.json())
	.then(
		data => {
			useData(data);
		},
		err => {
			if (err.name === 'AbortError') {
                console.log('request was aborted');
			}
		}
	)
	.finally(() => {
		clearTimeout(timeout);
	});

See test cases for more examples.

License

MIT

Acknowledgement

Thanks to github/fetch for providing a solid implementation reference. Thanks to node-fetch for providing a solid base to fork.