arantes555 / electron-fetch

A light-weight module that brings window.fetch to the background process of Electron
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electron-fetch

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

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

Difference from client-side fetch

Difference from node-fetch

Install

$ npm install 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)
})()

// providing proxy credentials (electron-specific)

fetch(url, {
  onLogin (authInfo) { // this 'authInfo' is the one received by the 'login' event. See https://www.electronjs.org/docs/latest/api/client-request#event-login
    return Promise.resolve({ username: 'testuser', password: 'testpassword' })
  }
})

See test cases for more examples.

API

fetch(url[, options])

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
    signal: null,       // the AbortSignal from an AbortController instance.

    // 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.,
    useElectronNet: true, // When running on Electron, defaults to true. On Node.js, defaults to false and cannot be set to true.
    useSessionCookies: true, // (/!\ only works when running on Electron >= 7) Whether or not to automatically send cookies from session.,
    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
    onLogin: undefined // When running on Electron behind an authenticated HTTP proxy, handler of electron.ClientRequest's login event. Can be used for acquiring proxy credentials in an async manner (e.g. prompting the user). Receives an `AuthInfo` object, and must return a `Promise<{ username: string, password: string }>`.
}

If no agent is specified, the default agent provided by Node.js is used. Note that this changed in Node.js 19 to have keepalive true by default. If you wish to enable keepalive in an earlier version of Node.js, you can override the agent as per the following code sample.

Default Headers

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

Header Value
Accept-Encoding gzip,deflate
Accept */*
Content-Length (automatically calculated, if possible)
User-Agent electron-fetch/1.0 (+https://github.com/arantes555/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:

The following electron-fetch extension properties are provided:

See options for exact meaning of these extensions.

new Request(input[, options])

(spec-compliant)

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:

new Response([body[, options]])

(spec-compliant)

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)

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:

body.body

(deviation from spec)

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)

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)

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

body.buffer()

(electron-fetch extension)

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

body.textConverted()

(electron-fetch extension)

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.

License

MIT

Acknowledgement

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