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protocol

Register a custom protocol and intercept existing protocol requests.

Process: Main

An example of implementing a protocol that has the same effect as the file:// protocol:

const { app, protocol } = require('electron')
const path = require('path')

app.whenReady().then(() => {
  protocol.registerFileProtocol('atom', (request, callback) => {
    const url = request.url.substr(7)
    callback({ path: path.normalize(`${__dirname}/${url}`) })
  }, (error) => {
    if (error) console.error('Failed to register protocol')
  })
})

Note: All methods unless specified can only be used after the ready event of the app module gets emitted.

Using protocol with a custom partition or session

A protocol is registered to a specific Electron session object. If you don't specify a session, then your protocol will be applied to the default session that Electron uses. However, if you define a partition or session on your browserWindow's webPreferences, then that window will use a different session and your custom protocol will not work if you just use electron.protocol.XXX.

To have your custom protocol work in combination with a custom session, you need to register it to that session explicitly.

const { session, app, protocol } = require('electron')
const path = require('path')

app.whenReady().then(() => {
  const partition = 'persist:example'
  const ses = session.fromPartition(partition)

  ses.protocol.registerFileProtocol('atom', (request, callback) => {
    const url = request.url.substr(7)
    callback({ path: path.normalize(`${__dirname}/${url}`) })
  }, (error) => {
    if (error) console.error('Failed to register protocol')
  })

  mainWindow = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      partition: partition
    }
  })
})

Methods

The protocol module has the following methods:

protocol.registerSchemesAsPrivileged(customSchemes)

Note: This method can only be used before the ready event of the app module gets emitted and can be called only once.

Registers the scheme as standard, secure, bypasses content security policy for resources, allows registering ServiceWorker and supports fetch API.

Specify a privilege with the value of true to enable the capability. An example of registering a privileged scheme, with bypassing Content Security Policy:

const { protocol } = require('electron')
protocol.registerSchemesAsPrivileged([
  { scheme: 'foo', privileges: { bypassCSP: true } }
])

A standard scheme adheres to what RFC 3986 calls generic URI syntax. For example http and https are standard schemes, while file is not.

Registering a scheme as standard, will allow relative and absolute resources to be resolved correctly when served. Otherwise the scheme will behave like the file protocol, but without the ability to resolve relative URLs.

For example when you load following page with custom protocol without registering it as standard scheme, the image will not be loaded because non-standard schemes can not recognize relative URLs:

<body>
  <img src='test.png'>
</body>

Registering a scheme as standard will allow access to files through the FileSystem API. Otherwise the renderer will throw a security error for the scheme.

By default web storage apis (localStorage, sessionStorage, webSQL, indexedDB, cookies) are disabled for non standard schemes. So in general if you want to register a custom protocol to replace the http protocol, you have to register it as a standard scheme.

protocol.registerSchemesAsPrivileged can be used to replicate the functionality of the previous protocol.registerStandardSchemes, webFrame.registerURLSchemeAs* and protocol.registerServiceWorkerSchemes functions that existed prior to Electron 5.0.0, for example:

before (<= v4.x)

// Main
protocol.registerStandardSchemes(['scheme1', 'scheme2'], { secure: true })
// Renderer
webFrame.registerURLSchemeAsPrivileged('scheme1', { secure: true })
webFrame.registerURLSchemeAsPrivileged('scheme2', { secure: true })

after (>= v5.x)

protocol.registerSchemesAsPrivileged([
  { scheme: 'scheme1', privileges: { standard: true, secure: true } },
  { scheme: 'scheme2', privileges: { standard: true, secure: true } }
])

protocol.registerFileProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
  • completion Function (optional)
    • error Error

Registers a protocol of scheme that will send the file as a response. The handler will be called with handler(request, callback) when a request is going to be created with scheme. completion will be called with completion(null) when scheme is successfully registered or completion(error) when failed.

To handle the request, the callback should be called with either the file's path or an object that has a path property, e.g. callback(filePath) or callback({ path: filePath }). The object may also have a headers property which gives a map of headers to values for the response headers, e.g. callback({ path: filePath, headers: {"Content-Security-Policy": "default-src 'none'"]}).

When callback is called with nothing, a number, or an object that has an error property, the request will fail with the error number you specified. For the available error numbers you can use, please see the net error list.

By default the scheme is treated like http:, which is parsed differently than protocols that follow the "generic URI syntax" like file:.

protocol.registerBufferProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
  • completion Function (optional)
    • error Error

Registers a protocol of scheme that will send a Buffer as a response.

The usage is the same with registerFileProtocol, except that the callback should be called with either a Buffer object or an object that has the data, mimeType, and charset properties.

Example:

const { protocol } = require('electron')

protocol.registerBufferProtocol('atom', (request, callback) => {
  callback({ mimeType: 'text/html', data: Buffer.from('<h5>Response</h5>') })
}, (error) => {
  if (error) console.error('Failed to register protocol')
})

protocol.registerStringProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
  • completion Function (optional)
    • error Error

Registers a protocol of scheme that will send a String as a response.

The usage is the same with registerFileProtocol, except that the callback should be called with either a String or an object that has the data, mimeType, and charset properties.

protocol.registerHttpProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
      • redirectRequest Object
  • completion Function (optional)
    • error Error

Registers a protocol of scheme that will send an HTTP request as a response.

The usage is the same with registerFileProtocol, except that the callback should be called with a redirectRequest object that has the url, method, referrer, uploadData and session properties.

By default the HTTP request will reuse the current session. If you want the request to have a different session you should set session to null.

For POST requests the uploadData object must be provided.

protocol.registerStreamProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
  • completion Function (optional)
    • error Error

Registers a protocol of scheme that will send a Readable as a response.

The usage is similar to the other register{Any}Protocol, except that the callback should be called with either a Readable object or an object that has the data, statusCode, and headers properties.

Example:

const { protocol } = require('electron')
const { PassThrough } = require('stream')

function createStream (text) {
  const rv = new PassThrough() // PassThrough is also a Readable stream
  rv.push(text)
  rv.push(null)
  return rv
}

protocol.registerStreamProtocol('atom', (request, callback) => {
  callback({
    statusCode: 200,
    headers: {
      'content-type': 'text/html'
    },
    data: createStream('<h5>Response</h5>')
  })
}, (error) => {
  if (error) console.error('Failed to register protocol')
})

It is possible to pass any object that implements the readable stream API (emits data/end/error events). For example, here's how a file could be returned:

const { protocol } = require('electron')
const fs = require('fs')

protocol.registerStreamProtocol('atom', (request, callback) => {
  callback(fs.createReadStream('index.html'))
}, (error) => {
  if (error) console.error('Failed to register protocol')
})

protocol.unregisterProtocol(scheme[, completion])

  • scheme String
  • completion Function (optional)
    • error Error

Unregisters the custom protocol of scheme.

protocol.isProtocolHandled(scheme)

  • scheme String

Returns Promise<Boolean> - fulfilled with a boolean that indicates whether there is already a handler for scheme.

protocol.interceptFileProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
      • filePath String
  • completion Function (optional)
    • error Error

Intercepts scheme protocol and uses handler as the protocol's new handler which sends a file as a response.

protocol.interceptStringProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
  • completion Function (optional)
    • error Error

Intercepts scheme protocol and uses handler as the protocol's new handler which sends a String as a response.

protocol.interceptBufferProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
      • buffer Buffer (optional)
  • completion Function (optional)
    • error Error

Intercepts scheme protocol and uses handler as the protocol's new handler which sends a Buffer as a response.

protocol.interceptHttpProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
      • redirectRequest Object
  • completion Function (optional)
    • error Error

Intercepts scheme protocol and uses handler as the protocol's new handler which sends a new HTTP request as a response.

protocol.interceptStreamProtocol(scheme, handler[, completion])

  • scheme String
  • handler Function
    • request Object
      • url String
      • headers Record<String, String>
      • referrer String
      • method String
      • uploadData UploadData[]
    • callback Function
  • completion Function (optional)
    • error Error

Same as protocol.registerStreamProtocol, except that it replaces an existing protocol handler.

protocol.uninterceptProtocol(scheme[, completion])

  • scheme String
  • completion Function (optional)
    • error Error

Remove the interceptor installed for scheme and restore its original handler.