Electron Documentation

protocol (NetworkService) (Draft)

This document describes the new protocol APIs based on the NetworkService.

We don't currently have an estimate of when we will enable the NetworkService by default in Electron, but as Chromium is already removing non-NetworkService code, we will probably switch before Electron 10.

The content of this document should be moved to protocol.md after we have enabled the NetworkService by default in Electron.

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.on('ready', () => {
  protocol.registerFileProtocol('atom', (request, callback) => {
    const url = request.url.substr(7)
    callback({ path: path.normalize(`${__dirname}/${url}`) })
  })
})

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.on('ready', () => {
  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}`) })
  })

  mainWindow = new BrowserWindow({ webPreferences: { 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, that bypasses 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 allows 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.registerFileProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

Registers a protocol of scheme that will send a file as the response. The handler will be called with request and callback where request is an incoming request for the scheme.

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 filePath must be an absolute path.

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

protocol.registerBufferProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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 property.

Example:

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

protocol.registerStringProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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 property.

protocol.registerHttpProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function
      • response ProtocolResponse

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 an object that has the url property.

protocol.registerStreamProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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

The usage is the same with registerFileProtocol, except that the callback should be called with either a ReadableStream object or an object that has the data property.

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>')
  })
})

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:

protocol.registerStreamProtocol('atom', (request, callback) => {
  callback(fs.createReadStream('index.html'))
})

protocol.unregisterProtocol(scheme)

  • scheme String

Unregisters the custom protocol of scheme.

protocol.isProtocolRegistered(scheme)

  • scheme String

Returns Boolean - Whether scheme is already registered.

protocol.interceptFileProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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

protocol.interceptStringProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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

protocol.interceptBufferProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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

protocol.interceptHttpProtocol(scheme, handler)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function
      • response ProtocolResponse

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)

  • scheme String
  • handler Function
    • request ProtocolRequest
    • callback Function

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

protocol.uninterceptProtocol(scheme)

  • scheme String

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

protocol.isProtocolIntercepted(scheme)

  • scheme String

Returns Boolean - Whether scheme is already intercepted.


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