# protocol
> Register a custom protocol and intercept existing protocol requests.
Process: [Main](../glossary.md#main-process)
An example of implementing a protocol that has the same effect as the
`file://` protocol:
```javascript
const { app, protocol } = require('electron')
const path = require('path')
const url = require('url')
app.whenReady().then(() => {
protocol.registerFileProtocol('atom', (request, callback) => {
const filePath = url.fileURLToPath('file://' + request.url.slice('atom://'.length))
callback(filePath)
})
})
```
**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`](./session.md)
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.
```javascript
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}`) })
})
mainWindow = new BrowserWindow({ webPreferences: { partition } })
})
```
## Methods
The `protocol` module has the following methods:
### `protocol.registerSchemesAsPrivileged(customSchemes)`
* `customSchemes` [CustomScheme[]](structures/custom-scheme.md)
**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, supports fetch API, and streaming
video/audio. Specify a privilege with the value of `true` to enable the capability.
An example of registering a privileged scheme, that bypasses Content Security
Policy:
```javascript
const { protocol } = require('electron')
protocol.registerSchemesAsPrivileged([
{ scheme: 'foo', privileges: { bypassCSP: true } }
])
```
A standard scheme adheres to what RFC 3986 calls [generic URI
syntax](https://tools.ietf.org/html/rfc3986#section-3). 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:
```html
```
Registering a scheme as standard will allow access to files through the
[FileSystem API][file-system-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.
Protocols that use streams (http and stream protocols) should set `stream: true`.
The `
```
Registering a scheme as standard will allow access to files through the
[FileSystem API][file-system-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.
Protocols that use streams (http and stream protocols) should set `stream: true`.
The `