# protocol
> Register a custom protocol and intercept existing protocol requests.
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')
app.on('ready', () => {
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.
## Methods
The `protocol` module has the following methods:
### `protocol.registerStandardSchemes(schemes)`
* `schemes` Array - Custom schemes to be registered as standard schemes.
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, 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:
```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:
```javascript
const {app, protocol} = require('electron')
protocol.registerStandardSchemes(['atom'])
app.on('ready', () => {
protocol.registerHttpProtocol('atom', '...')
})
```
**Note:** This method can only be used before the `ready` event of the `app`
module gets emitted.
### `protocol.registerServiceWorkerSchemes(schemes)`
* `schemes` Array - Custom schemes to be registered to handle service workers.
### `protocol.registerFileProtocol(scheme, handler[, completion])`
* `scheme` String
* `handler` Function
* `completion` Function (optional)
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.
* `request` Object
* `url` String
* `referrer` String
* `method` String
* `uploadData` Array (optional)
* `callback` Function
The `uploadData` is an array of `data` objects:
* `data` Object
* `bytes` Buffer - Content being sent.
* `file` String - Path of file being uploaded.
* `blobUUID` String - UUID of blob data. Use [ses.getBlobData](session.md#sesgetblobdataidentifier-callback) method
to retrieve the data.
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})`.
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][net-error].
By default the `scheme` is treated like `http:`, which is parsed differently
than protocols that follow the "generic URI syntax" like `file:`, so you
probably want to call `protocol.registerStandardSchemes` to have your scheme
treated as a standard scheme.
### `protocol.registerBufferProtocol(scheme, handler[, completion])`
* `scheme` String
* `handler` Function
* `completion` Function (optional)
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:
```javascript
const {protocol} = require('electron')
protocol.registerBufferProtocol('atom', (request, callback) => {
callback({mimeType: 'text/html', data: new Buffer('Response
')})
}, (error) => {
if (error) console.error('Failed to register protocol')
})
```
### `protocol.registerStringProtocol(scheme, handler[, completion])`
* `scheme` String
* `handler` Function
* `completion` Function (optional)
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
* `completion` Function (optional)
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.
* `redirectRequest` Object
* `url` String
* `method` String
* `session` Object (optional)
* `uploadData` Object (optional)
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.
* `uploadData` object
* `contentType` String - MIME type of the content.
* `data` String - Content to be sent.
### `protocol.unregisterProtocol(scheme[, completion])`
* `scheme` String
* `completion` Function (optional)
Unregisters the custom protocol of `scheme`.
### `protocol.isProtocolHandled(scheme, callback)`
* `scheme` String
* `callback` Function
The `callback` will be called with a boolean that indicates whether there is
already a handler for `scheme`.
### `protocol.interceptFileProtocol(scheme, handler[, completion])`
* `scheme` String
* `handler` Function
* `completion` Function (optional)
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
* `completion` Function (optional)
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
* `completion` Function (optional)
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
* `completion` Function (optional)
Intercepts `scheme` protocol and uses `handler` as the protocol's new handler
which sends a new HTTP request as a response.
### `protocol.uninterceptProtocol(scheme[, completion])`
* `scheme` String
* `completion` Function
Remove the interceptor installed for `scheme` and restore its original handler.
[net-error]: https://code.google.com/p/chromium/codesearch#chromium/src/net/base/net_error_list.h
[file-system-api]: https://developer.mozilla.org/en-US/docs/Web/API/LocalFileSystem