The document discusses URLProtocol and the URL loading system in iOS. It provides an overview of the URL loading system and describes how URLProtocol allows handling loading of protocol-specific URL data. It then demonstrates implementing a custom URLProtocol subclass to intercept and handle requests, including returning mock data or errors. It also discusses using URLProtocol with URLSession by registering custom protocol classes.

1. URLProtocol
2017/11/24

2. Introduction

3. •
• API
• API
•

4. #if DEBUG
DispatchQueue.global().async {
//
let user = User.mockData()
//
}
#else
let request = URLRequest(url: URL(string: "https://api.test.com/
users/foo")!)
let task = URLSession.shared.dataTask(with: request) { (data,
response, error) in
//
}
task.resume()
#endif

5. Demo

6. "NS" URLProtocol
Swift3 `Foundation` API "NS"
"NS"

7. URL Loading System

8. URL Loading System
The URL loading system is a set of classes and
protocols that allow your app to access content
referenced by a URL. At the heart of this
technology is the NSURL class, which lets your
app manipulate URLs and the resources they
refer to.
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/
URLLoadingSystem/URLLoadingSystem.html

9. URL loading system
• ftp://
• http://
• https://
• file:///
• data:

10. Foundation
• URL
•
•
•
•
•

13. URLProtocol

14. URLProtocol
An NSURLProtocol object handles the loading
of protocol-specific URL data. The
NSURLProtocol class itself is an abstract class
that provides the infrastructure for processing
URLs with a specific URL scheme. You create
subclasses for any custom protocols or URL
schemes that your app supports.
https://developer.apple.com/documentation/foundation/urlprotocol

15. •
•
•
•
•
https://www.raywenderlich.com/76735/using-nsurlprotocol-swift

17. • URLProtocol
• URLProtocol
registerClass(_:)

18. • class func canInit(with request: URLRequest) -
> Bool
• class func canonicalRequest(for request:
URLRequest) -> URLRequest
• func startLoading()
• func stopLoading()

20. •
•
•
•
•
https://www.raywenderlich.com/76735/using-nsurlprotocol-swift

21. URLProtocol

22. • `true`
•
• `false` URLProtocol
override class func canInit(with request: URLRequest) -> Bool {
return true
}

23. • 'canonical'
• 'canonical'
•
override class func canonicalRequest(for request: URLRequest) -> URLRequest {
return request
}

24. override func startLoading() {
// Bundle JSON
guard
let path = Bundle.main.path(forResource: "user", ofType: "json"),
let data = try? Data(contentsOf: URL(fileURLWithPath: path)) else
{
//
}
let client = self.client
let response = HTTPURLResponse(url: request.url!, statusCode: 200,
httpVersion: "HTTP/1.1", headerFields: ["Content-Type" : "application/
json;"])
//
client?.urlProtocol(self, didReceive: response!,
cacheStoragePolicy: .notAllowed)
//
client?.urlProtocol(self, didLoad: data)
//
client?.urlProtocolDidFinishLoading(self)
}

25. override func startLoading() {
...
//
let client = self.client
let response = HTTPURLResponse(url: request.url!, statusCode: 500,
httpVersion: "HTTP/1.1", headerFields: ["Content-Type" : "application/
json;"])
//
client?.urlProtocol(self, didReceive: response!,
cacheStoragePolicy: .notAllowed)
//
let error = NSError(domain: "CustomURLProtocolError", code: 10001,
userInfo: nil)
client?.urlProtocol(self, didFailWithError: error)
return
....
}

26. URLProtocolClient
• URLProtocol "URL Loading
System"
• func urlProtocol(URLProtocol, didReceive: URLResponse, cacheStoragePolicy: URLCache.StoragePolicy)
• func urlProtocol(URLProtocol, didLoad: Data)
• func urlProtocolDidFinishLoading(URLProtocol)
• func urlProtocol(URLProtocol, didFailWithError: Error)
• func urlProtocol(URLProtocol, didReceive: URLAuthenticationChallenge)
• func urlProtocol(URLProtocol, didCancel: URLAuthenticationChallenge)
• func urlProtocol(URLProtocol, wasRedirectedTo: URLRequest, redirectResponse: URLResponse)
• func urlProtocol(URLProtocol, cachedResponseIsValid: CachedURLResponse)

27. URLProtocolClient
• URLProtocol "URL Loading
System"
• func urlProtocol(URLProtocol, didReceive: URLResponse, cacheStoragePolicy: URLCache.StoragePolicy)
• func urlProtocol(URLProtocol, didLoad: Data)
• func urlProtocolDidFinishLoading(URLProtocol)
• func urlProtocol(URLProtocol, didFailWithError: Error)
• func urlProtocol(URLProtocol, didReceive: URLAuthenticationChallenge)
• func urlProtocol(URLProtocol, didCancel: URLAuthenticationChallenge)
• func urlProtocol(URLProtocol, wasRedirectedTo: URLRequest, redirectResponse: URLResponse)
• func urlProtocol(URLProtocol, cachedResponseIsValid: CachedURLResponse)

28. URLProtocolClient
• URLProtocol "URL Loading
System"
• func urlProtocol(URLProtocol, didReceive: URLResponse, cacheStoragePolicy: URLCache.StoragePolicy)
• func urlProtocol(URLProtocol, didLoad: Data)
• func urlProtocolDidFinishLoading(URLProtocol)
• func urlProtocol(URLProtocol, didFailWithError: Error)
• func urlProtocol(URLProtocol, didReceive: URLAuthenticationChallenge)
• func urlProtocol(URLProtocol, didCancel: URLAuthenticationChallenge)
• func urlProtocol(URLProtocol, wasRedirectedTo: URLRequest, redirectResponse: URLResponse)
• func urlProtocol(URLProtocol, cachedResponseIsValid: CachedURLResponse)

29. •
• URLSession
GCD
override func stopLoading() {
}

30. URLProtocol

31. • `application(_:
didFinishLaunchingWithOptions:)`
func application(_ application: UIApplication, didFinishLaunchingWithOptions
launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
//
URLProtocol.registerClass(CustomURLProtocol.self)
return true
}
URL Loading System

32. •
•
let request = URLRequest(url: URL(string: "https://api.test.com/users/
foo")!)
let task = URLSession.shared.dataTask(with: request) { (data, response,
error) in
//
}
task.resume()

33. • Flags
#if DEBUG
let path = Bundle.main.path(forResource: "user", ofType: "json")!
let data = try! Data(contentsOf: URL(fileURLWithPath: path))
DispatchQueue.global().async {
//
}
#else
let request = URLRequest(url: URL(string: "https://api.test.com/users/foo")!)
let task = URLSession.shared.dataTask(with: request) { (data, response, error)
in
//
}
task.resume()
#endif

34. URLSession.shared

36. •
•
• Flags
let request = URLRequest(url: URL(string: "https://api.test.com/users/
foo")!)
let task = URLSession.shared.dataTask(with: request) { (data, response,
error) in
//
}
task.resume()

37. • `application(_:
didFinishLaunchingWithOptions:)`
func application(_ application: UIApplication, didFinishLaunchingWithOptions
launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
//
URLProtocol.registerClass(CustomURLProtocol.self)
return true
}
URL Loading System

38. URLSession.shared
• The shared session uses the shared NSURLCache,
NSHTTPCookieStorage, and NSURLCredentialStorage
objects, uses a shared custom networking protocol list
(configured with registerClass(_:) and unregisterClass(_:)),
and is based on a default configuration.
• In other words, if you’re doing anything with caches,
cookies, authentication, or custom networking protocols,
you should probably be using a default session instead of
the shared session.
https://developer.apple.com/documentation/foundation/urlsession/1409000-shared

39. • URLSession.shared
URLSessionConfiguration
•
URLSessionConfiguration.default URLSession
• URLProtocol.registerClass
URLProtocol.registerClass(CustomURLProtocol.self)

40. • URLSessionConfiguration
var protocolClasses: [AnyClass]?
let config = URLSessionConfiguration.default
config.protocolClasses = [CustomURLProtocol.self]
let session = URLSession(configuration: config)
let task = session.dataTask(with: urlRequest) { (data, response, error) in
...
}

41. • URLProtocol URLSessionConfiguration
SessionManager
• ( ) SessionManager
let config = URLSessionConfiguration.default
config.protocolClasses = [CustomURLProtocol.self]
self.manager = SessionManager(configuration: config) //
manager.request(url).response { response in
...
}
Alamofire

42. • URLProtocol URLSessionConfiguration
URLSessionAdapter Session
let config = URLSessionConfiguration.default
config.protocolClasses = [CustomURLProtocol.self]
let adapter = URLSessionAdapter(configuration: config)
let session = Session(adapter: adapter)
session.send(request) { (result) in
...
}
APIKit

44. •
• API
• Qiita API
API

45. URLProtocol
• https://github.com/Alamofire/Alamofire/
blob/master/Tests/URLProtocolTests.swift
• https://github.com/ishkawa/APIKit/blob/
master/Tests/APIKitTests/TestComponents/
HTTPStub.swift
• https://github.com/AliSoftware/
OHHTTPStubs

46. Appendix
• [URL Loading System]: https://developer.apple.com/library/content/
documentation/Cocoa/Conceptual/URLLoadingSystem/
URLLoadingSystem.html
• [URLProtocol]: https://developer.apple.com/documentation/foundation/
urlprotocol
• [Using NSURLProtocol with Swift]: https://www.raywenderlich.com/76735/
using-nsurlprotocol-swift
• [iOS Advent Calendar 2011 5 / NSURLProtocol ]: http://
faultier.blog.jp/archives/1762587.html
• [Using NSURLProtocol for Testing]: https://yahooeng.tumblr.com/post/
141143817861/using-nsurlprotocol-for-testing