如何将依赖项传递给 URLProtocol 子类？

Question

我一直在研究拦截器，用于在我的应用程序中向网络请求添加身份验证标头。

final class AuthInterceptor: URLProtocol {


    private var token: String = "my.access.token"   
    private var dataTask: URLSessionTask?
    private struct UnexpectedValuesRepresentationError: Error { }
    
    override class func canInit(with request: URLRequest) -> Bool {
        guard URLProtocol.property(forKey: "is_handled", in: request) as? Bool == nil else { return false }

        return true
        
        //return false // URL Loading System will handle the request using the system’s default behavior
    }
    
    override class func canonicalRequest(for request: URLRequest) -> URLRequest {
        return request
    }
    
    override func startLoading() {
        guard let mutableRequest = (request as NSURLRequest).mutableCopy() as? NSMutableURLRequest else { return }
        URLProtocol.setProperty(true, forKey: "is_handled", in: mutableRequest)
        mutableRequest.addValue(token, forHTTPHeaderField: "Authorization")
        
        dataTask = URLSession.shared.dataTask(with: mutableRequest as URLRequest) { [weak self] data, response, error in
            guard let self = self else { return }
            if let error = error {
                self.client?.urlProtocol(self, didFailWithError: error)
            } else if let data = data, let response = response {
                self.client?.urlProtocol(self, didLoad: data)
                self.client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
            } else {
                self.client?.urlProtocol(self, didFailWithError: UnexpectedValuesRepresentationError())
            }
            self.client?.urlProtocolDidFinishLoading(self)
        }
        
        dataTask?.resume()
    }
    
    override func stopLoading() {
        dataTask?.cancel()
        dataTask = nil
    }
}

如您所见，我目前只是private var token: String = "my.access.token"用来模拟令牌。我想介绍一个TokenLoader将从它的缓存中获取我的令牌。

由于 URL 加载系统将根据需要初始化我的协议实例，我不确定如何注入它。它目前注册使用：URLProtocol.registerClass(AuthInterceptor.self)

想象一下我有一个这样的界面 -

public typealias LoadTokenResult = Result<String, Error>
public protocol TokenLoader {
  func load(_ key: String, completion: @escaping (LoadTokenResult) -> Void)
}

我想确保这是可测试的，所以我希望能够在测试用例中存根或使用间谍。

我怎样才能做到这一点？

Answer 1

一种可能的选择是为此使用泛型。

protocol TokenProvider {
    static var token: String {get}
}

class MockTokenProvider: TokenProvider {
    static var token: String = "my.access.token"
}

并像这样更改 AuthInterceptor：

    final class AuthInterceptor<T: TokenProvider>: URLProtocol {
      private var token: String = T.token
    ....
    ...
}

并像这样注册：

URLProtocol.registerClass(AuthInterceptor<MockTokenProvider>.self)

上面是在操场上编译的，但还没有在实际项目中尝试过。