了解AlamoFire OAuth示例

Question

我能够得到AlamoFire提供的OAuth示例的工作实现.但是,我希望了解某些代码行及其工作原理.

完整示例:

class OAuth2Handler: RequestAdapter, RequestRetrier {
    private typealias RefreshCompletion = (_ succeeded: Bool, _ accessToken: String?, _ refreshToken: String?) -> Void

    private let sessionManager: SessionManager = {
        let configuration = URLSessionConfiguration.default
        configuration.httpAdditionalHeaders = SessionManager.defaultHTTPHeaders

        return SessionManager(configuration: configuration)
    }()

    private let lock = NSLock()

    private var clientID: String
    private var baseURLString: String
    private var accessToken: String
    private var refreshToken: String

    private var isRefreshing = false
    private var requestsToRetry: [RequestRetryCompletion] = []

    // MARK: - Initialization

    public init(clientID: String, baseURLString: String, accessToken: String, refreshToken: String) {
        self.clientID = clientID
        self.baseURLString = baseURLString
        self.accessToken = accessToken
        self.refreshToken = refreshToken
    }

    // MARK: - RequestAdapter

    func adapt(_ urlRequest: URLRequest) throws -> URLRequest {
        if let urlString = urlRequest.url?.absoluteString, urlString.hasPrefix(baseURLString) {
            var urlRequest = urlRequest
            urlRequest.setValue("Bearer " + accessToken, forHTTPHeaderField: "Authorization")
            return urlRequest
        }

        return urlRequest
    }

    // MARK: - RequestRetrier

    func should(_ manager: SessionManager, retry request: Request, with error: Error, completion: @escaping RequestRetryCompletion) {
        lock.lock() ; defer { lock.unlock() }

        if let response = request.task?.response as? HTTPURLResponse, response.statusCode == 401 {
            requestsToRetry.append(completion)

            if !isRefreshing {
                refreshTokens { [weak self] succeeded, accessToken, refreshToken in
                    guard let strongSelf = self else { return }

                    strongSelf.lock.lock() ; defer { strongSelf.lock.unlock() }

                    if let accessToken = accessToken, let refreshToken = refreshToken {
                        strongSelf.accessToken = accessToken
                        strongSelf.refreshToken = refreshToken
                    }

                    strongSelf.requestsToRetry.forEach { $0(succeeded, 0.0) }
                    strongSelf.requestsToRetry.removeAll()
                }
            }
        } else {
            completion(false, 0.0)
        }
    }

    // MARK: - Private - Refresh Tokens

    private func refreshTokens(completion: @escaping RefreshCompletion) {
        guard !isRefreshing else { return }

        isRefreshing = true

        let urlString = "\(baseURLString)/oauth2/token"

        let parameters: [String: Any] = [
            "access_token": accessToken,
            "refresh_token": refreshToken,
            "client_id": clientID,
            "grant_type": "refresh_token"
        ]

        sessionManager.request(urlString, method: .post, parameters: parameters, encoding: JSONEncoding.default)
            .responseJSON { [weak self] response in
                guard let strongSelf = self else { return }

                if 
                    let json = response.result.value as? [String: Any], 
                    let accessToken = json["access_token"] as? String, 
                    let refreshToken = json["refresh_token"] as? String 
                {
                    completion(true, accessToken, refreshToken)
                } else {
                    completion(false, nil, nil)
                }

                strongSelf.isRefreshing = false
            }
    }
}

问题:

[weak self] succeeded, accessToken, refreshToken in
                    guard let strongSelf = self else { return }

1. 什么是目的[weak self]和guard为strongSelf？

       requestsToRetry.append(completion)
   
       if !isRefreshing {
           refreshTokens { [weak self] succeeded, accessToken, refreshToken in
               guard let strongSelf = self else { return }
   
               //Implementation
   
               strongSelf.requestsToRetry.forEach { $0(succeeded, 0.0) }
               strongSelf.requestsToRetry.removeAll()
           }
       }
   

2. 该请求如何重试？这requestsToRetry只是一个数组RequestRetryCompletion = (_ shouldRetry: Bool, _ timeDelay: TimeInterval)如何知道重试的请求？

strongSelf.lock.lock()

3. 在执行此方法时,是否NSLock允许self(OAuth2Handler)被任何其他线程访问？

Answer 1

1)正如Fonix评论的那样,你有一个强烈的参考self,如果self你没有开始收集保留周期,那就要避免这种情况.

我要求:

[weak self] ... in
guard let strongSelf = self else { return }

由于self将在异步调度的块中捕获,因此self将在块完成时隐式保留并再次释放,换句话说,self将延长直到块完成之后.制作此代码时,self如果self等于nil ,则可以避免延长生命周期并决定不执行块

2)根据你提到的线条:

if let response = request.task?.response as? HTTPURLResponse, response.statusCode == 401 {
            requestsToRetry.append(completion)
            ..

有一个数组requestsToRetry,其中包含重新启动所需的所有请求.在此代码中,您将所有具有401状态代码的请求附加到数组(当服务器返回状态代码401时)使用forEach循环遍历requestToRetry数组的代码:

strongSelf.requestsToRetry.forEach { $0(succeeded, 0.0) }
strongSelf.requestsToRetry.removeAll()

并启动所有项目.循环结束后,您将删除所有项目.

事实上,消息来源报道:

public typealias RequestRetryCompletion = (_ shouldRetry: Bool, _ timeDelay: TimeInterval) -> Void

public protocol RequestRetrier {
    func should(_ manager: SessionManager, retry request: Request, with error: Error, completion: @escaping RequestRetryCompletion)
}

你可以在这里找到更多细节

3)正如您所说的那样,所面临的常见并发问题是与从不同线程访问/修改共享资源相关的问题.这lock.lock()是在修改项目时锁定其他执行块的解决方案.defer在离开函数解锁块之前调用代码.