Alamofire 浅析 <六>SessionDe

about SessionDelegate

SessionDelegate 集所有URLSessionDelegate及其子类于一生
包含一下子类功能

basic:
URLSessionDelegate

extend:

URLSessionTaskDelegate

URLSessionDataDelegate

URLSessionDonwloadDelegate

URLSessionStreamDelegate

这样一个SessionDelegate类，就集成了所有session代理功能，不要针对某种具体的session，去初始化相应的URLSessionDelegate子类

Session delegate handle

Alamofire 提供用户多种处理session消息的方法

1. SessionDelegate 默认处理
2. SessionDelegate userHandleWithCompletion(message)
3. SessionDelegate userHandle(message)
4. TaskDelegate userHandle(message)
5. TaskDelegate 默认处理

那么这么多处理方法，不会冲突吗？ 比如一个向左一个向右的问题的情况下如何处理？
看下这个代码就明白了

SessionDelegate file

   open func urlSession(
        _ session: URLSession,
        task: URLSessionTask,
        didReceive challenge: URLAuthenticationChallenge,
        completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void)
    {
        guard taskDidReceiveChallengeWithCompletion == nil else {
            taskDidReceiveChallengeWithCompletion?(session, task, challenge, completionHandler)
            return
        }

        if let taskDidReceiveChallenge = taskDidReceiveChallenge {
            let result = taskDidReceiveChallenge(session, task, challenge)
            completionHandler(result.0, result.1)
        } else if let delegate = self[task]?.delegate {
            delegate.urlSession(
                session,
                task: task,
                didReceive: challenge,
                completionHandler: completionHandler
            )
        } else {
            urlSession(session, didReceive: challenge, completionHandler: completionHandler)
        }
    }

TaskDelegate file

  @objc(URLSession:task:didReceiveChallenge:completionHandler:)
    func urlSession(
        _ session: URLSession,
        task: URLSessionTask,
        didReceive challenge: URLAuthenticationChallenge,
        completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void)
    {
        var disposition: URLSession.AuthChallengeDisposition = .performDefaultHandling
        var credential: URLCredential?

        if let taskDidReceiveChallenge = taskDidReceiveChallenge {
            (disposition, credential) = taskDidReceiveChallenge(session, task, challenge)
        } else if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust {
            let host = challenge.protectionSpace.host

            if
                let serverTrustPolicy = session.serverTrustPolicyManager?.serverTrustPolicy(forHost: host),
                let serverTrust = challenge.protectionSpace.serverTrust
            {
                if serverTrustPolicy.evaluate(serverTrust, forHost: host) {
                    disposition = .useCredential
                    credential = URLCredential(trust: serverTrust)
                } else {
                    disposition = .cancelAuthenticationChallenge
                }
            }
        } else {
            if challenge.previousFailureCount > 0 {
                disposition = .rejectProtectionSpace
            } else {
                credential = self.credential ?? session.configuration.urlCredentialStorage?.defaultCredential(for: challenge.protectionSpace)

                if credential != nil {
                    disposition = .useCredential
                }
            }
        }

        completionHandler(disposition, credential)
    }

那么阅读这段代码优先级很明了了,优先级如下：

1. SessionDelegate userHandleWithCompletion(message)
2. SessionDelegate userHandle(message)
3. TaskDelegate userHandle(message)
4. TaskDelegate 默认处理
5. SessionDelegate 默认处理