版本記錄

前言

我們做APP發(fā)起網(wǎng)絡(luò)請(qǐng)求，都離不開一個(gè)非常有用的框架AFNetworking，可以說(shuō)這個(gè)框架的知名度已經(jīng)超過(guò)了蘋果的底層網(wǎng)絡(luò)請(qǐng)求部分，很多人可能不知道蘋果底層是如何發(fā)起網(wǎng)絡(luò)請(qǐng)求的，但是一定知道AFNetworking，接下來(lái)幾篇我們就一起詳細(xì)的解析一下這個(gè)框架。感興趣的可以看上面寫的幾篇。
1. AFNetworking源碼探究（一） —— 基本介紹
2. AFNetworking源碼探究（二） —— GET請(qǐng)求實(shí)現(xiàn)之NSURLSessionDataTask實(shí)例化（一）
3. AFNetworking源碼探究（三） —— GET請(qǐng)求實(shí)現(xiàn)之任務(wù)進(jìn)度設(shè)置和通知監(jiān)聽（一）
4. AFNetworking源碼探究（四） —— GET請(qǐng)求實(shí)現(xiàn)之代理轉(zhuǎn)發(fā)思想（一）
5. AFNetworking源碼探究（五） —— AFURLSessionManager中NSURLSessionDelegate詳細(xì)解析（一）

回顧

上一篇主要講了NSURLSessionDelegate中的三個(gè)代理方法，講述了它們的使用場(chǎng)景以及用法，這一篇主要講AFURLSessionManager中代理NSURLSessionTaskDelegate詳細(xì)解析。

1. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task willPerformHTTPRedirection:(NSHTTPURLResponse *)response newRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURLRequest *))completionHandler

首先看一下系統(tǒng)的API接口

/* An HTTP request is attempting to perform a redirection to a different
 * URL. You must invoke the completion routine to allow the
 * redirection, allow the redirection with a modified request, or
 * pass nil to the completionHandler to cause the body of the redirection 
 * response to be delivered as the payload of this request. The default
 * is to follow redirections. 
 *
 * For tasks in background sessions, redirections will always be followed and this method will not be called.
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                     willPerformHTTPRedirection:(NSHTTPURLResponse *)response
                                     newRequest:(NSURLRequest *)request
                              completionHandler:(void (^)(NSURLRequest * _Nullable))completionHandler;

下面看一下AFN中該代理方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionTask *)task
willPerformHTTPRedirection:(NSHTTPURLResponse *)response
        newRequest:(NSURLRequest *)request
 completionHandler:(void (^)(NSURLRequest *))completionHandler
{
    NSURLRequest *redirectRequest = request;

    if (self.taskWillPerformHTTPRedirection) {
        redirectRequest = self.taskWillPerformHTTPRedirection(session, task, response, request);
    }

    if (completionHandler) {
        completionHandler(redirectRequest);
    }
}

這里，主要做了下面幾個(gè)邏輯：

• 如果有對(duì)應(yīng)的block taskWillPerformHTTPRedirection，那么就調(diào)用self.taskWillPerformHTTPRedirection(session, task, response, request)，返回一個(gè)新的request。
• 接著就是利用生成的request重新請(qǐng)求

if (completionHandler) {
        completionHandler(redirectRequest);
    }

• 這個(gè)方法是在服務(wù)器去重定向的時(shí)候，才會(huì)被調(diào)用。
• 此方法只會(huì)在default session或者ephemeral session中調(diào)用，而在background session中，session task會(huì)自動(dòng)重定向。
• 補(bǔ)充一點(diǎn)，初始化NSURLSession對(duì)象的時(shí)候需要使用NSURLSessionConfiguration。有三個(gè)類工廠方法：
  • + defaultSessionConfiguration 返回一個(gè)標(biāo)準(zhǔn)的 configuration，具有相同的共享 NSHTTPCookieStorage，共享 NSURLCache 和共享NSURLCredentialStorage。
  • + ephemeralSessionConfiguration 返回一個(gè)預(yù)設(shè)配置，這個(gè)配置中不會(huì)對(duì)緩存，Cookie 和證書進(jìn)行持久性的存儲(chǔ)。這對(duì)于實(shí)現(xiàn)像秘密瀏覽這種功能來(lái)說(shuō)是很理想的。
  • + backgroundSessionConfiguration:(NSString *)identifier 的獨(dú)特之處在于，它會(huì)創(chuàng)建一個(gè)后臺(tái) session。后臺(tái) session 不同于常規(guī)的，普通的 session，它甚至可以在應(yīng)用程序掛起，退出或者崩潰的情況下運(yùn)行上傳和下載任務(wù)。初始化時(shí)指定的標(biāo)識(shí)符，被用于向任何可能在進(jìn)程外恢復(fù)后臺(tái)傳輸?shù)氖刈o(hù)進(jìn)程（daemon）提供上下文。

2. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler

首先看一下蘋果的API接口

/* The task has received a request specific authentication challenge.
 * If this delegate is not implemented, the session specific authentication challenge
 * will *NOT* be called and the behavior will be the same as using the default handling
 * disposition. 
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                            didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge 
                              completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler;

下面看一下AFN中該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionTask *)task
didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
 completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler
{
    NSURLSessionAuthChallengeDisposition disposition = NSURLSessionAuthChallengePerformDefaultHandling;
    __block NSURLCredential *credential = nil;

    if (self.taskDidReceiveAuthenticationChallenge) {
        disposition = self.taskDidReceiveAuthenticationChallenge(session, task, challenge, &credential);
    } else {
        if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
            if ([self.securityPolicy evaluateServerTrust:challenge.protectionSpace.serverTrust forDomain:challenge.protectionSpace.host]) {
                disposition = NSURLSessionAuthChallengeUseCredential;
                credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
            } else {
                disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
            }
        } else {
            disposition = NSURLSessionAuthChallengePerformDefaultHandling;
        }
    }

    if (completionHandler) {
        completionHandler(disposition, credential);
    }
}

這里我們需要知道：

• 這個(gè)是non-session-level級(jí)別的認(rèn)證
• 多了一個(gè)參數(shù)task，然后調(diào)用我們自定義的Block會(huì)多回傳這個(gè)task作為參數(shù)，這樣我們就可以根據(jù)每個(gè)task去自定義我們需要的https認(rèn)證方式。

3. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task needNewBodyStream:(void (^)(NSInputStream *bodyStream))completionHandler

首先看一下蘋果的API接口

/* Sent if a task requires a new, unopened body stream.  This may be
 * necessary when authentication has failed for any request that
 * involves a body stream. 
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                              needNewBodyStream:(void (^)(NSInputStream * _Nullable bodyStream))completionHandler;

看一下AFN對(duì)該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionTask *)task
 needNewBodyStream:(void (^)(NSInputStream *bodyStream))completionHandler
{
    NSInputStream *inputStream = nil;

    if (self.taskNeedNewBodyStream) {
        inputStream = self.taskNeedNewBodyStream(session, task);
    } else if (task.originalRequest.HTTPBodyStream && [task.originalRequest.HTTPBodyStream conformsToProtocol:@protocol(NSCopying)]) {
        inputStream = [task.originalRequest.HTTPBodyStream copy];
    }

    if (completionHandler) {
        completionHandler(inputStream);
    }
}

該代理方法會(huì)在下面兩種情況被調(diào)用

• 如果task是由uploadTaskWithStreamedRequest:創(chuàng)建的，那么提供初始的request body stream時(shí)候會(huì)調(diào)用該代理方法。
• 因?yàn)檎J(rèn)證挑戰(zhàn)或者其他可恢復(fù)的服務(wù)器錯(cuò)誤，而導(dǎo)致需要客戶端重新發(fā)送一個(gè)含有body stream的request，這時(shí)候會(huì)調(diào)用該代理。

4. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didSendBodyData:(int64_t)bytesSent totalBytesSent:(int64_t)totalBytesSent totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend;

首先看一下蘋果的API接口

/* Sent periodically to notify the delegate of upload progress.  This
 * information is also available as properties of the task.
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                                didSendBodyData:(int64_t)bytesSent
                                 totalBytesSent:(int64_t)totalBytesSent
                       totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend;

看一下AFN對(duì)該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionTask *)task
   didSendBodyData:(int64_t)bytesSent
    totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend
{

    int64_t totalUnitCount = totalBytesExpectedToSend;
    if(totalUnitCount == NSURLSessionTransferSizeUnknown) {
        NSString *contentLength = [task.originalRequest valueForHTTPHeaderField:@"Content-Length"];
        if(contentLength) {
            totalUnitCount = (int64_t) [contentLength longLongValue];
        }
    }

    if (self.taskDidSendBodyData) {
        self.taskDidSendBodyData(session, task, bytesSent, totalBytesSent, totalUnitCount);
    }
}

就是每次發(fā)送數(shù)據(jù)給服務(wù)器，會(huì)回調(diào)這個(gè)方法，通知已經(jīng)發(fā)送了多少。

5. - (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(nullable NSError *)error;

首先看一下蘋果的API接口

/* Sent as the last message related to a specific task.  Error may be
 * nil, which implies that no error occurred and this task is complete. 
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
                           didCompleteWithError:(nullable NSError *)error;

看一下AFN對(duì)該方法的實(shí)現(xiàn)

- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
    AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];

    // delegate may be nil when completing a task in the background
    if (delegate) {
        [delegate URLSession:session task:task didCompleteWithError:error];

        [self removeDelegateForTask:task];
    }

    if (self.taskDidComplete) {
        self.taskDidComplete(session, task, error);
    }
}

這個(gè)代理就是task完成了的回調(diào)，這里涉及到task和代理的綁定與接觸綁定，代碼不難，就不多說(shuō)了。

后記

本篇主要介紹了NSURLSessionTaskDelegate中五個(gè)代理方法的實(shí)現(xiàn)及其使用場(chǎng)景和注意事項(xiàng)。