/*
 * 处理session级的事件
 */
@protocol NSURLSessionDelegate <NSObject>
@optional

// 通知session的delegate session被invalid了
- (void)URLSession:(NSURLSession *)session didBecomeInvalidWithError:(nullable NSError *)error;

/*
* 只要访问的是HTTPS的路径就会调用
* 该方法的作用就是处理服务器返回的证书, 需要在该方法中告诉系统是否需要安装服务器返回的证书
* NSURLAuthenticationChallenge : 授权质问
*+ 受保护空间
*+ 服务器返回的证书类型
*/
- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
                                             completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler {
    // 1.从服务器返回的受保护空间中拿到证书的类型
    // 2.判断服务器返回的证书是否是服务器信任的
    if ([challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust]) {
        NSLog(@"是服务器信任的证书");
        // 3.根据服务器返回的受保护空间创建一个证书
//         void (^)(NSURLSessionAuthChallengeDisposition, NSURLCredential *)
//         代理方法的completionHandler block接收两个参数:
//         第一个参数: 代表如何处理证书
//         第二个参数: 代表需要处理哪个证书
        //创建证书
        NSURLCredential *credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
        // 4.安装证书   completionHandler(NSURLSessionAuthChallengeUseCredential , credential);    
    }
}

//处理应用切到后台之后
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session NS_AVAILABLE_IOS(7_0);

@end

/*
 * Messages related to the operation of a specific task.
 */
@protocol NSURLSessionTaskDelegate <NSURLSessionDelegate>
@optional

/* 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;

/* 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;

/* 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;

/* 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;

/*
 * Sent when complete statistics information has been collected for the task.
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didFinishCollectingMetrics:(NSURLSessionTaskMetrics *)metrics API_AVAILABLE(macosx(10.12), ios(10.0), watchos(3.0), tvos(10.0));

/* 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;

@end

/*
 * Messages related to the operation of a task that delivers data
 * directly to the delegate.
 */
@protocol NSURLSessionDataDelegate <NSURLSessionTaskDelegate>
@optional
/* The task has received a response and no further messages will be
 * received until the completion block is called. The disposition
 * allows you to cancel a request or to turn a data task into a
 * download task. This delegate message is optional - if you do not
 * implement it, you can get the response as a property of the task.
 *
 * This method will not be called for background upload tasks (which cannot be converted to download tasks).
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                 didReceiveResponse:(NSURLResponse *)response
                                  completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler;

/* Notification that a data task has become a download task.  No
 * future messages will be sent to the data task.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                              didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask;

/*
 * Notification that a data task has become a bidirectional stream
 * task.  No future messages will be sent to the data task.  The newly
 * created streamTask will carry the original request and response as
 * properties.
 *
 * For requests that were pipelined, the stream object will only allow
 * reading, and the object will immediately issue a
 * -URLSession:writeClosedForStream:.  Pipelining can be disabled for
 * all requests in a session, or by the NSURLRequest
 * HTTPShouldUsePipelining property.
 *
 * The underlying connection is no longer considered part of the HTTP
 * connection cache and won't count against the total number of
 * connections per host.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                didBecomeStreamTask:(NSURLSessionStreamTask *)streamTask;

/* Sent when data is available for the delegate to consume.  It is
 * assumed that the delegate will retain and not copy the data.  As
 * the data may be discontiguous, you should use 
 * [NSData enumerateByteRangesUsingBlock:] to access it.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                     didReceiveData:(NSData *)data;

/* Invoke the completion routine with a valid NSCachedURLResponse to
 * allow the resulting data to be cached, or pass nil to prevent
 * caching. Note that there is no guarantee that caching will be
 * attempted for a given resource, and you should not rely on this
 * message to receive the resource data.
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
                                  willCacheResponse:(NSCachedURLResponse *)proposedResponse 
                                  completionHandler:(void (^)(NSCachedURLResponse * _Nullable cachedResponse))completionHandler;

@end

/*
 * Messages related to the operation of a task that writes data to a
 * file and notifies the delegate upon completion.
 */
@protocol NSURLSessionDownloadDelegate <NSURLSessionTaskDelegate>

/* Sent when a download task that has completed a download.  The delegate should 
 * copy or move the file at the given location to a new location as it will be 
 * removed when the delegate message returns. URLSession:task:didCompleteWithError: will
 * still be called.
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                              didFinishDownloadingToURL:(NSURL *)location;

@optional
/* Sent periodically to notify the delegate of download progress. */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                           didWriteData:(int64_t)bytesWritten
                                      totalBytesWritten:(int64_t)totalBytesWritten
                              totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

/* Sent when a download has been resumed. If a download failed with an
 * error, the -userInfo dictionary of the error will contain an
 * NSURLSessionDownloadTaskResumeData key, whose value is the resume
 * data. 
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
                                      didResumeAtOffset:(int64_t)fileOffset
                                     expectedTotalBytes:(int64_t)expectedTotalBytes;

@end

@protocol NSURLSessionStreamDelegate <NSURLSessionTaskDelegate>
@optional

/* Indiciates that the read side of a connection has been closed.  Any
 * outstanding reads complete, but future reads will immediately fail.
 * This may be sent even when no reads are in progress. However, when
 * this delegate message is received, there may still be bytes
 * available.  You only know that no more bytes are available when you
 * are able to read until EOF. */
- (void)URLSession:(NSURLSession *)session readClosedForStreamTask:(NSURLSessionStreamTask *)streamTask;

/* Indiciates that the write side of a connection has been closed.
 * Any outstanding writes complete, but future writes will immediately
 * fail.
 */
- (void)URLSession:(NSURLSession *)session writeClosedForStreamTask:(NSURLSessionStreamTask *)streamTask;

/* A notification that the system has determined that a better route
 * to the host has been detected (eg, a wi-fi interface becoming
 * available.)  This is a hint to the delegate that it may be
 * desirable to create a new task for subsequent work.  Note that
 * there is no guarantee that the future task will be able to connect
 * to the host, so callers should should be prepared for failure of
 * reads and writes over any new interface. */
- (void)URLSession:(NSURLSession *)session betterRouteDiscoveredForStreamTask:(NSURLSessionStreamTask *)streamTask;

/* The given task has been completed, and unopened NSInputStream and
 * NSOutputStream objects are created from the underlying network
 * connection.  This will only be invoked after all enqueued IO has
 * completed (including any necessary handshakes.)  The streamTask
 * will not receive any further delegate messages.
 */
- (void)URLSession:(NSURLSession *)session streamTask:(NSURLSessionStreamTask *)streamTask
                                 didBecomeInputStream:(NSInputStream *)inputStream
                                         outputStream:(NSOutputStream *)outputStream;

@end