iOS网络——AFNetworking AFURLSessionManager源码解析

你要知道的NSURLSession都在这里

转载请注明出处 http://blog.youkuaiyun.com/u014205968/article/details/78481498

本系列文章主要讲解iOS中网络请求类NSURLSession的使用方法进行详解，同时也会以此为扩展，讲解SDWebImage中图片下载功能的源码分析，讲解AFNetworking相关源码分析。本系列文章主要分为以下几篇进行讲解，读者可按需查阅。

• iOS网络——NSURLSession详解及SDWebImage源码解析
• iOS网络——SDWebImage SDImageDownloader源码解析
• iOS网络——AFNetworking AFURLSessionManager源码解析
• iOS网络——AFNetworking AFHttpSessionManager源码解析

AFNetworking AFURLSessionManager源码解析

前面几篇文章讲解了NSURLSession的基础使用方法以及SDWebImage在下载图片时是如何使用NSURLSession，来完成下载任务的，本篇文章将阅读AFNetworking是如何封装NSURLSession来提供便捷的网络请求功能。

AFNetworking的使用方法就不赘述了，我们经常使用AFHttpSessionManager来发起一个GET或是POST请求，该类是继承自AFURLSessionManager并在其上进行了一个封装，提供了更加便捷的接口来发起网络请求，所以本篇将详细讲解AFURLSessionManager是如何封装NSURLSession的，建议读者对照源码阅读。

首先看一下头文件的声明:

//AFURLSessionManager类实现了NSURLSession相关的众多协议，用于帮助我们进行数据的处理
@interface AFURLSessionManager : NSObject <NSURLSessionDelegate, NSURLSessionTaskDelegate, NSURLSessionDataDelegate, NSURLSessionDownloadDelegate, NSSecureCoding, NSCopying>

//猪脚，NSURLSession 作为一个实例变量，AFN发起的网络请求都是通过该session创建的task实现的
@property (readonly, nonatomic, strong) NSURLSession *session;

//NSURLSession delegate方法执行队列
@property (readonly, nonatomic, strong) NSOperationQueue *operationQueue;

//响应序列化，不是本系列文章的关注点，有兴趣的读者可以自行阅读源码
@property (nonatomic, strong) id <AFURLResponseSerialization> responseSerializer;

///-------------------------------
/// @name Managing Security Policy
///-------------------------------
//安全策略，用于https等需要验证的地方
@property (nonatomic, strong) AFSecurityPolicy *securityPolicy;

#if !TARGET_OS_WATCH
///--------------------------------------
/// @name Monitoring Network Reachability
///--------------------------------------

//监测网络连通性，使用AFNetworkReachabilityManager，读者可自行阅读相关源码
@property (readwrite, nonatomic, strong) AFNetworkReachabilityManager *reachabilityManager;
#endif

///----------------------------
/// @name Getting Session Tasks
///----------------------------

//前面那个session管理的data upload download task的集合
@property (readonly, nonatomic, strong) NSArray <NSURLSessionTask *> *tasks;

//前面那个session管理的data task的集合
@property (readonly, nonatomic, strong) NSArray <NSURLSessionDataTask *> *dataTasks;

//前面那个session管理的upload task的集合
@property (readonly, nonatomic, strong) NSArray <NSURLSessionUploadTask *> *uploadTasks;

//前面那个session管理的download task的集合
@property (readonly, nonatomic, strong) NSArray <NSURLSessionDownloadTask *> *downloadTasks;

///-------------------------------
/// @name Managing Callback Queues
///-------------------------------

//完成网络请求后执行回调块的队列，如果为nil则使用主队列
@property (nonatomic, strong, nullable) dispatch_queue_t completionQueue;

//完成网络请求后回调块的
@property (nonatomic, strong, nullable) dispatch_group_t completionGroup;

///---------------------------------
/// @name Working Around System Bugs
///---------------------------------

//background类型的session是否尝试重新创建上传任务
@property (nonatomic, assign) BOOL attemptsToRecreateUploadTasksForBackgroundSessions;

///---------------------
/// @name Initialization
///---------------------

//初始化函数，根据指定NSURLSessionConfiguration创建session
- (instancetype)initWithSessionConfiguration:(nullable NSURLSessionConfiguration *)configuration NS_DESIGNATED_INITIALIZER;

//设置session无效，cancelPendingTasks标识是否取消session中正在执行的任务
//内部还是调用NSURLSession的invalidate方法
- (void)invalidateSessionCancelingTasks:(BOOL)cancelPendingTasks;

///-------------------------
/// @name Running Data Tasks
///-------------------------

//根据指定的request等信息创建一个NSURLSessionDataTask任务
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                            completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler DEPRECATED_ATTRIBUTE;

//根据指定的request等参数创建一个NSURLSessionDataTask任务
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request
                               uploadProgress:(nullable void (^)(NSProgress *uploadProgress))uploadProgressBlock
                             downloadProgress:(nullable void (^)(NSProgress *downloadProgress))downloadProgressBlock
                            completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler;

///---------------------------
/// @name Running Upload Tasks
///---------------------------

//根据指定request fileURL等参数构造一个NSURLSessionUploadTask任务
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request
                                         fromFile:(NSURL *)fileURL
                                         progress:(nullable void (^)(NSProgress *uploadProgress))uploadProgressBlock
                                completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject, NSError  * _Nullable error))completionHandler;

//根据指定request和data等参数构造一个上传任务
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request
                                         fromData:(nullable NSData *)bodyData
                                         progress:(nullable void (^)(NSProgress *uploadProgress))uploadProgressBlock
                                completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject, NSError * _Nullable error))completionHandler;

//根据指定的request构造一个上传任务
- (NSURLSessionUploadTask *)uploadTaskWithStreamedRequest:(NSURLRequest *)request
                                                 progress:(nullable void (^)(NSProgress *uploadProgress))uploadProgressBlock
                                        completionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject, NSError * _Nullable error))completionHandler;

///-----------------------------
/// @name Running Download Tasks
///-----------------------------

//构造下载任务
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request
                                             progress:(nullable void (^)(NSProgress *downloadProgress))downloadProgressBlock
                                          destination:(nullable NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
                                    completionHandler:(nullable void (^)(NSURLResponse *response, NSURL * _Nullable filePath, NSError * _Nullable error))completionHandler;

//构造下载任务
- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData
                                                progress:(nullable void (^)(NSProgress *downloadProgress))downloadProgressBlock
                                             destination:(nullable NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
                                       completionHandler:(nullable void (^)(NSURLResponse *response, NSURL * _Nullable filePath, NSError * _Nullable error))completionHandler;

///---------------------------------
/// @name Getting Progress for Tasks
///---------------------------------

//根据NSURLSessionTask获取对应的任务完成进度NSProgress
- (nullable NSProgress *)uploadProgressForTask:(NSURLSessionTask *)task;

//根据NSURLSessionTask获取对应下载任务的进度NSProgress
- (nullable NSProgress *)downloadProgressForTask:(NSURLSessionTask *)task;

///-----------------------------------------
/// @name Setting Session Delegate Callbacks
///-----------------------------------------
//设置session无效时执行的回调块
- (void)setSessionDidBecomeInvalidBlock:(nullable void (^)(NSURLSession *session, NSError *error))block;

//设置session收到challenge时执行的回调块
- (void)setSessionDidReceiveAuthenticationChallengeBlock:(nullable NSURLSessionAuthChallengeDisposition (^)(NSURLSession *session, NSURLAuthenticationChallenge *challenge, NSURLCredential * _Nullable __autoreleasing * _Nullable credential))block;

///--------------------------------------
/// @name Setting Task Delegate Callbacks
///--------------------------------------

//设置session需要新的流时执行的回调块
- (void)setTaskNeedNewBodyStreamBlock:(nullable NSInputStream * (^)(NSURLSession *session, NSURLSessionTask *task))block;

//设置session的任务需要执行重定向时执行的回调块
- (void)setTaskWillPerformHTTPRedirectionBlock:(nullable NSURLRequest * _Nullable (^)(NSURLSession *session, NSURLSessionTask *task, NSURLResponse *response, NSURLRequest *request))block;

//又是代理方法执行时需要执行的回调块
- (void)setTaskDidReceiveAuthenticationChallengeBlock:(nullable NSURLSessionAuthChallengeDisposition (^)(NSURLSession *session, NSURLSessionTask *task, NSURLAuthenticationChallenge *challenge, NSURLCredential * _Nullable __autoreleasing * _Nullable credential))block;

//同上
- (void)setTaskDidSendBodyDataBlock:(nullable void (^)(NSURLSession *session, NSURLSessionTask *task, int64_t bytesSent, int64_t totalBytesSent, int64_t totalBytesExpectedToSend))block;

//同上
- (void)setTaskDidCompleteBlock:(nullable void (^)(NSURLSession *session, NSURLSessionTask *task, NSError * _Nullable error))block;

///-------------------------------------------
/// @name Setting Data Task Delegate Callbacks
///-------------------------------------------

/**
 Sets a block to be executed when a data task has received a response, as handled by the `NSURLSessionDataDelegate` method `URLSession:dataTask:didReceiveResponse:completionHandler:`.

 @param block A block object to be executed when a data task has received a response. The block returns the disposition of the session response, and takes three arguments: the session, the data task, and the received response.
 */
- (void)setDataTaskDidReceiveResponseBlock:(nullable NSURLSessionResponseDisposition (^)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSURLResponse *response))block;

//同上
- (void)setDataTaskDidBecomeDownloadTaskBlock:(nullable void (^)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSURLSessionDownloadTask *downloadTask))block;

//同上
- (void)setDataTaskDidReceiveDataBlock:(nullable void (^)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSData *data))block;

//同上
- (void)setDataTaskWillCacheResponseBlock:(nullable NSCachedURLResponse * (^)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSCachedURLResponse *proposedResponse))block;

//同上
- (void)setDidFinishEventsForBackgroundURLSessionBlock:(nullable void (^)(NSURLSession *session))block;

///-----------------------------------------------
/// @name Setting Download Task Delegate Callbacks
///-----------------------------------------------
//同上
- (void)setDownloadTaskDidFinishDownloadingBlock:(nullable NSURL * _Nullable  (^)(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, NSURL *location))block;

//同上
- (void)setDownloadTaskDidWriteDataBlock:(nullable void (^)(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite))block;

//同上
- (void)setDownloadTaskDidResumeBlock:(nullable void (^)(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t fileOffset, int64_t expectedTotalBytes))block;

@end

///--------------------
/// @name Notifications
///--------------------

//一些通知的名称，使用FOUNDATION_EXPORT标识

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidResumeNotification;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidCompleteNotification;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidSuspendNotification;

FOUNDATION_EXPORT NSString * const AFURLSessionDidInvalidateNotification;

FOUNDATION_EXPORT NSString * const AFURLSessionDownloadTaskDidFailToMoveFileNotification;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidCompleteResponseDataKey;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidCompleteSerializedResponseKey;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidCompleteResponseSerializerKey;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidCompleteAssetPathKey;

FOUNDATION_EXPORT NSString * const AFNetworkingTaskDidCompleteErrorKey;

NS_ASSUME_NONNULL_END

通过头文件可以发现，AFURLSessionManager是封装了NSURLSession并实现了其相关的所有协议，提供了一系列方法用于构造各种网络请求任务，并提供回调块进行处理，还提供了一系列设置代理方法执行时的执行回调块的方法，这样，我们也可以监听整个网络请求的过程，当然也可以忽略这些代理方法执行情况，提供了各种通知，通过头文件可以看出，主要目的还是为了封装NSURLSession从而提供更加便捷的方法来实现网络请求。

接下来看一下实现的文件:

//C静态函数，GCD只执行一次，用于创建一个串行队列来执行各种网络请求任务的创建工作
static dispatch_queue_t url_session_manager_creation_queue() {
    static dispatch_queue_t af_url_session_manager_creation_queue;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        af_url_session_manager_creation_queue = dispatch_queue_create("com.alamofire.networking.session.manager.creat