AFNetworking 核心解析
AFNetworing 是 iOS 最常用的网络请求库，在最新的版本已经使用了 NSURLSession 来实现。
概况
AF 中有这么几个类
AFHTTPSessionManager：最常用的对外的接口，提供 HTTP 请求的接口，如 get，post，head 等。
AFNetworkReachabilityManager：网络监控类。
AFSecurityPolicy：请求安全策略类。
AFURLRequestSerialization：请求参数序列化类
AFURLResponseSerialization：请求返回数据解析类
AFURLSessionManager：对 NSURLSeesion 的封装，核心请求类。
AFURLSessionManagerTaskDelegate：NSURLSession 回调的封装。内部类。
本文为核心解析，丢弃一些细节，直入主题，AFHTTPSessionManager继承于AFURLSessionManager，实际请求使用AFURLSessionManager提供的接口来完成。所以本文直接介绍AFURLSessionManager。其他部分将会拆分其他的文章。
AFURLSessionManager
AFURLSessionManager是最核心的请求类。提供了对 NSURLSession 的封装。
初始化
AFURLSessionManager提供了一个参数为NSURLSessionConfiguration的指定构造器。如果没给NSURLSessionConfiguration那么默认将会是defaultSessionConfiguration
- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
self = [super init];
if (!self) {
return nil;
}
if (!configuration) {
configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
}
self.sessionConfiguration = configuration;
self.operationQueue = [[NSOperationQueue alloc] init];
self.operationQueue.maxConcurrentOperationCount = 1;
self.session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];
self.responseSerializer = [AFJSONResponseSerializer serializer];
self.securityPolicy = [AFSecurityPolicy defaultPolicy];
#if !TARGET_OS_WATCH
self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];
#endif
self.mutableTaskDelegatesKeyedByTaskIdentifier = [[NSMutableDictionary alloc] init];
self.lock = [[NSLock alloc] init];
self.lock.name = AFURLSessionManagerLockName;
[self.session getTasksWithCompletionHandler:^(NSArray *dataTasks, NSArray *uploadTasks, NSArray *downloadTasks) {
for (NSURLSessionDataTask *task in dataTasks) {
[self addDelegateForDataTask:task uploadProgress:nil downloadProgress:nil completionHandler:nil];
}
for (NSURLSessionUploadTask *uploadTask in uploadTasks) {
[self addDelegateForUploadTask:uploadTask progress:nil completionHandler:nil];
}
for (NSURLSessionDownloadTask *downloadTask in downloadTasks) {
[self addDelegateForDownloadTask:downloadTask progress:nil destination:nil completionHandler:nil];
}
}];
return self;
}
由此也可以看出，线程安全使用的锁为NSLock
请求
NSURLSession 分成 3 种请求，分别为 dataTask，uploadTask 和 downloadTask。在AFURLSessionManager也暴露出了这 3 种请求。
dataTask
- (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 {
__block NSURLSessionDataTask *dataTask = nil;
url_session_manager_create_task_safely(^{
dataTask = [self.session dataTaskWithRequest:request];
});
[self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
return dataTask;
}
uploadTask
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request
fromData:(NSData *)bodyData
progress:(void (^)(NSProgress *uploadProgress)) uploadProgressBlock
completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
__block NSURLSessionUploadTask *uploadTask = nil;
url_session_manager_create_task_safely(^{
uploadTask = [self.session uploadTaskWithRequest:request fromData:bodyData];
});
[self addDelegateForUploadTask:uploadTask progress:uploadProgressBlock completionHandler:completionHandler];
return uploadTask;
}
downloadTask
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request
progress:(void (^)(NSProgress *downloadProgress)) downloadProgressBlock
destination:(NSURL * (^)(NSURL *targetPath, NSURLResponse *response))destination
completionHandler:(void (^)(NSURLResponse *response, NSURL *filePath, NSError *error))completionHandler
{
__block NSURLSessionDownloadTask *downloadTask = nil;
url_session_manager_create_task_safely(^{
downloadTask = [self.session downloadTaskWithRequest:request];
});
[self addDelegateForDownloadTask:downloadTask progress:downloadProgressBlock destination:destination completionHandler:completionHandler];
return downloadTask;
}
这 3 个方法流程都很相似，使用 NSURLSession 来获取 task，之后将 3 种 task 添加到相应的 delegate 中，如 dataTask
AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] init];
delegate.manager = self;
delegate.completionHandler = completionHandler;
dataTask.taskDescription = self.taskDescriptionForSessionTasks;
[self setDelegate:delegate forTask:dataTask];
delegate.uploadProgressBlock = uploadProgressBlock;
delegate.downloadProgressBlock = downloadProgressBlock;
添加 delegate 的方法大概分成几部，首先生成AFURLSessionManagerTaskDelegate对象，此对象对应每次请求 task 的回调处理，将 completionHandler 请求完成的回调设置到 AFURLSessionManagerTaskDelegate 对象中，之后调用
[self setDelegate:delegate forTask:dataTask];
来把 task 添加到以 task 的 taskIdentifier 为 key，value 为 task 的字典中，后文中也会通过此字典来获取每一个 task
- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
forTask:(NSURLSessionTask *)task
{
NSParameterAssert(task);
NSParameterAssert(delegate);
[self.lock lock];
self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
[delegate setupProgressForTask:task];
[self addNotificationObserverForTask:task];
[self.lock unlock];
}
请求回调
AFURLSessionManager实现了 NSURLSeesion 的几个回调，除了处理 HTTPS 之外的所有回调都委托到各个的 task 的 AFURLSessionManagerTaskDelegate 来处理。
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data
{
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
[delegate URLSession:session dataTask:dataTask didReceiveData:data];
if (self.dataTaskDidReceiveData) {
self.dataTaskDidReceiveData(session, dataTask, data);
}
}
通过
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
来获取 task 的 AFURLSessionManagerTaskDelegate。
- (AFURLSessionManagerTaskDelegate *)delegateForTask:(NSURLSessionTask *)task {
NSParameterAssert(task);
AFURLSessionManagerTaskDelegate *delegate = nil;
[self.lock lock];
delegate = self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)];
[self.lock unlock];
return delegate;
}
通过 taskIdentifier 在字典中取得 AFURLSessionManagerTaskDelegate。
AFURLSessionManagerTaskDelegate
此类的主要作用是对每个 task 的 delegate 进行封装。封装独立性，包括下载的 task 的 downloadURL 处理等。
- (void)URLSession:(__unused NSURLSession *)session
task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
__strong AFURLSessionManager *manager = self.manager;
__block id responseObject = nil;
__block NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
userInfo[AFNetworkingTaskDidCompleteResponseSerializerKey] = manager.responseSerializer;
//Performance Improvement from #2672
NSData *data = nil;
if (self.mutableData) {
data = [self.mutableData copy];
//We no longer need the reference, so nil it out to gain back some memory.
self.mutableData = nil;
}
if (self.downloadFileURL) {
userInfo[AFNetworkingTaskDidCompleteAssetPathKey] = self.downloadFileURL;
} else if (data) {
userInfo[AFNetworkingTaskDidCompleteResponseDataKey] = data;
}
if (error) {
userInfo[AFNetworkingTaskDidCompleteErrorKey] = error;
dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
if (self.completionHandler) {
self.completionHandler(task.response, responseObject, error);
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
});
});
} else {
dispatch_async(url_session_manager_processing_queue(), ^{
NSError *serializationError = nil;
responseObject = [manager.responseSerializer responseObjectForResponse:task.response data:data error:&serializationError];
if (self.downloadFileURL) {
responseObject = self.downloadFileURL;
}
if (responseObject) {
userInfo[AFNetworkingTaskDidCompleteSerializedResponseKey] = responseObject;
}
if (serializationError) {
userInfo[AFNetworkingTaskDidCompleteErrorKey] = serializationError;
}
dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
if (self.completionHandler) {
self.completionHandler(task.response, responseObject, serializationError);
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
});
});
});
}
}
处理流程为
- 判断是否请求成功如果失败，填充
userInfo，并调用completionHandler，传递response和error更上层。 - 成功的话，填充
userInfo，并且调用completionHandler，传递 error 为 nil
小结
AFNetworking 使用 NSURLSession 来进行网络请求。
AFNetworking 内部使用的锁为 NSLock
AFNetworking 内部维护了一个以 task 的字典，key 为 task 的 taskIdentifier。
AFNetworking 对 每个 task 的 delegate 进行封装。系统只提供对 NSURLSession 的 delegate，对每个 task 不友好。