AFURLSessionManager这个类是AFNetworking最核心的类，它的任务就是管理会话，响应会话中的每一个任务
我们首先来梳理一下一次完整的网络请求及其响应，看看它是走哪些方法，按照什么顺序来走，我们就看一次最简单的GET请求
首先，我们还记得在最外层AFHTTPSessionManager类中发起了请求任务
__block NSURLSessionDataTask *dataTask = nil;
dataTask = [self dataTaskWithRequest:request
uploadProgress:uploadProgress
downloadProgress:downloadProgress
completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {
if (error) {
if (failure) {
failure(dataTask, error);
}
} else {
if (success) {
success(dataTask, responseObject);
}
}
}];
它调用了它的父类也就是AFURLSessionManager的任务创建方法
- (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 {
//根据请求创建一个任务
NSURLSessionDataTask *dataTask = [self.session dataTaskWithRequest:request];
//把创建的每一个任务交给一个AFURLSessionManagerTaskDelegate类来管理
[self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
return dataTask;
}
addDelegateForDataTask方法为每一个任务创建一个任务代理类，由它来全权独立管理每个任务的状态，进度和完成的回调，并且把它和每个任务进行一一对应，以便在会话中能正确响应每个任务的代理回调方法
这段代码我认为也是最能表现AFNetworking这个框架精髓的一段代码，它体现了AFNetworking的核心思想，公用session，没有必要进行多余的TCP连接，在一个会话里面创建多个任务，独立管理每个任务，这样既能节约资源也能很大程度缩短网络请求的时间，提高会话任务的效率
- (void)addDelegateForDataTask:(NSURLSessionDataTask *)dataTask
uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlock
downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlock
completionHandler:(void (^)(NSURLResponse *response, id responseObject, NSError *error))completionHandler
{
//根据任务来创建一个任务代理类
AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] initWithTask:dataTask];
//将会话管理类也传给任务代理类，以便使用会话管理中的方法
delegate.manager = self;
//完成任务的代码块也要传给它
delegate.completionHandler = completionHandler;
//任务描述
dataTask.taskDescription = self.taskDescriptionForSessionTasks;
//将每一个任务和它对应的任务管理类进行键值对关系绑定
[self setDelegate:delegate forTask:dataTask];
//上传进度代码块
delegate.uploadProgressBlock = uploadProgressBlock;
//下载进度代码块
delegate.downloadProgressBlock = downloadProgressBlock;
}
这里就是为任务和任务代理类关系进行绑定的方法，以任务的ID为键，AFURLSessionManagerTaskDelegate对象为值，这里还用了锁，来保证绑定过程的安全
- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
forTask:(NSURLSessionTask *)task
{
NSParameterAssert(task);
NSParameterAssert(delegate);
//这里用锁来保证线程安全，mutableTaskDelegatesKeyedByTaskIdentifier经常需要被改动
[self.lock lock];
self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
[self addNotificationObserverForTask:task];
[self.lock unlock];
}
发起请求后首先会进行https认证，前面说的安全策略类AFSecurityPolicy就是在这里进行认证
- (void)URLSession:(NSURLSession *)session
task:(NSURLSessionTask *)task
didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler
{
BOOL evaluateServerTrust = NO;
NSURLSessionAuthChallengeDisposition disposition = NSURLSessionAuthChallengePerformDefaultHandling;
NSURLCredential *credential = nil;
if (self.authenticationChallengeHandler) {
id result = self.authenticationChallengeHandler(session, task, challenge, completionHandler);
if (result == nil) {
return;
} else if ([result isKindOfClass:NSError.class]) {
objc_setAssociatedObject(task, AuthenticationChallengeErrorKey, result, OBJC_ASSOCIATION_RETAIN);
disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
} else if ([result isKindOfClass:NSURLCredential.class]) {
credential = result;
disposition = NSURLSessionAuthChallengeUseCredential;
} else if ([result isKindOfClass:NSNumber.class]) {
disposition = [result integerValue];
NSAssert(disposition == NSURLSessionAuthChallengePerformDefaultHandling || disposition == NSURLSessionAuthChallengeCancelAuthenticationChallenge || disposition == NSURLSessionAuthChallengeRejectProtectionSpace, @"");
evaluateServerTrust = disposition == NSURLSessionAuthChallengePerformDefaultHandling && [challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust];
} else {
@throw [NSException exceptionWithName:@"Invalid Return Value" reason:@"The return value from the authentication challenge handler must be nil, an NSError, an NSURLCredential or an NSNumber." userInfo:nil];
}
} else {
evaluateServerTrust = [challenge.protectionSpace.authenticationMethod isEqualToString:NSURLAuthenticationMethodServerTrust];
}
if (evaluateServerTrust) {
if ([self.securityPolicy evaluateServerTrust:challenge.protectionSpace.serverTrust forDomain:challenge.protectionSpace.host]) {
disposition = NSURLSessionAuthChallengeUseCredential;
credential = [NSURLCredential credentialForTrust:challenge.protectionSpace.serverTrust];
} else {
objc_setAssociatedObject(task, AuthenticationChallengeErrorKey,
[self serverTrustErrorForServerTrust:challenge.protectionSpace.serverTrust url:task.currentRequest.URL],
OBJC_ASSOCIATION_RETAIN);
disposition = NSURLSessionAuthChallengeCancelAuthenticationChallenge;
}
}
if (completionHandler) {
completionHandler(disposition, credential);
}
}
服务器收到请求后返回数据，这时候会响应NSURLSessionDataDelegate接收返回数据的方法，这里数据可能是分多次返回，可能会响应多次
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data
{
//根据任务找到对应的任务代理类
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
//调用代理类的数据接收方法，和NSURLSessionDataDelegate的代理方法一致，只是在delegate里拼接可能多次返回的数据
[delegate URLSession:session dataTask:dataTask didReceiveData:data];
//收到服务器返回数据回调的代码块
if (self.dataTaskDidReceiveData) {
self.dataTaskDidReceiveData(session, dataTask, data);
}
}
AFURLSessionManagerTaskDelegate中的- (void)URLSession:dataTask:didReceiveData:方法
- (void)URLSession:(__unused NSURLSession *)session
dataTask:(__unused NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data
{
//下载进度设置
self.downloadProgress.totalUnitCount = dataTask.countOfBytesExpectedToReceive;
self.downloadProgress.completedUnitCount = dataTask.countOfBytesReceived;
//拼接数据
[self.mutableData appendData:data];
}
接收服务器数据完成后，接着会响应NSURLSessionDataDelegate中的- (void)URLSession:task:didCompleteWithError:方法
- (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];
//移除对应任务代理对象
[self removeDelegateForTask:task];
}
if (self.taskDidComplete) {
self.taskDidComplete(session, task, error);
}
}
再继续调用delegate中的该方法，请求服务器数据完成回调
- (void)URLSession:(__unused NSURLSession *)session
task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error
{
//如果有认证质询错误也要返回
error = objc_getAssociatedObject(task, AuthenticationChallengeErrorKey) ?: error;
//强引用，防止被提前释放
__strong AFURLSessionManager *manager = self.manager;
__block id responseObject = nil;
//创建一个信息字典
NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
//存储响应数据序列化信息
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.
//这时mutableData已经没有用，清空
self.mutableData = nil;
}
#if AF_CAN_USE_AT_AVAILABLE && AF_CAN_INCLUDE_SESSION_TASK_METRICS
if (@available(iOS 10, macOS 10.12, watchOS 3, tvOS 10, *)) {
//任务度量（包含请求响应时间等度量）
if (self.sessionTaskMetrics) {
userInfo[AFNetworkingTaskDidCompleteSessionTaskMetrics] = self.sessionTaskMetrics;
}
}
#endif
//下载数据存储的位置
if (self.downloadFileURL) {
userInfo[AFNetworkingTaskDidCompleteAssetPathKey] = self.downloadFileURL;
} else if (data) {
userInfo[AFNetworkingTaskDidCompleteResponseDataKey] = data;
}
if (error) {
//存储错误信息
userInfo[AFNetworkingTaskDidCompleteErrorKey] = error;
//如果有定义的组和队列就用定义好的，如果没有就用默认的
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);
}
//发送一条包含信息字典的通知
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];
//返回存储位置
if (self.downloadFileURL) {
responseObject = self.downloadFileURL;
}
//返回数据保存到信息字典
if (responseObject) {
userInfo[AFNetworkingTaskDidCompleteSerializedResponseKey] = responseObject;
}
//序列化错误信息保存到信息字典
if (serializationError) {
userInfo[AFNetworkingTaskDidCompleteErrorKey] = serializationError;
}
dispatch_group_async(manager.completionGroup ?: url_session_manager_completion_group(), manager.completionQueue ?: dispatch_get_main_queue(), ^{
if (self.completionHandler) {
//网络请求完成代码块
self.completionHandler(task.response, responseObject, serializationError);
}
//异步发送通知，带有信息字典
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
});
});
});
}
}
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