AFNetworking3.2.1源码解读
2018-08-23 本文已影响0人
saige2011
AFNetworking3.2.1源码解读
下面是AFNetworking的源码结构图，主要分为：AFURLSessionManager、AFNetworkReachabilityManager、AFSecurityPolicy、Serialization和UIKit等5部分。
AFNetworking的源码结构图
AFNetworking
详细架构
下面我们就看一下AFN的详细架构
NSURLSession
- AFURLSessionManager
- AFHTTPSessionManager
Serialization
- <AFURLRequestSerialization>
- AFHTTPRequestSerializer
- AFJSONRequestSerializer
- AFPropertyListRequestSerializer
- <AFURLResponseSerialization>
- AFHTTPResponseSerializer
- AFJSONResponseSerializer
- AFXMLParserResponseSerializer
- AFXMLDocumentResponseSerializer (macOS)
- AFPropertyListResponseSerializer
- AFImageResponseSerializer
- AFCompoundResponseSerializer
Additional Functionality
- AFSecurityPolicy
- AFNetworkReachabilityManager
NSURLSessionDataTask实例化
先看一个项目中进行的GET请求，直接接入的就是AFN中的下面这个方法
**
不需要进度回调
Creates and runs an `NSURLSessionDataTask` with a `GET` request.
@param URLString The URL string used to create the request URL.
@param parameters The parameters to be encoded according to the client request serializer.
@param success A block object to be executed when the task finishes successfully. This block has no return value and takes two arguments: the data task, and the response object created by the client response serializer.
@param failure A block object to be executed when the task finishes unsuccessfully, or that finishes successfully, but encountered an error while parsing the response data. This block has no return value and takes a two arguments: the data task and the error describing the network or parsing error that occurred.
@see -dataTaskWithRequest:completionHandler:
*/
- (nullable NSURLSessionDataTask *)GET:(NSString *)URLString
parameters:(nullable id)parameters
success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure DEPRECATED_ATTRIBUTE;
/**
需要进度的回调
Creates and runs an `NSURLSessionDataTask` with a `GET` request.
@param URLString The URL string used to create the request URL.
@param parameters The parameters to be encoded according to the client request serializer.
@param downloadProgress A block object to be executed when the download progress is updated. Note this block is called on the session queue, not the main queue.
@param success A block object to be executed when the task finishes successfully. This block has no return value and takes two arguments: the data task, and the response object created by the client response serializer.
@param failure A block object to be executed when the task finishes unsuccessfully, or that finishes successfully, but encountered an error while parsing the response data. This block has no return value and takes a two arguments: the data task and the error describing the network or parsing error that occurred.
@see -dataTaskWithRequest:uploadProgress:downloadProgress:completionHandler:
*/
- (nullable NSURLSessionDataTask *)GET:(NSString *)URLString
parameters:(nullable id)parameters
progress:(nullable void (^)(NSProgress *downloadProgress))downloadProgress
success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;
Get请求实现
- 接口的调用
// 不需要进度回调
- (NSURLSessionDataTask *)GET:(NSString *)URLString
parameters:(id)parameters
success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
return [self GET:URLString parameters:parameters progress:nil success:success failure:failure];
}
// 需要进度回调
- (NSURLSessionDataTask *)GET:(NSString *)URLString
parameters:(id)parameters
progress:(void (^)(NSProgress * _Nonnull))downloadProgress
success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
{
NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"GET"
URLString:URLString
parameters:parameters
uploadProgress:nil
downloadProgress:downloadProgress
success:success
failure:failure];
[dataTask resume];
return dataTask;
}
这里面五个参数，很好理解，请求的URL、参数、进度block、成功block和失败block。
下面我们看NSURLSessionDataTask这个类
/*
* An NSURLSessionDataTask does not provide any additional
* functionality over an NSURLSessionTask and its presence is merely
* to provide lexical differentiation from download and upload tasks.
*/
@interface NSURLSessionDataTask : NSURLSessionTask
@end
NSURLSessionDataTask不提供NSURLSessionTask的任何附加功能，它的存在仅仅是为了提供下载和上载任务的词汇区分。
- NSURLSessionDataTask的实例化
- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
URLString:(NSString *)URLString
parameters:(id)parameters
uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
success:(void (^)(NSURLSessionDataTask *, id))success
failure:(void (^)(NSURLSessionDataTask *, NSError *))failure
{
NSError *serializationError = nil;
NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
if (serializationError) {
if (failure) {
dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
failure(nil, serializationError);
});
}
return nil;
}
__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);
}
}
}];
return dataTask;
}
这里没用到上传，所以uploadProgress参数为nil，这种调用方式大家是不是很熟悉，感觉很好，对了，SDWebImage下载图像的接口就是这么调用的，最后走的都是同一个方法，只是个别参数为nil或0，最后在这个参数最全的方法里面做一些差别化的处理。大神都是这么写代码，不仅代码逻辑清晰，而且调用和查看代码也很方便。
这里做了两个方面的工作：
- 实例化NSMutableURLRequest请求对象。
NSError *serializationError = nil;
NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
- 实例化NSURLSessionDataTask对象，并调用下面方法返回该对象。
- (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;
}
//为指定的任务添加代理
//首先实例化AFURLSessionManagerTaskDelegate，并对改类内部的属性进行赋值，并调用下面的方法为task设置delegate。
- (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
{
AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] initWithTask:dataTask];
delegate.manager = self;
delegate.completionHandler = completionHandler;
dataTask.taskDescription = self.taskDescriptionForSessionTasks;
[self setDelegate:delegate forTask:dataTask];
delegate.uploadProgressBlock = uploadProgressBlock;
delegate.downloadProgressBlock = downloadProgressBlock;
}
- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
forTask:(NSURLSessionTask *)task
{
NSParameterAssert(task);
NSParameterAssert(delegate);
//加锁 需要保护的内容放在中间，让数据更安全
[self.lock lock];
self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
[self addNotificationObserverForTask:task]; //通知 监听任务的开始和暂停
[self.lock unlock];
}
任务进度设置和通知监听
- 上传进度
- (instancetype)initWithTask:(NSURLSessionTask *)task {
self = [super init];
if (!self) {
return nil;
}
_mutableData = [NSMutableData data];
_uploadProgress = [[NSProgress alloc] initWithParent:nil userInfo:nil];
_downloadProgress = [[NSProgress alloc] initWithParent:nil userInfo:nil];
__weak __typeof__(task) weakTask = task;
for (NSProgress *progress in @[ _uploadProgress, _downloadProgress ])
{
progress.totalUnitCount = NSURLSessionTransferSizeUnknown;
progress.cancellable = YES;
progress.cancellationHandler = ^{
[weakTask cancel];
};
progress.pausable = YES;
progress.pausingHandler = ^{
[weakTask suspend];
};
#if AF_CAN_USE_AT_AVAILABLE
if (@available(iOS 9, macOS 10.11, *))
#else
if ([progress respondsToSelector:@selector(setResumingHandler:)])
#endif
{
progress.resumingHandler = ^{
[weakTask resume];
};
}
[progress addObserver:self
forKeyPath:NSStringFromSelector(@selector(fractionCompleted))
options:NSKeyValueObservingOptionNew
context:NULL];
}
return self;
}
- 取消
progress.cancellable = YES;
progress.cancellationHandler = ^{
[weakTask cancel];
};
首先要设置的就是可取消cancallable这个属性，需要设置为YES。
@property (getter=isCancellable) BOOL cancellable;
所做的工作是否可以分别取消或暂停。 默认情况下，NSProgresses是可取消的，但不可pausable。 对于这些属性，NSProgress默认为符合KVO标准，并且通知始终在更新属性的线程上发送。 这些属性用于传递是否应该在进度报告用户界面中显示取消和暂停的控件。 NSProgress本身不会对这些属性做任何事情，除了帮助将进度记录的值传递给进度观察员。 在NSProgress的生命周期中，这些属性的值实际上以任何方式改变都是有效的。 当然，如果一个NSProgress可以被取消，你应该通过设置一个取消处理程序或者让你的代码轮询调用-isCancelled的结果来实现可取消性。 同样适用于pausability。
- (void)cancel;
cancel立即返回，但将任务标记为被取消。 该任务将发信号-URLSession:task:didCompleteWithError:错误值为{NSURLErrorDomain，NSURLErrorCancelled}。 在某些情况下，任务可能在确认取消之前发出其他工作的信号。- cancel可能被发送到已被暂停的任务。
- 暂停
progress.pausable = YES;
progress.pausingHandler = ^{
[weakTask suspend];
};
暂停任务将阻止NSURLSession继续加载数据。 可能仍然存在代表此任务的代理在调用（例如，报告挂起时收到的数据），但不会有代表任务进行进一步的传输直到发送- resume。 与任务关联的超时定时器将在任务暂停时被禁用。 - ususpend和- resume是可嵌套的。
- 开始
#if AF_CAN_USE_AT_AVAILABLE
if (@available(iOS 9, macOS 10.11, *))
#else
if ([progress respondsToSelector:@selector(setResumingHandler:)])
#endif
{
progress.resumingHandler = ^{
[weakTask resume];
};
}
resumingHandler，开始进行任务的处理
@property (nullable, copy) void (^resumingHandler)(void) NS_AVAILABLE(10_11, 9_0);
调用resume时要调用的块。 即使该方法在接收方的super类上调用，或者由于发布接收方或接收方的super类而导致的另一个进程中的NSProgress实例，也会调用该block。 您的块不会在任何特定队列上调用。 如果它必须在特定的队列上工作，那么它应该在该队列上安排该工作。
- 下载进度
同上
- 上传下载进度增加KVO观察
[progress addObserver:self
forKeyPath:NSStringFromSelector(@selector(fractionCompleted))
options:NSKeyValueObservingOptionNew
context:NULL];
KVO的监听部分如下
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSString *,id> *)change context:(void *)context {
if ([object isEqual:self.downloadProgress]) {
if (self.downloadProgressBlock) {
self.downloadProgressBlock(object);
}
}
else if ([object isEqual:self.uploadProgress]) {
if (self.uploadProgressBlock) {
self.uploadProgressBlock(object);
}
}
}
AFURLSessionManager为任务添加通知监听
<!--添加通知监听-->
- (void)addNotificationObserverForTask:(NSURLSessionTask *)task {
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(taskDidResume:) name:AFNSURLSessionTaskDidResumeNotification object:task];
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(taskDidSuspend:) name:AFNSURLSessionTaskDidSuspendNotification object:task];
}
- 开始
- (NSString *)taskDescriptionForSessionTasks {
return [NSString stringWithFormat:@"%p", self];
}
- (void)taskDidResume:(NSNotification *)notification {
NSURLSessionTask *task = notification.object;
if ([task respondsToSelector:@selector(taskDescription)]) {
if ([task.taskDescription isEqualToString:self.taskDescriptionForSessionTasks]) {
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidResumeNotification object:task];
});
}
}
}
一起来看一下这里的逻辑，首先就是取出任务notification.object，然后判断[task.taskDescription isEqualToString:self.taskDescriptionForSessionTasks]，这里self.taskDescriptionForSessionTasks的意思就是当前实例化对象的地址。判断如果是YES，那么就在主线程发送通知。
- 暂停
- (void)taskDidSuspend:(NSNotification *)notification {
NSURLSessionTask *task = notification.object;
if ([task respondsToSelector:@selector(taskDescription)]) {
if ([task.taskDescription isEqualToString:self.taskDescriptionForSessionTasks]) {
dispatch_async(dispatch_get_main_queue(), ^{
[[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidSuspendNotification object:task];
});
}
}
}
暂停的逻辑参考开始，不同的地方就在于发送通知的name不一样而已。
代理转发思想
重写respondsToSelector方法
- (BOOL)respondsToSelector:(SEL)selector {
if (selector == @selector(URLSession:task:willPerformHTTPRedirection:newRequest:completionHandler:)) {
return self.taskWillPerformHTTPRedirection != nil;
} else if (selector == @selector(URLSession:dataTask:didReceiveResponse:completionHandler:)) {
return self.dataTaskDidReceiveResponse != nil;
} else if (selector == @selector(URLSession:dataTask:willCacheResponse:completionHandler:)) {
return self.dataTaskWillCacheResponse != nil;
}
#if !TARGET_OS_OSX
else if (selector == @selector(URLSessionDidFinishEventsForBackgroundURLSession:)) {
return self.didFinishEventsForBackgroundURLSession != nil;
}
#endif
return [[self class] instancesRespondToSelector:selector];
}
重写respondsToSelector的作用就是判断NSURLSession那几个代理是否能响应，如果响应了就去调用。复写了selector的方法，这几个方法是在本类有实现的，但是如果外面的Block没赋值的话，则返回NO，相当于没有实现。
这样如果没实现这些我们自定义的Block也不会去回调这些代理。因为本身某些代理，只执行了这些自定义的Block，如果Block都没有赋值，那我们调用代理也没有任何意义。
block的属性和值的设置
定义的block的属性
@property (readwrite, nonatomic, copy) AFURLSessionDidBecomeInvalidBlock sessionDidBecomeInvalid;
@property (readwrite, nonatomic, copy) AFURLSessionDidReceiveAuthenticationChallengeBlock sessionDidReceiveAuthenticationChallenge;
@property (readwrite, nonatomic, copy) AFURLSessionDidFinishEventsForBackgroundURLSessionBlock didFinishEventsForBackgroundURLSession AF_API_UNAVAILABLE(macos);
@property (readwrite, nonatomic, copy) AFURLSessionTaskWillPerformHTTPRedirectionBlock taskWillPerformHTTPRedirection;
@property (readwrite, nonatomic, copy) AFURLSessionTaskDidReceiveAuthenticationChallengeBlock taskDidReceiveAuthenticationChallenge;
@property (readwrite, nonatomic, copy) AFURLSessionTaskNeedNewBodyStreamBlock taskNeedNewBodyStream;
@property (readwrite, nonatomic, copy) AFURLSessionTaskDidSendBodyDataBlock taskDidSendBodyData;
@property (readwrite, nonatomic, copy) AFURLSessionTaskDidCompleteBlock taskDidComplete;
@property (readwrite, nonatomic, copy) AFURLSessionDataTaskDidReceiveResponseBlock dataTaskDidReceiveResponse;
@property (readwrite, nonatomic, copy) AFURLSessionDataTaskDidBecomeDownloadTaskBlock dataTaskDidBecomeDownloadTask;
@property (readwrite, nonatomic, copy) AFURLSessionDataTaskDidReceiveDataBlock dataTaskDidReceiveData;
@property (readwrite, nonatomic, copy) AFURLSessionDataTaskWillCacheResponseBlock dataTaskWillCacheResponse;
@property (readwrite, nonatomic, copy) AFURLSessionDownloadTaskDidFinishDownloadingBlock downloadTaskDidFinishDownloading;
@property (readwrite, nonatomic, copy) AFURLSessionDownloadTaskDidWriteDataBlock downloadTaskDidWriteData;
@property (readwrite, nonatomic, copy) AFURLSessionDownloadTaskDidResumeBlock downloadTaskDidResume;
typedef void (^AFURLSessionDidBecomeInvalidBlock)(NSURLSession *session, NSError *error);
typedef NSURLSessionAuthChallengeDisposition (^AFURLSessionDidReceiveAuthenticationChallengeBlock)(NSURLSession *session, NSURLAuthenticationChallenge *challenge, NSURLCredential * __autoreleasing *credential);
typedef NSURLRequest * (^AFURLSessionTaskWillPerformHTTPRedirectionBlock)(NSURLSession *session, NSURLSessionTask *task, NSURLResponse *response, NSURLRequest *request);
typedef NSURLSessionAuthChallengeDisposition (^AFURLSessionTaskDidReceiveAuthenticationChallengeBlock)(NSURLSession *session, NSURLSessionTask *task, NSURLAuthenticationChallenge *challenge, NSURLCredential * __autoreleasing *credential);
typedef void (^AFURLSessionDidFinishEventsForBackgroundURLSessionBlock)(NSURLSession *session);
typedef NSInputStream * (^AFURLSessionTaskNeedNewBodyStreamBlock)(NSURLSession *session, NSURLSessionTask *task);
typedef void (^AFURLSessionTaskDidSendBodyDataBlock)(NSURLSession *session, NSURLSessionTask *task, int64_t bytesSent, int64_t totalBytesSent, int64_t totalBytesExpectedToSend);
typedef void (^AFURLSessionTaskDidCompleteBlock)(NSURLSession *session, NSURLSessionTask *task, NSError *error);
typedef NSURLSessionResponseDisposition (^AFURLSessionDataTaskDidReceiveResponseBlock)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSURLResponse *response);
typedef void (^AFURLSessionDataTaskDidBecomeDownloadTaskBlock)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSURLSessionDownloadTask *downloadTask);
typedef void (^AFURLSessionDataTaskDidReceiveDataBlock)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSData *data);
typedef NSCachedURLResponse * (^AFURLSessionDataTaskWillCacheResponseBlock)(NSURLSession *session, NSURLSessionDataTask *dataTask, NSCachedURLResponse *proposedResponse);
typedef NSURL * (^AFURLSessionDownloadTaskDidFinishDownloadingBlock)(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, NSURL *location);
typedef void (^AFURLSessionDownloadTaskDidWriteDataBlock)(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t bytesWritten, int64_t totalBytesWritten, int64_t totalBytesExpectedToWrite);
typedef void (^AFURLSessionDownloadTaskDidResumeBlock)(NSURLSession *session, NSURLSessionDownloadTask *downloadTask, int64_t fileOffset, int64_t expectedTotalBytes);
typedef void (^AFURLSessionTaskProgressBlock)(NSProgress *);
typedef void (^AFURLSessionTaskCompletionHandler)(NSURLResponse *response, id responseObject, NSError *error);
下面看一下这些属性的值的设定。在.h文件中有接口，并在.m中是实现，这里就举一个例子，如下：
<!--.h-->
- (void)setSessionDidBecomeInvalidBlock:(nullable void (^)(NSURLSession *session, NSError *error))block;
<!--.m-->
- (void)setSessionDidBecomeInvalidBlock:(void (^)(NSURLSession *session, NSError *error))block {
self.sessionDidBecomeInvalid = block;
}
这么做的目的是为了我们这些用户使用起来方便，调用set方法去设置这些Block，能很清晰的看到Block的各个参数与返回值。
代理转发思想
AFURLSessionManager中是有关NSURLSession的代理，主要包含下面的几个代理的实现。
AFURLSessionManagerTaskDelegate2
上面的几个代理是什么关系，相信看过我写的SDWebImage的源码分析的应该很清楚，他们是继承的关系，就不多说了。而AFURLSessionManagerTaskDelegate实现了三个代理方法。
AFURLSessionManagerTaskDelegate
AFUrlSessionManager对这一大堆代理做了一些公共的处理，而转发到AF自定义代理的6条，则负责把每个task对应的数据回调出去。
那么是如何转发过去的呢，简单的调用就是这样的。
- (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);
}
}
- (AFURLSessionManagerTaskDelegate *)delegateForTask:(NSURLSessionTask *)task {
NSParameterAssert(task);
AFURLSessionManagerTaskDelegate *delegate = nil;
[self.lock lock];
delegate = self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)];
[self.lock unlock];
return delegate;
}
通过[delegate URLSession:session task:task didCompleteWithError:error];就转发了过去。这里首先就是从字典中找到该任务对应的代理AFURLSessionManagerTaskDelegate对象，然后就是转发到自定义代理中。
大家如果读过SDWebImage的源码的话，就应该明白，那里也用到了代理的转发，可见，这种转发思想有它的优点，值得我们去学习。
NSURLSessionDelegate详细解析
NSURLSession的代理在类AFURLSessionManager中实现，转发到AFURLSessionManagerTaskDelegate自定义的代理中。下面开始会介绍这个NSURLSession的代理的用法。
1. URLSession:didBecomeInvalidWithError:
先看一下系统的API。
/* The last message a session receives. A session will only become
* invalid because of a systemic error or when it has been
* explicitly invalidated, in which case the error parameter will be nil.
*/
- (void)URLSession:(NSURLSession *)session didBecomeInvalidWithError:(nullable NSError *)error;
下面是代理方法的实现
@property (readwrite, nonatomic, copy) AFURLSessionDidBecomeInvalidBlock sessionDidBecomeInvalid;
typedef void (^AFURLSessionDidBecomeInvalidBlock)(NSURLSession *session, NSError *error);
- (void)URLSession:(NSURLSession *)session
didBecomeInvalidWithError:(NSError *)error
{
if (self.sessionDidBecomeInvalid) {
self.sessionDidBecomeInvalid(session, error);
}
[[NSNotificationCenter defaultCenter] postNotificationName:AFURLSessionDidInvalidateNotification object:session];
}
如果你使用finishTasksAndInvalidate函数使该session失效，
那么session首先会先完成最后一个task，然后再调用URLSession:didBecomeInvalidWithError:代理方法，
如果你调用invalidateAndCancel方法来使session失效，那么该session会立即调用上面的代理方法。
这个就是该代理方法调用的时机。
这个代理方法做了两个事情：
- 调用了自定义的block - sessionDidBecomeInvalid
- 发送了一个通知，但是没有对象去监听，可能是作者故意留的接口吧，这个通知目前是没有用到。
2. URLSession:task:didReceiveChallenge:completionHandler:
我们先看一下系统定义的API
/* 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;
下面看一下在该类中的实现。
- (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);
}
}
这里其实就是HTTPS认证，服务器向客户端进行质询和挑战。这个类似的其实在SDWebImage中讲过，这里也简单的看一下。
web服务器接收到客户端请求时，有时候需要先验证客户端是否为正常用户，再决定是够返回真实数据。这种情况称之为服务端要求客户端接收挑战（NSURLAuthenticationChallenge *challenge）。接收到挑战后，客户端要根据服务端传来的challenge来生成completionHandler所需的NSURLSessionAuthChallengeDisposition disposition和NSURLCredential *credential（disposition指定应对这个挑战的方法，而credential是客户端生成的挑战证书，注意只有challenge中认证方法为NSURLAuthenticationMethodServerTrust的时候，才需要生成挑战证书）。最后调用completionHandler回应服务器端的挑战。
当某个session使用SSL/TLS协议，第一次和服务器端建立连接的时候，服务器会发送给iOS客户端一个证书，此方法允许你的app验证服务期端的证书链（certificate keychain）注：如果你没有实现该方法，该session会调用其NSURLSessionTaskDelegate的代理方法URLSession:task:didReceiveChallenge:completionHandler:。
3. URLSessionDidFinishEventsForBackgroundURLSession:
先看一下系统的API。
/* If an application has received an
* -application:handleEventsForBackgroundURLSession:completionHandler:
* message, the session delegate will receive this message to indicate
* that all messages previously enqueued for this session have been
* delivered. At this time it is safe to invoke the previously stored
* completion handler, or to begin any internal updates that will
* result in invoking the completion handler.
*/
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session API_AVAILABLE(ios(7.0), watchos(2.0), tvos(9.0)) API_UNAVAILABLE(macos);
下面看一下AFN中的实现
@property (readwrite, nonatomic, copy) AFURLSessionDidFinishEventsForBackgroundURLSessionBlock didFinishEventsForBackgroundURLSession AF_API_UNAVAILABLE(macos);
typedef void (^AFURLSessionDidFinishEventsForBackgroundURLSessionBlock)(NSURLSession *session);
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session {
if (self.didFinishEventsForBackgroundURLSession) {
dispatch_async(dispatch_get_main_queue(), ^{
self.didFinishEventsForBackgroundURLSession(session);
});
}
}
- 当session中所有已经入队的消息被发送出去后，会调用该代理方法。
- 在iOS中，当一个后台传输任务完成或者后台传输时需要证书，而此时你的app正在后台挂起，那么你的app在后台会自动重新启动运行，并且这个app的UIApplicationDelegate会发送一个application:handleEventsForBackgroundURLSession:completionHandler:消息。该消息包含了对应后台的session的identifier，而且这个消息会导致你的app启动。你的app随后应该先存储completion handler，然后再使用相同的identifier创建一个background configuration，并根据这个background configuration创建一个新的session。这个新创建的session会自动与后台任务重新关联在一起。
- 当你的app获取了一个URLSessionDidFinishEventsForBackgroundURLSession:消息，这就意味着之前这个session中已经入队的所有消息都转发出去了，这时候再调用先前存取的completion handler是安全的，或者因为内部更新而导致调用completion handler也是安全的。
NSURLSessionTaskDelegate
1. URLSession:task:willPerformHTTPRedirection:newRequest:completionHandler:
首先看一下系统的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中该代理方法的实现
- (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);
}
}
这里，主要做了下面几个逻辑：
如果有对应的block taskWillPerformHTTPRedirection，那么就调用self.taskWillPerformHTTPRedirection(session, task, response, request)，返回一个新的request。
接着就是利用生成的request重新请求
if (completionHandler) {
completionHandler(redirectRequest);
}
这个方法是在服务器去重定向的时候，才会被调用。
此方法只会在default session或者ephemeral session中调用，而在background session中，session task会自动重定向。
补充一点，初始化NSURLSession对象的时候需要使用NSURLSessionConfiguration。有三个类工厂方法：
-
+ defaultSessionConfiguration返回一个标准的 configuration，具有相同的共享 NSHTTPCookieStorage，共享 NSURLCache 和共享NSURLCredentialStorage。 -
+ ephemeralSessionConfiguration返回一个预设配置，这个配置中不会对缓存，Cookie 和证书进行持久性的存储。这对于实现像秘密浏览这种功能来说是很理想的。 -
+ backgroundSessionConfiguration:(NSString *)identifier的独特之处在于，它会创建一个后台 session。后台 session 不同于常规的，普通的 session，它甚至可以在应用程序挂起，退出或者崩溃的情况下运行上传和下载任务。初始化时指定的标识符，被用于向任何可能在进程外恢复后台传输的守护进程（daemon）提供上下文。
2. URLSession:task:didReceiveChallenge:completionHandler
首先看一下系统的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中该代理方法的实现
- (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);
}
}
这里我们需要知道：
- 这个是non-session-level级别的认证
- 多了一个参数task，然后调用我们自定义的Block会多回传这个task作为参数，这样我们就可以根据每个task去自定义我们需要的https认证方式。
3. URLSession:task:needNewBodyStream
首先看一下系统的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;
下面看一下AFN中该代理方法的实现
- (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);
}
}
该代理方法会在下面两种情况被调用
- 如果task是由uploadTaskWithStreamedRequest:创建的，那么提供初始的request body stream时候会调用该代理方法。
- 因为认证挑战或者其他可恢复的服务器错误，而导致需要客户端重新发送一个含有body stream的request，这时候会调用该代理。
4. URLSession:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend
首先看一下系统的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;
下面看一下AFN中该代理方法的实现
- (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];
}
}
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];
if (delegate) {
[delegate URLSession:session task:task didSendBodyData:bytesSent totalBytesSent:totalBytesSent totalBytesExpectedToSend:totalBytesExpectedToSend];
}
if (self.taskDidSendBodyData) {
self.taskDidSendBodyData(session, task, bytesSent, totalBytesSent, totalUnitCount);
}
}
就是每次发送数据给服务器，会回调这个方法，通知已经发送了多少。
5. URLSession:task:didCompleteWithError
首先看一下系统的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;
下面看一下AFN中该代理方法的实现
- (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);
}
}
这个代理就是task完成了的回调，这里涉及到task和代理的绑定与接触绑定，代码不难，就不多说了。
NSURLSessionDataDelegate
1. URLSession:dataTask:didReceiveResponse:completionHandler
首先看一下系统的API接口
/* 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;
下面看一下AFN中该代理方法的实现
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler
{
NSURLSessionResponseDisposition disposition = NSURLSessionResponseAllow;
if (self.dataTaskDidReceiveResponse) {
disposition = self.dataTaskDidReceiveResponse(session, dataTask, response);
}
if (completionHandler) {
completionHandler(disposition);
}
}
这里，NSURLSessionResponseDisposition disposition = NSURLSessionResponseAllow;表示默认为继续进行。
- completionHandler这个block，通过传入一个类型为NSURLSessionResponseDisposition的变量来决定该传输任务接下来该做什么：
- NSURLSessionResponseAllow 该task正常进行
- NSURLSessionResponseCancel 该task会被取消
- NSURLSessionResponseBecomeDownload 会调用URLSession:dataTask:didBecomeDownloadTask:方法来新建一个download task以代替当前的data task
- NSURLSessionResponseBecomeStream 转成一个StreamTask
- 当你把添加content-type的类型为multipart/x-mixed-replace那么服务器的数据会分片的传回来。然后这个方法是每次接受到对应片响应的时候会调被调用。你应该在这个函数中合理地处理先前的数据，否则会被新数据覆盖。
2. URLSession:dataTask:didBecomeDownloadTask
首先看一下系统的API接口
/*
* 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;
下面看一下AFN中该代理方法的实现
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask
{
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
if (delegate) {
[self removeDelegateForTask:dataTask];
[self setDelegate:delegate forTask:downloadTask];
}
if (self.dataTaskDidBecomeDownloadTask) {
self.dataTaskDidBecomeDownloadTask(session, dataTask, downloadTask);
}
}
当代理1方法中的disposition = NSURLSessionResponseBecomeDownload的时候，就会调用这个方法。
这个代理方法是被上面的代理方法触发的，作用就是新建一个downloadTask，替换掉当前的dataTask。所以我们在这里做了AF自定义代理的重新绑定操作[self setDelegate:delegate forTask:downloadTask];。
3. URLSession:dataTask:didReceiveData
首先看一下系统的API接口
/* 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;
下面看一下AFN中该代理方法的实现
- (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);
}
}
- 获取到数据就会调用，会被反复调用，请求到的数据就在这被拼装完整。
- 这个方法和上面didCompleteWithError算是NSURLSession的代理中最重要的两个方法。
- 我们转发了这个方法到AF的代理中去，所以数据的拼接都是在AF的代理中进行的。这也是情理中的，毕竟每个响应数据都是对应各个task，各个AF代理的。在AFURLSessionManager都只是做一些公共的处理。
4. URLSession:dataTask:willCacheResponse:completionHandler
首先看一下系统的API接口
/* 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;
下面看一下AFN中该代理方法的实现
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
willCacheResponse:(NSCachedURLResponse *)proposedResponse
completionHandler:(void (^)(NSCachedURLResponse *cachedResponse))completionHandler
{
NSCachedURLResponse *cachedResponse = proposedResponse;
if (self.dataTaskWillCacheResponse) {
cachedResponse = self.dataTaskWillCacheResponse(session, dataTask, proposedResponse);
}
if (completionHandler) {
completionHandler(cachedResponse);
}
}
- 该方法的作用就是询问data task或上传任务（upload task）是否缓存response。
- 当task接收到所有期望的数据后，session会调用此代理方法。
- 当task接收到所有期望的数据后，session会调用此代理方法。如果你没有实现该方法，那么就会使用创建session时使用的configuration对象决定缓存策略。这个代理方法最初的目的是为了阻止缓存特定的URLs或者修改NSCacheURLResponse对象相关的userInfo字典。
- 该方法只会当request决定缓存response时候调用。作为准则，responses只会当以下条件都成立的时候返回缓存：
- 该request是HTTP或HTTPS URL的请求（或者你自定义的网络协议，并且确保该协议支持缓存）
确保request请求是成功的（返回的status code为200-299） - 返回的response是来自服务器端的，而非缓存中本身就有的
- 提供的NSURLRequest对象的缓存策略要允许进行缓存
- 服务器返回的response中与缓存相关的header要允许缓存
- 该response的大小不能比提供的缓存空间大太多（比如你提供了一个磁盘缓存，那么response大小一定不能比磁盘缓存空间还要大5%）
NSURLSessionDownloadDelegate
1. URLSession:downloadTask:didFinishDownloadingToURL
首先看一下系统的API接口
/* 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;
看一下AFN中该方法的实现
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:downloadTask];
if (self.downloadTaskDidFinishDownloading) {
NSURL *fileURL = self.downloadTaskDidFinishDownloading(session, downloadTask, location);
if (fileURL) {
delegate.downloadFileURL = fileURL;
NSError *error = nil;
if (![[NSFileManager defaultManager] moveItemAtURL:location toURL:fileURL error:&error]) {
[[NSNotificationCenter defaultCenter] postNotificationName:AFURLSessionDownloadTaskDidFailToMoveFileNotification object:downloadTask userInfo:error.userInfo];
}
return;
}
}
if (delegate) {
[delegate URLSession:session downloadTask:downloadTask didFinishDownloadingToURL:location];
}
}
这里代码都很简单，就不多说了，这里也做了代理的转发。
2. URLSession:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite
首先看一下系统的API接口
/* 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;
看一下AFN中该方法的实现
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didWriteData:(int64_t)bytesWritten
totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:downloadTask];
if (delegate) {
[delegate URLSession:session downloadTask:downloadTask didWriteData:bytesWritten totalBytesWritten:totalBytesWritten totalBytesExpectedToWrite:totalBytesExpectedToWrite];
}
if (self.downloadTaskDidWriteData) {
self.downloadTaskDidWriteData(session, downloadTask, bytesWritten, totalBytesWritten, totalBytesExpectedToWrite);
}
}
这个方法和参数都很好理解，我就说一点，totalBytesExpectedToWrite这个参数表示期望收到的文件总字节数，是由Content-Length header提供。如果没有提供，默认是NSURLSessionTransferSizeUnknown。
3. URLSession:downloadTask:didResumeAtOffset:expectedTotalBytes
首先看一下系统的API接口
/* 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;
看一下AFN中该方法的实现
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:downloadTask];
if (delegate) {
[delegate URLSession:session downloadTask:downloadTask didResumeAtOffset:fileOffset expectedTotalBytes:expectedTotalBytes];
}
if (self.downloadTaskDidResume) {
self.downloadTaskDidResume(session, downloadTask, fileOffset, expectedTotalBytes);
}
}
- 当下载被取消或者失败后重新恢复下载时调用。
- 如果一个正在下载任务被取消或者失败了，你可以请求一个resumeData对象（比如在userInfo字典中通过NSURLSessionDownloadTaskResumeData这个键来获取到resumeData）并使用它来提供足够的信息以重新开始下载任务。
随后，你可以使用resumeData作为downloadTaskWithResumeData:或downloadTaskWithResumeData:completionHandler:的参数。当你调用这些方法时，你将开始一个新的下载任务。一旦你继续下载任务，session会调用它的代理方法URLSession:downloadTask:didResumeAtOffset:expectedTotalBytes:其中的downloadTask参数表示的就是新的下载任务，这也意味着下载重新开始了。 - 注意：fileOffset这个参数，如果文件缓存策略或者最后文件更新日期阻止重用已经存在的文件内容，那么该值为0。否则，该值表示当前已经下载data的偏移量。
- 前面几篇讲解的那么多代理方法中，我们做的处理都是相对于这个sessionManager所有的request的。是公用的处理。而转发的3个代理方法到AF的自定义deleagate，作用是需要对应每个task去私有化处理。
转发代理方法详细解析
AFN自定义代理AFURLSessionManagerTaskDelegate中六个代理转发的实现
1. URLSession:task:didCompleteWithError
先看一下该自定义代理方法的实现。
- (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];
});
});
});
}
}
这里有几点需要注意：
- userInfo参数
这个参数是一个可变字典。
NSString * const AFNetworkingTaskDidCompleteResponseSerializerKey = @"com.alamofire.networking.task.complete.responseserializer";
__block NSMutableDictionary *userInfo = [NSMutableDictionary dictionary];
userInfo[AFNetworkingTaskDidCompleteResponseSerializerKey] = manager.responseSerializer;
这个userInfo用来存储一些相关信息，存储responseSerializer响应解析对象。
- 释放mutableData内存
//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;
}
当我们不用self.mutableData这个对象的时候，就设置为nil，节省内存，数据通过data传出去了。
- 有错误error不为空
if (error) {
//首先就是更新userInfo信息
userInfo[AFNetworkingTaskDidCompleteErrorKey] = error;
//然后就是在主线程进行block回调，并发出了一个通知AFNetworkingTaskDidCompleteNotification。
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];
});
});
}
有错误的话，就按照上面的逻辑进行处理。
- 无错误
dispatch_async(url_session_manager_processing_queue(), ^{
//解析数据 验证response的有效性
NSError *serializationError = nil;
responseObject = [manager.responseSerializer responseObjectForResponse:task.response data:data error:&serializationError];
//如果是下载文件，那么responseObject为下载的路径
if (self.downloadFileURL) {
responseObject = self.downloadFileURL;
}
if (responseObject) {
//写入userInfo
userInfo[AFNetworkingTaskDidCompleteSerializedResponseKey] = responseObject;
}
if (serializationError) {
//如果解析response有错误，就更新userInfo
userInfo[AFNetworkingTaskDidCompleteErrorKey] = serializationError;
}
//结果的回调 在队列url_session_manager_completion_group中进行完成的处理
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];
});
});
});
首先我们注意下队列url_session_manager_processing_queue，是在一个并行队列执行的
static dispatch_queue_t url_session_manager_processing_queue() {
static dispatch_queue_t af_url_session_manager_processing_queue;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
af_url_session_manager_processing_queue = dispatch_queue_create("com.alamofire.networking.session.manager.processing", DISPATCH_QUEUE_CONCURRENT);
});
return af_url_session_manager_processing_queue;
}
无错误时候的处理，都是在这个队列中进行处理的。
2. URLSession:dataTask:didReceiveData
- (void)URLSession:(__unused NSURLSession *)session
dataTask:(__unused NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data
{
self.downloadProgress.totalUnitCount = dataTask.countOfBytesExpectedToReceive;
self.downloadProgress.completedUnitCount = dataTask.countOfBytesReceived;
[self.mutableData appendData:data];
}
这个很好理解，其实就是周期性的调用，在这个方法里面拼接了数据。
3. URLSession:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend
在向服务器上传数据时，代理周期性的接收
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didSendBodyData:(int64_t)bytesSent
totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend{
self.uploadProgress.totalUnitCount = task.countOfBytesExpectedToSend;
self.uploadProgress.completedUnitCount = task.countOfBytesSent;
}
回调来报告上传进度
4. URLSession:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite
在从服务器传输的过程中，任务代理周期性的接收回调来报告传输的进度
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didWriteData:(int64_t)bytesWritten
totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
self.downloadProgress.totalUnitCount = totalBytesExpectedToWrite;
self.downloadProgress.completedUnitCount = totalBytesWritten;
}
回调写入磁盘的进度
5. URLSession:downloadTask:didResumeAtOffset:expectedTotalBytes
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes{
self.downloadProgress.totalUnitCount = expectedTotalBytes;
self.downloadProgress.completedUnitCount = fileOffset;
}
6. URLSession:downloadTask:didFinishDownloadingToURL
下载成功了被NSURLSession代理转发到这里
- (void)URLSession:(NSURLSession *)session
downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
self.downloadFileURL = nil;
if (self.downloadTaskDidFinishDownloading) {
self.downloadFileURL = self.downloadTaskDidFinishDownloading(session, downloadTask, location);
if (self.downloadFileURL) {
NSError *fileManagerError = nil;
if (![[NSFileManager defaultManager] moveItemAtURL:location toURL:self.downloadFileURL error:&fileManagerError]) {
[[NSNotificationCenter defaultCenter] postNotificationName:AFURLSessionDownloadTaskDidFailToMoveFileNotification object:downloadTask userInfo:fileManagerError.userInfo];
}
}
}
}
这个大家是否注意到以前那个转发到这里的NSURLSession的代理方法，里面也有关于路径的处理，这里也进行了处理，两处都处理了，为什么呢？
转发前的NSURLSession代理的下载路径是所有request公用的下载路径，一旦设置，所有的request都会下载到之前那个路径。而这个是对应的每个task的，每个task可以设置各自下载路径。
数据解析
数据解析的类和协议
关于数据解析的类和接口，都存在AFURLResponseSerialization这个文件中，我们首先看一下这个文件中有多少类，以及它们是什么关系的。
- @protocol AFURLResponseSerialization <NSObject, NSSecureCoding, NSCopying>
- @interface AFHTTPResponseSerializer : NSObject <AFURLResponseSerialization>
- @interface AFJSONResponseSerializer : AFHTTPResponseSerializer
- @interface AFXMLParserResponseSerializer : AFHTTPResponseSerializer
- @interface AFXMLDocumentResponseSerializer : AFHTTPResponseSerializer
- @interface AFPropertyListResponseSerializer : AFHTTPResponseSerializer
- @interface AFImageResponseSerializer : AFHTTPResponseSerializer
- @interface AFCompoundResponseSerializer : AFHTTPResponseSerializer
AFURLResponseSerialization协议
/**
The response object decoded from the data associated with a specified response.
@param response The response to be processed.
@param data The response data to be decoded.
@param error The error that occurred while attempting to decode the response data.
@return The object decoded from the specified response data.
*/
- (nullable id)responseObjectForResponse:(nullable NSURLResponse *)response
data:(nullable NSData *)data
error:(NSError * _Nullable __autoreleasing *)error NS_SWIFT_NOTHROW;
根据服务器响应中的细节，AFURLResponseSerialization协议被一个对象采用，该对象将数据解码为更有用的对象表示。 Response序列化器还可以对传入响应和数据执行验证。例如，JSON响应序列化器可以检查可接受的状态码（2XX范围）和内容类型（application / json），将有效的JSON响应解码成对象
AFHTTPResponseSerializer
这个是所有其他解析类的父类，他遵守上面的AFURLResponseSerialization协议。
我们看一下协议在这个类中的实现
- (id)responseObjectForResponse:(NSURLResponse *)response
data:(NSData *)data
error:(NSError *__autoreleasing *)error
{
//这里调用了一个方法，进行了指定response和数据的验证。
[self validateResponse:(NSHTTPURLResponse *)response data:data error:error];
return data;
}
- (BOOL)validateResponse:(NSHTTPURLResponse *)response
data:(NSData *)data
error:(NSError * __autoreleasing *)error
{
BOOL responseIsValid = YES;
NSError *validationError = nil;
//就是如果response不是nil，并且response的类型是NSHTTPURLResponse。
if (response && [response isKindOfClass:[NSHTTPURLResponse class]]) {
if (self.acceptableContentTypes && ![self.acceptableContentTypes containsObject:[response MIMEType]] &&
!([response MIMEType] == nil && [data length] == 0)) {
if ([data length] > 0 && [response URL]) {
NSMutableDictionary *mutableUserInfo = [@{
NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedStringFromTable(@"Request failed: unacceptable content-type: %@", @"AFNetworking", nil), [response MIMEType]],
NSURLErrorFailingURLErrorKey:[response URL],
AFNetworkingOperationFailingURLResponseErrorKey: response,
} mutableCopy];
if (data) {
mutableUserInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
}
validationError = AFErrorWithUnderlyingError([NSError errorWithDomain:AFURLResponseSerializationErrorDomain code:NSURLErrorCannotDecodeContentData userInfo:mutableUserInfo], validationError);
}
responseIsValid = NO;
}
if (self.acceptableStatusCodes && ![self.acceptableStatusCodes containsIndex:(NSUInteger)response.statusCode] && [response URL]) {
NSMutableDictionary *mutableUserInfo = [@{
NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedStringFromTable(@"Request failed: %@ (%ld)", @"AFNetworking", nil), [NSHTTPURLResponse localizedStringForStatusCode:response.statusCode], (long)response.statusCode],
NSURLErrorFailingURLErrorKey:[response URL],
AFNetworkingOperationFailingURLResponseErrorKey: response,
} mutableCopy];
if (data) {
mutableUserInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
}
validationError = AFErrorWithUnderlyingError([NSError errorWithDomain:AFURLResponseSerializationErrorDomain code:NSURLErrorBadServerResponse userInfo:mutableUserInfo], validationError);
responseIsValid = NO;
}
}
if (error && !responseIsValid) {
*error = validationError;
}
return responseIsValid;
}
在其基本实现中，此方法检查可接受的状态码和内容类型。 子类可能希望添加其他域特定的检查。
