AFNetworking作为iOS开发中最常用的网络请求框架之一，其内部实现究竟是怎么一步一步实现的呢？现在我们来大致分析下其内部源码，由于本人水平有限，说错了的地方请大家积极指正，谢谢!
以3.0.0的版本为例,其源码结构如下:
源码结构.png
1.NSURLSession文件夹中的类专门用于网络通信,其中最核心的类是AFURLSessionManager,其中的AFHTTPSessionManager这个类是前者的子类，顾名思义，AFHTTPSessionManager这个类是专门用于Http请求,
2.Reachability中的AFNetworkRechabilityManager专门用于检测网络变化
3.Security用于网络安全策略
4.Serilization中的两个类专门用于请求头、响应头的处理
其类与类之间的关系如下图所示:
类与类之间关联.png
AF工作流程 .png
可以看到AFSessionManager中实现的最核心的类是Apple提供的系统类NSURLSession和NSURLSessionDataTask,这两个类提供了网络请求所需要的全部,由于我们最常使用的类是AFHTTPSessionManager,在进行网络请求时，我们一般使用一个AFHTTPSessionManager的实例变量来进行请求,如下代码所示:
AFHTTPSessionManager *httpClient = [[AFHTTPSessionManager alloc] initWithBaseURL:[NSURL URLWithString:@"www.baidu.com"]];
httpClient.requestSerializer = [AFHTTPRequestSerializer serializer];
httpClient.responseSerializer = [AFHTTPResponseSerializer serializer];
[httpClient POST:@""
parameters:@{}
success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
//获取responseObject的数据，在主线程做UI刷新操作
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
}];
首先设置基地址:
- (instancetype)initWithBaseURL:(NSURL *)url
sessionConfiguration:(NSURLSessionConfiguration *)configuration
{
self = [super initWithSessionConfiguration:configuration];
if (!self) {
return nil;
}
//http://www.baidu.com 确保完整路径的基地址
// Ensure terminal slash for baseURL path, so that NSURL +URLWithString:relativeToURL: works as expected
if ([[url path] length] > 0 && ![[url absoluteString] hasSuffix:@"/"]) {
url = [url URLByAppendingPathComponent:@""];
}
self.baseURL = url;
//请求和响应序列化工具
self.requestSerializer = [AFHTTPRequestSerializer serializer];
self.responseSerializer = [AFJSONResponseSerializer serializer];
return self;
}
这里设置了一个requestSerializer和responseSerializer,这两个类的作用是设置请求头、响应头相关的信息，主要用于传输不同类型的文件并设置不同的contentType等等,我们进入requestSerializer看下源码看具体做了什么:
- (instancetype)init {
self = [super init];
if (!self) {
return nil;
}
//编码
self.stringEncoding = NSUTF8StringEncoding;
//设置请求头
self.mutableHTTPRequestHeaders = [NSMutableDictionary dictionary];
// Accept-Language HTTP Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.4
NSMutableArray *acceptLanguagesComponents = [NSMutableArray array];
[[NSLocale preferredLanguages] enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
float q = 1.0f - (idx * 0.1f);
[acceptLanguagesComponents addObject:[NSString stringWithFormat:@"%@;q=%0.1g", obj, q]];
*stop = q <= 0.5f;
}];
//服务器接收语言
[self setValue:[acceptLanguagesComponents componentsJoinedByString:@", "] forHTTPHeaderField:@"Accept-Language"];
//用户代理
NSString *userAgent = nil;
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wgnu"
#if TARGET_OS_IOS
//获取请求设备的相关信息 用户代理
// User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
userAgent = [NSString stringWithFormat:@"%@/%@ (%@; iOS %@; Scale/%0.2f)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[UIDevice currentDevice] model], [[UIDevice currentDevice] systemVersion], [[UIScreen mainScreen] scale]];
#elif TARGET_OS_WATCH
// User-Agent Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.43
userAgent = [NSString stringWithFormat:@"%@/%@ (%@; watchOS %@; Scale/%0.2f)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[WKInterfaceDevice currentDevice] model], [[WKInterfaceDevice currentDevice] systemVersion], [[WKInterfaceDevice currentDevice] screenScale]];
#elif defined(__MAC_OS_X_VERSION_MIN_REQUIRED)
userAgent = [NSString stringWithFormat:@"%@/%@ (Mac OS X %@)", [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleExecutableKey] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleIdentifierKey], [[NSBundle mainBundle] infoDictionary][@"CFBundleShortVersionString"] ?: [[NSBundle mainBundle] infoDictionary][(__bridge NSString *)kCFBundleVersionKey], [[NSProcessInfo processInfo] operatingSystemVersionString]];
#endif
#pragma clang diagnostic pop
if (userAgent) {
if (![userAgent canBeConvertedToEncoding:NSASCIIStringEncoding]) {
NSMutableString *mutableUserAgent = [userAgent mutableCopy];
if (CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII; [:^ASCII:] Remove", false)) {
userAgent = mutableUserAgent;
}
}
[self setValue:userAgent forHTTPHeaderField:@"User-Agent"];
}
// HTTP Method Definitions; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec9.html
self.HTTPMethodsEncodingParametersInURI = [NSSet setWithObjects:@"GET", @"HEAD", @"DELETE", nil];
self.mutableObservedChangedKeyPaths = [NSMutableSet set];
for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
if ([self respondsToSelector:NSSelectorFromString(keyPath)]) {
[self addObserver:self forKeyPath:keyPath options:NSKeyValueObservingOptionNew context:AFHTTPRequestSerializerObserverContext];
}
}
return self;
}
这些信息主要是和后台人员沟通确定的，比如一般的后台请求，我们要设置AcceptableContentType为applicaiont/json，注明接受类型是已经被后台人员转好的json，在回调中我们就可以直接获取到json数据，而不用去进行转换, 有的时候，我们在勤奋求的时候，报错"Request failed: unacceptable content-type",就需要在请求头的contentype列表里面添加一些指定的contentType.
其次就是主体的请求代码：
[httpClient POST:@""
parameters:@{}
success:^(NSURLSessionDataTask * _Nonnull task, id _Nullable responseObject) {
//获取responseObject的数据，在主线程做UI刷新操作
} failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
}];
我们点进去看看,可以看到所有的请求方法都是基于下面这个方法来构建的：
/**
构建网络请求:所有请求(POST、GET、DELETE、PATCH、HEAD)都基于这个方法来构建起来的
@param method POST、GET、DELETE、PATCH、HEAD
@param URLString 请求地址
@param parameters 请求参数
@param uploadProgress 上传进度回调
@param downloadProgress 下载进度列表
@param success 成功回调
@param failure 失败回调
@return NSURLSessionDataTask网络请求
*/
- (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
我们重点来分析下这个方法里面的代码:
// 根据请求地址、方法、参数构建网络请求NSMutableURLRequest
NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
这里使用了requestSerializer 的私有方法 method、params来构建了一个NSMutableURLRequest,并设置了请求体，请求头信息等等:代码如下:
- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
withParameters:(id)parameters
error:(NSError *__autoreleasing *)error
{
NSParameterAssert(request);
NSMutableURLRequest *mutableRequest = [request mutableCopy];
///设置请求头信息
[self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
if (![request valueForHTTPHeaderField:field]) {
[mutableRequest setValue:value forHTTPHeaderField:field];
}
}];
NSString *query = nil;
if (parameters) {
if (self.queryStringSerialization) {
NSError *serializationError;
query = self.queryStringSerialization(request, parameters, &serializationError);
if (serializationError) {
if (error) {
*error = serializationError;
}
return nil;
}
} else {
switch (self.queryStringSerializationStyle) {
case AFHTTPRequestQueryStringDefaultStyle:
query = AFQueryStringFromParameters(parameters);
break;
}
}
}
//判断是否是GET/HEAD/DELETE方法， 对于GET/HEAD/DELETE方法，把参数加到URL后面,这也就是GET请求里面的参数会暴露在请求地址里面
if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {
if (query) {
mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];
}
} else {
// #2864: an empty string is a valid x-www-form-urlencoded payload
//一般用于POST请求
if (!query) {
query = @"";
}
///设置Content-Type HTTP头，告诉服务端body的参数编码类型
if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
[mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];
}
//设置请求体信息 将json字符串转化为NSData类型
[mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];
}
return mutableRequest;
}
接下来的就是构架一个NSURLSessionDataTask:
__block NSURLSessionDataTask *dataTask = nil;
dataTask = [self dataTaskWithRequest:request
uploadProgress:uploadProgress
downloadProgress:downloadProgress
completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {
//成功失败回调
if (error) {
if (failure) {
failure(dataTask, error);
}
} else {
if (success) {
success(dataTask, responseObject);
}
}
}]; //使用这个方法构建的task 需要手动resume 才会启动任务
///使用NSURLSession和NSURLSessionDataTask请求数据
- (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(^{
//这里使用了NSURLSession来实例化一个dataTask
dataTask = [self.session dataTaskWithRequest:request];
});
//为task添加代理来传输数据等相关信息
[self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];
return dataTask;
}
///给NSURLSessionDataTask对象实例设置Delegate。用于实时了解网络请求
- (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] init];
delegate.manager = self;
delegate.completionHandler = completionHandler;
dataTask.taskDescription = self.taskDescriptionForSessionTasks;
//为dataTask设置代理来接受并处理数据
[self setDelegate:delegate forTask:dataTask];
delegate.uploadProgressBlock = uploadProgressBlock;
delegate.downloadProgressBlock = downloadProgressBlock;
}
- (void)setDelegate:(AFURLSessionManagerTaskDelegate *)delegate
forTask:(NSURLSessionTask *)task
{
NSParameterAssert(task);
NSParameterAssert(delegate);
//加锁 避免同时修改数据，造成线程安全问题
[self.lock lock];
self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
[delegate setupProgressForTask:task];
[self addNotificationObserverForTask:task];
[self.lock unlock];
}
///这里使用KVO监测task的请求过程
- (void)setupProgressForTask:(NSURLSessionTask *)task {
__weak __typeof__(task) weakTask = task;
self.uploadProgress.totalUnitCount = task.countOfBytesExpectedToSend;
self.downloadProgress.totalUnitCount = task.countOfBytesExpectedToReceive;
[self.uploadProgress setCancellable:YES];
[self.uploadProgress setCancellationHandler:^{
__typeof__(weakTask) strongTask = weakTask;
[strongTask cancel];
}];
[self.uploadProgress setPausable:YES];
[self.uploadProgress setPausingHandler:^{
__typeof__(weakTask) strongTask = weakTask;
[strongTask suspend];
}];
if ([self.uploadProgress respondsToSelector:@selector(setResumingHandler:)]) {
[self.uploadProgress setResumingHandler:^{
__typeof__(weakTask) strongTask = weakTask;
[strongTask resume];
}];
}
[self.downloadProgress setCancellable:YES];
[self.downloadProgress setCancellationHandler:^{
__typeof__(weakTask) strongTask = weakTask;
[strongTask cancel];
}];
[self.downloadProgress setPausable:YES];
[self.downloadProgress setPausingHandler:^{
__typeof__(weakTask) strongTask = weakTask;
[strongTask suspend];
}];
if ([self.downloadProgress respondsToSelector:@selector(setResumingHandler:)]) {
[self.downloadProgress setResumingHandler:^{
__typeof__(weakTask) strongTask = weakTask;
[strongTask resume];
}];
}
[task addObserver:self
forKeyPath:NSStringFromSelector(@selector(countOfBytesReceived))
options:NSKeyValueObservingOptionNew
context:NULL];
[task addObserver:self
forKeyPath:NSStringFromSelector(@selector(countOfBytesExpectedToReceive))
options:NSKeyValueObservingOptionNew
context:NULL];
[task addObserver:self
forKeyPath:NSStringFromSelector(@selector(countOfBytesSent))
options:NSKeyValueObservingOptionNew
context:NULL];
[task addObserver:self
forKeyPath:NSStringFromSelector(@selector(countOfBytesExpectedToSend))
options:NSKeyValueObservingOptionNew
context:NULL];
[self.downloadProgress addObserver:self
forKeyPath:NSStringFromSelector(@selector(fractionCompleted))
options:NSKeyValueObservingOptionNew
context:NULL];
[self.uploadProgress addObserver:self
forKeyPath:NSStringFromSelector(@selector(fractionCompleted))
options:NSKeyValueObservingOptionNew
context:NULL];
}
//监听下载和上传任务的数据并回调
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
if ([object isKindOfClass:[NSURLSessionTask class]]) {
if ([keyPath isEqualToString:NSStringFromSelector(@selector(countOfBytesReceived))]) {
self.downloadProgress.completedUnitCount = [change[@"new"] longLongValue];
} else if ([keyPath isEqualToString:NSStringFromSelector(@selector(countOfBytesExpectedToReceive))]) {
self.downloadProgress.totalUnitCount = [change[@"new"] longLongValue];
} else if ([keyPath isEqualToString:NSStringFromSelector(@selector(countOfBytesSent))]) {
self.uploadProgress.completedUnitCount = [change[@"new"] longLongValue];
} else if ([keyPath isEqualToString:NSStringFromSelector(@selector(countOfBytesExpectedToSend))]) {
self.uploadProgress.totalUnitCount = [change[@"new"] longLongValue];
}
}
else if ([object isEqual:self.downloadProgress]) {
//下载回调
if (self.downloadProgressBlock) {
self.downloadProgressBlock(object);
}
}
else if ([object isEqual:self.uploadProgress]) {
if (self.uploadProgressBlock) {
//上传回调
self.uploadProgressBlock(object);
}
}
}
- (void)URLSession:(NSURLSession *)session
dataTask:(NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data {
//获取NSURLSessionDataTask代理对象
AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:dataTask];
//试用delegate追加数据
[delegate URLSession:session dataTask:dataTask didReceiveData:data];
//数据接受回调
if (self.dataTaskDidReceiveData) {
self.dataTaskDidReceiveData(session, dataTask, data);
}
}
//接收数据
- (void)URLSession:(__unused NSURLSession *)session
dataTask:(__unused NSURLSessionDataTask *)dataTask
didReceiveData:(NSData *)data
{
[self.mutableData appendData:data];
}
@interface AFURLSessionManagerTaskDelegate : NSObject
AFURLSessionManagerTaskDelegate接管了NSURLSessionTaskDelegate, NSURLSessionDataDelegate, NSURLSessionDownloadDelegate的各种回调，然后做内部数据处理，。这也是第三方网络请求框架的重点，让网络请求更加易用，好用。
当然，由于本人技术有限，很多东西没理解透彻，如果有错误之处，欢迎大家指正，共同进步,后续的深入理解会继续写文章大家一起谈论,如果亲觉着这篇文章对于理解AFN有帮助的话，请下方点赞，谢谢!
-------作者:mrChan1234