AFNetworking源码学习

简介

AFNetWorking是使用Objective-c开发iOS程序主流的网络请求开源库。

AFNetworking组织结构

AFNetWorking主要分为5个部分。NSURLSession、Reachability、security、Serialization、UIKit。其中NSURLSession是整个网络请求开源库的灵魂，对外提供了丰富的网络请求接口。包括GET、POST、HEAD、PUT、DELETE，与及文件上传的接口。
整个AFNetWorking组织结构如下：

源码解读

1.NSURLSession

NSURLSession包括AFURLSessionManager和AFHTTPSessionManager，AFHTTPSessionManager继承了AFURLSessionManager，对外提供了网络请求的接口。我们最常使用的GET、POST接口，底层都调用了

- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)methodURLString:(NSString *)URLStringparameters:(id)parametersuploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressdownloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgresssuccess:(void (^)(NSURLSessionDataTask *, id))successfailure:(void (^)(NSURLSessionDataTask *, NSError *))failure

整个方法的实现如下：

- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)methodURLString:(NSString *)URLStringparameters:(id)parametersuploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressdownloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgresssuccess:(void (^)(NSURLSessionDataTask *, id))successfailure:(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:requestuploadProgress:uploadProgressdownloadProgress:downloadProgresscompletionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {if (error) {if (failure) {failure(dataTask, error);}} else {if (success) {success(dataTask, responseObject);}}}];return dataTask;
}

文件上传的接口例外，文件上传涉及到数据分片的问题，使用的是一个叫

- (NSURLSessionDataTask *)POST:(NSString *)URLStringparameters:(id)parametersconstructingBodyWithBlock:(void (^)(id <AFMultipartFormData> formData))blockprogress:(nullable void (^)(NSProgress * _Nonnull))uploadProgresssuccess:(void (^)(NSURLSessionDataTask *task, id responseObject))successfailure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure

接口，这个接口的全部实现如下：

- (NSURLSessionDataTask *)POST:(NSString *)URLStringparameters:(id)parametersconstructingBodyWithBlock:(void (^)(id <AFMultipartFormData> formData))blockprogress:(nullable void (^)(NSProgress * _Nonnull))uploadProgresssuccess:(void (^)(NSURLSessionDataTask *task, id responseObject))successfailure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{NSError *serializationError = nil;NSMutableURLRequest *request = [self.requestSerializer multipartFormRequestWithMethod:@"POST" URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters constructingBodyWithBlock:block error:&serializationError];if (serializationError) {if (failure) {dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{failure(nil, serializationError);});}return nil;}__block NSURLSessionDataTask *task = [self uploadTaskWithStreamedRequest:request progress:uploadProgress completionHandler:^(NSURLResponse * __unused response, id responseObject, NSError *error) {if (error) {if (failure) {failure(task, error);}} else {if (success) {success(task, responseObject);}}}];[task resume];return task;
}

AFURLSessionManager

AFURLSessionManager是整个网络请求框架的核心。
创建了url_session_manager_creation_queue、url_session_manager_processing_queue、
url_session_manager_completion_group，这三个都是单例的形式。
AFURLSessionManager是以串行队列的方式进行session管理的。安全策略使用的是默认策略。

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)requestuploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgressBlockdownloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgressBlockcompletionHandler:(nullable void (^)(NSURLResponse *response, id _Nullable responseObject,  NSError * _Nullable error))completionHandler

以安全的方式，创建了一个dataTask，最后加入到mutableTask的NSMutableDictionary中。
AFURLSessionManager是AFHTTPSessionManager的基础，对AFHTTPSessionManager提供了downloadTask、uploadTask、dataTask等等的封装。

2.AFNetworkReachabilityManager

AFNetworkReachabilityManager监测网络状态。方法如下：

static AFNetworkReachabilityStatus AFNetworkReachabilityStatusForFlags(SCNetworkReachabilityFlags flags) {BOOL isReachable = ((flags & kSCNetworkReachabilityFlagsReachable) != 0);BOOL needsConnection = ((flags & kSCNetworkReachabilityFlagsConnectionRequired) != 0);BOOL canConnectionAutomatically = (((flags & kSCNetworkReachabilityFlagsConnectionOnDemand ) != 0) || ((flags & kSCNetworkReachabilityFlagsConnectionOnTraffic) != 0));BOOL canConnectWithoutUserInteraction = (canConnectionAutomatically && (flags & kSCNetworkReachabilityFlagsInterventionRequired) == 0);BOOL isNetworkReachable = (isReachable && (!needsConnection || canConnectWithoutUserInteraction));AFNetworkReachabilityStatus status = AFNetworkReachabilityStatusUnknown;if (isNetworkReachable == NO) {status = AFNetworkReachabilityStatusNotReachable;}
#if    TARGET_OS_IPHONEelse if ((flags & kSCNetworkReachabilityFlagsIsWWAN) != 0) {status = AFNetworkReachabilityStatusReachableViaWWAN;}
#endifelse {status = AFNetworkReachabilityStatusReachableViaWiFi;}return status;
}

根据传入的SCNetworkReachabilityFlags标志进行判断，返回对应的网络状态。

3.AFSecurityPolicy

AFSecurityPolicy，网络请求的安全策略。该类提供了三种安全策略：

typedef NS_ENUM(NSUInteger, AFSSLPinningMode) {AFSSLPinningModeNone,AFSSLPinningModePublicKey,AFSSLPinningModeCertificate,
};

默认的安全策略是AFSSLPinningModeNone，我们可以根据需要设置对应的安全策略。
开发中实际的设置栗子如下：

- (void)setupSecurityPolicy {AFSecurityPolicy *securityPolicy = [AFSecurityPolicy policyWithPinningMode:AFSSLPinningModePublicKey];[securityPolicy setAllowInvalidCertificates:YES];[securityPolicy setValidatesDomainName:YES];self.sessionManager.securityPolicy = securityPolicy;
}

我们当时使用的是SSL对传输的数据进行加密，来达到数据的安全传输。

4.AFURLRequestSerialization

里面是对客户端发起的请求的序列化。

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)requestwithParameters:(id)parameterserror:(NSError *__autoreleasing *)error
{NSParameterAssert(request);NSMutableURLRequest *mutableRequest = [request mutableCopy];[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;}}}if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {if (query && query.length > 0) {mutableRequest.URL = [NSURL URLWithString:[[mutableRequest.URL absoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];}} else {// #2864: an empty string is a valid x-www-form-urlencoded payloadif (!query) {query = @"";}if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {[mutableRequest setValue:@"application/x-www-form-urlencoded" forHTTPHeaderField:@"Content-Type"];}[mutableRequest setHTTPBody:[query dataUsingEncoding:self.stringEncoding]];}return mutableRequest;
}

对请求参数进行拼接，序列化，设置request的Content-Type，然后把序列化后的参数设置到HTTPBody中。
还有对应的序列化类AFJSONRequestSerializer & AFPropertyListRequestSerializer，可以把请求参数根据Content-Type序列化成application/json或者application/x-plist格式。

5.AFURLResponseSerialization

response序列化就是把响应数据使用数据解析器解析成对应的格式。AFURLResponseSerialization提供的解析器有：

AFJSONResponseSerializer -> application/json/text/json/text/javascript
AFXMLParserResponseSerializer -> application/xml/text/xml
AFPropertyListResponseSerializer -> application/x-plist
AFImageResponseSerializer -> image/jpeg/image/gif/image/png，这三种是常用的，还有其他好几种，可以到源码中查看。
AFCompoundResponseSerializer 合成解析器，是上面几种的集合。