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AFNetworking源码分析

西特张 2021-09-19 阅读 20
iOS面试

一、概述


从上图可以发现,AFNetworking框架的结构比较清晰简洁,主要范围5个部分:

  • 网络通信模块:URLSession
  • 网络状态监听模块:Reachability
  • 网络通信安全模块:Security
  • 网络通信序列化模块:Serialization
  • 对UIKit框架扩展部分:UIKit(以Catagory形式添加特性)
    AFNetworking的核心是AFURLSessionManager类,这个类基于NSURLSession,围绕NSURLSession做了一系列的封装,其余的四个类都是该类用于网络通信的一个属性或对已有UIKit的一个扩展工具包。
    其中AFHTTPSessionManager类是继承于AFURLSessionManager的,我们使用AFNetworking时,都是用AFHTTPSessionManager,但它本身没有做实事的,只是做了一些简单的封装,把请求逻辑分发给父类AFURLSessionManager

二、AFNetworking使用

例子:

AFHTTPSessionManager *session = [AFHTTPSessionManager manager];
session.responseSerializer.acceptableContentTypes = [NSSet setWithObjects:@"text/html",@"application/json", @"text/json" ,@"text/javascript", nil];
session.responseSerializer = [AFHTTPResponseSerializer serializer];
[session GET:@"https://www.baidu.com"
  parameters:nil
     headers:nil
    progress:nil
     success:^(NSURLSessionDataTask * _Nonnull task, id  _Nullable responseObject) {
         NSLog(@"请求成功");
     } failure:^(NSURLSessionDataTask * _Nullable task, NSError * _Nonnull error) {
          NSLog(@"请求失败");
     }];

三、AFNetworking使用的代码分析

3.1 [AFHTTPSessionManager manager]


AFHTTPSessionManager manage的实现

+ (instancetype)manager {
    return [[[self class] alloc] initWithBaseURL:nil];
}

- (instancetype)init {
    return [self initWithBaseURL:nil];
}

- (instancetype)initWithBaseURL:(NSURL *)url {
    return [self initWithBaseURL:url sessionConfiguration:nil];
}

- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
    return [self initWithBaseURL:nil sessionConfiguration:configuration];
}

- (instancetype)initWithBaseURL:(NSURL *)url sessionConfiguration:(NSURLSessionConfiguration *)configuration {
    self = [super initWithSessionConfiguration:configuration];
    if (!self) {
        return nil;
    }
    
    if ([[url path] length] > 0 && ![[url absoluteString] hasSuffix:@"/"]) {
        url = [url URLByAppendingPathComponent:@""];
    }
    
    self.baseURL = url;
    
    self.requestSerializer = [AFHTTPRequestSerializer serializer];
    self.responseSerializer = [AFJSONResponseSerializer serializer];
    
    return self;
}

进入到AFURLSessionManager- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration方法中分析

- (instancetype)initWithSessionConfiguration:(NSURLSessionConfiguration *)configuration {
    self = [super init];
    if (!self) {
        return nil;
    }

    if (!configuration) {
        configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    }
// 1. 设置全局的网络行为策略的配置
    self.sessionConfiguration = configuration;
// 2. 设置请求的队列,默认最大的并发数为1
    self.operationQueue = [[NSOperationQueue alloc] init];
// (1)这里的并发数指的是回调代理的线程并发数,而不是请求网络的线程并发数。请求网络是由NSURLSession来做的,它内部维护了一个线程池用来做网络请求。NSURLSession调度线程是基于底层的CFSocket去发送请求和接收数据,这些线程是并发的。
// (2)AF2.x所有回调是在一条线程,这条线程是AF的常驻线程,而这一条线程正式AF调度request的思想精髓所在。所以线程数设置为1的第一个目的是和之前版本保持一致;
// (3)因为跟代理相关的一些操作AF都使用了NSLock,所以Queue的并发数设置为n,也会因为多线程回调、锁的等待,导致提升的程序速度并不明显,反而多task回调导致的多线程并发,平白浪费了部分性能。至少回调的事件,是不需要多线程并发的,回调没有了NSLock的等待事件,所以对事件并没有多大影响。
    self.operationQueue.maxConcurrentOperationCount = 1;
// 3. 设置网络请求响应的数据解析实例
    self.responseSerializer = [AFJSONResponseSerializer serializer];
// 4. 设置网络请求安全策略实例(后续说明该实例)
    self.securityPolicy = [AFSecurityPolicy defaultPolicy];
// 5. 初始化全局的网络状态监听的实例
#if !TARGET_OS_WATCH
    self.reachabilityManager = [AFNetworkReachabilityManager sharedManager];
#endif
// 6. 将taskID与其Delegate绑定,实现解耦(后续进行分析)
    self.mutableTaskDelegatesKeyedByTaskIdentifier = [[NSMutableDictionary alloc] init];

    self.lock = [[NSLock alloc] init];
    self.lock.name = AFURLSessionManagerLockName;
// 7. self.session采用懒加载,根据configuration,operationQueue初始化全局的NSURLSession
    [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;
}

- (NSURLSession *)session {
    
    @synchronized (self) {
        if (!_session) {
            _session = [NSURLSession sessionWithConfiguration:self.sessionConfiguration delegate:self delegateQueue:self.operationQueue];
        }
    }
    return _session;
}

3.2 NSURLSessionConfiguration 全局的网络行为策略的配置

简单罗列以下两点:
1.NSURLSessionConfiguration可以控制网络请求中的缓存策略,超时设置等;
2.如果需要改变网络请求的行为策略,必须重新在更改NSURLSessionConfiguration后再创建一个新的NSURLSession。

3.3 AFHTTPSessionManager GET: parameters: headers: progress: success: failure: 方法

3.3.1 NSURLSessionTask

这里引入了一个新的类:NSURLSessionDataTaskNSURLSessionDataTask继承了NSURLSessionTask。** NSURLSessionTask**的官方说明:

简单罗列以下两点:
1.NSURLSessionTask是官方提供的几种网络任务类的基类;
2.官方提供了三种任务处理的子类:简单数据处理任务类、上传任务类和下载任务类。

3.3.2 AFHTTPSessionManager dataTaskWithHTTPMethod:...方法实现与分析

- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
                                       URLString:(NSString *)URLString
                                      parameters:(id)parameters
                                         headers:(NSDictionary<NSString *,NSString *> *)headers
                                  uploadProgress:(void (^)(NSProgress * _Nonnull))uploadProgress
                                downloadProgress:(void (^)(NSProgress * _Nonnull))downloadProgress
                                         success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
                                         failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure {
    NSError *serializationError = nil;
// 1.通过全局配置的requestSerializer初始化一个请求的实例
    NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];

    for (NSString *headerField in headers.keyEnumerator) {
        [request setValue:headers[headerField] forKey:headerField];
    }
    
    if (serializationError) {
        if (failure) {
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
        }
        return nil;
    }
    
    // 2.根据请求的实例再初始化一个task的实例
    __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;
}

3.3.3 [AFURLSessionManager addDelegateForDataTask:...]方法,用于task与delegate的绑定

// 1. 根据请求信息初始化一个task实例
- (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 {

    NSURLSessionDataTask *dataTask = [self.session dataTaskWithRequest:request];

    [self addDelegateForDataTask:dataTask uploadProgress:uploadProgressBlock downloadProgress:downloadProgressBlock completionHandler:completionHandler];

    return dataTask;
}


- (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
{
// 2.初始化一个任务的代理
    AFURLSessionManagerTaskDelegate *delegate = [[AFURLSessionManagerTaskDelegate alloc] initWithTask:dataTask];
    delegate.manager = self;

// 此处赋值了请求完成的回调,后续会用到
    delegate.completionHandler = completionHandler;
// 3.利用全局的字典存储绑定信息,key为taskID,value为代理的实例。
    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);

    [self.lock lock];
// 1.绑定taskID与代理self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
// 2.使用KVO对一些方法监听,返回上传或下载的进度
    self.mutableTaskDelegatesKeyedByTaskIdentifier[@(task.taskIdentifier)] = delegate;
    [self addNotificationObserverForTask:task];
    [self.lock unlock];
}

3.3.4 NSURLSessionTaskDelegate协议中的URLSession:task:didCompleteWithError:方法

NSURLSessionTaskDelegate协议包含NSURLSessionDelegate协议
当请求收到了响应后,会触发- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(nullable NSError *)error;回调(AFURLSessionManager的session属性懒加载时,设置了delegate为self,会触发该代理的方法),以下是方法中的具体处理。

// AFURLSessionManager.m中NSURLSessionTaskDelegate方法的实现,该方法由系统自动触发
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error {
// 1.根据task获取绑定的代理实例
    AFURLSessionManagerTaskDelegate *delegate = [self delegateForTask:task];

    // delegate may be nil when completing a task in the background
    if (delegate) {
// 2.统一处理,调用AFURLSessionManagerTaskDelegate的同名方法。
        [delegate URLSession:session task:task didCompleteWithError:error];

        [self removeDelegateForTask:task];
    }

    if (self.taskDidComplete) {
        self.taskDidComplete(session, task, error);
    }
}

// AFURLSessionManagerTaskDelegate.m中NSURLSessionTaskDelegate方法的实现,该方法在AFURLSessionManager中通过delegate调用。
- (void)URLSession:(__unused NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    error = objc_getAssociatedObject(task, AuthenticationChallengeErrorKey) ?: error;
    __strong AFURLSessionManager *manager = self.manager;

    __block id responseObject = nil;

    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 AF_CAN_USE_AT_AVAILABLE && AF_CAN_INCLUDE_SESSION_TASK_METRICS
    if (@available(iOS 10, macOS 10.12, watchOS 3, tvOS 10, *)) {
        if (self.sessionTaskMetrics) {
            userInfo[AFNetworkingTaskDidCompleteSessionTaskMetrics] = self.sessionTaskMetrics;
        }
    }
#endif

    if (self.downloadFileURL) {
        userInfo[AFNetworkingTaskDidCompleteAssetPathKey] = self.downloadFileURL;
    } else if (data) {
        userInfo[AFNetworkingTaskDidCompleteResponseDataKey] = data;
    }

    if (error) {
// 1.iOS网络框架返回的错误信息处理
        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 {
// 2.请求成功后需要用响应的数据解析类的responseSerializer实例处理返回的数据
// 数据通过NSURLSessionDataDelegate协议的- (void)URLSession:(__unused NSURLSession *)session dataTask:(__unused NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data方法返回
        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(), ^{
// 3.绑定task与处理的数据代理时,传入代理的完成的回调
                if (self.completionHandler) {
                    self.completionHandler(task.response, responseObject, serializationError);
                }

                dispatch_async(dispatch_get_main_queue(), ^{
                    [[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];
                });
            });
        });
    }
}

参考来源:
https://toutiao.io/posts/dibcw7/preview
https://www.cnblogs.com/ederwin/articles/10592839.html

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