你要知道的NSURLSession都在这里

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本系列文章主要讲解iOS中网络请求类NSURLSession的使用方法进行详解，同时也会以此为扩展，讲解SDWebImage中图片下载功能的源码分析，讲解AFNetworking相关源码分析。本系列文章主要分为以下几篇进行讲解，读者可按需查阅。

• iOS网络——NSURLSession详解及SDWebImage源码解析
• iOS网络——SDWebImage SDImageDownloader源码解析
• iOS网络——AFNetworking AFURLSessionManager源码解析
• iOS网络——AFNetworking AFHttpSessionManager源码解析

AFNetworking AFHTTPSessionManager源码解析

前一篇文章我们讲解了AFURLSessionManager的源码，最后还给了一个只使用AFURLSessionManager来创建NSURLSessionDataTask和NSURLSessionDownloadTask的栗子，但是发现创建下载任务真的很简单了，只需要传入要下载文件的NSURL对象，在传入几个回调块就能将文件下载到指定的目录中，并且可以监控下载进度，真的很方便，但NSURLSessionDataTask创建的任务默认是GET请求，如果需要其他如POST请求还需要修改request就显得有些麻烦了，今天要介绍的AFHTTPSessionManager就是继承自AFURLSessionManager，通过名称就知道这个类为HTTP访问提供了更加便捷的方法。

直接看头文件的声明源码:

//继承自AFURLSessionManager类
@interface AFHTTPSessionManager : AFURLSessionManager <NSSecureCoding, NSCopying>

//网络请求要访问的URL
@property (readonly, nonatomic, strong, nullable) NSURL *baseURL;

//请求序列化
@property (nonatomic, strong) AFHTTPRequestSerializer <AFURLRequestSerialization> * requestSerializer;

//响应序列化
@property (nonatomic, strong) AFHTTPResponseSerializer <AFURLResponseSerialization> * responseSerializer;

///-------------------------------
/// @name Managing Security Policy
///-------------------------------

//安全策略
@property (nonatomic, strong) AFSecurityPolicy *securityPolicy;

///---------------------
/// @name Initialization
///---------------------

//类方法返回一个AFHTTPSessionManager对象，不是单例，每次调用都重新创建
+ (instancetype)manager;

//构造函数
- (instancetype)initWithBaseURL:(nullable NSURL *)url;

//构造函数
- (instancetype)initWithBaseURL:(nullable NSURL *)url
           sessionConfiguration:(nullable NSURLSessionConfiguration *)configuration NS_DESIGNATED_INITIALIZER;

///---------------------------
/// @name Making HTTP Requests
///---------------------------

//获取一个GET请求
- (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;


//获取一个GET请求
- (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;

//获取一个HEAD请求
- (nullable NSURLSessionDataTask *)HEAD:(NSString *)URLString
                    parameters:(nullable id)parameters
                       success:(nullable void (^)(NSURLSessionDataTask *task))success
                       failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;

//获取一个POST请求
- (nullable NSURLSessionDataTask *)POST:(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;

//获取一个POST请求
- (nullable NSURLSessionDataTask *)POST:(NSString *)URLString
                             parameters:(nullable id)parameters
                               progress:(nullable void (^)(NSProgress *uploadProgress))uploadProgress
                                success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                                failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;

//获取一个POST请求
- (nullable NSURLSessionDataTask *)POST:(NSString *)URLString
                    parameters:(nullable id)parameters
     constructingBodyWithBlock:(nullable void (^)(id <AFMultipartFormData> formData))block
                       success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                       failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure DEPRECATED_ATTRIBUTE;

//获取一个POST请求
- (nullable NSURLSessionDataTask *)POST:(NSString *)URLString
                             parameters:(nullable id)parameters
              constructingBodyWithBlock:(nullable void (^)(id <AFMultipartFormData> formData))block
                               progress:(nullable void (^)(NSProgress *uploadProgress))uploadProgress
                                success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                                failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;

//获取一个PUT请求
- (nullable NSURLSessionDataTask *)PUT:(NSString *)URLString
                   parameters:(nullable id)parameters
                      success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                      failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;

//获取一个PATCH请求
- (nullable NSURLSessionDataTask *)PATCH:(NSString *)URLString
                     parameters:(nullable id)parameters
                        success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                        failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;

//获取一个DELETE请求
- (nullable NSURLSessionDataTask *)DELETE:(NSString *)URLString
                      parameters:(nullable id)parameters
                         success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                         failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure;

@end

AFHTTPSessionManager提供了一系列的构造方法以及HTTP访问的方法。

@interface AFHTTPSessionManager ()
@property (readwrite, nonatomic, strong) NSURL *baseURL;
@end

@implementation AFHTTPSessionManager
@dynamic responseSerializer;

//类方法，返回一个新创建的AFHTTPSessionManager对象
+ (instancetype)manager {
    return [[[self class] alloc] initWithBaseURL:nil];
}

//构造函数
- (instancetype)init {
    return [self initWithBaseURL:nil];
}

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

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

//构造函数
- (instancetype)initWithBaseURL:(NSURL *)url
           sessionConfiguration:(NSURLSessionConfiguration *)configuration
{
    //调用父类的构造函数
    self = [super initWithSessionConfiguration:configuration];
    if (!self) {
        return nil;
    }

    // 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;
    //获取单例的请求序列化和响应序列化器
    self.requestSerializer = [AFHTTPRequestSerializer serializer];
    self.responseSerializer = [AFJSONResponseSerializer serializer];

    return self;
}

#pragma mark -

//setter
- (void)setRequestSerializer:(AFHTTPRequestSerializer <AFURLRequestSerialization> *)requestSerializer {
    NSParameterAssert(requestSerializer);

    _requestSerializer = requestSerializer;
}

//setter
- (void)setResponseSerializer:(AFHTTPResponseSerializer <AFURLResponseSerialization> *)responseSerializer {
    NSParameterAssert(responseSerializer);

    [super setResponseSerializer:responseSerializer];
}

@dynamic securityPolicy;

//setter设置安全策略
- (void)setSecurityPolicy:(AFSecurityPolicy *)securityPolicy {
    if (securityPolicy.SSLPinningMode != AFSSLPinningModeNone && ![self.baseURL.scheme isEqualToString:@"https"]) {
        NSString *pinningMode = @"Unknown Pinning Mode";
        switch (securityPolicy.SSLPinningMode) {
            case AFSSLPinningModeNone:        pinningMode = @"AFSSLPinningModeNone"; break;
            case AFSSLPinningModeCertificate: pinningMode = @"AFSSLPinningModeCertificate"; break;
            case AFSSLPinningModePublicKey:   pinningMode = @"AFSSLPinningModePublicKey"; break;
        }
        NSString *reason = [NSString stringWithFormat:@"A security policy configured with `%@` can only be applied on a manager with a secure base URL (i.e. https)", pinningMode];
        @throw [NSException exceptionWithName:@"Invalid Security Policy" reason:reason userInfo:nil];
    }

    [super setSecurityPolicy:securityPolicy];
}

上面的方法就是一系列构造函数，用于初始化父类对象以及序列化器，设置安全策略等，没有太多复杂的内容。

//GET请求，调用下面那个方法
- (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];
}

//GET请求
- (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
{
    //调用另一个方法构造GET请求
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"GET"
                                                        URLString:URLString
                                                       parameters:parameters
                                                   uploadProgress:nil
                                                 downloadProgress:downloadProgress
                                                          success:success
                                                          failure:failure];
    
    /*
    启动任务
    使用AFHTTPSessionManager创建的任务默认都帮你启动了，所以不需要手动调用resume方法了
    上一篇中讲解的AFURLSessionManager默认没有启动，所以获取任务后要手动启动
    */
    [dataTask resume];

    return dataTask;
}
//获取HEAD请求
- (NSURLSessionDataTask *)HEAD:(NSString *)URLString
                    parameters:(id)parameters
                       success:(void (^)(NSURLSessionDataTask *task))success
                       failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
    //同样调用下面的一个方法来获取
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"HEAD" URLString:URLString parameters:parameters uploadProgress:nil downloadProgress:nil success:^(NSURLSessionDataTask *task, __unused id responseObject) {
        if (success) {
            success(task);
        }
    } failure:failure];
    
    //默认启动任务
    [dataTask resume];

    return dataTask;
}
//获取POST请求
- (NSURLSessionDataTask *)POST:(NSString *)URLString
                    parameters:(id)parameters
                       success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                       failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
    //调用下面的方法获取
    return [self POST:URLString parameters:parameters progress:nil success:success failure:failure];
}

//获取POST请求
- (NSURLSessionDataTask *)POST:(NSString *)URLString
                    parameters:(id)parameters
                      progress:(void (^)(NSProgress * _Nonnull))uploadProgress
                       success:(void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
                       failure:(void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
{
    //同GET HEAD方法一样，调用一个方法获取任务
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"POST" URLString:URLString parameters:parameters uploadProgress:uploadProgress downloadProgress:nil success:success failure:failure];
    //默认启动任务
    [dataTask resume];

    return dataTask;
}

//获取POST上传文件请求
- (NSURLSessionDataTask *)POST:(NSString *)URLString
                    parameters:(nullable id)parameters
     constructingBodyWithBlock:(nullable void (^)(id<AFMultipartFormData> _Nonnull))block
                       success:(nullable void (^)(NSURLSessionDataTask * _Nonnull, id _Nullable))success
                       failure:(nullable void (^)(NSURLSessionDataTask * _Nullable, NSError * _Nonnull))failure
{
    //调用下面的方法来构造上传文件的POST请求
    return [self POST:URLString parameters:parameters constructingBodyWithBlock:block progress:nil success:success failure:failure];
}

//上传文件POST请求
- (NSURLSessionDataTask *)POST:(NSString *)URLString
                    parameters:(id)parameters
     constructingBodyWithBlock:(void (^)(id <AFMultipartFormData> formData))block
                      progress:(nullable void (^)(NSProgress * _Nonnull))uploadProgress
                       success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                       failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
    //构造一个request请求
    NSError *serializationError = nil;
    NSMutableURLRequest *request = [self.requestSerializer multipartFormRequestWithMethod:@"POST" URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters constructingBodyWithBlock:block error:&serializationError];
    //如果在做序列化时出错在主线程调用failure回调块
    if (serializationError) {
        if (failure) {
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
        }

        return nil;
    }
    //调用父类的方法获取一个上传的任务
    __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);
            }
        }
    }];
    //默认启动任务
    [task resume];

    return task;
}

//获取PUT请求
- (NSURLSessionDataTask *)PUT:(NSString *)URLString
                   parameters:(id)parameters
                      success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                      failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
    //通过一个通用的方法来获取dataTask
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"PUT" URLString:URLString parameters:parameters uploadProgress:nil downloadProgress:nil success:success failure:failure];
    //默认启动任务
    [dataTask resume];

    return dataTask;
}

//同上
- (NSURLSessionDataTask *)PATCH:(NSString *)URLString
                     parameters:(id)parameters
                        success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                        failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"PATCH" URLString:URLString parameters:parameters uploadProgress:nil downloadProgress:nil success:success failure:failure];

    [dataTask resume];

    return dataTask;
}

//同上
- (NSURLSessionDataTask *)DELETE:(NSString *)URLString
                      parameters:(id)parameters
                         success:(void (^)(NSURLSessionDataTask *task, id responseObject))success
                         failure:(void (^)(NSURLSessionDataTask *task, NSError *error))failure
{
    NSURLSessionDataTask *dataTask = [self dataTaskWithHTTPMethod:@"DELETE" URLString:URLString parameters:parameters uploadProgress:nil downloadProgress:nil success:success failure:failure];

    [dataTask resume];

    return dataTask;
}

//一个通用的方法来构造NSURLSessionDataTask
- (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
{
    //通过请求序列化器构造一个request请求
    //需要传入请求方法GET POST DELETE PUT这样的字符串 以及相关参数
    NSError *serializationError = nil;
    NSMutableURLRequest *request = [self.requestSerializer requestWithMethod:method URLString:[[NSURL URLWithString:URLString relativeToURL:self.baseURL] absoluteString] parameters:parameters error:&serializationError];
    //如果序列化失败在主线程中执行failure回调块
    if (serializationError) {
        if (failure) {
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
        }

        return nil;
    }
    
    //序列化成功，调用父类的方法获取dataTask
    __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);
            }
        }
    }];
    //返回dataTask
    return dataTask;
}

上面的代码也很简单，是在AFURLSessionManager之上做了一些处理，其中涉及的AFURLRequestSerialization和AFURLResponseSerialization由于不是本系列文章的关注点所以没有相关讲解，有需要的读者请自行查阅。

AFHTTPSessionManager继承自AFURLSessionManager并提供了更加便捷的网络请求接口，如果阅读了前一篇AFURLSessionManager可以发现它才是重点。AFHTTPSessionManager只是在它的基础上做了一些简单的封装，提供了更加便捷的接口。

通过AFURLSessionManager和AFHTTPSessionManager源码的阅读可以学习到AFNetworking在代码设计方面的优点，以及对NSURLSession的使用更清晰了。

备注

由于作者水平有限，难免出现纰漏，如有问题还请不吝赐教。