AFNetworking源码解析之AFURLResponseSe

简介

AFURLResponseSerialization可以理解成对网络请求的序列化操作,它是一个协议,用于验证数据的有效性并提供反序列化的方式,我们只需根据不同的响应类型选择合适的反序列化方式

@protocol AFURLResponseSerialization <NSObject, NSSecureCoding, NSCopying>
//对返回的数据进行解析，解析response为对应的数据类型（JSON、XML、plist、Image）,AFHTTPResponseSerializer的子类会重写这个方法，根据不同的需要解析成不同的结果，如AFJSONResponseSerializer会将数据解析成为JSON数据
- (nullable id)responseObjectForResponse:(nullable NSURLResponse *)response
                           data:(nullable NSData *)data
                          error:(NSError * _Nullable __autoreleasing *)error NS_SWIFT_NOTHROW;

@end

UML

UML

AFHTTPResponseSerializer

我们可以看到许多类都是继承该类,该类的结构图如下:

AFHTTPResponseSerializer

//创建一个序列化对象,使用默认配置
+ (instancetype)serializer;

//可接受的状态码集合, (默认)200-299,不在这个范围内将会在验证期间得到一个error
@property (nonatomic, copy, nullable) NSIndexSet *acceptableStatusCodes;

//可接受的 MIME类型 (Content-Type)
@property (nonatomic, copy, nullable) NSSet <NSString *> *acceptableContentTypes;


//通过验证MIMEType（数据类型），StatusCode（状态码：2xx为成功状态）是否满足条件来判断网络返回的数据是否有效
- (BOOL)validateResponse:(nullable NSHTTPURLResponse *)response
                    data:(nullable NSData *)data
                   error:(NSError * _Nullable __autoreleasing *)error;

关于状态码的解释

状态码的职责是当客户端向服务器端发送请求时，描述返回的请求结果。借助状态码，用户可以知道服务器端是正常处理了请求，还是出现了错误。
如:200,表示请求成功.状态码一般以3位数字和原因短语组成
分类如下:

	类别	原因短语
1XX	信息性状态码	接收的请求正在处理
2XX	成功状态码	请求正常处理完毕
3XX	重定向状态码	需要进行附加操作以完成请求
4XX	客户端错误状态码	服务器无法处理请求
5XX	服务器错误状态码	服务器处理请求出错

Content-Type说明了实体主体内对象的媒体类型,例如JSON数据的Content-Type为application/json, text/json, text/javascript.

主要验证响应方法:(验证Content-Type,StatusCode)

- (BOOL)validateResponse:(NSHTTPURLResponse *)response
                    data:(NSData *)data
                   error:(NSError * __autoreleasing *)error
{
    BOOL responseIsValid = YES;
    NSError *validationError = nil;

    if (response && [response isKindOfClass:[NSHTTPURLResponse class]]) {
        //不在接受的MIME类型
        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);
            }
            //验证失败
            responseIsValid = NO;
        }
   
        //验证状态码
        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;
}

子类只需修改相应的Content-Type类型和重写协议方法实现数据的解析即可,可查看下面列表:

类别	解析数据类型	Content-Type	解析数据用到的类
AFJSONResponseSerializer	JSON	application/json, text/json, text/javascript	NSJSONSerialization
AFXMLParserResponseSerializer	XML	application/xml, text/xml	NSXMLDocument
AFXMLDocumentResponseSerializer	XML(MAC-OS)	application/xml, text/xml	NSXMLDocument
AFPropertyListResponseSerializer	plist	application/x-plist	NSPropertyListSerialization
AFImageResponseSerializer	image	image/tiff,image/jpeg,image/gif,image/png,image/ico,image/x-icon,image/bmp,image/x-bmp,image/x-xbitmap,image/x-win-bitmap	NSData->image

AFCompoundResponseSerializer表示一组Serializer的集合,用于可能不确定返回的Content-type,也就是数据类型时使用.

- (id)responseObjectForResponse:(NSURLResponse *)response
                           data:(NSData *)data
                          error:(NSError *__autoreleasing *)error
{
    
    // 可能确实不能确定返回的responsed的content-type，此时可以使用AFCompoundResponseSerializer,遍历找到合适的Serializer
    for (id <AFURLResponseSerialization> serializer in self.responseSerializers) {
        if (![serializer isKindOfClass:[AFHTTPResponseSerializer class]]) {
            continue;
        }

        NSError *serializerError = nil;
        id responseObject = [serializer responseObjectForResponse:response data:data error:&serializerError];
        if (responseObject) {
            if (error) {
                *error = AFErrorWithUnderlyingError(serializerError, *error);
            }
            return responseObject;
        }
    }

    return [super responseObjectForResponse:response data:data error:error];
}