AFNetworking 3.0 源码解析之Serialization

AFNetworking 3.0 源码解析之Serialization

本部分主要的作用：网络通信信息序列化/反序列化

一、AFURLRequestSerialization

功能：   

负责参数转换成NSMutableURLRequest类型，进行网络请求。

1)构建普通请求：格式化请求参数，生成HTTP Header

2)构建multipart请求

类关系：

父类：AFHTTPRequestSerializer,二进制格式（query字符串转换成二进制）

子类：AFJSONRequestSerializer,Json格式（Json序列化成NSData类型）

          AFPropertyListRequestSerializer，Plist（一种特殊的XML，解析起来相对容易）

封装思路：

所有类遵循一个协议AFURLRequestSerialization，协议中一个非必须实现的方法：

 - (nullableNSURLRequest*)requestBySerializingRequest:(NSURLRequest*)request                                 withParameters:(nullableid)parameters                                    error:(NSError* _Nullable__autoreleasing *)error NS_SWIFT_NOTHROW;

父类AFHTTPRequestSerializer中提供外部调用接口：

- (NSMutableURLRequest*)requestWithMethod:(NSString*)method                                 URLString:(NSString*)URLString                                parameters:(id)parameters                                     error:(NSError*__autoreleasing*)error

在这个方法中调用协议方法：

mutableRequest = [[selfrequestBySerializingRequest:mutableRequestwithParameters:parameterserror:error]mutableCopy];

而这个方法的实现是父类以及各个子类分别实现。所以，此处self如果是AFHTTPRequestSerializer那么走AFHTTPRequestSerializer类下的实现，如果是

AFJSONRequestSerializer，那么走AFJSONRequestSerializer类下的实现。然后再分别实现这个方法不同功能的实现。

下面看一下各个类不同职能分别的实现：

AFURLRequestSerialization中的实现:

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request                               withParameters:(id)parameters                                        error:(NSError *__autoreleasing *)error{    NSParameterAssert(request);    NSMutableURLRequest *mutableRequest = [requestmutableCopy];    [self.HTTPRequestHeadersenumerateKeysAndObjectsUsingBlock:^(id field,id value, BOOL *__unused stop) {        if (![requestvalueForHTTPHeaderField:field]) {            [mutableRequest setValue:valueforHTTPHeaderField:field];        }    }];    NSString *query =nil;    if (parameters) {        if (self.queryStringSerialization) {            NSError *serializationError;            query = self.queryStringSerialization(request, parameters, &serializationError);            if (serializationError) {                if (error) {                    *error = serializationError;                }                returnnil;            }        } else {            switch (self.queryStringSerializationStyle) {                caseAFHTTPRequestQueryStringDefaultStyle:                    query = AFQueryStringFromParameters(parameters);                    break;            }        }    }    if ([self.HTTPMethodsEncodingParametersInURIcontainsObject:[[request HTTPMethod]uppercaseString]]) { //普通GET，HEAD等，参数直接拼接在url后面用&分开        if (query && query.length >0) {            mutableRequest.URL = [NSURLURLWithString:[[mutableRequest.URLabsoluteString] stringByAppendingFormat:mutableRequest.URL.query ? @"&%@" : @"?%@", query]];        }    } else {        // #2864: an empty string is a valid x-www-form-urlencoded payload        if (!query) {            query = @"";        }        if (![mutableRequestvalueForHTTPHeaderField:@"Content-Type"]) {            [mutableRequest setValue:@"application/x-www-form-urlencoded"forHTTPHeaderField:@"Content-Type"];        }        [mutableRequest setHTTPBody:[querydataUsingEncoding:self.stringEncoding]];// 普通的POST请求参数，直接转换成NSData设置到HTTP的body中。    }    return mutableRequest;}

我们可以看到AFNetworking对于GET，POST请求参数的处理，一个是直接拼接在URL上面，一个是设置在HTTPBody里面。

其中，HTTPMethodsEncodingParametersInURI的初始化如下：

self.HTTPMethodsEncodingParametersInURI = [NSSet setWithObjects:@"GET", @"HEAD", @"DELETE", nil]; // 支持GET，HEAD，DELETE

也就是GET,HEAD,DELETE支持的是参数直接拼接URL的方式。

AFJSONRequestSerialization中的实现:

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request                               withParameters:(id)parameters                                        error:(NSError *__autoreleasing *)error{    NSParameterAssert(request);    if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {        return [super requestBySerializingRequest:request withParameters:parameters error:error];    }    NSMutableURLRequest *mutableRequest = [request mutableCopy];    [self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {        if (![request valueForHTTPHeaderField:field]) {            [mutableRequest setValue:value forHTTPHeaderField:field];        }    }]; // 设置公共的请求头    if (parameters) {        if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {            [mutableRequest setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];        }        [mutableRequest setHTTPBody:[NSJSONSerialization dataWithJSONObject:parameters options:self.writingOptions error:error]];    }    return mutableRequest;}

OK，跟AFURLRequestSerialization中的实现差不多，如果是HTTPMethodsEncodingParametersInURI请求方式是GET，HEAD，DELETE，则直接调用父类的解析方法。如果是POST等其他的，那么做了一下设置请求头Content-Type = “application/json”,并且将paramters参数Json序列化成NSData,设置到HTTPBody里面。

AFPropertyListRequestSerialization中的实现:

- (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request                               withParameters:(id)parameters                                        error:(NSError *__autoreleasing *)error{    NSParameterAssert(request);    if ([self.HTTPMethodsEncodingParametersInURI containsObject:[[request HTTPMethod] uppercaseString]]) {        return [super requestBySerializingRequest:request withParameters:parameters error:error];    }    NSMutableURLRequest *mutableRequest = [request mutableCopy];    [self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {        if (![request valueForHTTPHeaderField:field]) {            [mutableRequest setValue:value forHTTPHeaderField:field];        }    }];    if (parameters) {        if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {            [mutableRequest setValue:@"application/x-plist" forHTTPHeaderField:@"Content-Type"];        }        [mutableRequest setHTTPBody:[NSPropertyListSerialization dataWithPropertyList:parameters format:self.format options:self.writeOptions error:error]];    }    return mutableRequest;}

好吧，封装思路跟AFJSONRequestSerialization一样，区别在于json序列化变成Plist的转换。

二、AFURLResponseSerialization

功能：   

负责对网络请求返回的数据进行解析。

类关系：

父类：AFHTTPResponseSerializer，二进制格式

子类：AFJSONResponseSerializer, JSON格式

          AFXMLParseResponseSerializer, XML（只能返回XMLParser，还需要自己通过代理解析）

          AFXMLDocumentResponseSerializer, （Mac OS X）

          AFPropertyListResponseSerializer,  Plist

          AFImageResponseSerializer,  Image

          AFCompoundResponseSerializer, 组合

封装思路：

跟Request的封装思路基本相同。只不过这个是在数据请求到之后进行的处理。遵循的是AFURLResponseSerialization协议。实现方法：

- (id)responseObjectForResponse:(NSURLResponse *)response                           data:(NSData *)data                          error:(NSError *__autoreleasing *)error

此处的返回值是id类型的，也就是数据解析完之后的数据。

顺便提一下返回值解析的调用函数是在AFURLSessionManager中的网络请求成功的回调中：

- (void)URLSession:(__unused NSURLSession *)session              task:(NSURLSessionTask *)taskdidCompleteWithError:(NSError *)error{#pragma clang diagnostic push#pragma clang diagnostic ignored "-Wgnu"    __strong AFURLSessionManager *manager = self.manager;    __block id responseObject = nil;    __block 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 (self.downloadFileURL) {        userInfo[AFNetworkingTaskDidCompleteAssetPathKey] = self.downloadFileURL;    } else if (data) {        userInfo[AFNetworkingTaskDidCompleteResponseDataKey] = data;    }    if (error) {        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 {        dispatch_async(url_session_manager_processing_queue(), ^{            NSError *serializationError = nil;            responseObject = [manager.responseSerializer responseObjectForResponse:task.response data:data error:&serializationError]; // 此处进行数据的解析            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(), ^{                if (self.completionHandler) {                    self.completionHandler(task.response, responseObject, serializationError);                }                dispatch_async(dispatch_get_main_queue(), ^{                    [[NSNotificationCenter defaultCenter] postNotificationName:AFNetworkingTaskDidCompleteNotification object:task userInfo:userInfo];                });            });        });    }#pragma clang diagnostic pop}

下面看一下各个类不同职能分别的实现：

父类AFHTTPResponseSerializer 中的实现：

- (id)responseObjectForResponse:(NSURLResponse *)response                           data:(NSData *)data                          error:(NSError *__autoreleasing *)error{    [self validateResponse:(NSHTTPURLResponse *)response data:data error:error];    return data;}

此处就一个方法，就是做了一个返回的数据是否有效。但是数据是否有错，都会返回原始数据，没有做任何的修改。

看一下返回数据有效性的方法实现：

- (BOOL)validateResponse:(NSHTTPURLResponse *)response                    data:(NSData *)data                   error:(NSError * __autoreleasing *)error{    BOOL responseIsValid = YES;    NSError *validationError = nil;    if (response && [response isKindOfClass:[NSHTTPURLResponse class]]) {        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);            }            responseIsValid = NO;        }        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;}

这里主要做了判断是不是支持的返回content-type类型，再就是状态码是不是200+，如果不满足就不是有效的返回数据。

看下初始化值：

self.acceptableContentTypes = [NSSet setWithObjects:@"application/json", @"text/json", @"text/javascript", nil];self.acceptableStatusCodes = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(200, 100)];

子类AFJSONResponseSerializer中的实现：

- (id)responseObjectForResponse:(NSURLResponse *)response                           data:(NSData *)data                          error:(NSError *__autoreleasing *)error{    if (![self validateResponse:(NSHTTPURLResponse *)response data:data error:error]) {        if (!error || AFErrorOrUnderlyingErrorHasCodeInDomain(*error, NSURLErrorCannotDecodeContentData, AFURLResponseSerializationErrorDomain)) {            return nil;        }    }    id responseObject = nil;    NSError *serializationError = nil;    // Workaround for behavior of Rails to return a single space for `head :ok` (a workaround for a bug in Safari), which is not interpreted as valid input by NSJSONSerialization.    // See https://github.com/rails/rails/issues/1742    BOOL isSpace = [data isEqualToData:[NSData dataWithBytes:" " length:1]];    if (data.length > 0 && !isSpace) {        responseObject = [NSJSONSerialization JSONObjectWithData:data options:self.readingOptions error:&serializationError];    } else {        return nil;    }    if (self.removesKeysWithNullValues && responseObject) {        responseObject = AFJSONObjectByRemovingKeysWithNullValues(responseObject, self.readingOptions);    }    if (error) {        *error = AFErrorWithUnderlyingError(serializationError, *error);    }    return responseObject;}

此处看到在父类中对有效性的判断结果并没有做处理，而在Json转换类中，如果返回数据是无效的，直接就返回nil。然后就是对返回数据进行了Json转换。并对结果进行了空值进行了排空。

其他的子类的封装思路也都相似，不再一一赘述。注意的是不同的功能的子类对返回值的类型支持是不同的。

如果文中有什么错误，欢迎大家指正。