AFNetworking到底長啥樣(上)

AFNetworking是iOS界知名的網(wǎng)絡(luò)三方庫，現(xiàn)已完全取代了ASI。最新的AFNetworking3.0也早已從NSURLConnection切換到了NSURLSession，使用起來也更加方便。作為一名不斷探索的資深iOSer，還是要看看源碼提升下內(nèi)功。

一、概述

首先看下AFNetworking的結(jié)構(gòu)及其繼承關(guān)系：

涉及的主要類都在上表中了，下面簡單說下其他的輔助類：

(1)_AFURLSessionTaskSwizzling:這個類只做一件事：使用Method Swizzling更改NSURLSessionDataTask及其父類的resume及suspend實現(xiàn)，在其調(diào)用時發(fā)送消息：AFNSURLSessionTaskDidResumeNotification和AFNSURLSessionTaskDidSuspendNotification即：

- (void)af_resume {
    NSAssert([self respondsToSelector:@selector(state)], @"Does not respond to state");
    NSURLSessionTaskState state = [self state];
    [self af_resume];

    if (state != NSURLSessionTaskStateRunning) {
        [[NSNotificationCenter defaultCenter] postNotificationName:AFNSURLSessionTaskDidResumeNotification object:self];
    }
}

- (void)af_suspend {
    NSAssert([self respondsToSelector:@selector(state)], @"Does not respond to state");
    NSURLSessionTaskState state = [self state];
    [self af_suspend];

    if (state != NSURLSessionTaskStateSuspended) {
        [[NSNotificationCenter defaultCenter] postNotificationName:AFNSURLSessionTaskDidSuspendNotification object:self];
    }
}

(2)AFJSONRequestSerializer：是AFHTTPRequestSerializer的子類，相比于AFHTTPRequestSerializer，它增加了對parameters是否是合法JSON格式的校驗。在POST情況下，parameters會通過NSJSONSerialization轉(zhuǎn)化為NSData放到HTTPBody里。此外，header的Content-Type也會被設(shè)置為application/json。

(3)AFQueryStringPair：包含field和value屬性，用于表示參數(shù)（eg. name='layne'），并且field和value要經(jīng)過“PercentEscaped”處理，處理函數(shù)如下：

NSString * AFPercentEscapedStringFromString(NSString *string) {
    static NSString * const kAFCharactersGeneralDelimitersToEncode = @":#[]@"; // does not include "?" or "/" due to RFC 3986 - Section 3.4
    static NSString * const kAFCharactersSubDelimitersToEncode = @"!$&'()*+,;=";

    NSMutableCharacterSet * allowedCharacterSet = [[NSCharacterSet URLQueryAllowedCharacterSet] mutableCopy];
    [allowedCharacterSet removeCharactersInString:[kAFCharactersGeneralDelimitersToEncode stringByAppendingString:kAFCharactersSubDelimitersToEncode]];

    // FIXME: https://github.com/AFNetworking/AFNetworking/pull/3028
    // return [string stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];

    static NSUInteger const batchSize = 50;

    NSUInteger index = 0;
    NSMutableString *escaped = @"".mutableCopy;

    while (index < string.length) {
        NSUInteger length = MIN(string.length - index, batchSize);
        NSRange range = NSMakeRange(index, length);

        // To avoid breaking up character sequences such as emoji
        range = [string rangeOfComposedCharacterSequencesForRange:range];

        NSString *substring = [string substringWithRange:range];
        NSString *encoded = [substring stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacterSet];
        [escaped appendString:encoded];

        index += range.length;
    }

    return escaped;
}

這里有兩點需要說明：

①對于字符截斷問題（eg.emoji），這里使用了：rangeOfComposedCharacterSequencesForRange:，根據(jù)給定的range調(diào)整實際的range來防止字符截斷。

②這里設(shè)置了batchSize分塊進行escape。為啥要這么做？FIXME: https://github.com/AFNetworking/AFNetworking/pull/3028給出了具體解釋：

Batching is required for escaping due to an internal bug in iOS 8.1 and 8.2. Encoding more than a few hundred Chinese characters causes various malloc error crashes. To avoid this issue until iOS 8 is no longer supported, batching MUST be used for encoding. This introduces roughly a 20% overhead.

簡單說就是，在8.1和8.2上超過100個中文字符會掛。

(4)AFStreamingMultipartFormData用于multipart方式上傳的formData.

(5)AFHTTPBodyPart

(6)AFMultipartBodyStream

(7)AFJSONResponseSerializer：AFHTTPResponseSerializer的子類，解析JSON格式的response.

(8)AFXMLParserResponseSerializer：AFHTTPResponseSerializer的子類，解析(NSXMLParser)XML格式的response.

(9)AFXMLDocumentResponseSerializer：AFHTTPResponseSerializer的子類，解析(NSXMLDocument)XML格式的response.

(10)AFPropertyListResponseSerializer：AFHTTPResponseSerializer的子類，解析(NSXMLDocument)PropertyList格式的response，

(11)AFImageResponseSerializer：AFHTTPResponseSerializer的子類，解析圖片response。

(12)AFCompoundResponseSerializer：AFHTTPResponseSerializer的子類，解析復(fù)合類型的response。

二、類分析

1.AFURLSessionManager

AFURLSessionManager是管理網(wǎng)絡(luò)請求的主類，它的結(jié)構(gòu)如下：

• 管理著

  一個session(NSURLSession實例)，用于發(fā)起網(wǎng)絡(luò)請求。

  一個operationQueue,用于執(zhí)行代理回調(diào)。

  一個responseSerializer(實現(xiàn)了AFURLResponseSerialization)，用于response解析。

  一個securityPolicy(AFSecurityPolicy實例)，用于HTTPs配置。

  一個reachabilityManager(AFNetworkReachabilityManager實例)，用于網(wǎng)絡(luò)連通性監(jiān)聽。

• 通過重寫tasks、dataTasks、uploadTasks和downloadTasks屬性的getter方法，使用getTasksWithCompletionHandler:獲取session管理的tasks。

• 提供多種生成task的函數(shù)。如：

  -dataTaskWithRequest:completionHandler:
  -dataTaskWithRequest:uploadProgress:downloadProgress:completionHandler:
  
  -uploadTaskWithRequest:fromFile:progress:completionHandler:
  -uploadTaskWithRequest:fromData:progress:completionHandler:
  -uploadTaskWithStreamedRequest:progress:completionHandler:
  
  -downloadTaskWithRequest:progress:destination:completionHandler:
  -downloadTaskWithResumeData:progress:destination:completionHandler:

• 監(jiān)控上傳/下載進度。

  -uploadProgressForTask:   
  -downloadProgressForTask:

• 定義回調(diào)block屬性，每個block對應(yīng)NSURLSession相關(guān)的delegate方法。

  @property (readwrite, nonatomic, copy) AFURLSessionDidBecomeInvalidBlock sessionDidBecomeInvalid;
  @property (readwrite, nonatomic, copy) AFURLSessionDidReceiveAuthenticationChallengeBlock sessionDidReceiveAuthenticationChallenge;
  @property (readwrite, nonatomic, copy) AFURLSessionDidFinishEventsForBackgroundURLSessionBlock didFinishEventsForBackgroundURLSession AF_API_UNAVAILABLE(macos);
  @property (readwrite, nonatomic, copy) AFURLSessionTaskWillPerformHTTPRedirectionBlock taskWillPerformHTTPRedirection;
  @property (readwrite, nonatomic, copy) AFURLSessionTaskDidReceiveAuthenticationChallengeBlock taskDidReceiveAuthenticationChallenge;
  @property (readwrite, nonatomic, copy) AFURLSessionTaskNeedNewBodyStreamBlock taskNeedNewBodyStream;
  @property (readwrite, nonatomic, copy) AFURLSessionTaskDidSendBodyDataBlock taskDidSendBodyData;
  @property (readwrite, nonatomic, copy) AFURLSessionTaskDidCompleteBlock taskDidComplete;
  #if AF_CAN_INCLUDE_SESSION_TASK_METRICS
  @property (readwrite, nonatomic, copy) AFURLSessionTaskDidFinishCollectingMetricsBlock taskDidFinishCollectingMetrics;
  #endif
  @property (readwrite, nonatomic, copy) AFURLSessionDataTaskDidReceiveResponseBlock dataTaskDidReceiveResponse;
  @property (readwrite, nonatomic, copy) AFURLSessionDataTaskDidBecomeDownloadTaskBlock dataTaskDidBecomeDownloadTask;
  @property (readwrite, nonatomic, copy) AFURLSessionDataTaskDidReceiveDataBlock dataTaskDidReceiveData;
  @property (readwrite, nonatomic, copy) AFURLSessionDataTaskWillCacheResponseBlock dataTaskWillCacheResponse;
  @property (readwrite, nonatomic, copy) AFURLSessionDownloadTaskDidFinishDownloadingBlock downloadTaskDidFinishDownloading;
  @property (readwrite, nonatomic, copy) AFURLSessionDownloadTaskDidWriteDataBlock downloadTaskDidWriteData;
  @property (readwrite, nonatomic, copy) AFURLSessionDownloadTaskDidResumeBlock downloadTaskDidResume;

• 聲明了常量。

  //通知
  AFNetworkingTaskDidResumeNotification
  AFNetworkingTaskDidCompleteNotification
  AFNetworkingTaskDidSuspendNotification
  
  AFURLSessionDidInvalidateNotification
  AFURLSessionDownloadTaskDidFailToMoveFileNotification
  
  //通知AFNetworkingTaskDidCompleteNotification中userInfo的key
  AFNetworkingTaskDidCompleteResponseDataKey
  AFNetworkingTaskDidCompleteSerializedResponseKey
  AFNetworkingTaskDidCompleteResponseSerializerKey
  AFNetworkingTaskDidCompleteAssetPathKey
  AFNetworkingTaskDidCompleteErrorKey

• 在生成task時為每個task生成對應(yīng)的delegate(AFURLSessionManagerTaskDelegate實例),并使用{<taskID:delegate>}的形式保存在可變字典mutableTaskDelegatesKeyedByTaskIdentifier中。

• 作為NSURLSession的delegate，實現(xiàn)的delegate方法有：

  /* ----------NSURLSessionDelegate---------- */
  //執(zhí)行sessionDidBecomeInvalid block并發(fā)通知
  - (void)URLSession:didBecomeInvalidWithError:
  //生成disposition(NSURLSessionAuthChallengeDisposition實例)，并調(diào)用completionHandler
  - (void)URLSession:didReceiveChallenge:completionHandler:
  //執(zhí)行didFinishEventsForBackgroundURLSession block
  - (void)URLSessionDidFinishEventsForBackgroundURLSession:
  
  /* ----------NSURLSessionTaskDelegate---------- */
  //執(zhí)行taskWillPerformHTTPRedirectionBlock生成新的request，并調(diào)用completionHandler
  - (void)URLSession:task:willPerformHTTPRedirection:newRequest:completionHandler:
  //生成disposition(NSURLSessionAuthChallengeDisposition實例)，并調(diào)用completionHandler
  - (void)URLSession:task:didReceiveChallenge:completionHandler:
  //生成inputStream(NSInputStream實例)，并調(diào)用completionHandler
  - (void)URLSession:task:needNewBodyStream:
  //轉(zhuǎn)到task delegate中執(zhí)行，并執(zhí)行taskDidSendBodyData block
  - (void)URLSession:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend:
  //轉(zhuǎn)到task delegate中執(zhí)行，并執(zhí)行taskDidComplete block
  - (void)URLSession:task:didCompleteWithError:
  
  /* ----------NSURLSessionDataDelegate---------- */
  //執(zhí)行dataTaskDidReceiveResponse block生成disposition，并調(diào)用completionHandler
  - (void)URLSession:dataTask:didReceiveResponse:completionHandler:
  //重新設(shè)置task delegate,并調(diào)用dataTaskDidBecomeDownloadTask block
  - (void)URLSession:dataTask:didBecomeDownloadTask:
  //轉(zhuǎn)到task delegate中執(zhí)行，并調(diào)用dataTaskDidReceiveData block
  - (void)URLSession:dataTask:didReceiveData:
  //執(zhí)行dataTaskWillCacheResponse block生成cacheResponse，并調(diào)用completionHandler
  - (void)URLSession:dataTask:willCacheResponse:completionHandler:
  
  /* ----------NSURLSessionDownloadDelegate---------- */
  //轉(zhuǎn)到task delegate中執(zhí)行，并移動文件
  - (void)URLSession:downloadTask:didFinishDownloadingToURL:
  //轉(zhuǎn)到task delegate中執(zhí)行，并執(zhí)行downloadTaskDidWriteData block
  - (void)URLSession:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite:
  //轉(zhuǎn)到task delegate中執(zhí)行，并執(zhí)行downloadTaskDidResume block
  - (void)URLSession:downloadTask:didResumeAtOffset:expectedTotalBytes:

2.AFURLSessionManagerTaskDelegate

AFURLSessionManagerTaskDelegate這個類雖然后綴是·-Delegate,但它并不是一個協(xié)議，而是一個繼承自NSObject的類。它和AFURLSessionManager都定義在文件AFURLSessionManager.m中。它的實例作為task的代理使用。

• 包含一個manager屬性，使用weak回指使用它的AFURLSessionManager實例。

• 包含控制上傳和下載進度的屬性uploadProgress和downloadProgress(均為NSProgress實例),通過KVO監(jiān)測各自的fractionCompleted，從而在結(jié)束時調(diào)用downloadProgressBlock和uploadProgressBlock。

• 實現(xiàn)的delegate包括：

  /* ----------NSURLSessionTaskDelegate---------- */
  //構(gòu)造userInfo，并使用manager的responseSerializer解析response,最后調(diào)用self.completionHandler.
  - (void)URLSession:task:didCompleteWithError:
  //更新uploadProgress屬性
  - (void)URLSession:task:didSendBodyData:totalBytesSent:totalBytesExpectedToSend:
  
  /* ----------NSURLSessionDataTask---------- */
  //更新downloadProgress屬性，并用mutableData保存接收到的數(shù)據(jù)
  - (void)URLSession:dataTask:didReceiveData:
  
  /* ----------NSURLSessionDownloadTask-------- */
  //更新downloadProgress屬性
  - (void)URLSession:downloadTask:didWriteData:totalBytesWritten:totalBytesExpectedToWrite:
  //更新downloadProgress屬性
  - (void)URLSession:downloadTask:didResumeAtOffset:expectedTotalBytes:
  //清空downloadFileURL(nil),并移動文件
  - (void)URLSession:downloadTask:didFinishDownloadingToURL:

注：AFURLSessionManagerTaskDelegate實例本身不持有task，它們之間的代理關(guān)系是以{<taskID:delegate>}的形式保存在可變字典mutableTaskDelegatesKeyedByTaskIdentifier中的。

3.AFHTTPSessionManager

AFHTTPSessionManager是AFURLSessionManager的子類，它針對HTTP請求封裝了更為便利的方法。它的結(jié)構(gòu)如下:

• 主要包含requestSerializer(AFHTTPRequestSerializer實例)和responseSerializer(AFHTTPResponseSerializer實例)，分別用于request的封裝及response的解析。

• 提供三個實例初始化方法：

  + (instancetype)manager;
  - (instancetype)initWithBaseURL:(nullable NSURL *)url;
  - (instancetype)initWithBaseURL:(nullable NSURL *)url sessionConfiguration:(nullable NSURLSessionConfiguration *)configuration;

  最終調(diào)用的都是第三個函數(shù)。

• 封裝的Convenience Method如下：

  • GET

  - GET:parameters:headers:progress:success:failure:

  • POST

  - POST:parameters:headers:progress:success:failure:
  - POST:paramters:headers:constructingBodyWithBlock:progress:success:failure:

  • HEAD

  - HEAD:parameters:headers:success:failure:

  • PUT

  - PUT:parameters:headers:success:failure:

  • PATCH

  - PATCH:parameters:headers:success:failure:

  • DELETE

  - DELETE:paramaters:headers:success:failure:

  注：上面只列出了有效的方法，其他的都已經(jīng)被標(biāo)記為DEPRECATED_ATTRIBUTE了。

• 除了包含...constructingBodyWithBlock…的POST函數(shù)外，其余的convenience methods都是通過以下函數(shù)生成對應(yīng)的dataTask：

  - (NSURLSessionDataTask *)dataTaskWithHTTPMethod:
                                                                          URLString:
                                                                        parameters:
                                                                 uploadProgress:
                                                              downloadProgress:
                                                                               success:
                                                                               failure:

  在上述函數(shù)中，requestSerializer會通過HTTPMethod、URLString和parameters生成request，然后會調(diào)用父類的：dataTaskWithRequest:uploadProgress:downloadProgress: completionHandler:生成dataTask并返回。返回的dataTask會被resume啟動。

4.AFHTTPRequestSerializer

AFHTTPRequestSerializer繼承自NSObject,用于封裝request。

• 實現(xiàn)了協(xié)議AFURLRequestSerialization。這個協(xié)議只有一個函數(shù)：

  - (NSURLRequest *)requestBySerializingRequest:(NSURLRequest *)request
                               withParameters:(id)parameters
                                        error:(NSError *__autoreleasing *)error;

  用于將參數(shù)包含到原始request中形成新的request。

• 使用數(shù)組mutableHTTPRequestHeaders保存要包含在request header中的數(shù)據(jù)。默認(rèn)包含Accept-Language和User-Agent。其中，在設(shè)置User-Agent時，為了保證ASCII編碼規(guī)則，作者使用了ICU文本變換。

  CFStringTransform((__bridge CFMutableStringRef)(mutableUserAgent), NULL, (__bridge CFStringRef)@"Any-Latin; Latin-ASCII; [:^ASCII:] Remove", false)

  ICU 庫提供了一整套強大的文本變換功能，可以實現(xiàn)不用語系之間的字符轉(zhuǎn)換，如漢字轉(zhuǎn)拼音。在上面的例子中，User-Agent字段會先被轉(zhuǎn)換為Latin，接著變換為Latin-ASCII，最后清除所有不是ASCII的字符。 其他的變換可參考 ICU 用戶手冊。

• 采用KVO機制監(jiān)測相關(guān)屬性，若用戶設(shè)置了對應(yīng)屬性，該屬性會被記錄下來，在生成request時加入。

  allowsCellularAccess
  cachePolicy
  HTTPShouldHandleCookies
  HTTPShouldUsePipelining
  networkServiceType
  timeoutInterval

  • 首先重寫+ (BOOL)automaticallyNotifiesObserversForKey:(NSString *)key，禁止以上6個字段的KVO自動觸發(fā)。
  • 在以上6個字段的setter中使用willChangeValueForKey和didChangeValueForKey手動觸發(fā)KVO。

• 生成request使用以下函數(shù)：

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

  執(zhí)行的操作包括：

  ① 根據(jù)URLString和method創(chuàng)建mutableRequest

  NSMutableURLRequest *mutableRequest = [[NSMutableURLRequest alloc] initWithURL:url];
  mutableRequest.HTTPMethod = method;

  ② 使用KVC將KVO監(jiān)測的6個字段(用戶設(shè)置過的)包含進mutableRequest中。

  for (NSString *keyPath in AFHTTPRequestSerializerObservedKeyPaths()) {
        if ([self.mutableObservedChangedKeyPaths containsObject:keyPath]) {
            [mutableRequest setValue:[self valueForKeyPath:keyPath] forKey:keyPath];
        }
  }

  ③ 調(diào)用AFURLRequestSerialization協(xié)議方法- requestBySerializingRequest: withParameters: error:。在這個協(xié)議方法內(nèi)部執(zhí)行：

  • 設(shè)置request的header
  • 將parameters格式化。默認(rèn)的格式化形如name=layne$age=30&job=engineer。
  • 根據(jù)請求的Method(GET、POST、HEAD等)不同將參數(shù)加到request的不同位置(URL or Body)。

5.AFJSONRequestSerializer

AFJSONRequestSerializer是AFHTTPRequestSerializer的子類，使用NSJSONSerialization將參數(shù)編碼成JSON格式，并設(shè)置Content-Type為application/json。它重寫了AFURLRequestSerialization協(xié)議方法：

- (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];
    }//若為GET/HEAD/DELETE方法，由于參數(shù)都拼接在URL中，因此無所謂json不json，直接調(diào)用父類的方法即可。

    NSMutableURLRequest *mutableRequest = [request mutableCopy];

    [self.HTTPRequestHeaders enumerateKeysAndObjectsUsingBlock:^(id field, id value, BOOL * __unused stop) {
        if (![request valueForHTTPHeaderField:field]) {
            [mutableRequest setValue:value forHTTPHeaderField:field];
        }
    }];//更新header數(shù)據(jù)

    if (parameters) {
        if (![mutableRequest valueForHTTPHeaderField:@"Content-Type"]) {
            [mutableRequest setValue:@"application/json" forHTTPHeaderField:@"Content-Type"];
        }//設(shè)置Content-Type字段為“application/json”

        if (![NSJSONSerialization isValidJSONObject:parameters]) {
            if (error) {
                NSDictionary *userInfo = @{NSLocalizedFailureReasonErrorKey: NSLocalizedStringFromTable(@"The `parameters` argument is not valid JSON.", @"AFNetworking", nil)};
                *error = [[NSError alloc] initWithDomain:AFURLRequestSerializationErrorDomain code:NSURLErrorCannotDecodeContentData userInfo:userInfo];
            }
            return nil;
        }//非法的json格式(NSDictionary)數(shù)據(jù)

        NSData *jsonData = [NSJSONSerialization dataWithJSONObject:parameters options:self.writingOptions error:error];//json序列化

        if (!jsonData) {
            return nil;
        }

        [mutableRequest setHTTPBody:jsonData];
    }

    return mutableRequest;
}

6.AFHTTPResponseSerializer

AFHTTPResonseSerializer繼承自NSObject，實現(xiàn)了AFURLResponseSerialization協(xié)議：

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

在協(xié)議方法中根據(jù)acceptableStatusCodes和acceptableContentTypes判斷response合法性。

7.AFJSONResponseSerializer

AFJSONResponseSerializer是AFHTTPResponseSerializer的子類。

• 設(shè)置acceptableContentTypes指定合法的content-type:

  application/json
  text/json
  text/javascript

• 重寫AFURLResponseSerialization協(xié)議方法：

  - (BOOL)validateResponse:(nullable NSHTTPURLResponse *)response
                    data:(nullable NSData *)data
                   error:(NSError * _Nullable __autoreleasing *)error;

  在內(nèi)部：

  (1)根據(jù)acceptableStatusCodes和acceptableContentTypes判斷response合法性；

  (2)使用NSJSONSerialization將data轉(zhuǎn)換為NSDictionary

  (3)根據(jù)removesKeysWithNullValues的值決定是否將NSDictionary中NSNull的數(shù)據(jù)清除。

以上就是AFNetworking主要的類結(jié)構(gòu)及其功能。下一篇博客我們會以一個簡單的POST請求來走一遍邏輯，看看AFN到底是如何工作的。