Interpretation of afnetworking4.0 request principle

brief introduction

AFNetworking4.0 It's right NSURLSession Encapsulation , Previous versions had NSURLConnection Encapsulation , Now it's abandoned .

Have a brief talk , Why? AF Discard the previous NSURLConnection encapsulation , In pairs NSURLSession encapsulation .

First ,NSURLSession Is in iOS7.0 Apple pushed it out . and NSURLSession And can support Http2.0 Of . Everybody knows Http Is based on TCP Agreed , In the early Http It's short connected , Every time you transmit data, you need to reconnect , Each time you connect, you need to shake hands three times , This leads to a waste of resources and time . then , stay Http2.0 Time to update Connection：keep-alive Options , This optimization item , Make the client and server in the same config Reuse the same TCP Connect , Reduced time per request , Improve the data transmission rate . therefore ,AFNetworking Also decisive change in pairs NSURLSession Encapsulation .

AFNetworking Five modules of

AFNetworking This tripartite library mainly includes the following five modules ：

• NSURLSession Network communication module
• Reachability Network status monitoring module
• Security Network communication security policy module
• Serialization Serialization module
• UIKit Yes UIKit Expansion module for

The following is mainly about the use process , Initialization process and internal implementation process of the request method

initialization

First ,AFHttpSessonManager Inherited from AFURLSessonManager.

When we call the initialization method [AFHTTPSessionManager manager], Look at what has been done in the code ？

- (instancetype)initWithBaseURL:(NSURL *)url
           sessionConfiguration:(NSURLSessionConfiguration *)configuration
{
    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;

    self.requestSerializer = [AFHTTPRequestSerializer serializer];
    self.responseSerializer = [AFJSONResponseSerializer serializer];

    return self;
}

️： although AF Naming manager, however , The internal implementation is not a singleton , Instead, a new one will be created every time HttpSessonManager object .

1. First, the parent class will be called （AFURLSessonManager） Initialization method of .
2. to URL Format , add to “/”
3. Set up requestSerializer and responseSerializer

Where the parent class （AFURLSessonManager） The initialization method of is mainly set configuration, And by setting maxConcurrentOperationCount = 1 Set up a serial queue . And the way of parsing 、 Monitor the network status and create a lock To ensure thread safety .

Request Method

- (NSURLSessionDataTask *)dataTaskWithHTTPMethod:(NSString *)method
                                       URLString:(NSString *)URLString
                                      parameters:(nullable id)parameters
                                         headers:(nullable NSDictionary <NSString *, NSString *> *)headers
                                  uploadProgress:(nullable void (^)(NSProgress *uploadProgress)) uploadProgress
                                downloadProgress:(nullable void (^)(NSProgress *downloadProgress)) downloadProgress
                                         success:(nullable void (^)(NSURLSessionDataTask *task, id _Nullable responseObject))success
                                         failure:(nullable void (^)(NSURLSessionDataTask * _Nullable task, NSError *error))failure
{
NSError *serializationError = nil;
    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] forHTTPHeaderField:headerField];
    }
    if (serializationError) {
        if (failure) {
            dispatch_async(self.completionQueue ?: dispatch_get_main_queue(), ^{
                failure(nil, serializationError);
            });
        }

        return nil;
    }

    __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;
}

In this way ,AF Returned a dataTask object . What have you done roughly ？

1. Through the first requestwithmethod Method to get a request object , When getting this object , Request type through request method get、head、delete To judge is to splice parameters directly to url Later, it is added to body in .

2. And then through the method dataTaskWithRequest Method , Will be on top of request Generate a task object . among addDelegateForDataTask Lieutenant general task and delegate Bind together . Every task There are corresponding agents .

In the specific request method （post、get、delete、put etc. ） in , For returned task Object call [dataTask resume]; Method .

[dataTask resume]

This is the last step in making a network request ,AF In the parent class , To the system resume Methods by method_exchangeImplementations Method and custom af_resume Method to exchange . And in the custom af_resume In the method, various result states are passed AFNSURLSessionTaskDidResumeNotification notice .