AFNetworking - How to setup requests to be retried

问题:

I have recently migrated from ASIHTTPRequest to AFNetworking, which has been great. However, the server that I am connecting with has some issues and sometimes causes my requests to timeout. When using ASIHTTPRequest it was possible to setup a retry count on a request in the event of a timeout using the following selector

-setNumberOfTimesToRetryOnTimeout:

This can be further referenced in this post, Can an ASIHTTPRequest be retried?

This is AFNetworking if you are unfamiliar https://github.com/AFNetworking/AFNetworking#readme

I was unable to find an equivalent api in AFNetworking, has anyone found a solution for retrying network requests in the event of timeout using AFNetworking?

回答1:

Matt Thompson developer of AFNetworking was kind enough to answer this for me. Below is the github link explaining the solution.

https://github.com/AFNetworking/AFNetworking/issues/393

Basically, AFNetworking doesn't support this functionality. It is left to the developer to implement on a case by case basis as shown below (taken from Matt Thompson's answer on github)

- (void)downloadFileRetryingNumberOfTimes:(NSUInteger)ntimes 
                              success:(void (^)(id responseObject))success 
                              failure:(void (^)(NSError *error))failure
{
    if (ntimes <= 0) {
        if (failure) {
            NSError *error = ...;
            failure(error);
        }
    } else {
        [self getPath:@"/path/to/file" parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
            if (success) {
                success(...);
            }
        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            [self downloadFileRetryingNumberOfTimes:ntimes - 1 success:success failure:failure];
        }];
    }
}

回答2:

I implemented private method in my ApiClient class:

- (void)sendRequest:(NSURLRequest *)request successBlock:(void (^)(AFHTTPRequestOperation *operation, id responseObject))successBlock failureBlock:(void (^)(AFHTTPRequestOperation *operation, NSError *error))failureBlock
{
    __block NSUInteger numberOfRetries = 3;
    __block __weak void (^weakSendRequestBlock)(void);
    void (^sendRequestBlock)(void);
    weakSendRequestBlock = sendRequestBlock = ^{
        __strong typeof (weakSendRequestBlock)strongSendRequestBlock = weakSendRequestBlock;
        numberOfRetries--;

        AFHTTPRequestOperation *operation = [self.httpManager HTTPRequestOperationWithRequest:request success:successBlock failure:^(AFHTTPRequestOperation *operation, NSError *error) {
            NSInteger statusCode = [[[error userInfo] objectForKey:AFNetworkingOperationFailingURLResponseErrorKey] statusCode];

            if (numberOfRetries > 0 && (statusCode == 500 || statusCode == 502 || statusCode == 503 || statusCode == 0)) {
                dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 2 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
                    strongSendRequestBlock();
                });
            } else {
                if (failureBlock) {
                    failureBlock(operation, error);
                }
            }
        }];

        [self.httpManager.operationQueue addOperation:operation];
    };

    sendRequestBlock();
}

Example of usage:

- (void)getSomeDetails:(DictionaryResultBlock)block
    {
        if (!block) {
            return;
        }

        NSString *urlString = @"your url string";
        NSMutableURLRequest *request = [self.httpManager.requestSerializer requestWithMethod:@"POST" URLString:[[NSURL URLWithString:urlString relativeToURL:self.defaultUrl] absoluteString] parameters:nil error:nil];

        // Configure you request here
       [request setValue:version forHTTPHeaderField:@"client-version"];

        NSMutableDictionary *bodyParams = @{};   
        [request setHTTPBody:[NSJSONSerialization dataWithJSONObject:bodyParams options:0 error:nil]];

        [self sendRequest:request successBlock:^(AFHTTPRequestOperation *operation, id responseObject) {
            id response = [NSJSONSerialization JSONObjectWithData:responseObject options:0 error:nil];
            block(response, nil);
        } failureBlock:^(AFHTTPRequestOperation *operation, NSError *error) {
            block(nil, error);
        }];
    }

回答3:

In my case, I frequently required retry functionality so I came up wit this retry policy category that will help you with that AFNetworking+RetryPolicy

With respect to AFNetworking 3.0 it could serve well.

回答4:

Based on your answers, you could do something even more generic (and tricky) by using a block taking as parameter a block :

typedef void (^CallbackBlock)(NSError* error, NSObject* response);
- (void) performBlock:(void (^)(CallbackBlock callback)) blockToExecute retryingNumberOfTimes:(NSUInteger)ntimes onCompletion:(void (^)(NSError* error, NSObject* response)) onCompletion {
    blockToExecute(^(NSError* error, NSObject* response){
        if (error == nil) {
            onCompletion(nil, response);
        } else {
            if (ntimes <= 0) {
                if (onCompletion) {
                    onCompletion(error, nil);
                }
            } else {
                [self performBlock:blockToExecute retryingNumberOfTimes:(ntimes - 1) onCompletion:onCompletion];
            }
        };
    });
}

Then surround your asynchronous HTTP requests like the following :

[self performBlock:^(CallbackBlock callback) {

        [...]
        AFHTTPRequestOperationManager *manager = [WSManager getHTTPRequestOperationManager];
        [manager POST:base parameters:parameters success:^(AFHTTPRequestOperation *operation, id responseObject) {

            dispatch_async(dispatch_get_main_queue(), ^(void){
                    if (callback) {
                        callback(nil, responseObject);
                    }
                });

            } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
                if (callback) {
                    NSError* errorCode = [[NSError alloc] initWithDomain:AppErrorDomain code:[operation.response statusCode] userInfo:@{ NSLocalizedDescriptionKey :error.localizedDescription}];
                    callback(errorCode, nil);
                }
            }];

    } retryingNumberOfTimes:5 onCompletion:^(NSError *error,  NSObject* response) {
        //everything done
    }];

This way the retries wait for the HTTP request to finish and you don't have to implement the retry loop in each request methods.