Understanding AFNetworking - Error

Contents

1. 1. NSError in failure block
2. 2. How AFNetworking creates NSError
   1. 2.1. AFURLSessionManager.m
   2. 2.2. AFErrorWithUnderlyingError
   3. 2.3. Error Domain
3. 3. HTTP Status code
   1. 3.1. Inspect userInfo of NSError
   2. 3.2. Replace NSError
4. 4. Reference

When using AFNetworking, I want to get the status code in case of failure

NSError in failure block

AFHTTPSessionManager *sessionManager = [AFHTTPSessionManager manager];
    [sessionManager GET:@"" parameters:nil success:^(NSURLSessionDataTask *task, id responseObject) {

    } failure:^(NSURLSessionDataTask *task, NSError *error) {
        NSLog(@"%@", error);
    }];

The error.code is not the HTTP status code, it is NSError that AFNetworking creates due to serializer error

How AFNetworking creates NSError

AFURLSessionManager.m

In URLSession:task:didCompleteWithError:

NSError *serializationError = nil;
            responseObject = [manager.responseSerializer responseObjectForResponse:task.response data:[NSData dataWithData:self.mutableData] error:&serializationError];

AFErrorWithUnderlyingError

This is called in validateResponse:data:error: and responseObjectForResponse:data:error of AFURLResponseSerialization classes

static NSError * AFErrorWithUnderlyingError(NSError *error, NSError *underlyingError) {
    if (!error) {
        return underlyingError;
    }

    if (!underlyingError || error.userInfo[NSUnderlyingErrorKey]) {
        return error;
    }

    NSMutableDictionary *mutableUserInfo = [error.userInfo mutableCopy];
    mutableUserInfo[NSUnderlyingErrorKey] = underlyingError;

    return [[NSError alloc] initWithDomain:error.domain code:error.code userInfo:mutableUserInfo];
}

Error Domain

In AFURLResponseSerialization.h

Error codes for AFURLResponseSerializationErrorDomain correspond to codes in NSURLErrorDomain.

For example

validationError = AFErrorWithUnderlyingError([NSError errorWithDomain:AFURLResponseSerializationErrorDomain code:NSURLErrorCannotDecodeContentData userInfo:mutableUserInfo], validationError);

HTTP Status code

Inspect userInfo of NSError

The NSError userInfo contains AFNetworkingOperationFailingURLResponseErrorKey and AFNetworkingOperationFailingURLResponseDataErrorKey that we can inspect to get NSURLResponse and NSData

Replace NSError

Sometimes we don’t care about NSURLErrorDomain, we can get HTTP Status Code from NSURResponse and replace the code in the NSError

NSURLSessionDataTask *task = [self.manager dataTaskWithRequest:request
                                                     completionHandler:^(NSURLResponse *response, id responseObject, NSError *error)
                                      {
                                         if (error) {
                                             error = [self errorFromError:error
                                                           responseObject:responseObject
                                                                 response:response];
                                              [subscriber sendError:error];
                                          } else {
                                              [subscriber sendNext:responseObject];
                                              [subscriber sendCompleted];
                                          }
                                      }];
- (NSError *)errorFromError:(NSError *)error
             responseObject:(id)responseObject
                   response:(NSURLResponse *)response {

    NSMutableDictionary *userInfo = [NSMutableDictionary dictionaryWithDictionary:error.userInfo];
    if (responseObject) {
        userInfo[kNetworkProviderResponseObjectKey] = responseObject;
    }

    NSInteger HTTPStatusCode = error.code;
    if (response) {
        if ([response isKindOfClass:[NSHTTPURLResponse class]]) {
            NSHTTPURLResponse *HTTPResponse = (id)response;
            HTTPStatusCode = HTTPResponse.statusCode;
        }
    } else {
        HTTPStatusCode = 408;
    }

    return [NSError errorWithDomain:error.domain code:HTTPStatusCode userInfo:userInfo];
}

Reference

1. OSStatus