JenkinsRequest.h

#import <Foundation/Foundation.h>

typedef void(^SuccessBlock)(id object);
typedef void(^ErrorBlock)(NSString *error);

@interface JenkinsRequest : NSObject

@property (copy) SuccessBlock successBlock;
@property (copy) ErrorBlock errorBlock;

@end

JenkinsRequest.m

#import "JenkinsRequest.h"

@implementation JenkinsRequest

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    NSXMLDocument * document = [[NSXMLDocument alloc] initWithData: receivedData options:0 error: nil];
    id result = [translator translateDocument: document];
    if (result == nil) {
        if (self.errorBlock)
            self.errorBlock(@"Document translation failed.");
    }
    else {
        if (self.successBlock)
            self.successBlock(result);
    }
    
    receivedData = nil;
}

@end

stuff.m

- (void)doStuff {
    JenkinsRequest *request = [[JenkinsRequest alloc] init];
    
    request.successBlock = ^ (id results) {
        [self doStuffWithResults:results];
    };
    
    reuest.errorBlock = ^ (NSString *error) {
        NSLog(@"Error! %@", error);
    }
}