How to intercept networking calls (REST) in iOS using NSURLProtocol

Question

I need to intercept the networking call that the client will make in the application while the call will successfully complete. I found out that a solution is implementing the NSURLProtocol abstract class and register to the application.

This seemed to solve my problems but then I hit a wall, request timeout. I use AFNetworking latest 1.x version because I need to support iOS 5.0.

So now I need to find either how to extend the timeout of the initial request or another more appropriate solution to my problem.

Here is what I've done. The NSURLProtocol implementation:

@implementation SLKURLProtocol

+ (NSURLRequest*) canonicalRequestForRequest:(NSURLRequest *)request
    {
    return request;
    }

+ (BOOL) canInitWithRequest:(NSURLRequest *)request
    {
    return [[[request URL] scheme] isEqualToString:@"http"];
    }

- (void) startLoading
    {
    dispatch_async(kBgQueue,
        ^{
        NSLog(@"Intercept Request startLoading");
        NSURLRequest* request = self.request;
        NSLog(@"URL: %@", request.URL);
        NSLog(@"HTTP Method: %@", request.HTTPMethod);
        NSLog(@"Data: %@", [NSString stringWithUTF8String:[request.HTTPBody bytes]]);
        });
    }

- (void) stopLoading
    {
    dispatch_async(kBgQueue,
        ^{
        NSLog(@"Intercept Request stopLoading");
        });
    }

@end

The networking ViewController:

@implementation SLKViewController

- (void) viewDidLoad
    {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    [NSURLProtocol registerClass:[SLKURLProtocol class]];
    [self initRequest];
    }

- (void) initRequest
    {
    NSMutableURLRequest* urlRequest = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:@"http://requestb.in/19kcum21"]
            cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:10.0f];
    [urlRequest setHTTPMethod:@"POST"];

    NSMutableData* postData = [NSMutableData data];
    [postData appendData:[@"REQUEST AFNETWORKING" dataUsingEncoding:NSUTF8StringEncoding]];
    [urlRequest setHTTPBody:postData];
    AFHTTPRequestOperation* operation = [[AFHTTPRequestOperation alloc] initWithRequest:urlRequest];

    [operation setCompletionBlockWithSuccess:
        ^(AFHTTPRequestOperation *operation, id responseObject)
        {
        NSString* serverResponse = [operation responseString];
        NSLog(@"AFNetworking Response: %@", serverResponse);
        } failure:
            ^(AFHTTPRequestOperation *operation, NSError *error)
        {
        NSLog(@"AFNetworking Error: %@", error.description);
        }];

    [operation start];
    }

@end

Here is the log output:

2014-01-15 17:07:19.518 InterceptionHttp[510:1303] Intercept Request startLoading 2014-01-15 17:07:19.520 InterceptionHttp[510:1303] URL: http://requestb.in/19kcum21 2014-01-15 17:07:19.521 InterceptionHttp[510:1303] HTTP Method: POST 2014-01-15 17:07:19.522 InterceptionHttp[510:1303] Data: REQUEST AFNETWORKING 2014-01-15 17:07:29.522 InterceptionHttp[510:400b] Intercept Request stopLoading 2014-01-15 17:07:29.522 InterceptionHttp[510:70b] AFNetworking Error: Error Domain=NSURLErrorDomain Code=-1001 "The request timed out." UserInfo=0x8a5cb10 {NSErrorFailingURLStringKey=http://requestb.in/19kcum21, NSErrorFailingURLKey=http://requestb.in/19kcum21, NSLocalizedDescription=The request timed out., NSUnderlyingError=0x8a5c220 "The request timed out."}

EDIT:

After jqyao answer and reading the article I have learned some topics about subclassing NSURLProtocol. But unfortunately I still can't intercept the HTTP, meaning that I want the original request to normally continue.

Meanwhile, if I add the 3 lines invoking the URLProtocol delegate selectors, original request will continue but with a response of the data and not the server's.

Here is what I added in startLoading method.

[[self client] URLProtocol:self didReceiveResponse:[[NSURLResponse alloc] init] cacheStoragePolicy:NSURLCacheStorageNotAllowed];
[[self client] URLProtocol:self didLoadData:data];
[[self client] URLProtocolDidFinishLoading:self];

Here is my output log.

2014-02-04 17:27:22.253 InterceptionHttp[419:3a03] Intercept Request startLoading 2014-02-04 17:27:22.254 InterceptionHttp[419:3a03] URL: http://requestb.in/tsvc14ts 2014-02-04 17:27:22.255 InterceptionHttp[419:3a03] HTTP Method: POST 2014-02-04 17:27:22.255 InterceptionHttp[419:3a03] Data: { 'message': 'JSON_MESSAGE' } 2014-02-04 17:27:22.258 InterceptionHttp[419:70b] AFNetworking Response: { 'message': 'JSON_MESSAGE' } 2014-02-04 17:27:22.260 InterceptionHttp[419:1303] Intercept Request stopLoading

Answer 1

OK, I borrowed some code from this really cool network and data debugging component https://github.com/square/PonyDebugger and did the job very nice and smooth.

The regarding class is https://github.com/square/PonyDebugger/blob/master/ObjC/PonyDebugger/PDNetworkDomainController.m

Hope that helps to other people looking something similar.

Answer 2

I suggest you to take a look on this article http://robnapier.net/offline-uiwebview-nsurlprotocol and the implementation https://github.com/rnapier/RNCachingURLProtocol. How often do you see the timeout issue ?