Programmatically monitor URLSession requests – Ios swift

The goal is to see data like URL, headers and body of those requests

If you want to track only requests (but not responses), then it’s as simple as adding an extra layer of NSURLProtocol to the session object. Since public API of the NSURLSession accepts tasks only, you can limit tracking to canInitWithTask: method:

@interface TDWWatcherProtocol : NSURLProtocol

@end

@implementation TDWWatcherProtocol

#pragma mark NSURLProtocol

+ (BOOL)canInitWithTask:(NSURLSessionTask *)task {
    [self p_printRequestData:task.originalRequest];
    return NO;
}

+ (BOOL)canInitWithRequest:(NSURLRequest *)request {
    // no-op
    return NO;
}

#pragma mark Private

+ (void)p_printRequestData:(NSURLRequest *)request {
    NSLog(@"==========================");
    NSString *httpMethods = request.HTTPMethod ? request.HTTPMethod : @"GET";
    NSLog(@"Request: %@ %@", httpMethods,  request.URL);
    NSLog(@"Headers: %@", request.allHTTPHeaderFields);
    if (request.HTTPBody && request.HTTPBody.length) {
        NSLog(@"Body: %@", [[NSString alloc] initWithData:request.HTTPBody encoding:NSUTF8StringEncoding]);
    }
}

@end

You cannot omit implementation of canInitWithRequest: because in this case URL loading system will forward it to the base implementation of NSURLProtocol, which throws an error (the class is considered abstract). You provide your custom protocol to a NSURLSession instance by incorporating it to the configuration’s protocolClasses property:

NSURLSessionConfiguration *configuration = NSURLSessionConfiguration.defaultSessionConfiguration;
NSMutableArray<Class> *protocolClasses = [configuration.protocolClasses mutableCopy];
[protocolClasses addObject:[TDWWatcherProtocol class]];
configuration.protocolClasses = protocolClasses;
NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];

If you additionally want to track all requests made by the sharedSession instance you must register your class globally with NSURLProtocol helper methods:

[NSURLProtocol registerClass:[TDWWatcherProtocol class]];

This also makes URL loading system to forward web views to requests to your protocol class.

You may want to track canInitWithRequest: invocations as well, but be advised that in this case you will also get modified requests from internal implementation in addition to the original requests.