CustomNSURLProtocol.swift

import Foundation

let session = NSURLSession.sharedSession()
let requestIsBeingHandledKey = "RequestIsBeingHandledKey"

class CustomNSURLProtocol: NSURLProtocol {

    override class func canInitWithRequest(request: NSURLRequest) -> Bool {
        if NSURLProtocol.propertyForKey(requestIsBeingHandledKey, inRequest: request) != nil {
            return false // Prevent recursize loop
        }

        return false // Add condition here
    }

    override class func canonicalRequestForRequest(request: NSURLRequest) -> NSURLRequest {
        return request
    }

    override class func requestIsCacheEquivalent(aRequest: NSURLRequest, toRequest bRequest: NSURLRequest) -> Bool {
        return super.requestIsCacheEquivalent(aRequest, toRequest:bRequest)
    }

    override func startLoading() {
        let newRequest = request.mutableCopy() as! NSMutableURLRequest
        NSURLProtocol.setProperty(true, forKey: requestIsBeingHandledKey, inRequest: newRequest)

        session.dataTaskWithRequest(newRequest) { data, response, error in
            if let error = error {
                self.client!.URLProtocol(self, didFailWithError: error)
            } else if let data = data {

                self.completeRequestWithData(data)
            } else {
                fatalError("Data is nil")
            }
        }.resume()
    }

    override func stopLoading() { }

    private func completeRequestWithData(data: NSData) {
        self.client!.URLProtocol(self, didReceiveResponse: NSHTTPURLResponse(URL: request.URL!, statusCode: 200, HTTPVersion: nil, headerFields: nil)!, cacheStoragePolicy: .NotAllowed)
        self.client!.URLProtocol(self, didLoadData: data)
        self.client!.URLProtocolDidFinishLoading(self)
    }
}