How to use urlSession? (urlSession as proxy)

[pquerner]

Hello,

I am having trouble getting a URLSession to work, since our sentry instance is not reachable from public internet, I want to route the traffic first to a public facing server, which will act as a proxy.
Please note I am not really a Swift developer, I only know a few things here and there. ;)

With #3811 its possible to define a own URLSession, and to my understanding can be used in a more-or-less similar way as the tunnel option from the Sentry JS SDK.

So I've created a delegate class for URLSession like that:

class OmSentry: NSObject, URLSessionDelegate
{
    func urlSession(_ session: URLSession, task: URLSessionTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
            // todo: modify request.url to point to proxy
            completionHandler(.allow)
        }
    
    func urlSession(_ session: URLSession, task: URLSessionTask, willBeginDelayedRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void) {
        // todo: modify request.url to point to proxy
        completionHandler(newRequest)
    }
    
    // Override the willPerformHTTPRedirection method
    func urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: @escaping (URLRequest?) -> Void) {
        // todo: modify request.url to point to proxy
        var newRequest = request
        completionHandler(newRequest)
    }
}

And setup the Sentry iOS SDK (8.28) like that in our AppDelegate:

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

        let configuration = URLSessionConfiguration.ephemeral
        let session = URLSession(configuration: configuration, delegate: OmSentry(), delegateQueue: nil)
        
        let fakeDSN = "https://user@0.0.0.0/123" # also tried user@example.com, user@our-real-domain.com, a valid DSN
        SentrySDK.start { options in
            options.dsn = fakeDSN
            options.urlSession = session
            options.enableTracing = true
            #if DEBUG
            options.tracesSampleRate = 1.0
            options.profilesSampleRate = 1.0
            options.debug = true
            #else
            options.tracesSampleRate = 0.2
            options.profilesSampleRate = 0.2
            options.debug = false
            #endif

            options.attachScreenshot = true
            options.attachViewHierarchy = true
        }
        SentrySDK.capture(message: "Hello World!")

and put some breakpoints on the OmSentry overwritten functions to see if they are triggered.
However, they never are triggered. In all cases they arent.

My goal is to fix the "fakedsn" (on the SentrySDK configuration part) to a new URL which will receive the envelope data as-is and simply forwards that data (after checks) to the actual sentry instance.

Thanks for reading!

[brustolin]

So, this is what you need to redirect a request:

class CustomURLProtocol: URLProtocol {
    override class func canInit(with request: URLRequest) -> Bool {
        return URLProtocol.property(forKey: "Handled", in: request) == nil
    }
    
    override class func canonicalRequest(for request: URLRequest) -> URLRequest {
        guard let newUrl = URL(string: "https://redirectUrl.com/forwardSentry") else { return request }
        var newRequest = URLRequest(url: newUrl)
        newRequest.httpBody = request.httpBody
        newRequest.httpMethod = request.httpMethod
        newRequest.allHTTPHeaderFields = request.allHTTPHeaderFields
        return newRequest
    }
    
    override func startLoading() {
        URLProtocol.setProperty(true, forKey: "Handled", in: request as! NSMutableURLRequest)
        let newTask = URLSession.shared.dataTask(with: request) { data, response, error in
            if let data = data { self.client?.urlProtocol(self, didLoad: data) }
            if let response = response { self.client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed) }
            if let error = error { self.client?.urlProtocol(self, didFailWithError: error) }
            self.client?.urlProtocolDidFinishLoading(self)
        }
        newTask.resume()
    }
    
    override func stopLoading() {
        // Not implemented on purpose
    }
}

static func startSentry() {
    var config = URLSessionConfiguration.default
    config.protocolClasses = [CustomURLProtocol.self]
        
    SentrySDK.start { options in
        options.dsn = "..."
        options.urlSession = URLSession(configuration: config)
    }
}

You can call startSentry() from you application(_:didFinishLaunchingWithOptions:) function. Or copy the code there.

[pquerner]

Maybe because its gzipped, however unzipping it on the host also only gives me empty result. Where is content for the content-length? :D

[brustolin]

Ow,
it also needs

newRequest.httpBodyStream = request.httpBodyStream

because the body could be a Data or a Stream

[pquerner]

Do I have to fetch the stream (to string?)? Changeing httpBody to httpBodyStream alone does not help.

[brustolin]

You should not change but add both:

 override class func canonicalRequest(for request: URLRequest) -> URLRequest {
        guard let newUrl = URL(string: "https://redirectUrl.com/forwardSentry") else { return request }
        var newRequest = URLRequest(url: newUrl)
        newRequest.httpBody = request.httpBody
        newRequest.httpBodyStream = request.httpBodyStream
        newRequest.httpMethod = request.httpMethod
        newRequest.allHTTPHeaderFields = request.allHTTPHeaderFields
        return newRequest
    }

[pquerner]

Wonderful. That works just fine. :)