URLSessionUploadTask getting automatically cancelled instantly

Question

I\'m having this weird issue in which a newly created URLSessionUploadTask gets cancelled instantly. I\'m not sure if it\'s a bug with the current beta of Xcode

Answer 1

After struggling non-stop with this for 6 days, and after googling non-stop for a solution, I'm really happy to say I have finally figured it out.

Turns out that, for whatever mysterious reason, the from: parameter in uploadTask(with:from:completionHandler) cannot be nil. Despite the fact that the parameter is marked as an optional Data, it gets cancelled instantly when it is missing. This is probably a bug on Apple's side, and I opened a bug when I couldn't get this to work, so I will update my bug report with this new information.

With that said, everything I had to do was to update my buildPOSTTask method to account for the possibility of the passed dictionary to be nil. With that in place, it works fine now:

internal func buildPOSTTask(onURLSession urlSession: URLSession, appendingPath path: String, withPostParameters postParams: [String : String]?, getParameters getParams: [String : String]?, httpHeaders: [String : String]?, completionHandler completion: URLSessionUploadTaskCompletionHandler) -> URLSessionUploadTask {
    let fullURL: URL
    if let gets = getParams {
        fullURL = buildURL(appendingPath: path, withGetParameters: gets)
    } else {
        fullURL = URL(string: path, relativeTo: baseURL)!
    }

    var request = URLRequest(url: fullURL)
    request.httpMethod = "POST"

    var postParameters: Data

    if let posts = postParams {
        do {
            postParameters = try JSONSerialization.data(withJSONObject: posts, options: [])
        } catch let error as NSError {
            fatalError("[\(#function) \(#line)]: Could not build POST task: \(error.localizedDescription)")
        }
    } else {
        postParameters = Data()
    }

    let postTask = urlSession.uploadTask(with: request, from: postParameters, completionHandler: completion)
    return postTask
}

Answer 2

Are you by any chance using a third party library such as Ensighten? I had the exact same problem in XCode 8 beta (works fine in XCode 7) and all of my blocks with nil parameters were causing crashes. Turns out it was the library doing some encoding causing the issue.

Answer 3

Your server is broken..

tcp_connection_cancel 1
nw_socket_handle_socket_event Event mask: 0x4
nw_socket_handle_socket_event Socket received WRITE_CLOSE event
nw_endpoint_handler_cancel [1 anilist.co:443 ready resolver (satisfied)]
nw_endpoint_handler_cancel [1.1 104.28.1.44:443 ready socket-flow (satisfied)]
__nw_socket_service_writes_block_invoke sendmsg(fd 9, 31 bytes): socket has been closed
nw_endpoint_flow_protocol_error [1.1
104.28.1.44:443 cancelled socket-flow (null)] Socket protocol sent error: [32] Broken pipe
nw_endpoint_flow_protocol_disconnected [1.1 104.28.1.44:443 cancelled socket-flow (null)] Output protocol disconnected
nw_endpoint_handler_cancel [1.2 104.28.0.44:443 initial path (null)] 
nw_resolver_cancel_on_queue 0x60800010da40
[NWConcrete_tcp_connection dealloc] 1
[User Defaults] CFPrefsPlistSource<0x6180000f8700> (Domain: XIO.PrivateAPITest, User: kCFPreferencesCurrentUser, ByHost: No, Container: (null)) is waiting for writes to complete so it can determine if new data is available

It waits infinitely for "writes" to complete..

It sends the request.. does the SSL handshake and gets no response. It times out and considers it a broken request..

class WTF : NSObject, URLSessionDelegate {

    var urlSession: URLSession!

    override init() {
        super.init()

        urlSession = URLSession(configuration: .default, delegate: self, delegateQueue: nil)

        var request = URLRequest(url: URL(string: "https://anilist.co/api/auth/access_token?client_secret=REMOVED&grant_type=authorization_code&redirect_uri=genericwebsitethatshouldntexist.bo&client_id=ibanez-hod6w&code=REMOVED")!)
        request.httpMethod = "POST"

        let data = try! JSONSerialization.data(withJSONObject: ["Test":"Test"], options: [])

        urlSession.uploadTask(with: request, from: data).resume()
    }

    func urlSession(_ session: URLSession, didReceive challenge: URLAuthenticationChallenge, completionHandler: (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) {

        completionHandler(.performDefaultHandling, nil)

    }

    func urlSession(_ session: URLSession, task: URLSessionTask, didSendBodyData bytesSent: Int64, totalBytesSent: Int64, totalBytesExpectedToSend: Int64) {

    }

    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: NSError?) {

    }

    func urlSession(_ session: URLSession, task: URLSessionTask, willPerformHTTPRedirection response: HTTPURLResponse, newRequest request: URLRequest, completionHandler: (URLRequest?) -> Void) {

        completionHandler(request)

    }

    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: (URLSession.ResponseDisposition) -> Void) {

        completionHandler(.allow)

    }

    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {

    }
}