I am using URLSessionConfiguration.background and uploadTask to upload a file from an iOS app.

The upload session is configured in the following way:

let configuration = URLSessionConfiguration.background(withIdentifier: "com.mycompany.myapp.fileUploader")
configuration.isDiscretionary = false
configuration.allowsCellularAccess = true
uploadURLSession = URLSession(configuration: configuration, delegate: self, delegateQueue: nil)

and the request is:

request.httpMethod = "POST"
request.setValue("application/octect-stream", forHTTPHeaderField: "Content-Type")


let task = uploadURLSession.uploadTask(with: request, fromFile: fileURL)

I'd like to understand how to manage the error handling.

How the http errors 4xx or 5xx are handled by the URLSession.uploadTask?

How can I trigger the retrying on 5xx errors?

CodePudding user response：

Create the upload task like this:

let task = uploadSession?.uploadTask(with: request, fromFile: fileURL, completionHandler: { data, response, error in
        if let error = error {
            print("Upload error: \(error.localizedDescription)")
        } else {
            if let response = response as? HTTPURLResponse {
                print("Response status code: \(response.statusCode)")
            }
        }
    })

    task?.resume()

you can handle errors and responsecode in the callback ☝️, alternatively you can look at URLSessionTaskDelegate and and URLSessionDataDelegate for a fine-grained control over the upload task.

CodePudding user response：

URLSession.uploadTask does not handle the http server side errors. It handles retrying and errors only for client side or network issues.

The http status/error has to be retrieved from the task response casting it to an HTTPURLResponse.

Directly from the uploadTask call (not supported by background URLSession):

let task = uploadSession?.uploadTask(with: request, fromFile: fileURL, completionHandler: { data, response, error in
    if let error = error {
        print("Upload error:\(error)")
        //Client side error
        return
    }
    
    guard let res = response as? HTTPURLResponse else {
        print("Upload completed with response:\(response.description ?? "undefined")")
        //It should not happen at all
        return
    }
    
    if (200...299).contains(res.statusCode) {
        print("Upload completed successfully. Status code:\(res.statusCode)")
    }
    else if (400...499).contains(res.statusCode) {
        print("Upload fatal issue. Status code:\(res.statusCode)")
        //Fatal issue, do not retry the upload
    }
    else if (500...599).contains(res.statusCode) {
        print("Upload issue. Status code:\(res.statusCode)")
        //Schedules a new uploading task for the file
    }
    else {
        print("Upload completed with status code:\(res.statusCode)")
    }
})

or, if you are using a background URLSession, from the URLSessionTaskDelegate:

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
    if let error = error {
        print("Upload error:\(error)")
        //Client side error
        return
    }

    guard let res = task.response as? HTTPURLResponse else {
        print("Upload completed with response:\(task.response?.description ?? "undefined")")
        //It should not happen at all
        return
    }

    if (200...299).contains(res.statusCode) {
        print("Upload completed successfully. Status code:\(res.statusCode)")
    }
    else if (400...499).contains(res.statusCode) {
        print("Upload fatal issue. Status code:\(res.statusCode)")
        //Fatal issue, do not retry the upload
    }
    else if (500...599).contains(res.statusCode) {
        print("Upload issue. Status code:\(res.statusCode)")
        //Schedules a new uploading task for the file
    }
    else {
        print("Upload completed with status code:\(res.statusCode)")
    }
}