Upload Very Large Files In Background on iOS - Alamofire.upload multipart in background

BackgroundTransferSample.swift

// You have a very very large video file you need to upload to a server while your app is backgrounded.
// Solve by using URLSession background functionality. I will here use Alamofire to enable multipart upload.

class Networking {
  static let sharedInstance = Networking()
  public var sessionManager: Alamofire.SessionManager // most of your web service clients will call through sessionManager
  public var backgroundSessionManager: Alamofire.SessionManager // your web services you intend to keep running when the system backgrounds your app will use this
  private init() {
    self.sessionManager = Alamofire.SessionManager(configuration: URLSessionConfiguration.default)
    self.backgroundSessionManager = Alamofire.SessionManager(configuration: URLSessionConfiguration.background(withIdentifier: "com.lava.app.backgroundtransfer"))
  }
}

class VideoUploadClient {
  class func upload(videoURL: URL, success: (() -> Void)?, failure: ((Error) -> Void)?) {
    
    Networking.sharedInstance.backgroundSessionManager.upload(multipartFormData: { (multipartData) in 
      // multipart setup
    }, usingThreshold: SessionManager.multipartFormDataEncodingMemoryThreshold, to: url, method: .post, headers: ["Content-Type":"multipart/form-data"], encodingCompletion: { encodingResult in
      // transmission closure
      switch (encodingResult) {
        // encodingResult success
        case .success(let request, let streamingFromDisk, let streamFileURL):           
                
                // upload progress closure
                request.uploadProgress(closure: { (progress) in
                    print("upload progress: \(progress.fractionCompleted)")
                    // here you can send out to a delegate or via notifications the upload progress to interested parties
                })
        
                // response handler
                request.responseJSON(completionHandler: { response in
                    switch response.result {
                      case .success(let jsonData):
                        // do any parsing on your request's response if needed
                        success?()
                      case .failure(let error):
                        failure?(error)
                    }
                })
        
        // encodingResult failure
        case .failure(let error):
          failure?(error)
        
      } // end encodingresult switch
    }) // end upload call
    
  }
} // end VideoUploadClient class




// meanwhile, from a call site somewhere
// ...
class UploadViewController {
  // ...
  
  // assume defined and ready
  let localVideoURL = URL(someLocalFile)! // force unwrap just for brevity of example, don't do this in real life.
  let successClosure: (() -> Void)? = { 
    print("succeeded :)")
  }
  let failClosure: ((Error) -> Void)? = {
    print("failed :(")
  }
  
  func uploadButtonAction() {
    VideoUploadClient.upload(localVideoURL, successClosure, failClosure)
  }
}