NSURLSession Background File Upload using Bound Streams

Question

History:

I am working on a project for which we need to support:

• Background Upload of files using NSURLSession.
• The server expects file to be uploaded using Content-Type: multipart/form-data
• Previously, I was using NSURLConnection with bound pair of Streams as depicted in this Apple Sample.
• Now, I wish to follow similar approach with NSURLSession(Background Session) by using uploadTaskWithStreamedRequest:.
• I have written a small stand-alone iOS Sample + a PHP server to validate my concept.

Problem: Everything works if app stays in foreground, but if during upload I press the home key, the upload fails after some time with error:

Domain=NSURLErrorDomain Code=-997 "Lost connection to background transfer service"

Also a little before the upload fails the Write/Producer Stream's NSStreamEventEndEncountered is encountered.

Note: I know the work-around where I can write whole HTTP Post body to a temp file and use NSURLSession's file upload API instead. But above is more appropriate if I can make it work.

Question: Can anyone guess what could be possible reason for the upload getting failed?

Sample Code: I have uploaded the iOS Sample Code + PHP Server Code to drop box. Here is the CODE

Thanks!

Breban

Have you tried setting up the session as a "Background Session"? See + (NSURLSessionConfiguration *)backgroundSessionConfigurationWithIdentifier:(NSString *)identifier – Savitt

@Savitt Yes, I did. – Breban

Answer 1

You can't upload streamed tasks using Background Configuration. I successfully upload data only in two cases:

1. Download task with data stored in request body.
2. Upload task from file. In that case you will not receive response body.

Rodroda

What you wrote is true for iOS 7. But for iOS 8+ you can use data tasks and background session. – Barbed

@Barbed yes, but they can't be streamed data tasks (as stated in Apple docs): * Only upload tasks from a file are supported (uploading from data objects or a stream will fail after the program exits). – Rodroda

Sorry, I didn't noticed that it's about streams. – Barbed