How to upload an image file in a background session (iOS)? - background-process

Question

I am unable to upload an image from my device's Photos in a background session. When I call [session uploadTaskWithRequest:req fromFile:nsurl] the system immediately complains by sending
Failed to issue sandbox extension for file file:///var/mobile/Media/DCIM/103APPLE/IMG_3984.JPG, errno = 1
to the console. (A similar Stack Overflow issue is here)
However, if I create my NSURLSessionConfiguration with [NSURLSessionConfiguration defaultSessionConfiguration] (instead of [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:id], which I need) and if I construct an NSData object out of the NSURL and upload that instead of uploading straight from a file (which is required by a background session) then the upload succeeds. Btw I'm uploading files into our Rackspace Cloud account, and am able to do this successfully with a simple Postman PUT.
The problem occurs in my uploadObject method, which looks like:
-(void) uploadObject:(NSURL*)urlToBeUploadedIn
{
NSDictionary *headers = #{ #"x-auth-token": state.tokenID,
#"content-type": #"image/jpeg",
#"cache-control": #"no-cache" };
// create destination url for Rackspace cloud upload
NSString *sURL = [NSString stringWithFormat:#"%#/testing_folder/%#.jpg", state.publicURL, [state generateImageName]];
NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:sURL]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:10.0];
[request setHTTPMethod:#"PUT"];
[request setAllHTTPHeaderFields:headers];
self.sessionIdentifier = [NSString stringWithFormat:#"my-background-session"];
// NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration]; // when I use this instead of the line below the sandbox error goes away
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:self.sessionIdentifier];
self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
NSURLSessionUploadTask *uploadTask = [self.session uploadTaskWithRequest:request fromFile:urlToBeUploadedIn];
[uploadTask resume];
}
My call that invokes uploadObject: looks like:
PHFetchResult *fetchResult = [PHAsset fetchAssetsWithLocalIdentifiers:state.arrImagesToBeUploaded options:nil];
PHAsset *phAsset = [fetchResult objectAtIndex:0]; // yes the 0th item in array is guaranteed to exist, above.
[phAsset requestContentEditingInputWithOptions:nil
completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info) {
NSURL *imageURL = contentEditingInput.fullSizeImageURL;
[self uploadObject:imageURL];
}];
Btw I first validate the NSURL I send to uploadObject: with a call to fileExistsAtPath: so I know my reference to the file is good. Finally, my delegate calls
(void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)dataIn
(void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error does get invoked, although the data
do get called by the server (although the response won't parse) so, I am getting something back from the server which never correctly receives the image.

Answer 1

A solution is to first copy the image to be uploaded into the app's sandbox. I used:
NSError *err;
BOOL bVal = [myNSDataOb writeToURL:myDestinationURL options:0 error:&err];
and copied into my app's 'Documents' directory, but one might also use:
NSError *err;
BOOL bVal = [[NSFileManager defaultManager] copyItemAtURL:myImageURL toURL:myDestinationURL error:&err];