NSURLSession and amazon S3 uploads

Question

I have an app which is currently uploading images to amazon S3. I have been trying to switch it from using NSURLConnection to NSURLSession so that the uploads can continue w

Answer 1

For background uploading/downloading you need to use NSURLSession with background configuration. Since AWS SDK 2.0.7 you can use pre signed requests:

PreSigned URL Builder** - The SDK now includes support for pre-signed Amazon Simple Storage Service (S3) URLs. You can use these URLS to perform background transfers using the NSURLSession class.

Init background NSURLSession and AWS Services

- (void)initBackgroundURLSessionAndAWS
{
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration backgroundSessionConfigurationWithIdentifier:AWSS3BackgroundSessionUploadIdentifier];
    self.urlSession = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:nil];
    AWSServiceConfiguration *configuration = [AWSServiceConfiguration configurationWithRegion:DefaultServiceRegionType credentialsProvider:credentialsProvider];
    [AWSServiceManager defaultServiceManager].defaultServiceConfiguration = configuration;
    self.awss3 = [[AWSS3 alloc] initWithConfiguration:configuration];
}

Implement upload file function

- (void)uploadFile
{
    AWSS3GetPreSignedURLRequest *getPreSignedURLRequest = [AWSS3GetPreSignedURLRequest new];
    getPreSignedURLRequest.bucket = @"your_bucket";
    getPreSignedURLRequest.key = @"your_key";
    getPreSignedURLRequest.HTTPMethod = AWSHTTPMethodPUT;
    getPreSignedURLRequest.expires = [NSDate dateWithTimeIntervalSinceNow:3600];
    //Important: must set contentType for PUT request
    getPreSignedURLRequest.contentType = @"your_contentType";

    [[[AWSS3PreSignedURLBuilder defaultS3PreSignedURLBuilder] getPreSignedURL:getPreSignedURLRequest] continueWithBlock:^id(BFTask *task) {
        if (task.error)
        {
            NSLog(@"Error BFTask: %@", task.error);
        }
        else
        {
            NSURL *presignedURL = task.result;
            NSLog(@"upload presignedURL is: \n%@", presignedURL);

            NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:presignedURL];
            request.cachePolicy = NSURLRequestReloadIgnoringLocalCacheData;
            [request setHTTPMethod:@"PUT"];
            [request setValue:contentType forHTTPHeaderField:@"Content-Type"];

//          Background NSURLSessions do not support the block interfaces, delegate only.
            NSURLSessionUploadTask *uploadTask = [self.session uploadTaskWithRequest:request fromFile:@"file_path"];

            [uploadTask resume];
        }
        return nil;
    }];
}

NSURLSession Delegate Function:

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
    if (error)
    {
        NSLog(@"S3 UploadTask: %@ completed with error: %@", task, [error localizedDescription]);
    }
    else
    {
//      AWSS3GetPreSignedURLRequest does not contain ACL property, so it has to be set after file was uploaded
        AWSS3PutObjectAclRequest *aclRequest = [AWSS3PutObjectAclRequest new];
        aclRequest.bucket = @"your_bucket";
        aclRequest.key = @"yout_key";
        aclRequest.ACL = AWSS3ObjectCannedACLPublicRead;

        [[self.awss3 putObjectAcl:aclRequest] continueWithBlock:^id(BFTask *bftask) {
            dispatch_async(dispatch_get_main_queue(), ^{
                if (bftask.error)
                {
                    NSLog(@"Error putObjectAcl: %@", [bftask.error localizedDescription]);
                }
                else
                {
                    NSLog(@"ACL for an uploaded file was changed successfully!");
                }
            });
            return nil;
        }];
    }
}