Upload a UIImage to S3 and get its URL

S3Upload.swift

/*
 * Credit to JC https://github.com/kharmabum for most of this code.
 *
 * Frameworks used:
 * - Alamofire https://github.com/Alamofire/Alamofire
 * - Async https://github.com/duemunk/Async
 * - AWS SDK http://aws.amazon.com/mobile/sdk/
 */

import Foundation

import Alamofire
import Async
import AWSCore
import AWSS3

class NetworkManager: Alamofire.Manager {

    private static let AWSAccessKey = "ACCESS KEY"
    private static let AWSSecret = "SECRET"
    private static let AWSRegion = AWSRegionType.USWest2
    private static let S3Bucket = "my-bucket"

    private static let instance: NetworkManager = {
        let configuration = NSURLSessionConfiguration.defaultSessionConfiguration()
        configuration.HTTPAdditionalHeaders = Manager.defaultHTTPHeaders
        return NetworkManager(configuration: configuration)
    }()

    var backgroundQueue: dispatch_queue_t
    var awsConfigurationToken: dispatch_once_t = 0

    init(configuration: NSURLSessionConfiguration) {
        let attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_BACKGROUND, 0)
        backgroundQueue = dispatch_queue_create("com.yourname.NetworkManager", attr)
        super.init(configuration: configuration)
    }

    class func uploadFileWithURL(URL: NSURL, contentType: String, destination: String, completion: (Result<String, NSError>) -> Void) {
        dispatch_once(&self.instance.awsConfigurationToken) {
            let credentialsProvider = AWSStaticCredentialsProvider(accessKey: NetworkManager.AWSAccessKey, secretKey: NetworkManager.AWSSecret)
            let configuration = AWSServiceConfiguration(region: NetworkManager.AWSRegion, credentialsProvider: credentialsProvider)
            AWSServiceManager.defaultServiceManager().defaultServiceConfiguration = configuration
        }

        Async.customQueue(self.instance.backgroundQueue) {
            // unique key for the image based on the time and a random UUID
            let key = "\(NSDate().timeIntervalSince1970)" + "-" + NSUUID().UUIDString

            let uploadRequest = AWSS3TransferManagerUploadRequest()
            uploadRequest.key = key
            uploadRequest.body = URL
            uploadRequest.contentType = contentType
            uploadRequest.ACL = .PublicRead
            uploadRequest.bucket = NetworkManager.S3Bucket + "/" + destination

            let transferManager = AWSS3TransferManager.defaultS3TransferManager()
            transferManager.upload(uploadRequest).continueWithBlock { (task) -> AnyObject? in
                guard task.error == nil else {
                    debugPrint("Failed to upload file: " + task.error.debugDescription)
                    Async.main() {
                        completion(Result.Failure(task.error!))
                    }
                    return nil
                }

                let imageURLString = "https://s3-us-west-2.amazonaws.com/\(NetworkManager.S3Bucket)/\(destination)/\(key)"
                Async.main() { completion(Result.Success(imageURLString)) }
                return nil
            }
        }
    }

    class func uploadData(data: NSData, contentType: String, destination: String, completion: (Result<String, NSError>) -> Void) {
        Async.customQueue(self.instance.backgroundQueue) {
            let tmpURL = NSURL(fileURLWithPath: NSTemporaryDirectory().stringByAppendingString("/" + NSUUID().UUIDString))
            data.writeToURL(tmpURL, atomically: true)
            uploadFileWithURL(tmpURL, contentType: contentType, destination: destination, completion: completion)
        }
    }

    class func uploadImage(image: UIImage, completion: (Result<String, NSError>) -> Void) {
        Async.customQueue(self.instance.backgroundQueue) {
            if let data = UIImageJPEGRepresentation(image, 0.5) {
                let contentType = "image/jpeg"  // MIME type
                uploadData(data, contentType: contentType, destination: "images", completion: completion)
            } else {
                Async.main() {
                    completion(Result.Failure(NSError(domain: NSURLErrorDomain, code: NSURLErrorUnknown, userInfo: nil)))
                }
            }
        }
    }
    
}