File Upload to S3 in Swift

multipart_form_upload.swift

//
//  UploadFileToS3Operation.swift
//  VecinioAPIKit
//
//  Created by Oscar Swanros on 9/2/17.
//  Copyright © 2017 Vecinio Technologies Inc. All rights reserved.
//

final public class UploadFileToS3Operation: P3Operation {
    public let image: UIImage
    public var uploadDescriptor: S3UploadDescriptor?
    
    public var uploadedFile: NetworkFile?
    
    var session: URLSession?
    
    private lazy var boundaryString: String = {
        return "\(NSUUID().uuidString)"
    }()
    
    public init(image: UIImage, uploadDescriptor: S3UploadDescriptor? = nil) {
        self.image = image
        self.uploadDescriptor = uploadDescriptor
        
        super.init()
        
        addObserver(observer: P3NetworkActivityObserver())
    }
    
    public override func execute() {
        guard let uploadDescriptor = uploadDescriptor else { fatalError("Can't start an upload without an upload descriptor") }
        
        let url = URL(string: "https://bucket.s3.amazonaws.com/")
        var request = URLRequest(url: url!, cachePolicy: .reloadIgnoringLocalAndRemoteCacheData)
        request.httpMethod = P3HTTPMethod.post.rawValue
        request.setValue("multipart/form-data; boundary=\(boundaryString)", forHTTPHeaderField: "Content-Type")
        request.httpBody = httpBody(with: uploadDescriptor.toDictionary, image: image)
        
        session = URLSession(configuration: .default)
        
        guard let s = session else {
            finish();
            return
        }
        
        let task = s.dataTask(with: request) { (data, response, error) in
            defer { self.finish() }
            
            let decoder = JSONDecoder()
            
            guard let data = data else { return }
            
            do {
                let model = try decoder.decode(P3JSONResponseWrapper<NetworkFile>.self, from: data)
                guard let inflated = model.data else { return }
                
                self.uploadedFile = inflated
                self.finished(model: inflated)
            } catch {
                print(error)
            }
        }
        
        task.resume()
    }
    
    open func finished(model: NetworkFile) {
        // For subclassing if needed
    }
    
    private func httpBody(with params: [String:String], image: UIImage) -> Data {
        var body = Data()
        
        guard let imageData = UIImageJPEGRepresentation(image, 0.5) else { return body }
        
        for (key, value) in params {
            body.append("--\(boundaryString)\r\n")
            body.append("Content-Disposition: form-data; name=\"\(key)\"\r\n\r\n")
            body.append("\(value)\r\n")
        }
        
        body.append("--\(boundaryString)\r\n")
        body.append("Content-Disposition: form-data; name=\"file\"\r\n\r\n")
        body.append(imageData)
        body.append("\r\n")
        
        body.append("--\(boundaryString)--\r\n")
        
        return body
    }
}


extension Data {
    mutating func append(_ string: String) {
        if let data = string.data(using: .utf8) {
            append(data)
        }
    }
}