Swift URLRequest Multipart Form-Data

URLSession-MultipartFormData.swift

import Foundation
import UIKit

extension URLRequest {
    
    typealias BuilderFunction = ((MultipartFormDataInclusion) -> Void) -> Void
    
    struct MultipartFormDataInclusion {
        var data: Data
        var name: String
        var fileName: String
        var contentType: String
    }
    
    mutating func addMultipartFormData(_ builder: BuilderFunction)  {
        
        let boundary = UUID().uuidString
        let lineBreak = "\r\n"
        
        setValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
        
        let body: NSMutableData = .init()
        
        builder { inclusion in
            body.append("--\(boundary)")
            body.append(lineBreak)
            body.append("Content-Disposition: form-data; name=\"\(inclusion.name)\"; filename=\"\(inclusion.fileName)\"")
            body.append(lineBreak)
            body.append("Content-Type: \(inclusion.contentType)")
            body.append(lineBreak)
            body.append(lineBreak)
            body.append(inclusion.data)
            body.append(lineBreak)
            body.append("--\(boundary)--")
            body.append(lineBreak)
        }
        
        httpBody = body as Data
    }
}

fileprivate extension NSMutableData {
    func append(_ string: String) {
        append(string.data(using: .utf8)!)
    }
}

let red10x10 = Data(base64Encoded: "iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAFUlEQVR42mP8z8AARIQB46hC+ioEAGX8E/cKr6qsAAAAAElFTkSuQmCC")!

let green10x10 = Data(base64Encoded: "iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAFElEQVR42mNk+A+ERADGUYX0VQgAXAYT9xTSUocAAAAASUVORK5CYII=")!

let blue10x10 = Data(base64Encoded: "iVBORw0KGgoAAAANSUhEUgAAAAoAAAAKCAYAAACNMs+9AAAAFUlEQVR42mNkYJD8z0AEYBxVSF+FAIKSCvtG3YaKAAAAAElFTkSuQmCC")!

var request = URLRequest(url: .init(string: "https://example.com")!)

request.httpMethod = "POST"

request.addMultipartFormData { include in
    include(.init(data: red10x10, name: "red", fileName: "red.png", contentType: "image/png"))
    include(.init(data: green10x10, name: "green", fileName: "green.png", contentType: "image/png"))
    include(.init(data: blue10x10, name: "blue", fileName: "blue.png", contentType: "image/png"))
}

URLSession
    .shared
    .dataTask(with: request)
    .resume()