How to upload jpeg image using URLSession.

AnyError.swift

import Foundation

struct AnyError: Error {

    let error: Error

    init(_ error: Error) {
        self.error = error
    }
}

Data+MIMEType.swift

import Foundation

extension Data {

    var mimeType: String? {
        var values = [UInt8](repeating: 0, count: 1)
        copyBytes(to: &values, count: 1)

        switch values[0] {
        case 0xFF:
            return "image/jpeg"
        case 0x89:
            return "image/png"
        case 0x47:
            return "image/gif"
        case 0x49, 0x4D:
            return "image/tiff"
        default:
            return nil
        }
    }
}

ImageUploader.swift

import UIKit

typealias HTTPHeaders = [String: String]

final class ImageUploader {

    let uploadImage: UIImage
    let number: Int
    let boundary = "example.boundary.\(ProcessInfo.processInfo.globallyUniqueString)"
    let fieldName = "upload_image"
    let endpointURI: URL = .init(string: "https://example.com/uploadImage")!

    var parameters: Parameters? {
        return [
            "number": number
        ]
    }
    var headers: HTTPHeaders {
        return [
            "Content-Type": "multipart/form-data; boundary=\(boundary)",
            "Accept": "application/json"
        ]
    }

    init(uploadImage: UIImage, number: Int) {
        self.uploadImage = uploadImage
        self.number = number
    }
    
    func uploadImage(completionHandler: (ImageUploadResult) -> Void) {
        let imageData = image.jpegData(compressionQuality: 1)!
        let mimeType = imageData.mimeType!

        var request = URLRequest(url: endpointURI, method: "POST", headers: headers)
        request.httpBody = createHttpBody(binaryData: imageData, mimeType: mimeType)
        
        let session = URLSession(configuration: .default)
        let task = session.dataTask(with: request) { (data, urlResponse, error) in
            let statusCode = (urlResponse as? HTTPURLResponse)?.statusCode ?? 0
            if let data = data, case (200..<300) = statusCode {
                do {
                    let value = try Response(from: data, statusCode: statusCode)
                    completionHandler(.success(value))
                } catch {
                    let _error = ResponseError(statusCode: statusCode, error: AnyError(error))
                    completionHandler(.failure(_error))
                }
            }
            let tmpError = error ?? NSError(domain: "Unknown", code: 499, userInfo: nil)
            let _error = ResponseError(statusCode: statusCode, error: AnyError(error))
            completionHandler(.failure(_error))
        }
        task.resume()
    }
    
    private func createHttpBody(binaryData: Data, mimeType: String) -> Data {
        var postContent = "--\(boundary)\r\n"
        let fileName = "\(UUID().uuidString).jpeg"
        postContent += "Content-Disposition: form-data; name=\"\(fieldName)\"; filename=\"\(fileName)\"\r\n"
        postContent += "Content-Type: \(mimeType)\r\n\r\n"

        var data = Data()
        guard let postData = postContent.data(using: .utf8) else { return data }
        data.append(postData)
        data.append(binaryData)

        // その他パラメータがあれば追加
        if let parameters = parameters {
            var content = ""
            parameters.forEach {
                content += "\r\n--\(boundary)\r\n"
                content += "Content-Disposition: form-data; name=\"\($0.key)\"\r\n\r\n"
                content += "\($0.value)"
            }
            if let postData = content.data(using: .utf8) { data.append(postData) }
        }

        // HTTPBodyの終了を設定
        guard let endData = "\r\n--\(boundary)--\r\n".data(using: .utf8) else { return data }
        data.append(endData)
        return data
    }
}

main.swift

import UIKit

let url = URL(string: "https://d1f5hsy4d47upe.cloudfront.net/ac/ac6d5a8d05f5792627a8039a2bddbe79_t.jpeg")!
let data = try! Data(contentsOf: url)
let image = UIImage(data: data)!

let request = ImageUploader(uploadImage: image, number: 1)
request.uploadImage { (result) in
    switch result {
    case .success(let value):
        assert(value.statusCode == 201)
    case .failure(let error):
        print(error.localizedDescription)
    }
}

ResponseResult.swift

import Foundation

typealias ImageUploadResult = Result<Response, ResponseError>

typealias Parameters = [String: Any]

struct Response {

    let statusCode: Int
    let body: Parameters?

    init(from data: Data, statusCode: Int) throws {
        self.statusCode = statusCode
        let jsonObject = try JSONSerialization.jsonObject(with: data, options: []) as? Parameters
        self.body = jsonObject
    }
}

struct ResponseError: Error {

    let statusCode: Int
    let error: AnyError
}

URLRequest+Init.swift

extension URLRequest {

    init(url: URL, method: String, headers: HTTPHeaders?) {
        self.init(url: url)
        httpMethod = method

        if let headers = headers {
            headers.forEach {
                setValue($0.1, forHTTPHeaderField: $0.0)
            }
        }
    }
}