Simple function to upload files to S3 in Swift with no dependencies

s3upload.swift

import Foundation
import CryptoKit

extension String {
    func hmac(key: String) -> String {
        let secret = key.data(using: .utf8)!
        let message = self.data(using: .utf8)!

        var hmac = HMAC<Insecure.SHA1>(key: SymmetricKey(data: secret))
        hmac.update(data: message)

        return Data(hmac.finalize()).base64EncodedString()
    }
}

struct S3 {
    static func upload(_ data: Data, to bucket: String, name: String, contentType: String, publicRead: Bool = false, callback: @escaping (String?, Error?) -> Void) {
        let s3_access_key = "<s3_access_key>"
        let s3_secret_key = "<s3_secret_key>"
        
        let filepath = "/\(bucket)/\(name)"
        
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "E, d MMM yyyy HH:mm:ss Z"
        let date = dateFormatter.string(from: Date())
        
        // construct the signature hash, the order of the elements is important
        var signature = ["PUT", "", contentType, date]
        if publicRead { signature.append("x-amz-acl:public-read") }
        signature.append(filepath)
        let signature_hash = signature.joined(separator: "\n").hmac(key: s3_secret_key)

        // Upload the file to S3
        let url = "https://\(bucket).s3.amazonaws.com/\(name)"
        var request = URLRequest(url: URL(string: url)!)
        request.httpMethod = "PUT"
        request.httpBody = data
        request.setValue("\(bucket).s3.amazonaws.com", forHTTPHeaderField: "Host")
        if publicRead { request.setValue("public-read", forHTTPHeaderField: "x-amz-acl") }
        request.setValue(date, forHTTPHeaderField: "Date")
        request.setValue(contentType, forHTTPHeaderField: "Content-Type")
        request.setValue("AWS \(s3_access_key):\(signature_hash)", forHTTPHeaderField: "Authorization")
        URLSession.shared.dataTask(with: request) { data, response, error in callback(url, error) }.resume()
    }
}