String+md5.swift

import Foundation
import var CommonCrypto.CC_MD5_DIGEST_LENGTH
import func CommonCrypto.CC_MD5
import typealias CommonCrypto.CC_LONG

extension String {
    func md5() -> String {
        let length = Int(CC_MD5_DIGEST_LENGTH)
        let messageData = data(using: .utf8)!
        var digestData = Data(count: length)

        _ = digestData.withUnsafeMutableBytes { digestBytes -> UInt8 in
            messageData.withUnsafeBytes { messageBytes -> UInt8 in
                if let messageBytesBaseAddress = messageBytes.baseAddress,
                   let digestBytesBlindMemory =
                        digestBytes.bindMemory(to: UInt8.self).baseAddress {
                    let messageLength = CC_LONG(messageData.count)
                    CC_MD5(messageBytesBaseAddress,
                           messageLength,
                           digestBytesBlindMemory)
                }
                return 0
            }
        }

        let md5Hex =  digestData.map { String(format: "%02hhx", $0) }.joined()
        return md5Hex
    }
}