String md5 extension for Swift 3

String+md5.swift

//
// Based on https://gist.github.com/finder39/f6d71f03661f7147547d
// NOTE: There's no CommonCrypto module for Swift. To make the import CommonCrypto line work do something like what's described in http://stackoverflow.com/a/29189873/257577
//
import CommonCrypto

extension String {
    /**
        Get the MD5 hash of this String
     
        - returns: MD5 hash of this String
     */
    func md5() -> String! {
        let str = self.cString(using: String.Encoding.utf8)
        let strLen = CUnsignedInt(self.lengthOfBytes(using: String.Encoding.utf8))
        let digestLength = Int(CC_MD5_DIGEST_LENGTH)
        let result = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: digestLength)
        
        CC_MD5(str!, strLen, result)
        
        let hash = NSMutableString()
        
        for i in 0..<digestLength {
            hash.appendFormat("%02x", result[i])
        }
        
        result.deinitialize()
        
        return String(format: hash as String)
    }
}