Hex string to text conversion - swift 3 - swift

Question

I'm trying to convert an hex string to text.
This is what i have:
// Str to Hex
func strToHex(text: String) -> String {
let hexString = text.data(using: .utf8)!.map{ String(format:"%02x", $0) }.joined()
return "0x" + hexString
}
and I'm trying to reverse the hex string that I've just created back to the original one.
So, for example:
let foo: String = strToHex(text: "K8") //output: "0x4b38"
and i would like to do something like
let bar: String = hexToStr(hex: "0x4b38") //output: "K8"
can someone help me?
Thank you

Answer 1

You probably can use something like this:
func hexToStr(text: String) -> String {
let regex = try! NSRegularExpression(pattern: "(0x)?([0-9A-Fa-f]{2})", options: .caseInsensitive)
let textNS = text as NSString
let matchesArray = regex.matches(in: textNS as String, options: [], range: NSMakeRange(0, textNS.length))
let characters = matchesArray.map {
Character(UnicodeScalar(UInt32(textNS.substring(with: $0.rangeAt(2)), radix: 16)!)!)
}
return String(characters)
}

Answer 2

NSRegularExpression is overkill for the job. You can convert the string to byte array by grabbing two characters at a time:
func hexToString(hex: String) -> String? {
guard hex.characters.count % 2 == 0 else {
return nil
}
var bytes = [CChar]()
var startIndex = hex.index(hex.startIndex, offsetBy: 2)
while startIndex < hex.endIndex {
let endIndex = hex.index(startIndex, offsetBy: 2)
let substr = hex[startIndex..<endIndex]
if let byte = Int8(substr, radix: 16) {
bytes.append(byte)
} else {
return nil
}
startIndex = endIndex
}
bytes.append(0)
return String(cString: bytes)
}

Answer 3

Solution that supports also special chars like emojis etc.
static func hexToPlain(input: String) -> String {
let pairs = toPairsOfChars(pairs: [], string: input)
let bytes = pairs.map { UInt8($0, radix: 16)! }
let data = Data(bytes)
return String(bytes: data, encoding: .utf8)!
}