How to convert Data to hex string in swift

Question

I want the hexadecimal representation of a Data value in Swift.

Eventually I\'d want to use it like this:

let data = Data(base64Encoded: \"aGVsbG8gd2         


        

Answer 1

An alternative implementation (taken from How to crypt string to sha1 with Swift?, with an additional option for uppercase output) would be

extension Data {
    struct HexEncodingOptions: OptionSet {
        let rawValue: Int
        static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
    }

    func hexEncodedString(options: HexEncodingOptions = []) -> String {
        let format = options.contains(.upperCase) ? "%02hhX" : "%02hhx"
        return map { String(format: format, $0) }.joined()
    }
}

I chose a hexEncodedString(options:) method in the style of the existing method base64EncodedString(options:).

Data conforms to the Collection protocol, therefore one can use map() to map each byte to the corresponding hex string. The %02x format prints the argument in base 16, filled up to two digits with a leading zero if necessary. The hh modifier causes the argument (which is passed as an integer on the stack) to be treated as a one byte quantity. One could omit the modifier here because $0 is an unsigned number (UInt8) and no sign-extension will occur, but it does no harm leaving it in.

The result is then joined to a single string.

Example:

let data = Data(bytes: [0, 1, 127, 128, 255])
print(data.hexEncodedString()) // 00017f80ff
print(data.hexEncodedString(options: .upperCase)) // 00017F80FF

---

The following implementation is faster by a factor about 120 (tested with 1000 random bytes). It is similar to RenniePet's solution and Nick Moore's solution, but based on UTF-16 code units, which is what Swift strings (currently) use as internal storage.

extension Data {
    struct HexEncodingOptions: OptionSet {
        let rawValue: Int
        static let upperCase = HexEncodingOptions(rawValue: 1 << 0)
    }

    func hexEncodedString(options: HexEncodingOptions = []) -> String {
        let hexDigits = Array((options.contains(.upperCase) ? "0123456789ABCDEF" : "0123456789abcdef").utf16)
        var chars: [unichar] = []
        chars.reserveCapacity(2 * count)
        for byte in self {
            chars.append(hexDigits[Int(byte / 16)])
            chars.append(hexDigits[Int(byte % 16)])
        }
        return String(utf16CodeUnits: chars, count: chars.count)
    }
}