Question :
Python has two very useful library method (binascii.a2b_hex(keyStr) and binascii.hexlify(keyBytes)) which I have been struggling with in Swift. Is there anything readily available in Swift. If not, how would one implement it? Given all the bounds and other checks (like even-length key) are done.
Answer #1:
Data
from Swift 3 has no “built-in” method to print its contents as
a hex string, or to create a Data
value from a hex string.
“Data to hex string” methods can be found e.g. at How to convert Data to hex string in swift or How to print the content of a variable type Data using swift? or converting string to data in swift 3.0. Here is an implementation from the first link:
extension Data {
func hexEncodedString() -> String {
return map { String(format: "%02hhx", $0) }.joined()
}
}
Here is a possible implementation of the reverse “hex string to Data”
conversion (taken from Hex String to Bytes (NSData) on Code Review, translated to Swift 3 and improved)
as a failable inititializer:
extension Data {
init?(fromHexEncodedString string: String) {
// Convert 0 ... 9, a ... f, A ...F to their decimal value,
// return nil for all other input characters
func decodeNibble(u: UInt16) -> UInt8? {
switch(u) {
case 0x30 ... 0x39:
return UInt8(u - 0x30)
case 0x41 ... 0x46:
return UInt8(u - 0x41 + 10)
case 0x61 ... 0x66:
return UInt8(u - 0x61 + 10)
default:
return nil
}
}
self.init(capacity: string.utf16.count/2)
var even = true
var byte: UInt8 = 0
for c in string.utf16 {
guard let val = decodeNibble(u: c) else { return nil }
if even {
byte = val << 4
} else {
byte += val
self.append(byte)
}
even = !even
}
guard even else { return nil }
}
}
Example:
// Hex string to Data:
if let data = Data(fromHexEncodedString: "0002468A13579BFF") {
let idata = Data(data.map { 255 - $0 })
// Data to hex string:
print(idata.hexEncodedString()) // fffdb975eca86400
} else {
print("invalid hex string")
}
Answer #2:
Not really familiar with Python and the checks it performs when convert the numbers, but you can expand the function below:
func convert(_ str: String, fromRadix r1: Int, toRadix r2: Int) -> String? {
if let num = Int(str, radix: r1) {
return String(num, radix: r2)
} else {
return nil
}
}
convert("11111111", fromRadix: 2, toRadix: 16)
convert("ff", fromRadix: 16, toRadix: 2)
Answer #3:
Swift 2
extension NSData {
class func dataFromHexString(hex: String) -> NSData? {
let regex = try! NSRegularExpression(pattern: "^[0-9a-zA-Z]*$", options: .CaseInsensitive)
let validate = regex.firstMatchInString(hex, options: NSMatchingOptions.init(rawValue: 0), range: NSRange(location: 0, length: hex.characters.count))
if validate == nil || hex.characters.count % 2 != 0 {
return nil
}
let data = NSMutableData()
for i in 0..<hex.characters.count/2 {
let hexStr = hex.substring(i * 2, length: 2)
var ch: UInt32 = 0
NSScanner(string: hexStr).scanHexInt(&ch)
data.appendBytes(&ch, length: 1)
}
return data
}
}
let a = 0xabcd1234
print(String(format: "%x", a)) // Hex to String
NSData.dataFromHexString("abcd1234") // String to hex