Converting Hex String to NSData in Swift

Question

I got the code to convert String to HEX-String in Objective-C:

- (NSString *) CreateDataWithHexString:(NSString*)inputString {     NSUInteger inLength = [inputString length];                unichar *inCharacters = alloca(sizeof(unichar) * inLength);     [inputString getCharacters:inCharacters range:NSMakeRange(0, inLength)];          UInt8 *outBytes = malloc(sizeof(UInt8) * ((inLength / 2) + 1));          NSInteger i, o = 0;     UInt8 outByte = 0;      for (i = 0; i < inLength; i++) {         UInt8 c = inCharacters[i];         SInt8 value = -1;                  if      (c >= '0' && c <= '9') value =      (c - '0');         else if (c >= 'A' && c <= 'F') value = 10 + (c - 'A');         else if (c >= 'a' && c <= 'f') value = 10 + (c - 'a');                  if (value >= 0) {             if (i % 2 == 1) {                 outBytes[o++] = (outByte << 4) | value;                 outByte = 0;             } else {                 outByte = value;             }                      } else {             if (o != 0) break;         }     }          NSData *a = [[NSData alloc] initWithBytesNoCopy:outBytes length:o freeWhenDone:YES];     NSString* newStr = [NSString stringWithUTF8String:[a bytes]];     return newStr; } 

I want the same in Swift. Can anybody translate this code in Swift, or is there any easy way to do this in Swift?

Answer 1

This is my hex string to Data routine:

extension String {          /// Create `Data` from hexadecimal string representation     ///     /// This creates a `Data` object from hex string. Note, if the string has any spaces or non-hex characters (e.g. starts with '<' and with a '>'), those are ignored and only hex characters are processed.     ///     /// - returns: Data represented by this hexadecimal string.          var hexadecimal: Data? {         var data = Data(capacity: count / 2)                  let regex = try! NSRegularExpression(pattern: "[0-9a-f]{1,2}", options: .caseInsensitive)         regex.enumerateMatches(in: self, range: NSRange(startIndex..., in: self)) { match, _, _ in             let byteString = (self as NSString).substring(with: match!.range)             let num = UInt8(byteString, radix: 16)!             data.append(num)         }                  guard data.count > 0 else { return nil }                  return data     }      } 

And for the sake of completeness, this is my Data to hex string routine:

extension Data {          /// Hexadecimal string representation of `Data` object.          var hexadecimal: String {         return map { String(format: "%02x", $0) }             .joined()     } } 

---

Note, as shown in the above, I generally only convert between hexadecimal representations and NSData instances (because if the information could have been represented as a string you probably wouldn't have created a hexadecimal representation in the first place). But your original question wanted to convert between hexadecimal representations and String objects, and that might look like so:

extension String {          /// Create `String` representation of `Data` created from hexadecimal string representation     ///     /// This takes a hexadecimal representation and creates a String object from that. Note, if the string has any spaces, those are removed. Also if the string started with a `<` or ended with a `>`, those are removed, too.     ///     /// For example,     ///     ///     String(hexadecimal: "<666f6f>")     ///     /// is     ///     ///     Optional("foo")     ///     /// - returns: `String` represented by this hexadecimal string.          init?(hexadecimal string: String, encoding: String.Encoding = .utf8) {         guard let data = string.hexadecimal() else {             return nil         }                  self.init(data: data, encoding: encoding)     }                  /// Create hexadecimal string representation of `String` object.     ///     /// For example,     ///     ///     "foo".hexadecimalString()     ///     /// is     ///     ///     Optional("666f6f")     ///     /// - parameter encoding: The `String.Encoding` that indicates how the string should be converted to `Data` before performing the hexadecimal conversion.     ///     /// - returns: `String` representation of this String object.          func hexadecimalString(encoding: String.Encoding = .utf8) -> String? {         return data(using: encoding)?             .hexadecimal     }      } 

You could then use the above like so:

let hexString = "68656c6c 6f2c2077 6f726c64" print(String(hexadecimal: hexString)) 

Or,

let originalString = "hello, world" print(originalString.hexadecimalString()) 

For permutations of the above for earlier Swift versions, see the revision history of this question.