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 = [inputSt         


        

Answer 1

convert hex string to data and string:

Swift1

func dataWithHexString(hex: String) -> NSData {
    var hex = hex
    let data = NSMutableData()
    while(countElements(hex) > 0) {
        var c: String = hex.substringToIndex(advance(hex.startIndex, 2))
        hex = hex.substringFromIndex(advance(hex.startIndex, 2))
        var ch: UInt32 = 0
        NSScanner(string: c).scanHexInt(&ch)
        data.appendBytes(&ch, length: 1)
    }
    return data
}

use:

let data = dataWithHexString("68656c6c6f2c20776f726c64") // <68656c6c 6f2c2077 6f726c64>
if let string = NSString(data: data, encoding: 1) {
    print(string) // hello, world
}

Swift2

func dataWithHexString(hex: String) -> NSData {
    var hex = hex
    let data = NSMutableData()
    while(hex.characters.count > 0) {
        let c: String = hex.substringToIndex(hex.startIndex.advancedBy(2))
        hex = hex.substringFromIndex(hex.startIndex.advancedBy(2))
        var ch: UInt32 = 0
        NSScanner(string: c).scanHexInt(&ch)
        data.appendBytes(&ch, length: 1)
    }
    return data
}

use:

let data = dataWithHexString("68656c6c6f2c20776f726c64") // <68656c6c 6f2c2077 6f726c64>
if let string = String(data: data, encoding: NSUTF8StringEncoding) {
    print(string) //"hello, world"
}

Swift3

func dataWithHexString(hex: String) -> Data {
    var hex = hex
    var data = Data()
    while(hex.characters.count > 0) {
        let c: String = hex.substring(to: hex.index(hex.startIndex, offsetBy: 2))
        hex = hex.substring(from: hex.index(hex.startIndex, offsetBy: 2))
        var ch: UInt32 = 0
        Scanner(string: c).scanHexInt32(&ch)
        var char = UInt8(ch)
        data.append(&char, count: 1)
    }
    return data
}

use:

let data = dataWithHexString(hex: "68656c6c6f2c20776f726c64") // <68656c6c 6f2c2077 6f726c64>
let string = String(data: data, encoding: .utf8) // "hello, world"

Swift4

func dataWithHexString(hex: String) -> Data {
    var hex = hex
    var data = Data()
    while(hex.count > 0) {
        let subIndex = hex.index(hex.startIndex, offsetBy: 2)
        let c = String(hex[..<subIndex])
        hex = String(hex[subIndex...])
        var ch: UInt32 = 0
        Scanner(string: c).scanHexInt32(&ch)
        var char = UInt8(ch)
        data.append(&char, count: 1)
    }
    return data
}

use:

let data = dataWithHexString(hex: "68656c6c6f2c20776f726c64") // <68656c6c 6f2c2077 6f726c64>
let string = String(data: data, encoding: .utf8) // "hello, world"

Answer 2

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: characters.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.

Answer 3

Supposing your string is even size, you can use this to convert to hexadecimal and save it to Data:

Swift 5.2

func hex(from string: String) -> Data {
    .init(stride(from: 0, to: string.count, by: 2).map {
        string[string.index(string.startIndex, offsetBy: $0) ... string.index(string.startIndex, offsetBy: $0 + 1)]
    }.map {
        UInt8($0, radix: 16)!
    })
}

Answer 4

Here is my Swifty 5 way to do it:

• does take care of "0x" prefixes
• use subscript instead of allocated Array(), no C style [i+1] too
• add .hexadecimal to String.data(using encoding:) -> Data?

.

String Extension:

    extension String {
        enum ExtendedEncoding {
            case hexadecimal
        }

        func data(using encoding:ExtendedEncoding) -> Data? {
            let hexStr = self.dropFirst(self.hasPrefix("0x") ? 2 : 0)

            guard hexStr.count % 2 == 0 else { return nil }

            var newData = Data(capacity: hexStr.count/2)

            var indexIsEven = true
            for i in hexStr.indices {
                if indexIsEven {
                    let byteRange = i...hexStr.index(after: i)
                    guard let byte = UInt8(hexStr[byteRange], radix: 16) else { return nil }
                    newData.append(byte)
                }
                indexIsEven.toggle()
            }
            return newData
        }
    }

Usage:

    "5413".data(using: .hexadecimal)
    "0x1234FF".data(using: .hexadecimal)

Tests:

    extension Data {
        var bytes:[UInt8] { // fancy pretty call: myData.bytes -> [UInt8]
            return [UInt8](self)
        }

        // Could make a more optimized one~
        func hexa(prefixed isPrefixed:Bool = true) -> String {
            return self.bytes.reduce(isPrefixed ? "0x" : "") { $0 + String(format: "%02X", $1) }
        }
    }

    print("000204ff5400".data(using: .hexadecimal)?.hexa() ?? "failed") // OK
    print("0x000204ff5400".data(using: .hexadecimal)?.hexa() ?? "failed") // OK
    print("541".data(using: .hexadecimal)?.hexa() ?? "failed") // fails
    print("5413".data(using: .hexadecimal)?.hexa() ?? "failed") // OK

Answer 5

One more solution that is simple to follow and leverages swifts built-in hex parsing

func convertHexToBytes(_ str: String) -> Data? {
    let values = str.compactMap { $0.hexDigitValue } // map char to value of 0-15 or nil
    if values.count == str.count && values.count % 2 == 0 {
        var data = Data()
        for x in stride(from: 0, to: values.count, by: 2) {
          let byte = (values[x] << 4) + values[x+1] // concat high and low bits
          data.append(UInt8(byte))
        }
        return data
    }
    return nil
}

let good = "e01AFd"
let bad = "e0671"
let ugly = "GT40"
print("\(convertHexToBytes(good))") // Optional(3 bytes)
print("\(convertHexToBytes(bad))") // nil
print("\(convertHexToBytes(ugly))") // nil

Answer 6

The code worked for me in Swift 3.0.2.

extension String {
    /// Expanded encoding
    ///
    /// - bytesHexLiteral: Hex string of bytes
    /// - base64: Base64 string
    enum ExpandedEncoding {
        /// Hex string of bytes
        case bytesHexLiteral
        /// Base64 string
        case base64
    }

    /// Convert to `Data` with expanded encoding
    ///
    /// - Parameter encoding: Expanded encoding
    /// - Returns: data
    func data(using encoding: ExpandedEncoding) -> Data? {
        switch encoding {
        case .bytesHexLiteral:
            guard self.characters.count % 2 == 0 else { return nil }
            var data = Data()
            var byteLiteral = ""
            for (index, character) in self.characters.enumerated() {
                if index % 2 == 0 {
                    byteLiteral = String(character)
                } else {
                    byteLiteral.append(character)
                    guard let byte = UInt8(byteLiteral, radix: 16) else { return nil }
                    data.append(byte)
                }
            }
            return data
        case .base64:
            return Data(base64Encoded: self)
        }
    }
}