Scala hex string to bytes - scala

Question

Is there a neat way in Scala to convert a hexadecimally encoded String to a protobuf ByteString (and back again)?

Answer 1

You can use (without additional dependencies) DatatypeConverter as:
import com.google.protobuf.ByteString
import javax.xml.bind.DatatypeConverter
val hexString: String = "87C2D268483583714CD5"
val byteString: ByteString = ByteString.copyFrom(
DatatypeConverter.parseHexBinary(hexString)
)
val originalString = DatatypeConverter.printHexBinary(byteString.toByteArray)

Answer 2

You can use java.math.BigInteger to parse a String, get the Array[Byte] and from there turn it into a ByteString. Here would be the first step:
import java.math.BigInteger
val s = "f263575e7b00a977a8e9a37e08b9c215feb9bfb2f992b2b8f11e"
val bs = new BigInteger(s, 16).toByteArray
The content of bs is now:
Array(0, -14, 99, 87, 94, 123, 0, -87, 119, -88, -23, -93, 126, 8, -71, -62, 21, -2, -71, -65, -78, -7, -110, -78, -72, -15, 30)
You can then use (for example) the copyFrom method (JavaDoc here) to turn it into a ByteString.

Answer 3

Starting with Java 17, you can use a standard API for parsing HEX strings to byte array.
import java.util.HexFormat
HexFormat.of.parseHex("d719af")

Answer 4

Since the title of the question doesn't mention Protobuf, if anyone is looking for a solution that doesn't require any dependencies for converting a hex String to Seq[Byte] for any sized array: (don't forget to add input validation as necessarily)
val zeroChar: Byte = '0'.toByte
val aChar: Byte = 'a'.toByte
def toHex(bytes: Seq[Byte]): String = bytes.map(b => f"$b%02x").mkString
def toBytes(hex: String): Seq[Byte] = {
val lowerHex = hex.toLowerCase
val (result: Array[Byte], startOffset: Int) =
if (lowerHex.length % 2 == 1) {
// Odd
val r = new Array[Byte]((lowerHex.length >> 1) + 1)
r(0) = toNum(lowerHex(0))
(r, 1)
} else {
// Even
(new Array[Byte](lowerHex.length >> 1), 0)
}
var inputIndex = startOffset
var outputIndex = startOffset
while (outputIndex < result.length) {
val byteValue = (toNum(lowerHex(inputIndex)) * 16) +
toNum(lowerHex(inputIndex + 1))
result(outputIndex) = byteValue.toByte
inputIndex += 2
outputIndex += 1
}
result
}
def toNum(lowerHexChar: Char): Byte =
(if (lowerHexChar < 'a') lowerHexChar.toByte - zeroChar else 10 +
lowerHexChar.toByte - aChar).toByte
https://scalafiddle.io/sf/PZPHBlT/2

Answer 5

A simple solution without any dependency or intermediate object could be
def toBytes(hex: String): Seq[Byte] = {
assert(hex.length % 2 == 0) // only manage canonical case
hex.sliding(2, 2).map(Integer.parseInt(_, 16).toByte).toSeq
}
assert(toBytes("1234") == Seq[Byte](18,52))
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