W3C context propagation hex encodes in capital letters causing failure to read the identifiers

[pnerg]

Issue

When propagating using W3C it hex encodes the identifiers like this:

 def idToHex(identifier: Identifier, length: Int): String = {
      val leftPad = (string: String) => "0" * (length - string.length) + string
      leftPad(identifier.bytes.map("%02X" format _).mkString)
    }

SpanPropagation.scala#L105

"%02X"causes the generated hex to be in capital letters.
According to the W3C specification the identifiers shall be in lowercase.
"HEXDIGLC = DIGIT / "a" / "b" / "c" / "d" / "e" / "f" ; lowercase hex character"

Effect

This breaks when the request is received on the other end as Kamon fails to parse the identifier due to being uppercase
E.g.

  val identityProvider = Identifier.Scheme.Double

  val s = "2f2b727a4a0dcfd8c0bed5f6209f2694"

  println(identityProvider.traceIdFactory.from(s.toLowerCase).isEmpty)
  println(identityProvider.traceIdFactory.from(s.toLowerCase).string)

  println(identityProvider.traceIdFactory.from(s.toUpperCase).isEmpty)
  println(identityProvider.traceIdFactory.from(s.toUpperCase).string)

yields

false
2f2b727a4a0dcfd8c0bed5f6209f2694
true

Solution

Change to leftPad(identifier.bytes.map("%02x" format _).mkString)
Note the 'x' to dictate lower caps.

[SimunKaracic]

Fixed in 2.1.16!