// We've exhausted the source stream.
    if (limit == -1L && source.exhausted()) return END_OF_DATA

    // Read the tag.
    val tagAndClass = source.readByte().toInt() and 0xff
    val tagClass = tagAndClass and 0b1100_0000
    val constructed = (tagAndClass and 0b0010_0000) == 0b0010_0000
    val tag =
      when (val tag0 = tagAndClass and 0b0001_1111) {
        0b0001_1111 -> readVariableLengthLong()

        return when {
          peekHeader.tagClass == Adapters.UTC_TIME.tagClass &&
            peekHeader.tag == Adapters.UTC_TIME.tag -> {
            Adapters.UTC_TIME.fromDer(reader)
          }

          peekHeader.tagClass == Adapters.GENERALIZED_TIME.tagClass &&
            peekHeader.tag == Adapters.GENERALIZED_TIME.tag -> {