/**
       * Read `byteCount` bytes of headers from the source stream. This implementation does not
       * propagate the never indexed flag of a header.
       */
      @Throws(IOException::class)
      fun readHeaders() {
        while (!source.exhausted()) {
          val b = source.readByte() and 0xff
          when {
            b == 0x80 -> {
              // 10000000
              throw IOException("index == 0")