Sending code to ESP32 slow using EspruinoTools -- says "Set Slow Write = true"

@Wilberforce the best bet would be to tweak Telnet to add flow control in the firmware itself?

It should be very easy. Just make: https://github.com/espruino/Espruino/blo­b/master/libs/network/telnet/jswrap_teln­et.c#L292

Check jshHasEventSpaceForChars.

Maybe lower the buffer size a bit to make it a bit more fine-grained, but something like:

  char buff[64];
  if (!jshHasEventSpaceForChars(sizeof(buff))­) return false;
  int r = netRecv(net, ST_NORMAL, tnSrv.cliSock-1, buff, sizeof(buff));
  if (r > 0) {
    jshPushIOCharEvents(EV_TELNET, buff, (unsigned int)r);
  } else if (r < 0) {
    telnetRelease(net);
  }

would probably be perfect, and then TCP/IP should handle all the flow control stuff itself.