[serial-monitor][gRPC] Unhandled `EINTR` error leaves the serial port opened

[kittaakos]

Bug Report

Current behavior

There are two issues here:

• select and read can throw the following errors: EINTR, EAGAIN, and EWOULDBLOCK . These should be handled in go-serial and the CLI should recover and continue on such errors.
• Once we hit an error, the serial port is not closed, hence the connected clients have no chance to reconnect. The port will be busy. See the corresponding code:
  

  arduino-cli/commands/daemon/monitor.go

  Lines 130 to 131 in da8fc05

  	case err := <-targetClosed:
  	return err

Expected behavior

EINTR, and EAGAIN should be handled. After an error, clients can open a new client streaming duplex for the serial monitor.

Environment

• CLI version (output of arduino-cli version): From source
• OS and platform: 10.15.1 (19B88)

Additional context

[kittaakos]

This was reported independently by a PRO IDE user: arduino/arduino-pro-ide#157