[firmata] Handling loss of connection with the TCPAdaptor

[abishekmuthian]

I'm using ESP8266(server) and so TCPAdaptor(firmata) along with MQTTAdapter.

I tried different methodologies to handle connection loss,

1. Checking at regular intervals for connections, but connections are returned even if the actual WiFi connection is lost (switching off the ESP8266).

2. Trying to connect with adaptor at regular intervals, but returns "client is already connected" even when connection
   is lost.

I found setAutoReconnect for MQTTAdaptor, which I assume handles connection loss for the same. But what is the recommended strategy to handle connection loss of TCPAdaptor?

[dustinblackman]

I'm still working through learning the library, but my understanding is there's no real connection management for TCPAdapters. Attempting to do it manually you find yourself stuck as Disconnect() doesn't properly cleanup the old connection, preventing you from being able to reconnect yourself.

I've put together this really bad hack that uses the ESP8266 onboard LED as a healthcheck, and when it fails it'll disconnect and clear out the existing private connection fields on the adapter struct, and then connect again. Once I get more familiar I'll find time to PR a fix so you won't require the need for reflection/unsafe.

Example:

package main

import (
	"log"
	"reflect"
	"time"
	"unsafe"

	"gobot.io/x/gobot"
	"gobot.io/x/gobot/drivers/gpio"
	"gobot.io/x/gobot/platforms/firmata"
)

func main() {
	firmataAdaptor := firmata.NewTCPAdaptor("192.168.1.3:3030")
	led := gpio.NewLedDriver(firmataAdaptor, "2")

	work := func() {
		gobot.Every(5*time.Second, func() {
			err := led.Toggle()
			if err != nil {
				log.Print("Failed to toggle leg, will attempt reconnecting")
				log.Print(err)

				firmataAdaptor.Disconnect()

				sp, connErr := firmataAdaptor.PortOpener(firmataAdaptor.Port())
				if connErr != nil {
					log.Print("Failed to reconnect to esp directly, will panic")
					panic(connErr)
				}

				connField := reflect.ValueOf(firmataAdaptor).Elem().FieldByName("conn")
				reflect.NewAt(connField.Type(), unsafe.Pointer(connField.UnsafeAddr())).
					Elem().
					Set(reflect.ValueOf(sp))

				err = firmataAdaptor.Connect()
				if err != nil {
					log.Print("Could not reconnect to esp")
					log.Print(err)
					return
				}

				log.Print("Successfully reconnected")
			}
		})
	}

	robot := gobot.NewRobot("bot",
		[]gobot.Connection{firmataAdaptor},
		[]gobot.Device{led},
		work,
	)

	robot.Start()
}