Panic on lost connection

[junavarg]

Hello, I am developing a program for unattended systems in remote locations (3G/4G connected) that has to publish events to MQTT broker. I have encountered an unexpected behaviour when testing lost of connectivity conditions of such system in a Ubuntu Server 18.04.2 (on VirtualBox 6.1.1 on Windows 10)

Once first connection is stablished wiht broker,
if a loss of connectivity arise (for example shutting down MQTT broker, or deleting default router to internet, or shutting down Ethernet IF)
Linux process unexpectedly ends showing:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x496b78]

It occurs with all transport protocols: tcp, ssl, ws, wss.
It also ocurss in Ubuntu 16.04
However same code compiled in ARM (Raspbian) works correctly.

This is a minimal testing code that reproduce the error. SetKeepAlive and SetPingTimeout are intentionally settled to short times for fast showing the effect. Note than no client activity is performed (other than a dot print).

package main

import (
	"fmt"
	"os"
	"time"
	"github.com/eclipse/paho.mqtt.golang"
)
func onConnectHandler(c mqtt.Client){
	fmt.Println("¡¡ conexión!! ")
}

func onConnetionLostHandler(c mqtt.Client, er error ){
	fmt.Println("¡¡ conexión perdida !! ", er)
}

func main() {
	opts := mqtt.NewClientOptions()
	opts.AddBroker("tcp://broker.hivemq.com:1883")
	opts.SetClientID("50695833")
	opts.SetKeepAlive(2 * time.Second)
	opts.SetPingTimeout(2 * time.Second)
	opts.SetOnConnectHandler(onConnectHandler)	
	opts.SetConnectionLostHandler(onConnetionLostHandler)	
	c := mqtt.NewClient(opts)
	fmt.Println("Conexión inicial...")
	if token := c.Connect(); token.Wait() && token.Error() != nil {
		fmt.Println("Error de conexión inicial", token.Error())
		os.Exit(-1)
	}
	for i := 0; ; i++ {
		time.Sleep(time.Second*5)
		fmt.Printf(".")
	}
}

This is the output few second later you, for any way, you cause a lack (with enough duration) of connectivity.

$ ./pruebamq
Conexion inicial...
¡¡ conexión!!
..................................¡¡ conexión perdida !! EOF
¡¡ conexión!!
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x496b78]

goroutine 36 [running]:
io.ReadAtLeast(0x0, 0x0, 0xc00001c598, 0x1, 0x1, 0x1, 0x0, 0x0, 0x0)
/usr/local/go/src/io/io.go:310 +0x58
io.ReadFull(...)
/usr/local/go/src/io/io.go:329
github.com/eclipse/paho.mqtt.golang/packets.ReadPacket(0x0, 0x0, 0x0, 0x0, 0x0, 0x0)
/home/juan/go/src/github.com/eclipse/paho.mqtt.golang/packets/packets.go:105 +0x94
github.com/eclipse/paho%2emqtt%2egolang.startIncoming.func1(0x0, 0x0, 0xc000093060, 0xc000093050, 0xc000083140)
/home/juan/go/src/github.com/eclipse/paho.mqtt.golang/net.go:105 +0x11c
created by github.com/eclipse/paho%2emqtt%2egolang.startIncoming
/home/juan/go/src/github.com/eclipse/paho.mqtt.golang/net.go:103 +0x131

Notice that after disconnection (¡¡ conexión perdida !! ) a callback OnConnect is ¿erroneously? called.

Thank in advance.

[MattBrittan]

Apologies @junavarg; this was caused by a bug in a PR #381 (I suspect there may be a few more issues in there; it was a fairly major change that I had intended to test further). It should be corrected by PR #416 - when retrying the connection the code checks if Disconnect() has been called and, if so, drops out of the loop - unfortunately it was checking for the reverse...

[junavarg]

Thank you @MattBrittan.
I see that the matter is under control.
I take this opportunity to thank you for your good work.

Saludos.