NodeJS Error Callback was already called

Question

I know that this error exists here, and I try to read and that code but I always get this Error: Callback was already called.

My code is:

switch(data.type) {
   case 1:
     console.log('blablabla');
     break; 
   case 2:
     /* SSH - login */
     pool.query('SELECT INET_NTOA(ip) AS ip, pass, server FROM servers WHERE id=?',[data.id], function(err, rows, fields){
            /* SSH - connection */
            conn.connect({
                host: rows[0].ip,
                port: '22',
                username: 'root',
                password: decrypt(rows[0].pass, password)
            })

            /* SSH - ready */
            conn.on('error', function(err) {
                /* SSH - connection failed */
                return callback('Login To <b>'+rows[0].server+'</b> Failed!');
            })

            conn.on('end', function() {
                /* SSH - closed */
                console.log('ssh closed...')
            })

            conn.on('ready', function() {
                console.log('ready to execute terminal commands...')
            })
        })
        break;
    })

First time I call this function it works and I got

Login To Server Failed!

I call this function again and I got this error:

Error: Callback was already called.

After doing console.log I see that second time I call this function it is called twice so this is why this error about callback gets...so the problem is I try to put callback outside conn.on functions and inside but the second time that is called this function I get always this error..where in what place callbacks needs to be placed so that function does not get called twice?

UPDATE QUESTION:

I see when i add console.log to error and close event that each time i call this function i get one more event error and close called...see this:

First time called this function i get:

calling ssh...
error connecting to server...
ssh closed...

Second calling function:

calling ssh...
error connecting to server...
error connecting to server...
ssh closed...
ssh closed...

Third time calling function:

calling ssh...
error connecting to server...
error connecting to server...
error connecting to server...
ssh closed...
ssh closed...
ssh closed...

So is there a bug in SSH2 node js library or i im doing something wrong?

Answer 1

The events listenners are organised as an array; an regarding your code, the object << conn >> is external to the method you used. When you call it twice, you add a new listener to the array of the listenners of the object conn, making two listenners <<.on('error',... >> instead of one. See the picture below ( https://nodejs.org/api/events.html )

So you just need to initialize the object << conn >> before making a connection with it, to ensure that only one listener << on('error',... >> are affected.