Unhandled 'error' event and PROTOCOL_CONNECTION_LOST

Hello, First of all, thank you for your work building this amazing library!

I am having the following problem when trying to connect on purpose for testing into a server using an invalid username:

events.js:187
      throw er; // Unhandled 'error' event
      ^
Error: Connection lost: The server closed the connection.
    at Socket.<anonymous> (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:88:31)
    at Socket.emit (events.js:210:5)
    at TCP.<anonymous> (net.js:658:12)
Emitted 'error' event on PoolConnection instance at:
    at PoolConnection._notifyError (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:218:12)
    at Socket.<anonymous> (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:94:12)
    at Socket.emit (events.js:210:5)
    at TCP.<anonymous> (net.js:658:12) {
  fatal: true,
  code: 'PROTOCOL_CONNECTION_LOST'
}

This is how I setup my connection pool:

this.connectionPool = mysql.createPool({
                host: this.cfg.dbServer,
                user: this.cfg.dbUserName,
                database: this.cfg.dbSchema,
                password: this.cfg.dbPassword,                
        
             }).promise();

This is how I attach the error listener, I use the following techniques (tried both):

this.connectionPool.on('connection', (connection) => {
                console.log('[MYSQL-DRIVER]-NEW CONNECTION ' + connection.threadId);
                connection.on('error', function(err){
                    console.log('[MYSQL-DRIVER]-PROBLEM: ' + err);
                })
            });

Or:
this.connectionPool.on('error', function(err) {
                console.log("[MYSQL-DRIVER]-PROBLEM(ATTACHED ON POOL): " + err);
             });

I have a simple test routine, so everytime I start my nodeJS server, after the pool is created, I run the following:

await this.connTest().then((result)=>{
                this.connected = 1;                
            }).catch((err) => {
                this.connected = 0;
            });

connTest() {
        return new Promise((resolve, reject) => {
            this.connectionPool.execute('SELECT 1 + 1 AS SOLUTION;', function (error, resulds, fields) {
                if (error) reject();
                resolve();
            })
        });
    }

Now the strange part. I am developing in a Windows 10 machine with MySQL hosted on another machine on the network. This problem “Unhandled ‘error’ event” does NOT always occur. Sometimes I work for hours and disconnections are handled JUST FINE by the ATTACHED ERROR FUNCTION. I repeat: sometimes the disconnections ARE handled by the handlers!

I don´t know exactly what changes for the behavior appear, but it appears to be after I restart MySQL server.

I decided to turn on the mysql2 library debug, to see what kind of information it shows, during the times the error is happening. Everytime I run my test routine, just before the error, I see this:

raw: 0a382e302e313800c50300001e014540076c0f0f00ffffe00200ffc71500000000000000000000235744157b3f7557525e27020063616368696e675f736861325f70617373776f726400
Trace
    at PoolConnection.handlePacket (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:393:17)
    at PacketParser.onPacket (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:70:12)
    at PacketParser.executeStart (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\packet_parser.js:75:16)
    at Socket.<anonymous> (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:77:25)
    at Socket.emit (events.js:210:5)
    at addChunk (_stream_readable.js:308:12)
    at readableAddChunk (_stream_readable.js:289:11)
    at Socket.Readable.push (_stream_readable.js:223:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:182:23)
0 undefined ==> undefined#unknown name(0,,78)
 raw: fe7368613235365f70617373776f726400717e517834167a03770763452506255719282e4100
Trace
    at PoolConnection.handlePacket (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:393:17)
    at PacketParser.onPacket (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:70:12)
    at PacketParser.executeStart (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\packet_parser.js:75:16)
    at Socket.<anonymous> (G:\dev\giamcis\gwsi\aarm-api-n\node_modules\mysql2\lib\connection.js:77:25)
    at Socket.emit (events.js:210:5)
    at addChunk (_stream_readable.js:308:12)
    at readableAddChunk (_stream_readable.js:289:11)
    at Socket.Readable.push (_stream_readable.js:223:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:182:23)
0 965 ==> undefined#unknown name(2,,42)

I wonder if is there any reason why the emitted error in this situation does not arrive at my error handler?

Thank you!

[ianbale]

You were too quick! I just edited my comment above having just checked the logs that were produced in the last 30 mins… That was indeed the cause!

[chris-heathwood]

Just in case someone else finds this thread I had an issue with the PROTOCOL_CONNECTION_LOST on my local machine and in github actions and it was just me being too fast.

Waiting for 10 seconds or so and then try the connection worked.