Crash when connection to mySQL is lost

[borrys]

What are you doing?

When using replication configuration with mysql dialect the whole nodejs process crashes when connection to database is lost.

To reproduce it locally turn DB on, start the code below and after one or more Success messages turn DB off.

const Sequelize = require('sequelize');
const sequelize = new Sequelize(<database>, <user>, <password>, {
  replication: {
    read: {host: 'localhost'},
    write: {host: 'localhost'}
  },
  port: <port>,
  dialect: 'mysql',
  pool: {
    max: 1,
    min: 5
  }
});

function performTest(msg, callback) {
  sequelize
    .query('SELECT VERSION();', {
      type: Sequelize.QueryTypes.SELECT
    })
    .then(result => console.log('Success', result))
    .catch(err => console.log('Failure', err))
    .then(() => setTimeout(performTest, 1000));
}
performTest();

What do you expect to happen?

Failure messages on the console as long as DB is down.

What is actually happening?

The whole process crashes with error:

<project_dir>\node_modules\sequelize\lib\dialects\abstract\connection-manager.js:166
        return this.pool[mayBeConnection.queryType].destroy(mayBeConnection)
                                                    ^

TypeError: Cannot read property 'destroy' of undefined
    at Object.destroy (<project_dir>\node_modules\sequelize\lib\dialects\abstract\connection-manager.js:166:53)
    at Connection.errorHandler (<project_dir>\node_modules\sequelize\lib\dialects\mysql\connection-manager.js:103:23)
    at emitOne (events.js:116:13)
    at Connection.emit (events.js:211:7)
    at Connection._notifyError (<project_dir>\node_modules\mysql2\lib\connection.js:229:16)
    at Socket.<anonymous> (<project_dir>\node_modules\mysql2\lib\connection.js:107:16)
    at emitNone (events.js:111:20)
    at Socket.emit (events.js:208:7)
    at endReadableNT (_stream_readable.js:1056:12)
    at _combinedTickCallback (internal/process/next_tick.js:138:11)
    at process._tickCallback (internal/process/next_tick.js:180:9)

Dialect: mysql
Dialect version: mysql2 v.1.5.3
Database version: 5.7.22, 5.6.40
Sequelize version: 4.37.10
Tested with latest release: Yes

[borrys]

For what I found during debugging abstract/connection-manager.js on line 166 assumes that mayBeConnection.queryType is set but it is undefined.
I believe it is due to the fact that mysql/connection-manager.js registers error handler on connection before the connection gets queryType assigned (here or here)

[stale]

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