Node-mysql2: How can I catch this connection error

[elhigu]

const mysql = require('mysql2');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  database: 'knex_test'
});

connection.query(
  'kill connection_id()',
  function(err, results, fields) {
    console.log('CALLBACK', err);
  }
);

process.on('uncaughtException', function (err) {
  console.log('uncaughtException', err);
})

This simple test program returns

Mikaels-MacBook-Pro-2:knex mikaelle$ node mysql2-test.js 
CALLBACK { Error: Connection was killed
    at Packet.asError (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/packets/packet.js:703:13)
    at Query.Command.execute (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/commands/command.js:28:22)
    at Connection.handlePacket (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/connection.js:515:28)
    at PacketParser.onPacket (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/connection.js:94:16)
    at PacketParser.executeStart (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/packet_parser.js:77:14)
    at Socket.<anonymous> (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/connection.js:102:29)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:188:7)
    at readableAddChunk (_stream_readable.js:176:18)
    at Socket.Readable.push (_stream_readable.js:134:10) code: undefined, errno: 1927, sqlState: '#70100' }
uncaughtException { Error: Connection lost: The server closed the connection.
    at Socket.<anonymous> (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/connection.js:113:35)
    at emitNone (events.js:91:20)
    at Socket.emit (events.js:185:7)
    at endReadableNT (_stream_readable.js:974:12)
    at _combinedTickCallback (internal/process/next_tick.js:80:11)
    at process._tickCallback (internal/process/next_tick.js:104:9) fatal: true, code: 'PROTOCOL_CONNECTION_LOST' }

The problem is that there is no way that I can catch the uncaughtException, which means that in this situation my app will be killed... Is there any good way to catch that Socket error? Shouldn't mysql2 driver subscribe and handle that error?

[sidorares]

hi @elhigu
You need to attach error handler to connection object itself ( in fact, it's best practice to always do that )

const mysql = require('mysql2');

const connection = mysql.createConnection({
  host: 'localhost',
  user: 'root',
  database: 'knex_test'
});

connection.on('error', function(err) {
  console.log("I'm dead");
})

connection.query(
  'kill connection_id()',
  function(err, results, fields) {
    console.log('CALLBACK', err);
  }
);

Or you can use connections pool, In that case pool will take care on connection level error handling

[elhigu]

Thanks for the response, setting connection.on('error', ...) indeed seems to work fine in this case, though I'm still seeing

    connection.on('error', ...) prints 
{ Error: Connection lost: The server closed the connection.
        at Socket.<anonymous> (/Users/mikaelle/Projects/Vincit/knex/node_modules/mysql2/lib/connection.js:113:35)
        at emitNone (events.js:91:20)
        at Socket.emit (events.js:185:7)
        at endReadableNT (_stream_readable.js:974:12)
        at _combinedTickCallback (internal/process/next_tick.js:80:11)
        at process._tickCallback (internal/process/next_tick.js:104:9) fatal: true, code: 'PROTOCOL_CONNECTION_LOST' }

process.on('uncaughtException',...) still prints in some cases:

Error: MySQL server has gone away
    at Error (native)

errors in my knex test code. I'll try to keep on reproducing that error and come back if I'm able to track the issue here :)