MySQL fields not returned

[brainsiq]

Describe the bug

The mysql module's query function has three parameters in the callback as shown by the example in the README

https://github.com/mysqljs/mysql#introduction

connection.query('SELECT 1 + 1 AS solution', function (error, results, fields) {
if (error) throw error;
console.log('The solution is: ', results[0].solution);
});

It appears that when using dd-trace-js that the final fields parameter is undefined.

Environment

• Operation system: Docker image node:12.12.0-alpine
• Node version: 12.12.0
• Tracer version: 0.26.1
• Agent version: 7.22.1
• MySQL module version: 2.14.1

[brainsiq]

I believe the bug is here:

dd-trace-js/packages/datadog-plugin-mysql/src/index.js

Lines 59 to 71 in 40e5617

	return tracer.scope().bind((err, res) => {
	if (err) {
	span.addTags({
	'error.type': err.name,
	'error.msg': err.message,
	'error.stack': err.stack
	})
	}
	span.finish()
	done(err, res)
	}, parent)

I assume this should have the same callback parameters as the mysql library. I have tried to use your tests to verify this but have not been able to get the tests to run - firstly seemed I had to use node 8, and even then have errors from node-gyp when building the couchbase module 🤷‍♂️

[brainsiq]

In addition to this we can see an error in DataDog caused by our application code calling .forEach() on the undefined argument. The stack refers to the LOC referenced above (/usr/src/app/node_modules/dd-trace/packages/datadog-plugin-mysql/src/index.js:70:5):

TypeError: Cannot read property 'forEach' of undefined
at /usr/src/app/lib/mysqlHelpers/index.js:540:22
at bound (domain.js:420:14)
at runBound (domain.js:433:12)
at Query.<anonymous> (/usr/src/app/node_modules/dd-trace/packages/datadog-plugin-mysql/src/index.js:70:5)
at /usr/src/app/node_modules/dd-trace/packages/dd-trace/src/scope/base.js:54:19
at Scope._activate (/usr/src/app/node_modules/dd-trace/packages/dd-trace/src/scope/async_hooks.js:53:14)
at Scope.activate (/usr/src/app/node_modules/dd-trace/packages/dd-trace/src/scope/base.js:12:19)
at Query.bound [as _callback] (/usr/src/app/node_modules/dd-trace/packages/dd-trace/src/scope/base.js:53:20)
at Query.Sequence.end (/usr/src/app/node_modules/mysql/lib/protocol/sequences/Sequence.js:88:24)
at Query._handleFinalResultPacket (/usr/src/app/node_modules/mysql/lib/protocol/sequences/Query.js:139:8)
at Query.EofPacket (/usr/src/app/node_modules/mysql/lib/protocol/sequences/Query.js:123:8)
at Protocol._parsePacket (/usr/src/app/node_modules/mysql/lib/protocol/Protocol.js:279:23)
at Parser.write (/usr/src/app/node_modules/mysql/lib/protocol/Parser.js:76:12)
at Protocol.write (/usr/src/app/node_modules/mysql/lib/protocol/Protocol.js:39:16)
at Socket.<anonymous> (/usr/src/app/node_modules/mysql/lib/Connection.js:103:28)
at /usr/src/app/node_modules/dd-trace/packages/dd-trace/src/scope/base.js:54:19

[bengl]

@brainsiq This is fixed by #1116, and should be in the next release (0.27.0).