Apps with socket.io have 3x duplicate telemetry for incoming HTTP requests

[OsvaldoRosado]

Socket.io creates its own listeners on the HTTP server passed in, which later call the users’s own listeners. The SDK patches each listener, causing the unintentional duplication at each level.

We perform a simple check for avoiding duplication on outgoing HTTP dependencies (https://github.com/Microsoft/ApplicationInsights-node.js/blob/develop/AutoCollection/HttpDependencies.ts#L61) but no such check is done for incoming HTTP requests. Adding this simple check for ensuring the request object was not acted upon yet would fix this bug. In the meantime, it can also be implemented within a telemetry processor for anyone hitting this bug.

The bug can be reproduced with:

const appInsights = require('applicationinsights');
appInsights.setup('ikey').start();

const express = require('express');
const app = express();
const server = require('http').createServer(app);
const io = require('socket.io')(server);

const router = express.Router();

router.get('/test', (req, res, next) => {
        res.status(200).send('Hello!');
});

app.use('/', router);


io.on('connection', function(){ 

});
server.listen(3000);