Restify inflight request counter leaks when using handleUncaughtExceptions and throwing an exception after connection is aborted

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Bug Report

Restify Version

Proven reproducible on 8.2.0 and 7.3.0

Node.js Version

Proven reproducible on v8.15.0 and v10.15.1

Expected behaviour

Restify inflight counter should not leak

Inflight requests: 1
Inflight requests: 1
Inflight requests: 1
Inflight requests: 1
...

Actual behaviour

Restify inflight counter leaks

Inflight requests: 1
Inflight requests: 2
Inflight requests: 3
Inflight requests: 4
...

Repro case

const restify = require('restify');
const http = require('http');

const server = restify.createServer({ handleUncaughtExceptions: true });
const delay = 100;

server.pre((req, res, next) => {
    console.log(`Inflight requests: ${server.inflightRequests()}`);
    next();
});

server.get('/', (req, res, next) => {
    setTimeout(() => { throw new Error('foo'); }, delay);
});

server.on('uncaughtException', (req, res) => res.send('foo'));

server.listen(8080, () => {
    console.log('Server now up on port 8080');

    setInterval(() => {
        const req = http.get("http://localhost:8080/").on('error', () => {});
        setTimeout(() => req.abort(), delay / 2);
    }, delay);
});

Cause

Something in Restify's domain handling causes this function to never get called with res._handlersFinished === true: https://github.com/restify/node-restify/blob/f363b36b0e5176c3f134b345c057ec6199d70b83/lib/server.js#L1347

I'm still working out the precise bug here but I should be able to trace more precisely what the bug is from there and update this ticket with more details.

Are you willing and able to fix this?

Yes (but extra eyes are appreciated)

Start in lib/server.js around line 1347, focusing on domain handling, handleUncaughtExceptions, and the _handlersFinished condition described in the report. Run the provided Node.js reproduction and trace why the request completion path is skipped after the connection is aborted. Done means repeated aborted requests no longer increase server.inflightRequests().