Recover from Uncaught Exception in Node.JS - exception

Question

OK, so I have a problem. If an uncaught exception occurs while I am handling an HTTP request, I have no opportunity to call the end() method on the http.ServerResponse object. Therefore, the server hangs forever and never fulfills the request.
Here's an example:
var express = require('express');
var app = express.createServer();
var reqNum = 0;
app.get('/favicon.ico', function(req, res) {res.send(404);});
app.get('*', function(req, res, next) {
console.log("Request #", ++reqNum, ":", req.url);
next();
});
app.get('/error', function(req, res, next) {
throw new Error("Problem occurred");
});
app.get('/hang', function(req, res, next) {
console.log("In /hang route");
setTimeout(function() {
console.log("In /hang callback");
if(reqNum >= 3)
throw new Error("Problem occurred");
res.send("It worked!");
}, 2000);
});
process.on('uncaughtException', function(err) {
console.log("Uncaught exception!", err);
});
app.listen(8080);
If you visit /error, an exception occurs, but it is caught. The user receives an error message - no problem. If I visit /hang, though, the server will eventually throw an uncaught exception and hang forever. Any subsequent requests for /hang will hang.
This sucks. Any advice for how to fix this issue?

Answer 1

When an uncaught exception occurs, you're in an unclean state. Let the process die and restart it, there's nothing else you can do to safely bring it back to a known-good state. Use forever, it'll restart your process as soon as it dies.

Answer 2

If error is thrown synchronously, express won't stop working, only returning 500.
this.app.get("/error", (request, response) => {
throw new Error("shouldn't stop");
});
If error is thrown asynchronously, express will crash. But according to it's official documentation, there is still a way to recover from it by calling next:
this.app.get("/error", (request, response, next) => {
setTimeout(() => {
try {
throw new Error("shouldn't stop");
} catch (err) {
next(err);
}
}, 0);
});
This will let express do its duty to response with a 500 error.

Answer 3

Use try/catch/finally.
app.get('/hang', function(req, res, next) {
console.log("In /hang route");
setTimeout(function() {
console.log("In /hang callback");
try {
if(reqNum >= 3)
throw new Error("Problem occurred");
} catch (err) {
console.log("There was an error", err);
} finally {
res.send("It worked!");
}
}, 2000);
});