CODEWITHSUNDEEP
javascriptnode.jsexpressnpmnode.js-connect
Lee Benson
Lee Benson

Reputation: 11599

Node.js - Domain per Express request, inside another domain

Error handling in Node. Argh!

I'm trying to layout a basic Node app like this...

Cluster -> Worker -> Server Domain -> Express Request Domain

So, if an error is thrown 18 layers deep into a call stack because someone misspelled their name on a login form, the entire server doesn't crash.

Here's some basic code to simulate the worker part:

var domain, server;

domain = require('domain');
server = domain.create();

server.on('error', function(e) {
    console.log('total meltdown...', e.stack);
});

server.run(function() {

    var express = require('express')();

    express.configure(function() {

        // Domain on EVERY request
        express.use(function(req, res, next) {
            var d = domain.create();

            d.on('error', function(e) {
                console.log('fired REQUEST error', e.stack);
                next(e);
            });

            d.run(next);

        });

        // Generic error handler
        express.use(function(e, req, res, next) {
            res.status(500);
            res.end('oops');
        });

        // Serve the request with a blatent error
        express.get('/', function(req, res) {

            this_function_does_not_exist();
            res.end('we will never get here');

        });
    });

    // Fire 'er up
    express.listen(3000);
});

What I'm expecting...

I curl http://localhost:3000/, get a nice little 'oops' error, and see 'fired REQUEST error' and the error stack in the console.

What actually happens...

I get this both as the browser response, and in the console...

ReferenceError: this_function_does_not_exist is not defined at /Stuff/test.js:38:13 at callbacks (/Stuff/node_modules/express/lib/router/index.js:161:37) at param (/Stuff/node_modules/express/lib/router/index.js:135:11) at pass (/Stuff/node_modules/express/lib/router/index.js:142:5) at Router._dispatch (/Stuff/node_modules/express/lib/router/index.js:170:5) at Object.router (/Stuff/node_modules/express/lib/router/index.js:33:10) at next (/Stuff/node_modules/express/node_modules/connect/lib/proto.js:190:15) at next (/Stuff/node_modules/express/node_modules/connect/lib/proto.js:192:9) at b (domain.js:183:18) at Domain.run (domain.js:123:23)

Now why would it go and do something like that?

Upvotes: 3

Views: 2193

Answers (1)

Lee Benson
Lee Benson

Reputation: 11599

Ok, solved - Express has a try/catch block, which is getting to my non-existent function call first.

To have the domain catch it, it needs to be taken out of the current call stack, like...

        process.nextTick(function() {
            this_function_does_not_exist();
            res.end('we will never get here');
        });

THEN the domain will grab it.

Upvotes: 2

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