Promises on prerequisites makes handler to swallow exceptions

[nakardo]

I've this issue when using Promises on a prerequisite handler and throwing an error from a handler.

var Promise = require('promise');


exports.register = function (server, options, next) {

    var pre = function (request, reply) {

        return reply(Promise.resolve('value'));
    };

    server.route({
        method: 'GET',
        path: '/bar',
        config: {
            pre: [
                { method: pre, assign: 'pre' }
            ],
            handler: function (request, reply) {

                // throws here will get swallowed

                throw new Error('will timeout');
                return reply();
            }
        }
    });

    return next();
};

exports.register.attributes = {
    pkg: require('./package.json')
};

Replying with a literal value on the pre() does it make it work. Using Promises on the handler will too, but it sounds more like a workaround to me.

Here's the dependencies I'm using:

[email protected] node_modules/code
└── [email protected]

[email protected] node_modules/promise
└── [email protected]

[email protected] node_modules/hapi
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected] ([email protected])
├── [email protected] ([email protected], [email protected], [email protected])
├── [email protected] ([email protected], [email protected])
└── [email protected] ([email protected])

[email protected] node_modules/lab
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected]
├── [email protected] ([email protected])
├── [email protected] ([email protected])
├── [email protected] ([email protected], [email protected], [email protected], [email protected])
├── [email protected] ([email protected], [email protected], [email protected], [email protected])
├── [email protected] ([email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected])
└── [email protected] ([email protected], [email protected], [email protected])

I can upload an small repo with a few tests if it helps.

[devinivy]

I've experienced something like this too while playing around. Possibly related to outmoded/discuss#155.

[hueniverse]

Since I don't use promises I can't really help you. Maybe someone who knows promises well can look into it. I'll leave this open for a bit.

[devinivy]

@dmacosta if you put a repo up with some tests, I'll definitely take a peek.

[nlf]

my gut says this is because of domains. likely something is causing the request handler's domain to get lost.

[nlf]

@devinivy i'm online in gitter if you want a second pair of eyes on this when you get around to checking it out

[nakardo]

@devinivy @nlf https://github.com/dmacosta/hapi-issue-2771

[nlf]

confirmed this is a domains issue, i think i have a fix

[nlf]

ok, i don't have a fix, but i can definitely confirm it's an issue with domains..

adding logging to the error handler in lib/protect.js reveals the error isn't caught at all. logging process.domain within the handler that is run after a normal prerequisite gives a domain object, however in a handler that is run after a prerequisite that returns a promise, it's undefined.

that's as far as i got. domains are hard.

[devinivy]

Yeah, I spent about 15mins with this and didn't get far at all. The promise library used (https://github.com/then/promise) does have a note about domains in the README worth looking at.

[hueniverse]

I'm going to label this as a bug but close it because we can't do anything about these issues. I am going to add a domains-free option soon.

[devinivy]

Worth adding that I revisited this. The "done" handler that hapi calls for the promise escapes the domain (i.e., onDone in promiseFromPre.then(onDone, onDone)), but there was no way I could fix it. Different promise libraries behaved slightly differently, too. The promise library used in this particular example looks like it executes the callbacks outside a domain intentionally via the asap module.

[hueniverse]

You can now try turning off domains if you want.

[rubennorte]

I ended up in this issue after loosing the active domain in my handlers. After some investigation I tested replacing native promises with Bluebird and it works fine.

I created a gist with examples of this behaviour in case it helps someone: https://gist.github.com/rubennorte/f10d2f6ec376b28589a98bb17ef6ae85

[kanongil]

Node will support domain bindings for promises, which has already been implemented in the master branch, see nodejs/node#12489.