When and how to return an http response only when a promise is complete?

Question

I have the following code

api.stuff_by_id = function (req, res) {
    var collection = collectionName;
    var search = getLuceneSearchString(req.body);

    luceneDb.search(collection, search)
        .then(function (result) {
            var result_message = result.body;
            console.log(result_message);
            res.send(result);  // this is the response I'd actually like to see returned.
        })
        .fail(function (err) {
            console.log(err);
            res.send(err);  // or this one if there is an error.
        })

    res.send('test');  // however this is the only one that gets returned.
};

I realize that the only response that will show when doing a curl request against this call is the last response, since the others are still processing for a split second. However I actually need to have the res.send(result) or res.send(err) calls give the response instead of the res.send('test'). What is a way to make the server wait to respond with one of the correct responses instead? Is there a way to wait somehow or some other method for doing this?

Thanks!

Solution (@NotMyself answered below, but helped me get to the following code offline). The solution was fairly easy, albeit not entirely obvious at first.

We pulled the abstraction to a better level, where api.stuff_by_id just returned a promise of the promise returned from the luceneDb.search function. Once that got bubbled up to the upper level then that was used, under a .then call of the promise to complete and send the respond (res.send) back up to the client. Here's what the method looked like afterwards.

The function setup for the post looks like this:

app.post('/identity/by',
    passport.authenticate('bearer', { session: false}),
    function (req, res) {
        luceneDb.search(req.body)
            .then(function (result) {
                res.send(result);
            })
            .fail(function (err) {
                res.statusCode = 400;
                res.send(err);
            });
    });

and the luceneDb.search function looks like this:

luceneDb.search = function (body) {
    var collection = data_tier.collection_idents;
    var search = getLuceneSearch(body);

    if (search === '') {
        throw new Error
        'Invalid search string.';
    }

    return orchestrator.search(collection, search)
        .then(function (result) {
            var result_message = result.body;
            console.log(result_message);
            return result.body;
        })
};

Providing less leakage of concerns too.

Answer 1

You need to remove the res.send('test');. The way you have it written her that send will complete the request before the promises have had a change to execute.

Answer 2

The problem with the res.send('test') is that the response will sent to the client before the end of the call of Lucene and because of that, the client is already gone when you will have a second res.send.

About promise, I use .them(function(result) {}, function(err) {}); Not .then().fail(), what module do you use?

And for LuceneDB what module do you use too? I'm just curious.