sending a streaming response to a REST query with async operation - node.js

Question

update: clarified and edited code to reflect what I really want, that is, send a streaming response, that is, send back matched results as they arrive from their own async matching process.
consider (using expressjs-ish code)
app.post('/', jsonParser, function (req, res) {
if (!req.body) return res.sendStatus(400)
// matches is not needed for this scenario so
// commenting it out
// var matches = [];
req.body.forEach(function(element, index) {
foo.match(
element,
function callback(error, result) {
if (error) {
console.log(error); // on error
}
else {
⇒ if (some condition) {
// matches.push(result);
⇒ res.send(result);
}
}
}
);
});
// moved this above, inside the callback
// ⇒ res.send(matches);
});
The input to post('/') is an array of terms. Each term is matched using foo which has a callback after every call. I want to send back all the matches that satisfy "some condition" (see ⇒ in the code above). Ideally, it would be good to send back a streaming response, that is, send a response back as the matches occur (because foo.match() might take a while for each term). How do I go about this?

Answer 1

Does something like that works for you? I' ve used the stream-array module. Possibly this can be helpful for you? How to emit/pipe array values as a readable stream in node.js?
var streamify = require('stream-array');
app.post('/', jsonParser, function (req, res) {
if (!req.body) {
return res.sendStatus(400);
}
var matches = [];
req.body.forEach(function (element, index) {
foo.match(
element,
function callback(error, result) {
if (error) {
console.log(error); // on error
} else {
if (some condition) {
streamify([result]).pipe(res);
}
}
}
);
});
// res.json(req.body);
});