Send 'Received post' back to requester before async finishes (NodeJS, ExpressJS) - node.js

Question

I have an API POST route where I receive data from a client and upload the data to another service. This upload is done inside of the post request (async) and takes awhile. The client wants to know their post req was received prior to the async (create project function) is finished. How can I send without ending the POST? (res.send stops, res.write doesn't send it out)
I thought about making an http request back to their server as soon as this POST route is hit. . .
app.post('/v0/projects', function postProjects(req, res, next) {
console.log('POST notice to me');
// *** HERE, I want to send client message
// This is the async function
createProject(req.body, function (projectResponse) {
projectResponse.on('data', function (data) {
parseString(data.toString('ascii'), function (err, result) {
res.message = result;
});
});
projectResponse.on('end', function () {
if (res.message.error) {
console.log('MY ERROR: ' + JSON.stringify(res.message.error));
next(new Error(res));
} else {
// *** HERE is where they finally receive a message
res.status(200).send(res.message);
}
});
projectResponse.on('error', function (err) {
res.status(500).send(err.message);
});
});
});
The internal system requires that this createProject function is called in the POST request (needs to exist and have something uploaded or else it doesn't exist) -- otherwise I'd call it later.
Thank you!

Answer 1

I think you can't send first response that post request received and send another when internal job i.e. createProject has finished no matter success or fail.
But possibly, you can try:
createProject(payload, callback); // i am async will let you know when done! & it will push payload.jobId in doneJobs
Possibility 1, If actual job response is not required:
app.post('/v0/projects', function (req, res, next) {
// call any async job(s) here
createProject(req.body);
res.send('Hey Client! I have received post request, stay tuned!');
next();
});
});
Possibility 2, If actual job response is required, try maintaining queue:
var q = []; // try option 3 if this is not making sense
var jobsDone = []; // this will be updated by `createProject` callback
app.post('/v0/projects', function (req, res, next) {
// call async job and push it to queue
let randomId = randomId(); // generates random but unique id depending on requests received
q.push({jobId: randomId });
req.body.jobId = randomId;
createProject(req.body);
res.send('Hey Client! I have received post request, stay tuned!');
next();
});
});
// hit this api after sometime to know whether job is done or not
app.get('/v0/status/:jobId', function (req, res, next) {
// check if job is done
// based on checks if done then remove from **q** or retry or whatever is needed
let result = jobsDone.indexOf(req.params.jobId) > -1 ? 'Done' : 'Still Processing';
res.send(result);
next();
});
});
Possibility 3, redis can be used instead of in-memory queue in possibility 2.
P.S. There are other options available as well to achieve the desired results but above mentioned are possible ones.