Why is using Firebase Functions as an API endpoint so slow? - node.js

Question

I built an app in Slack, that on interactions in Slack, will send an HTTP POST request to a URL. That URL is a Firebase Function that is triggered with an HTTP request.
The Firebase Function looks like this...
// process incoming shortcuts
exports.interactions = functions.https.onRequest(async (request, response) => {
response.send();
const payload = JSON.parse(request.body.payload);
functions.logger.log(payload);
if (payload.type === 'shortcut') {
functions.logger.log('Found a shortcut...');
const shortcuts = require('./shortcuts');
await shortcuts(payload);
} else if (payload.type === 'block_actions') {
functions.logger.log('Found a block action...');
const blockActions = require('./blockActions');
await blockActions(payload);
} else if (payload.type === 'view_submission') {
functions.logger.log('Found a view submission...');
const viewSubmissions = require('./viewSubmissions');
await viewSubmissions(payload);
}
functions.logger.log('Done with interactions.');
});
The problem is, is that Firebase is taking 5-10 seconds to respond, and Slack is expecting a response in 3 seconds.
So the app in Slack erroring out.

Answer 1

It turns out while I thought it would be useful to do a response.send() immediately when the function was called so that Slack had its instant response, I was then also inadvertently starting background activities in Firebase.
The line in the above Firebase docs that gave me the biggest clue was:
Background activity can often be detected in logs from individual invocations, by finding anything that is logged after the line saying that the invocation finished.
Which I found here... the function started, and completed, and then the code to open a modal began to be executed...
I then found in the Firebase docs
Terminate HTTP functions with res.redirect(), res.send(), or res.end().
So all I really had to do was move response.send() to the end of the function. Also I had to make sure that I had await statements before my async functions, so that async functions waited to be resolved before executing the final response.send()
// process incoming shortcuts
exports.interactions = functions.https.onRequest(async (request, response) => {
const payload = JSON.parse(request.body.payload);
functions.logger.log(payload);
if (payload.type === 'shortcut') {
functions.logger.log('Found a shortcut...');
const shortcuts = require('./shortcuts');
await shortcuts(payload);
} else if (payload.type === 'block_actions') {
functions.logger.log('Found a block action...');
const blockActions = require('./blockActions');
await blockActions(payload);
} else if (payload.type === 'view_submission') {
functions.logger.log('Found a view submission...');
const viewSubmissions = require('./viewSubmissions');
await viewSubmissions(payload);
}
functions.logger.log('Done with interactions.');
response.send();
});
The modal interaction response times in Slack are much quicker and usable now.