Firebase Functions - ERROR, but no Event Message in Console - node.js

Question

I have written a function on firebase that downloads an image (base64) from firebase storage and sends that as response to the user:
const functions = require('firebase-functions');
import os from 'os';
import path from 'path';
const storage = require('firebase-admin').storage().bucket();
export default functions.https.onRequest((req, res) => {
const name = req.query.name;
let destination = path.join(os.tmpdir(), 'image-randomNumber');
return storage.file('postPictures/' + name).download({
destination
}).then(() => {
res.set({
'Content-Type': 'image/jpeg'
});
return res.status(200).sendFile(destination);
});
});
My client calls that function multiple times after one another (in series) to load a range of images for display, ca. 20, of an average size of 4KB.
After 10 or so pictures have been loaded (amount varies), all other pictures fail. The reason is that my function does not respond correctly, and the firebase console shows me that my function threw an error:
The above image shows that
A request to the function (called "PostPictureView") suceeds
Afterwards, three requests to the controller fail
In the end, after executing a new request to the "UserLogin"-function, also that fails.
The response given to the client is the default "Error: Could not handle request". After waiting a few seconds, all requests get handled again as they are supposed to be.
My best guesses:
The project is on free tier, maybe google is throttling something? (I did not hit any limits afaik)
Is there a limit of messages the google firebase console can handle?
Could the tmpdir from the functions-app run low? I never delete the temporary files so far, but would expect that either google deletes them automatically, or warns me in a different way that the space is running low.
Does someone know an alternative way to receive the error messages, or has experienced similar issues? (As Firebase Functions is still in Beta, it could also be an error from google)
Btw: Downloading the image from the client (android app, react-native) directly is not possible, because I will use the function to check for access permissions later. The problem is reproducable for me.

Answer 1

In Cloud Functions, the /tmp directory is backed by memory. So, every file you download there is effectively taking up memory on the server instance that ran the function.
Cloud Functions may reuses server instances for repeated calls to the same function. This means your function is downloading another file (to that same instance) with each invocation. Since the names of the files are different each time, you are accumulating files in /tmp that each occupy memory.
At some point, this server instance is going to run out of memory with all these files in /tmp. This is bad.
It's a best practice to always clean up files after you're done with them. Better yet, if you can stream the file content from Cloud Storage to the client, you'll use even less memory (and be billed even less for the memory-hours you use).

Answer 2

After some more research, I've found the solution: The Firebase Console seems to not show all error information.
For detailed information to your functions, and errors that might be omitted in the Firebase Console, check out the website from google cloud functions.
There I saw: The memory (as suggested by #Doug Stevensson) usage never ran over 80MB (limit of 256MB) and never shut the server down. Moreover, there is a DNS resolution limit for the free tier, that my application hit.
The documentation points to a limit of DNS resolutions: 40,000 per 100 seconds. In my case, this limit was never hit - firebase counts a total executions of roundabout 8000 - but it seems there is a lower, undocumented limit for the free tier. After upgrading my account (I started the trial that GCP offers, so actually not paying anything) and linking the project to the billing account, everything works perfectly.