Firebase Function Returns Before All Callback functions complete execution - async-await

Question

I'm using the Google Storage NodeJS client library to list GCS Bucket paths.
Here's the code to the Firebase Function:
import * as functions from 'firebase-functions';
import { Storage } from '#google-cloud/storage';
import { globVars } from '../admin/admin';
const projectId = process.env.GCLOUD_PROJECT;
// shared global variables setup
const { keyFilename } = globVars;
// Storage set up
const storage = new Storage({
projectId,
keyFilename,
});
export const gcsListPath = functions
.region('europe-west2')
.runWith({ timeoutSeconds: 540, memory: '256MB' })
.https.onCall(async (data, context) => {
if (context.auth?.token.email_verified) {
const { bucketName, prefix, pathList = false, fileList = false } = data;
let list;
const options = {
autoPaginate: false,
delimiter: '',
prefix,
};
if (pathList) {
options.delimiter = '/';
let test: any[] = [];
const callback = (_err: any, _files: any, nextQuery: any, apiResponse: any) => {
test = test.concat(apiResponse.prefixes);
console.log('test : ', test);
console.log('nextQuery : ', nextQuery);
if (nextQuery) {
storage.bucket(bucketName).getFiles(nextQuery, callback);
} else {
// prefixes = The finished array of prefixes.
list = test;
}
}
storage.bucket(bucketName).getFiles(options, callback);
}
if (fileList) {
const [files] = await storage
.bucket(bucketName)
.getFiles(options);
list = files.map((file) => file.name);
}
return { list }; //returning null as it exec before callback fns finish
} else {
return {
error: { message: 'Bad Request', status: 'INVALID_ARGUMENT' },
};
}
});
My problem is that my Firebase function returns the list (null) before all the callback functions finish execution.
Could someone spot and point out what needs to be changed/added to make the function wait for all the callback functions to finish. I've tried adding async/await but can't seem to get it right.

Answer 1

The reason for your error is that you use a callback. It's not awaited in the code. I would recommend to turn the callback code to a promise. Something like this.
import * as functions from "firebase-functions";
import { Storage } from "#google-cloud/storage";
import { globVars } from "../admin/admin";
const projectId = process.env.GCLOUD_PROJECT;
// shared global variables setup
const { keyFilename } = globVars;
// Storage set up
const storage = new Storage({
projectId,
keyFilename,
});
const getList = (bucketName, options) => {
return new Promise((resolve, reject) => {
let list;
let test: any[] = [];
const callback = (
_err: any,
_files: any,
nextQuery: any,
apiResponse: any
) => {
test = test.concat(apiResponse.prefixes);
console.log("test : ", test);
console.log("nextQuery : ", nextQuery);
if (nextQuery) {
storage.bucket(bucketName).getFiles(nextQuery, callback);
} else {
// prefixes = The finished array of prefixes.
list = test;
}
resolve(list);
};
try {
storage.bucket(bucketName).getFiles(options, callback);
} catch (error) {
reject(eror);
}
});
};
export const gcsListPath = functions
.region("europe-west2")
.runWith({ timeoutSeconds: 540, memory: "256MB" })
.https.onCall(async (data, context) => {
if (context.auth?.token.email_verified) {
const { bucketName, prefix, pathList = false, fileList = false } = data;
let list;
const options = {
autoPaginate: false,
delimiter: "",
prefix,
};
if (pathList) {
options.delimiter = "/";
list = await getList(bucketName, options);
}
if (fileList) {
const [files] = await storage.bucket(bucketName).getFiles(options);
list = files.map((file) => file.name);
}
return { list }; //returning null as it exec before callback fns finish
} else {
return {
error: { message: "Bad Request", status: "INVALID_ARGUMENT" },
};
}
});
I'm not sure if the part with fileList will work as expectedt. It looks like the API doesn't support await but only callbacks.

Answer 2

import * as functions from "firebase-functions";
import { GetFilesOptions, Storage } from "#google-cloud/storage";
import { globVars } from "../admin/admin";
const projectId = process.env.GCLOUD_PROJECT;
// shared global variables setup
const { keyFilename } = globVars;
// Storage set up
const storage = new Storage({
projectId,
keyFilename,
});
const getList = (bucketName: string, options: GetFilesOptions) => {
return new Promise((resolve, reject) => {
// let test: any[] = [];
let list: any[] = [];
const callback = (
_err: any,
_files: any,
nextQuery: any,
apiResponse: any
) => {
list = list.concat(apiResponse.prefixes);
console.log("list : ", list);
console.log("nextQuery : ", nextQuery);
if (nextQuery) {
storage.bucket(bucketName).getFiles(nextQuery, callback);
} else {
// prefixes = The finished array of prefixes.
resolve(list);
}
};
try {
storage.bucket(bucketName).getFiles(options, callback);
} catch (error) {
reject(error);
}
});
};
export const gcsListPath = functions
.region("europe-west2")
.runWith({ timeoutSeconds: 540, memory: "256MB" })
.https.onCall(async (data, context) => {
if (context.auth?.token.email_verified) {
const { bucketName, prefix, pathList = false, fileList = false } = data;
let list;
const options = {
autoPaginate: false,
delimiter: "",
prefix,
};
if (pathList) {
options.delimiter = "/";
list = await getList(bucketName, options);
}
if (fileList) {
const [files] = await storage.bucket(bucketName).getFiles(options);
list = files.map((file) => file.name);
}
return { list }; //returning null as it exec before callback fns finish
} else {
return {
error: { message: "Bad Request", status: "INVALID_ARGUMENT" },
};
}
});