Promise not resolve inside async function in express middleware - node.js

Question

This one is starting to get under my skin...
I'm playing around with Firebase and Functions right now and made a very simple API with express as the middleware.
So I have this route:
...
app.get('/getAuthUrl', async (req, res) => {
const s: sessionManagement.ISessionManagement =
sessionManagement.SessionFactory.createSession(
functions.config().aproxy.session.mode, req, db)
// ...this work
const getback = req.query.getback;
await db.collection('tokens').doc('getback').set({getback});
// this not?!
s.setReturnURL(req.query.getback);
res.setHeader('Cache-Control', 'private');
res.status(200).json(new Message(redirectUri));
})
At first, I use the 2 lines under the comment "...this work" and it did work; writing an URL to a Firestore database. So far, so good.
Then I decided to get fancy and decide to use a object factory to manage the fact that using Express session on a localhost serving functions (with the emulator) on one port and the angular frontend on an other was causing some headache with session management. Long story short, I setup a factory that will return me a object that will manage if I was running localy or on Firebase cloud hosting and used a different strategy.
This is where Promise started to not holding their... promise!?
The line s.setReturnURL(.. call this method inside my factory:
export interface ISessionManagement {
setReturnURL: (value: string) => void
}
export class FirestoreSession implements ISessionManagement {
private database: FirebaseFirestore.Firestore
private fingerprint: string
constructor(database: FirebaseFirestore.Firestore, fingerprint: string) {
this.database = database
this.fingerprint = fingerprint
}
setReturnURL(value: string) {
console.log('setReturnURL')
this.writeDoc(value, 'getback')
}
writeDoc(value: string, document: string) {
(async () => {
console.log('inside async')
const doc = this.database.collection('tokens').doc(document).set({value})
const result = await doc
console.log(result)
})().catch(error => {
console.log(error)
})
console.log('finish writeDoc')
}
}
export class SessionFactory {
public static createSession(mode: string, req: express.Request, db: FirebaseFirestore.Firestore) : ISessionManagement {
if (mode === 'fingerprint' ) {
console.log('fingerprint mode');
// Use for local testing, since in multiport solution, cookie will not be unique to a session
return new FirestoreSession(db, fingerPrintMe(req));
} else {
// For production
return new ExpressSession(req);
}
}
}
So, here the console output of the flow of execution if a use my factory object:
✔ functions[app]: http function initialized (http://localhost:5000/myplayground/us-central1/app).
i functions: Beginning execution of "app"
> fingerprint mode
> setReturnURL
> inside async
> finish writeDoc
i functions: Finished "app" in ~1s
The code above is my latest attempt to make this work. I tried A LOT of variation, moving my async/await around but nothing budge!
What am I missing??? I feel the answer will make me crawl under some rock but I don't care, I need to take this one off my mind :-)
UPDATE
Turns out that I need to async/await all the way down to the call that return a promise to make this work AND ALSO, you cannot await a function that return void, so I had to change the interface signature. So here the code fragment that work :
app.get('/getAuthUrl', async (req, res) => {
...
await s.setReturnURL(req.query.getback)
...
})
...
export interface ISessionManagement {
setReturnURL: (value: string) => any
}
export class FirestoreSession implements ISessionManagement {
...
async setReturnURL(value: string) {
await this.writeDoc(value, 'getback')
}
...
async writeDoc(value: string, document: string) {
try {
const doc = await this.database.collection('tokens').doc(document).set({value})
console.log(doc)
} catch (error) {
console.log(error)
}
}
}

Answer 1

const doc = this.database.collection('tokens').doc(document).set({value})
const result = await doc
Why not just const result = await this.database.collection('tokens').doc(document).set({value})?
`writeDoc(value: string, document: string) {
(async () => {
console.log('inside async')
const doc = this.database.collection('tokens').doc(document).set({value})
const result = await doc
console.log(result)
})().catch(error => {
console.log(error)
})
console.log('finish writeDoc')
}`
First, writedoc is not a promise and isn't awaited. The internal async function isn't awaited either, so once execution pauses the rest of the function moves on. So it will execute and the rest of internal async function will be queued for the next event loop. Then everything returns and exits.
Make writedoc async, and await it and the internal async function.