Firestore listeners miss events when app put in the background

[mathone1]

Description

Using a snapshot listener, if a document is updated while the app is in the background, this update will not be retrieved.
However, if the app is back in the foreground, the listener continues to work.
Only updates that occurred while the app was in the background are lost.

This means manually implementing a wrapper to detect the state change, closing the listener when the app goes to background and reopening it when it returns to background to make sure you don't miss any updates.
This generates a cost when reopening the listener (if no update has taken place).
Can this mechanism be avoided?

Reproducing the issue

Initiate a snapshot listener, put the application in the background, modify a document and put the application back in the foreground.

Firebase SDK Version

10.15.0

Xcode Version

15.0.1

Installation Method

Swift Package Manager

Firebase Product(s)

Firestore

Targeted Platforms

iOS

Relevant Log Output

No response

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[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[MarkDuckworth]

@mathone1, I was unable to reproduce the behavior you are experiencing.

I attached a listener using addSnapshotListener, put my ios app in the background, modified a document in another app, and saw that the listener was not called when the app was in the background, but when I bring my app back to the foreground, my listener is called with a snapshot that includes all updates. This was the case for snapshot listeners on a single document and on a collection.

Can you provide us with additional information to help us understand how to reproduce what you're seeing?

[mathone1]

Hi, thank you for your prompt reply.

Indeed, I may not have been precise enough, I apologize.

The listener is initiated as such:

db.collection("users").document(userId).collection(collection)
            .whereField("requestHash", isEqualTo: hash)
            .order(by: "lastUpdate", descending: true)
            .limit(to: 1)
            .addSnapshotListener { }

I have exactly the same behavior, except that when the app returns to the foreground, the listener is not called.
It's only called when I perform a new update with the app still in foreground.
The problem may lie in the "limit" (uninformed assumption).

I thank you in advance

[MarkDuckworth]

@mathone1, Thanks, that code is helpful. Is it possible that you can also provide a sample document and and a sample document update, so that I can be most effective when trying to reproduce the issue?

Also, do you see this behavior on a simpler query in your app? For example, with db.collection("users").document(userId).collection(collection).addSnapshotListener { }, does the listener get called after the app comes back to the foreground?

[google-oss-bot]

Hey @mathone1. We need more information to resolve this issue but there hasn't been an update in 5 weekdays. I'm marking the issue as stale and if there are no new updates in the next 5 days I will close it automatically.

If you have more information that will help us get to the bottom of this, just add a comment!