sdk 10.3.0 changed firestore webchannel to use xhr instead of fetch

[atsjo]

Operating System

Windows 11

Browser Version

Chrome/Edge latest

Firebase SDK Version

10.3.0

Firebase SDK Product:

Firestore

Describe your project's tooling

Angular app using esbuild builder

Describe the problem

In sdk 10.2.0 fetch is used for firestore webchannel (I can se that from network tab in devtools, I think it's been used since 9.0), but 10.3.0 changed firestore webchannel to use xhr instead.

Overriding via undocumented useFetchStreams param in initializeFirestore doesn't work anymore either, so guessing this is a bug, and related to #7569. This is supposed to "fix how we enable fetch streams" to correct a bug, but seems to completely disable it. I can observe more aborted/cancelled communication in devtools with xhr, but it's still working...

Steps and code to reproduce issue

upgrade to 10.3.0 and observe communication via devtools

[sampajano]

@atsjo Thanks for the report!

I've taken a quick look — I think with #7569, it is expected that all POST (client -> server) request will now be using XHR, but the GET (server -> client streaming) requests should still be using Fetch. (This was the original intent of the useFetchStreams on the WebChannel side.)

Is that inline with what you have observed also?

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Disclaimer: I'm not familiar with Firestore requirements overall so i'm not sure if this is a breaking issue for anyone. I'll let members of the Firebase team comment later.

@wu-hui FYI

[atsjo]

in 10.2.0 and earlier both GET and POST for the webchannel uses fetch, but direct requests, like getCountFromServer uses xhr.

I am using persistent multitab cache if that matters...

in 10.3.0 both GET and POST for the webchannel uses xhr...

[wu-hui]

Note the fix does what @sampajano described in #7581 (comment)

"all POST (client -> server) request will now be using XHR, but the GET (server -> client streaming) requests should still be using Fetch."

[maccman]

@wu-hui Can you elaborate on why it's bad if Firebase uses XHR versus Fetch? Is it just that the XHR API is deprecated?

[wu-hui]

Yeah, pretty much. I don't think XHR vs Fetch with requests makes much difference, it's more about we want to use newer APIs as long as it makes sense.

Using Fetch both directions with webchannel's bidi-streams is under-tested however, so we will stay on the default configuration for now, and maybe flip to that later. Again, I don't think there is much to gain here performance-wise.