[Messaging] sendEachForMulticast with a lot of tokens throws error

[ShadowWolf308]

[READ] Step 1: Are you in the right place?

• For issues related to the code in this repository file a Github issue.
• If the issue pertains to Cloud Firestore, read the instructions in the "Firestore issue" template.
• For general technical questions, post a question on StackOverflow with the firebase tag.
• For general Firebase discussion, use the firebase-talk google group.
• For help troubleshooting your application that does not fall under one of the above categories, reach out to the personalized Firebase support channel.

[REQUIRED] Step 2: Describe your environment

• Operating System version: Docker version 28.0.1, build 068a01e (image is: oven/bun:1.2.12-alpine)
• Firebase SDK version: 13.4.0
• Firebase Product: messaging
• Node.js version: v20.18.0
• NPM version: 10.8.2

[REQUIRED] Step 3: Describe the problem

Steps to reproduce:

When using Http/2 with sendEachForMulticast will throw an error (Error while making requests: GOAWAY - exceeded_max_concurrent_streams, Error code: 1) when sending with a lot fcm tokens (lowest that i have tested that got rejected is 214)

if legacy http transport is enabled, this issue does not occur.

best guess why this happens is the fact that it sends a request for every token, therefore sending up to 500 requests at once which is too many for the http/2 implemenation of it.

Relevant Code:

const app = admin.initializeApp();
const messaging = app.messaging();

const tokens = []; // List of a lot of FCM tokens

try {
    const result = await messaging.sendEachForMulticast({ tokens });
} catch (err) {
    console.error(err);
}