idle connection close

[stager0909]

[REQUIRED] Step 2: Describe your environment

• Operating System version: ubuntu
• Firebase SDK version: firebase-admin-java 9.4.0
• Library version: jdk 17
• Firebase Product: fcm (auth, database, storage, etc)

[REQUIRED] Step 3: Describe the problem

Steps to reproduce:

I am testing with firebase-admin-java 9.4.0.
Since communication is via HTTP/2, I expected the connection to remain open if there were no issues. However, after making a request, if there are no additional requests, the connection is dropped after about 3 minutes.
The strange part is that the entity sending the FIN packet is not the client, but the FCM server.
Is there any specific reason why the server is sending a FIN packet and closing the connection, even though it's using HTTP/2?

[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.