okhttp: OkHttp does not close connection when server sends a FIN, ACK

We’ve recently encountered an issue on production wherein an HTTP server, which is shutting down, sends back a FIN, ACK packet, but OkHttp still continues sending traffic on that connection instead of closing it and started a new connection.

Here is a screenshot of one such incident on Wireshark on my local setup (10.101.84.85 is the server, 172.17.0.6 is the client),

My test setup is as follows,

• Hosted on Kubernetes.
• Client side running using OkHttp 4.5.0 (Java 18)
• Server side running a Golang HTTP server (Golang 1.18)
• Client side uses Kubernetes FQDN to talk to the server.
• Client maintains a connection pool of 10 connections.
• Client side code: https://gist.github.com/tejasjadhav/d5a4b4efca8e7400236ce18e86dcb00a#file-app-java
• Server side code: https://gist.github.com/tejasjadhav/d5a4b4efca8e7400236ce18e86dcb00a#file-main-go

Expectation

OkHttp client should remove the connection from the pool when server sends back FIN, ACK packet.

Actual

OkHttp does not terminate the connection for which server sends back FIN, ACK packet and still sends traffic on that connection, which results in a connection resets and failures on subsequent calls.

Steps to reproduce

1. Create an OkHttp client with a connection pool to an HTTP server.
2. Make 1-2 requests using that client to initialise the pool.
3. Shutdown the server. Observe that FIN, ACK packets are being sent by the server on shutdown.
4. While the server is shutting down, send 1-2 requests using the OkHttp client.
5. The requests should fail with an error unexpected end of stream. Server would have sent an RST in response.

Environment

• OkHttp 4.5.0
• Java 18