bug: App occasionally shows Wi-Fi connected ghost robots that don't actually exist on the network

[SyntaxColoring]

Overview

The Opentrons App is occasionally haunted by ghost robots.

Current behavior

When I took this screenshot, I was connected to S1-R10 over USB. S1-R1 is a robot on a completely different network; I'm quite certain my computer couldn't possibly have heard anything from it.

If I click S1-R1, I see this:

Unfortunately, neither error.log nor combined.log contain any recent mention of S1-R1.

The ghost robot persists for a while, but it does eventually disappear from the list.

Steps to reproduce

This seems to happen randomly. It's not clear what causes it.

When I've noticed it happen, I've been connected to a different robot over USB.

I had been connected to the ghost robot over Wi-Fi before, along with several other robots all sharing a WLAN. That WLAN is isolated, so I'm sure my computer isn't seeing its traffic.

[mcous]

Presumed fixed by #6193. Two properties of the discovery client in versions prior to 3.20 would allow this to happen:

• All state is tracked per IP address, which could have allowed stale data from S1-R1 to sneak in if it had ever used the same IP address as S1-R10
• The inherently faulty "your robot is advertising its IP address" logic was removed in favor of simpler logic that:
  • Tracks if a given IP address has been seen in any way (mDNS or health polling) while the app has been open
  • Notes whether a given IP address is responding with an HTTP error code or is unreachable from a networking standpoint