xds client sometimes loses updates when canceling/re-subscribing to same resource concurrently

[dfawley]

This was causing a test to be flaky but was worked around via #4377

[menghanl]

Client is watch for resource A

req(A, "")
resp(A, v1)
req(A, v1) // this is ACK

user cancels watch for A

req([], v1) // this removes A from the requested resources

user re-adds watch for A
What version to send with the request?
We will send

req(A, v1)

In the failed test, the controller (go-control-plane) doesn't resend (A, v1) to the client.

[dfawley]

@menghanl is this now confirmed to be caused by envoyproxy/go-control-plane#431 ? If so I think we can close it here.

[menghanl]

Yes. Closing now.