xds: Preserve nonce for unsubscribing type on ADS stream

[ejona86]

If a type was used and then fully-unsubscribed, the nonce needs to be preserved on the ads stream because the xds_protocol says:

The management server should not send a DiscoveryResponse for any DiscoveryRequest that has a stale nonce.

It appears grpc-node forgets the nonce here:

grpc-node/packages/grpc-js-xds/src/xds-client.ts

Line 462 in 263c478

this.typeStates.delete(type);

It appears there's another bug, in that the nonce isn't per-ADS stream. That can cause re-creations of the ADS stream to never receive a response, because they are sending the wrong nonce. Either the nonce can be stored in per-ADS stream state, or can be cleared when creating a new ADS stream. The only place I see it set is here, so it doesn't seem to be cleared on new ADS stream:

grpc-node/packages/grpc-js-xds/src/xds-client.ts

Line 347 in 263c478

typeState.nonce = result.nonce;

The xds_protocol says:

Note that the nonce is valid only in the context of an individual xDS stream; it does not survive stream restarts.

See also grpc/grpc-java#11796 and b/374697875

[ejona86]

You also potentially need to remember nonces for unknown types. See grpc/grpc-java#11799

[murgatroid99]

The line you reference for setting the nonce is in the per-ADS stream state management code, and I don't see any mechanism in my code to move that state between ADS streams, so I believe that part of the behavior is correct.

[ejona86]

I see. I was thrown off by ResourceTypeState including subscribedResources. I don't actually understand how you are managing the non-ADS state then, because I don't see where it is keeping the resources for re-creating the ADS stream. Doesn't matter. (Nevermind; I see it gets copied from authorityState)