To fix a bug in the retry logic caused when the auth token is cleared after receiving `ErrInvalidAuthToken` from the server and the subsequent call to `getToken` also fails due to some reason (eg. context deadline exceeded).
This leaves the client without a token and the retry will continue to fail with `ErrUserEmpty` unless the token is refreshed.
A client-side optimization was made in #6100 to filter ascending key sorts to avoid an unnecessary re-sort since this is the order already returned by the back-end logic.
It seems to me that this really belongs on the server side since it's tied to the server implementation and should apply for any caller of the kv api (for example non-go clients).
Related, the client/v3 syncer depends on this default sorting which isn't explicit in the kv api contract. So I'm proposing the required sort parameters be included explicitly; it will take the fast path either way.
`Client.dial` can be called multiple times. For example, from regular
`NewClient` and [from the `Maintenance`
wrapper](6d451ab61d/client/v3/maintenance.go (L81-L84)).
This ends up creating two (if `Client.dial` is called twice) independent
`credentials.Bundle` instances:
- the first one is wired into `PerRPCCredentials` callback in gRPC
client.
- the second one is in `Client.authTokenBundle` and receives the latest
auth token updates.
When using username/password authentication and the server is configured
to issue JWTs, token rotation logic breaks because of the above
`credentials.Bundle` confusion.
- ErrGRPCNotCapable("etcdserver: not capable") -> codes.FailedPrecondition (it will not autofix, it requires new version of server)
- ErrGPRCNotSupportedForLearner("etcdserver: rpc not supported for learner") -> codes.FailedPrecondition (as long as its learner, the call will not work)
- ErrGRPCClusterVersionUnavailable("etcdserver: cluster version not found during downgrade") -> codes.FailedPrecondition (backend does not contain the version (old etcd?) so retry will not help)
https://github.com/etcd-io/etcd/runs/2599598633?check_suite_focus=true
```
{"level":"warn","ts":"2021-05-17T09:55:30.246Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc000539880/#initially=[unix://localhost:m30]","attempt":0,"error":"rpc error: code = Unavailable desc = etcdserver: rpc not supported for learner"}
{"level":"warn","ts":"2021-05-17T09:55:30.270Z","logger":"etcd-client","caller":"v3/retry_interceptor.go:62","msg":"retrying
of unary invoker
failed","target":"etcd-endpoints://0xc000539880/#initially=[unix://localhost:m30]","attempt":1,"error":"rpc
error: code = Unavailable desc = etcdserver: rpc not supported for
learner"}`
```
clientv3 logs (especially tests) were poluted with unattributed to testing.T log lines:
```
{"level":"warn","ts":"2021-04-29T12:42:11.055+0200","logger":"etcd-client","caller":"v3/retry_interceptor.go:64","msg":"retrying of unary invoker failed","target":"etcd-endpoints://0xc0000fafc0/#initially=[unix://localhost:m10]","attempt":0,"error":"rpc error: code = ResourceExhausted desc = etcdserver: mvcc: database space exceeded"}
```
The reasons were 2 fold:
- Interceptors were copying logger before "WithLogger" could modify it.
- We were not propagating the loggers in a few testing contexts.
