Deprecate usage of `gresolver.Address.Metadata`

[siyuanfoundation]

What would you like to be added?

Deprecate usage of gresolver.Address.Metadata in client/v3/naming/resolver/resolver.go, and add Attributes field.

Why is this needed?

gresolver.Address.Metadata in grpc is deprecated, and should use Attributes instead.
https://github.com/grpc/grpc-go/blob/51d6a43ec59753d42ccd02bb12d2e9e40c164f0f/resolver/resolver.go#L117-L121

[amosehiguese]

Hi @siyuanfoundation, I'd like to work on implementing this feature. I'll follow the gRPC resolver API changes to deprecate the Metadata usage in favor of Attributes.

[amosehiguese]

Hi @siyuanfoundation

I just sent in a pr with the implementation in place.

[siyuanfoundation]

/assign @amosehiguese

Thank you!

[siyuanfoundation]

We should also have use the supported fields in tests like #19702

[amosehiguese]

Yeah, I noticed the tests still uses the metadata field, so my first attempt was to introduce the new field and make it backward compatible.

However, now that you've mentioned the Metadata field should remain in the Endpoint, I will revert back to that only and handle the conversion process underneath. If this is fine, please signify.

Lastly, I will love to mention that creating a new Attribute with the attributes.New(k, v any) to be used in the gresolver.Address Attribute field, takes in a key and a value as opposed to a single "any" argument(i.e the metadata passed)

Would you say it's okay to use the up.Key for the key and the up.Endpoint.Metadata for the value?

[ahrtr]

link to #15145

Let's follow the same pattern as grpc-go: add Attributes *attributes.Attributes into Endpoint, and deprecate Metadata

We might also want to backport the fix to release-3.6, depending on the complexity of the change.

cc @dfawley please chime in in case we miss anything, thx