Unexpected blocked when custom lookup service returns ipv6 addresses

[chensk]

Bug description

If we registered a custom lookup service that returns ipv6 addresses, grpc client request would block forever. After tracking source code, I guess the bug exists in build_endpoint method:

fn build_endpoint(&self, ip_address: &SocketAddr) -> Option<Endpoint> {
        let uri = format!(
            "{}://{}:{}",
            self.scheme,
            ip_address.ip(),
            ip_address.port()
        );
        // ...
}

If the type of ip_address is SocketAddr::V6, the correct patten should be {}://[{}]:{} instead of {}://{}:{} which would fail the endpoint building. Then the create_changeset method would always report nothing because build_endpoint returns None:

changeset.extend(
            add_set
                .into_iter()
                .filter_map(|addr| self.build_endpoint(&addr).map(|endpoint| (addr, endpoint)))
                .map(|(addr, endpoint)| Change::Insert(addr, endpoint)),
        );

To Reproduce

Implement a custom lookup service that returns ipv6 addresses and register it.

Expected behavior

Custom lookup service returns either ipv4 or ipv6 addresses should work correctly.

Environment

Environment independent