implement k8s service discovery (#988)

* implement k8s service discovery

* simplify code

* use default namespace if not provided

* disable codecov bot comment

* ignore adhoc dir

* simplify building target in NewClient

* reformat code

* Fix filepath (#990)

* format code, and reorg imports (#991)

* add more unit test

Co-authored-by: anqiansong <anqiansong@gmail.com>

zrpc/internal/resolver/directbuilder.go

@@ -20,9 +20,11 @@ func (d *directBuilder) Build(target resolver.Target, cc resolver.ClientConn, op
 			Addr: val,
 		})
 	}
-	cc.UpdateState(resolver.State{
+	if err := cc.UpdateState(resolver.State{
 		Addresses: addrs,
-	})
+	}); err != nil {
+		return nil, err
+	}
 
 	return &nopResolver{cc: cc}, nil
 }