cleanup client/selector/lookup (#1937)

* cleanup client/selector/lookup

* add mdns router, remove registry from client

* fix roundtripper

* remove comment

* fix compile issue

* fix mucp test

* fix api router

client/lookup.go

@@ -0,0 +1,44 @@
+package client
+
+import (
+	"context"
+
+	"github.com/micro/go-micro/v3/errors"
+	"github.com/micro/go-micro/v3/router"
+)
+
+// LookupFunc is used to lookup routes for a service
+type LookupFunc func(context.Context, Request, CallOptions) ([]string, error)
+
+// LookupRoute for a request using the router and then choose one using the selector
+func LookupRoute(ctx context.Context, req Request, opts CallOptions) ([]string, error) {
+	// check to see if an address was provided as a call option
+	if len(opts.Address) > 0 {
+		return opts.Address, nil
+	}
+
+	// construct the router query
+	query := []router.QueryOption{router.QueryService(req.Service())}
+
+	// if a custom network was requested, pass this to the router. By default the router will use it's
+	// own network, which is set during initialisation.
+	if len(opts.Network) > 0 {
+		query = append(query, router.QueryNetwork(opts.Network))
+	}
+
+	// lookup the routes which can be used to execute the request
+	routes, err := opts.Router.Lookup(query...)
+	if err == router.ErrRouteNotFound {
+		return nil, errors.InternalServerError("go.micro.client", "service %s: %s", req.Service(), err.Error())
+	} else if err != nil {
+		return nil, errors.InternalServerError("go.micro.client", "error getting next %s node: %s", req.Service(), err.Error())
+	}
+
+	var addrs []string
+
+	for _, route := range routes {
+		addrs = append(addrs, route.Address)
+	}
+
+	return addrs, nil
+}