router: use dns as default router

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

router/dns.go

@@ -0,0 +1,91 @@
+package router
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+)
+
+// NewRouter returns an initialized dns router
+func NewRouter(opts ...Option) Router {
+	options := NewOptions(opts...)
+	return &dns{options}
+}
+
+type dns struct {
+	options Options
+}
+
+func (d *dns) Init(opts ...Option) error {
+	for _, o := range opts {
+		o(&d.options)
+	}
+	return nil
+}
+
+func (d *dns) Options() Options {
+	return d.options
+}
+
+func (d *dns) Table() Table {
+	return nil
+}
+
+func (d *dns) Close() error {
+	return nil
+}
+
+func (d *dns) Lookup(opts ...QueryOption) ([]Route, error) {
+	options := NewQuery(opts...)
+	// check to see if we have the port provided in the service, e.g. go-micro-srv-foo:8000
+	host, port, err := net.SplitHostPort(options.Service)
+	if err == nil {
+		// lookup the service using A records
+		ips, err := net.LookupHost(host)
+		if err != nil {
+			return nil, err
+		}
+
+		p, _ := strconv.Atoi(port)
+
+		// convert the ip addresses to routes
+		result := make([]Route, len(ips))
+		for i, ip := range ips {
+			result[i] = Route{
+				Service: options.Service,
+				Address: fmt.Sprintf("%s:%d", ip, uint16(p)),
+			}
+		}
+		return result, nil
+	}
+
+	// we didn't get the port so we'll lookup the service using SRV records. If we can't lookup the
+	// service using the SRV record, we return the error.
+	_, nodes, err := net.LookupSRV(options.Service, "tcp", d.options.Network)
+	if err != nil {
+		return nil, err
+	}
+
+	// convert the nodes (net services) to routes
+	result := make([]Route, len(nodes))
+	for i, n := range nodes {
+		result[i] = Route{
+			Service: options.Service,
+			Address: fmt.Sprintf("%s:%d", n.Target, n.Port),
+			Network: d.options.Network,
+		}
+	}
+	return result, nil
+}
+
+func (d *dns) Watch(opts ...WatchOption) (Watcher, error) {
+	return nil, nil
+}
+
+func (d *dns) Name() string {
+	return d.options.Name
+}
+
+func (d *dns) String() string {
+	return "dns"
+}

router/router.go

@@ -7,7 +7,7 @@ import (
 
 var (
 	// DefaultRouter is the global default router
-	DefaultRouter Router
+	DefaultRouter Router = NewRouter()
 	// DefaultNetwork is default micro network
 	DefaultNetwork = "micro"
 	// ErrRouteNotFound is returned when no route was found in the routing table