router: add to service options; add dns and static implementations (#1733)

* config/cmd: add router to service options

* router/service: use micro client

dns.go

@@ -0,0 +1,130 @@
+package dns
+
+import (
+	"fmt"
+	"net"
+	"strconv"
+
+	"github.com/micro/go-micro/v2/router"
+)
+
+// NewRouter returns an initialized dns router
+func NewRouter(opts ...router.Option) router.Router {
+	options := router.DefaultOptions()
+	for _, o := range opts {
+		o(&options)
+	}
+	if len(options.Network) == 0 {
+		options.Network = "micro"
+	}
+	return &dns{options, &table{options}}
+}
+
+type dns struct {
+	options router.Options
+	table   *table
+}
+
+func (d *dns) Init(opts ...router.Option) error {
+	for _, o := range opts {
+		o(&d.options)
+	}
+	d.table.options = d.options
+	return nil
+}
+
+func (d *dns) Options() router.Options {
+	return d.options
+}
+
+func (d *dns) Table() router.Table {
+	return d.table
+}
+
+func (d *dns) Advertise() (<-chan *router.Advert, error) {
+	return nil, nil
+}
+
+func (d *dns) Process(*router.Advert) error {
+	return nil
+}
+
+func (d *dns) Lookup(opts ...router.QueryOption) ([]router.Route, error) {
+	return d.table.Query(opts...)
+}
+
+func (d *dns) Watch(opts ...router.WatchOption) (router.Watcher, error) {
+	return nil, nil
+}
+
+func (d *dns) Close() error {
+	return nil
+}
+
+func (d *dns) String() string {
+	return "dns"
+}
+
+type table struct {
+	options router.Options
+}
+
+func (t *table) Create(router.Route) error {
+	return nil
+}
+
+func (t *table) Delete(router.Route) error {
+	return nil
+}
+
+func (t *table) Update(router.Route) error {
+	return nil
+}
+
+func (t *table) List() ([]router.Route, error) {
+	return nil, nil
+}
+
+func (t *table) Query(opts ...router.QueryOption) ([]router.Route, error) {
+	options := router.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([]router.Route, len(ips))
+		for i, ip := range ips {
+			result[i] = router.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", t.options.Network)
+	if err != nil {
+		return nil, err
+	}
+
+	// convert the nodes (net services) to routes
+	result := make([]router.Route, len(nodes))
+	for i, n := range nodes {
+		result[i] = router.Route{
+			Service: options.Service,
+			Address: fmt.Sprintf("%s:%d", n.Target, n.Port),
+			Network: t.options.Network,
+		}
+	}
+	return result, nil
+}