Add service discovery helper

Use MDNS-SD to discover ReachRS services on the local network

emlid/discovery.go

@@ -0,0 +1,70 @@
+package emlid
+
+import (
+	"net"
+	"sync"
+	"time"
+
+	"github.com/oleksandr/bonjour"
+)
+
+// Service is a ReachRS service discovered via MDNS-SD
+type Service struct {
+	Name   string
+	AddrV4 net.IP
+	Port   int
+}
+
+// Discover tries to discover ReachRS services on the local network via MDNS-SD
+func Discover(timeout time.Duration) ([]Service, error) {
+
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+
+	resolver, err := bonjour.NewResolver(nil)
+	if err != nil {
+		return nil, err
+	}
+
+	services := make([]Service, 0)
+	entries := make(chan *bonjour.ServiceEntry)
+	timer := time.NewTimer(timeout)
+	defer timer.Stop()
+
+	stop := func() {
+		resolver.Exit <- true
+		wg.Done()
+	}
+
+	go func() {
+		for {
+			select {
+
+			case e, ok := <-entries:
+				if !ok {
+					stop()
+					return
+				}
+				services = append(services, Service{
+					Name:   e.Instance,
+					AddrV4: e.AddrIPv4,
+					Port:   e.Port,
+				})
+
+			case <-timer.C:
+				stop()
+				return
+			}
+		}
+	}()
+
+	if err = resolver.Browse("_reach._tcp", ".local", entries); err != nil {
+		return nil, err
+	}
+
+	wg.Wait()
+
+	return services, nil
+
+}

emlid/discovery_test.go

@@ -0,0 +1,29 @@
+package emlid
+
+import (
+	"testing"
+	"time"
+)
+
+func TestDiscovery(t *testing.T) {
+
+	if !*runDiscoveryIntegrationTests {
+		t.Skip("To run this test, use: go test -discovery-integration")
+	}
+
+	services, err := Discover(3 * time.Second)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if g, e := len(services), 1; g != e {
+		t.Fatalf("len(services): got '%d', expected '%d'", g, e)
+	}
+
+	s := services[0]
+
+	if g, e := s.Name, "reach"; g != e {
+		t.Errorf("services[0].Name: got '%s', expected '%s'", g, e)
+	}
+
+}

emlid/option.go

@@ -34,6 +34,13 @@ func WithEndpoint(host string, port int) OptionFunc {
 	}
 }
 
+// WithService configures the client to target the given ReachRS service
+func WithService(service Service) OptionFunc {
+	return func(opts *Options) {
+		opts.Endpoint = gosocketio.GetUrl(service.AddrV4.String(), service.Port, false)
+	}
+}
+
 // WithPingInterval configures the client to use the given ping interval
 func WithPingInterval(interval time.Duration) OptionFunc {
 	return func(opts *Options) {

emlid/util_test.go

@@ -0,0 +1,8 @@
+package emlid
+
+import "flag"
+
+var runDiscoveryIntegrationTests = flag.Bool(
+	"discovery-integration", false,
+	"Run the 'Discovery' integration tests (in addition to the unit tests)",
+)