Merge pull request #2 from arduino/error_events

Added error handling in sync mode

Author: cmaglie

discovery_server.go

@@ -66,7 +66,7 @@ type Discovery interface {
 	// StartSync is called to put the discovery in event mode. When the
 	// function returns the discovery must send port events ("add" or "remove")
 	// using the eventCB function.
-	StartSync(eventCB EventCallback) error
+	StartSync(eventCB EventCallback, errorCB ErrorCallback) error
 
 	// Stop stops the discovery internal subroutines. If the discovery is
 	// in event mode it must stop sending events through the eventCB previously
@@ -83,6 +83,12 @@ type Discovery interface {
 // is detected.
 type EventCallback func(event string, port *Port)
 
+// ErrorCallback is a callback function to signal unrecoverable errors to the
+// client while the discovery is in event mode. Once the discovery signal an
+// error it means that no more port-events will be delivered until the client
+// performs a STOP+START_SYNC cycle.
+type ErrorCallback func(err string)
+
 // A DiscoveryServer is a pluggable discovery protocol handler,
 // it must be created using the NewDiscoveryServer function.
 type DiscoveryServer struct {
@@ -233,7 +239,7 @@ func (d *DiscoveryServer) startSync() {
 	}
 	c := make(chan interface{}, 10) // buffer up to 10 events
 	d.syncChannel = c
-	if err := d.impl.StartSync(d.syncEvent); err != nil {
+	if err := d.impl.StartSync(d.syncEvent, d.errorEvent); err != nil {
 		d.outputError("start_sync", "Cannot START_SYNC: "+err.Error())
 		close(d.syncChannel) // do not leak channel...
 		d.syncChannel = nil
@@ -278,6 +284,19 @@ func (d *DiscoveryServer) syncEvent(event string, port *Port) {
 	}
 }
 
+func (d *DiscoveryServer) errorEvent(msg string) {
+	type syncOutputJSON struct {
+		EventType string `json:"eventType"`
+		Error     bool   `json:"error"`
+		Message   string `json:"message"`
+	}
+	d.syncChannel <- &syncOutputJSON{
+		EventType: "start_sync",
+		Error:     true,
+		Message:   msg,
+	}
+}
+
 type genericMessageJSON struct {
 	EventType       string `json:"eventType"`
 	Message         string `json:"message"`

dummy-discovery/main.go

@@ -71,7 +71,7 @@ func (d *DummyDiscovery) Stop() error {
 	return nil
 }
 
-func (d *DummyDiscovery) StartSync(eventCB discovery.EventCallback) error {
+func (d *DummyDiscovery) StartSync(eventCB discovery.EventCallback, errorCB discovery.ErrorCallback) error {
 	d.startSyncCount++
 	if d.startSyncCount%5 == 0 {
 		return errors.New("could not start_sync every 5 times")
@@ -89,7 +89,10 @@ func (d *DummyDiscovery) StartSync(eventCB discovery.EventCallback) error {
 		eventCB("add", CreateDummyPort())
 
 		// Start sending events
-		for {
+		count := 0
+		for count < 2 {
+			count++
+
 			select {
 			case <-closeChan:
 				return
@@ -110,6 +113,9 @@ func (d *DummyDiscovery) StartSync(eventCB discovery.EventCallback) error {
 				Protocol: port.Protocol,
 			})
 		}
+
+		errorCB("unrecoverable error, cannot send more events")
+		<-closeChan
 	}()
 
 	return nil