consul: Adding user event handler for callbacks

consul/client.go

@@ -300,14 +300,22 @@ func (c *Client) localEvent(event serf.UserEvent) {
 		return
 	}
 
-	switch event.Name {
+	switch name := event.Name; {
-	case newLeaderEvent:
+	case name == newLeaderEvent:
 		c.logger.Printf("[INFO] consul: New leader elected: %s", event.Payload)
 
 		// Trigger the callback
 		if c.config.ServerUp != nil {
 			c.config.ServerUp()
 		}
+	case isUserEvent(name):
+		event.Name = rawUserEventName(name)
+		c.logger.Printf("[DEBUG] consul: user event: %s", event.Name)
+
+		// Trigger the callback
+		if c.config.UserEventHandler != nil {
+			c.config.UserEventHandler(event)
+		}
 	default:
 		c.logger.Printf("[WARN] consul: Unhandled local event: %v", event)
 	}

consul/config.go

@@ -163,6 +163,10 @@ type Config struct {
 	// ServerUp callback can be used to trigger a notification that
 	// a Consul server is now up and known about.
 	ServerUp func()
+
+	// UserEventHandler callback can be used to handle incoming
+	// user events. This function should not block.
+	UserEventHandler func(serf.UserEvent)
 }
 
 // CheckVersion is used to check if the ProtocolVersion is valid

consul/serf.go

@@ -1,7 +1,6 @@
 package consul
 
 import (
-	"fmt"
 	"net"
 	"strings"
 
@@ -12,11 +11,24 @@ const (
 	// StatusReap is used to update the status of a node if we
 	// are handling a EventMemberReap
 	StatusReap = serf.MemberStatus(-1)
+
+	// userEventPrefix is pre-pended to a user event to distinguish it
+	userEventPrefix = "consul:event:"
 )
 
 // userEventName computes the name of a user event
 func userEventName(name string) string {
-	return fmt.Sprintf("consul:event:%s")
+	return userEventPrefix + name
+}
+
+// isUserEvent checks if a serf event is a user event
+func isUserEvent(name string) bool {
+	return strings.HasPrefix(name, userEventPrefix)
+}
+
+// rawUserEventName is used to get the raw user event name
+func rawUserEventName(name string) string {
+	return strings.TrimPrefix(name, userEventPrefix)
 }
 
 // lanEventHandler is used to handle events from the lan Serf cluster
@@ -108,14 +120,22 @@ func (s *Server) localEvent(event serf.UserEvent) {
 		return
 	}
 
-	switch event.Name {
+	switch name := event.Name; {
-	case newLeaderEvent:
+	case name == newLeaderEvent:
 		s.logger.Printf("[INFO] consul: New leader elected: %s", event.Payload)
 
 		// Trigger the callback
 		if s.config.ServerUp != nil {
 			s.config.ServerUp()
 		}
+	case isUserEvent(name):
+		event.Name = rawUserEventName(name)
+		s.logger.Printf("[DEBUG] consul: user event: %s", event.Name)
+
+		// Trigger the callback
+		if s.config.UserEventHandler != nil {
+			s.config.UserEventHandler(event)
+		}
 	default:
 		s.logger.Printf("[WARN] consul: Unhandled local event: %v", event)
 	}