Bump bus_dropped counter when subscriber buffer is full

msgbus.go

@@ -38,9 +38,9 @@ const (
 )
 
 var (
-	// ErrSubscriberBufferFull is logged in Subscribe() when a subscriber's
+	// BufferFull is logged in Subscribe() when a subscriber's
 	// buffer is full and messages can no longer be enqueued for delivery
-	ErrSubscriberBufferFull = errors.New("error: subscriber buffer full")
+	ErrBufferFull = errors.New("error: subscriber buffer full")
 )
 
 // TODO: Make this configurable?
@@ -606,7 +606,8 @@ func (mb *MessageBus) Subscribe(id, topic string, opts ...SubscribeOption) chan
 				case ch <- msg:
 					n++
 				default:
-					return ErrSubscriberBufferFull
+					mb.metrics.Counter("bus", "dropped").Inc()
+					return ErrBufferFull
 				}
 			}
 			return nil
@@ -626,7 +627,8 @@ func (mb *MessageBus) Subscribe(id, topic string, opts ...SubscribeOption) chan
 				case ch <- msg:
 					n++
 				default:
-					return ErrSubscriberBufferFull
+					mb.metrics.Counter("bus", "dropped").Inc()
+					return ErrBufferFull
 				}
 			}
 			return nil