multi: CancelPending error for no pending conns.

This modifies the CancelPending method of the connection manager to
return an error when there are no pending connections for the provided
address or the connection manager is already shutting down.

This change, in turn, ensures that attempts to remove a pending
connection that doesn't exist via RPC returns an error as expected.

connmgr/connmanager.go

@@ -183,7 +183,7 @@ type handleFailed struct {
 // handleCancelPending is used to remove failing connections from retries.
 type handleCancelPending struct {
 	addr net.Addr
-	done chan struct{}
+	done chan error
 }
 
 // ConnManager provides a manager to handle network connections.
@@ -369,14 +369,15 @@ out:
 						idToRemove, connReq = id, req
 						break
 					}
-
 				}
 				if connReq != nil {
 					delete(pending, idToRemove)
 					connReq.updateState(ConnCanceled)
 					log.Debugf("Canceled pending connection to %v", msg.addr)
+					msg.done <- nil
+				} else {
+					msg.done <- fmt.Errorf("no pending connection to %v", msg.addr)
 				}
-				close(msg.done)
 			}
 
 		case <-cm.quit:
@@ -534,11 +535,13 @@ func (cm *ConnManager) Remove(id uint64) {
 
 // CancelPending removes the connection corresponding to the given address
 // from the list of pending failed connections.
-func (cm *ConnManager) CancelPending(addr net.Addr) {
+// Returns an error if the connection manager is stopped or there is no pending
+// connection for the given address.
+func (cm *ConnManager) CancelPending(addr net.Addr) error {
 	if atomic.LoadInt32(&cm.stop) != 0 {
-		return
+		return fmt.Errorf("connection manager stopped")
 	}
-	done := make(chan struct{})
+	done := make(chan error, 1)
 
 	select {
 	case cm.requests <- handleCancelPending{addr, done}:
@@ -548,9 +551,10 @@ func (cm *ConnManager) CancelPending(addr net.Addr) {
 	// Wait for the connection to be removed from the conn manager's
 	// internal state.
 	select {
-	case <-done:
+	case err := <-done:
+		return err
 	case <-cm.quit:
-		return
+		return fmt.Errorf("connection manager stopped")
 	}
 }
 

server.go

@@ -1955,8 +1955,7 @@ func (s *server) handleQuery(state *peerState, querymsg interface{}) {
 			msg.reply <- err
 			return
 		}
-		s.connManager.CancelPending(netAddr)
-		msg.reply <- nil
+		msg.reply <- s.connManager.CancelPending(netAddr)
 	case getOutboundGroup:
 		count, ok := state.outboundGroups[msg.key]
 		if ok {