Fail when there already is a pending sluice request for the local add…

…ress

sluice/request.go

@@ -11,7 +11,7 @@ import (
 )
 
 const (
-	defaultSluiceTTL = 5 * time.Minute
+	defaultSluiceTTL = 30 * time.Second
 )
 
 var (
@@ -44,12 +44,11 @@ func AwaitRequest(connInfo *network.Connection, callbackFn RequestCallbackFunc)
 		return fmt.Errorf("sluice for network %s %w", network, ErrSluiceOffline)
 	}
 
-	sluice.AwaitRequest(&Request{
+	return sluice.AwaitRequest(&Request{
 		ConnInfo:   connInfo,
 		CallbackFn: callbackFn,
 		Expires:    time.Now().Add(defaultSluiceTTL),
 	})
-	return nil
 }
 
 func getNetworkFromConnInfo(connInfo *network.Connection) string {

sluice/sluice.go

@@ -54,7 +54,7 @@ func StartSluice(network, address string) {
 }
 
 // AwaitRequest pre-registers a connection.
-func (s *Sluice) AwaitRequest(r *Request) {
+func (s *Sluice) AwaitRequest(r *Request) error {
 	// Set default expiry.
 	if r.Expires.IsZero() {
 		r.Expires = time.Now().Add(defaultSluiceTTL)
@@ -63,8 +63,16 @@ func (s *Sluice) AwaitRequest(r *Request) {
 	s.lock.Lock()
 	defer s.lock.Unlock()
 
+	// Check if a pending request already exists for this local address.
 	key := net.JoinHostPort(r.ConnInfo.LocalIP.String(), strconv.Itoa(int(r.ConnInfo.LocalPort)))
+	_, exists := s.pendingRequests[key]
+	if exists {
+		return fmt.Errorf("a pending request for %s already exists", key)
+	}
+
+	// Add to pending requests.
 	s.pendingRequests[key] = r
+	return nil
 }
 
 func (s *Sluice) getRequest(address string) (r *Request, ok bool) {