nat: add HasDiscoveredNAT method for checking NAT environments (#2358)

* nat: add HasNAT method for checking NAT environments

* rename to better variable

p2p/host/basic/basic_host.go

@@ -843,11 +843,10 @@ func (h *BasicHost) AllAddrs() []ma.Multiaddr {
 
 	finalAddrs = network.DedupAddrs(finalAddrs)
 
-	// natmgr is nil if we do not use nat option;
-	if h.natmgr != nil {
+	// use nat mappings if we have them
+	if h.natmgr != nil && h.natmgr.HasDiscoveredNAT() {
 		// We have successfully mapped ports on our NAT. Use those
 		// instead of observed addresses (mostly).
-
 		// Next, apply this mapping to our addresses.
 		for _, listen := range listenAddrs {
 			extMaddr := h.natmgr.GetMapping(listen)

p2p/host/basic/natmgr.go

@@ -21,6 +21,7 @@ import (
 // and tries to obtain port mappings for those.
 type NATManager interface {
 	GetMapping(ma.Multiaddr) ma.Multiaddr
+	HasDiscoveredNAT() bool
 	io.Closer
 }
 
@@ -86,6 +87,12 @@ func (nmgr *natManager) Close() error {
 	return nil
 }
 
+func (nmgr *natManager) HasDiscoveredNAT() bool {
+	nmgr.natMx.RLock()
+	defer nmgr.natMx.RUnlock()
+	return nmgr.nat != nil
+}
+
 func (nmgr *natManager) background(ctx context.Context) {
 	defer nmgr.refCount.Done()