p2p: fix portMappingLoop unwanted termination

which was causing the defer function to be called and trigger “Deleting port mapping” 2 minutes after the initial launch

p2p/server_nat.go

@@ -127,7 +127,7 @@ func (srv *Server) portMappingLoop() {
 			} else if !ip.Equal(lastExtIP) {
 				log.Debug("External IP changed", "ip", extip, "interface", srv.NAT)
 			} else {
-				return
+				continue
 			}
 			// Here, we either failed to get the external IP, or it has changed.
 			lastExtIP = ip

p2p/server_nat_test.go

@@ -75,6 +75,65 @@ func TestServerPortMapping(t *testing.T) {
 	}
 }
 
+func TestExtipLoop(t *testing.T) {
+	clock := new(mclock.Simulated)
+	mockNAT := &mockNAT{mappedPort: 30000}
+	srv := Server{
+		Config: Config{
+			PrivateKey: newkey(),
+			NoDial:     true,
+			ListenAddr: ":0",
+			NAT:        mockNAT,
+			Logger:     testlog.Logger(t, log.LvlTrace),
+			clock:      clock,
+		},
+	}
+	err := srv.Start()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer srv.Stop()
+
+	// Wait for the port mapping to be registered. Synchronization with the port mapping
+	// goroutine works like this: For each iteration, we allow other goroutines to run and
+	// also advance the virtual clock by 1 second. Waiting stops when the NAT interface
+	// has received some requests, or when the clock reaches a timeout.
+	deadline := clock.Now().Add(portMapRefreshInterval + extipRetryInterval)
+	for clock.Now() < deadline && mockNAT.mapRequests.Load() < 2 {
+		clock.Run(1 * time.Second)
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	if mockNAT.ipRequests.Load() != 1 {
+		t.Fatal("external IP was never requested")
+	}
+
+	reqCount := mockNAT.mapRequests.Load()
+	if reqCount != 2 {
+		t.Error("wrong request count:", reqCount)
+	}
+
+	// Wait for the External IP to be checked.
+	for clock.Now() < deadline && mockNAT.ipRequests.Load() < 2 {
+		clock.Run(extipRetryInterval)
+		time.Sleep(10 * time.Millisecond)
+	}
+
+	ipRequestsCount := mockNAT.ipRequests.Load()
+	if ipRequestsCount != 2 {
+		t.Fatal("wrong external IP request count:", ipRequestsCount)
+	}
+
+	// Verify that no unmapRequests were sent.
+	// Handles an edge case where the port mapping loop was prematurely terminated,
+	// causing the defer function to be called and delete the UPnP mappings.
+	// ref: https://github.com/etclabscore/core-geth/pull/611
+	unmapReqCount := mockNAT.unmapRequests.Load()
+	if unmapReqCount != 0 {
+		t.Fatal("wrong unmap request count:", unmapReqCount)
+	}
+}
+
 type mockNAT struct {
 	mappedPort    uint16
 	mapRequests   atomic.Int32