fix bug of host.Extract (#1481)

internal/host/host.go

@@ -36,7 +36,7 @@ func Port(lis net.Listener) (int, bool) {
 // Extract returns a private addr and port.
 func Extract(hostPort string, lis net.Listener) (string, error) {
 	addr, port, err := net.SplitHostPort(hostPort)
-	if err != nil {
+	if err != nil && lis == nil {
 		return "", err
 	}
 	if lis != nil {

internal/host/host_test.go

@@ -76,6 +76,13 @@ func TestExtract(t *testing.T) {
 			}
 		})
 	}
+	lis, err := net.Listen("tcp", ":12345")
+	assert.NoError(t, err)
+	res, err := Extract("", lis)
+	assert.NoError(t, err)
+	expect, err := Extract(lis.Addr().String(), nil)
+	assert.NoError(t, err)
+	assert.Equal(t, expect, res)
 }
 
 func TestExtract2(t *testing.T) {