判断 ErrClosed

main.go

@@ -100,7 +100,10 @@ func openPort(ctx context.Context, target, localAddr string, portu uint16, stun
 	errCh := make(chan error, 1)
 	m, s, err := natmap.NatMap(ctx, stun, localAddr, uint16(portu), func(s error) {
 		cancel()
-		errCh <- ErrNatMap{err: s}
+		select {
+		case errCh <- ErrNatMap{err: s}:
+		default:
+		}
 	})
 	if err != nil {
 		return fmt.Errorf("openPort: %w", err)

natmap/natmap.go

@@ -2,6 +2,7 @@ package natmap
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -100,6 +101,9 @@ func Forward(ctx context.Context, port uint16, target string, log func(string))
 			c, err := l.Accept()
 			if err != nil {
 				log(err.Error())
+				if errors.Is(err, net.ErrClosed) {
+					return
+				}
 				continue
 			}
 			var d net.Dialer