fix(tcp): return a dummy connection instead of nil

internal/acl/tcp_listener.go

@@ -1,7 +1,9 @@
 package acl
 
 import (
+	"io"
 	"net"
+	"time"
 )
 
 type TCPListener struct {
@@ -9,6 +11,17 @@ type TCPListener struct {
 	lis net.Listener
 }
 
+type noConn struct{}
+
+func (noConn) Read(b []byte) (int, error)         { return 0, io.EOF }
+func (noConn) Write(b []byte) (int, error)        { return 0, io.EOF }
+func (noConn) Close() error                       { return nil }
+func (noConn) LocalAddr() net.Addr                { return nil }
+func (noConn) RemoteAddr() net.Addr               { return nil }
+func (noConn) SetDeadline(t time.Time) error      { return nil }
+func (noConn) SetReadDeadline(t time.Time) error  { return nil }
+func (noConn) SetWriteDeadline(t time.Time) error { return nil }
+
 func (cfg *Config) WrapTCP(lis net.Listener) net.Listener {
 	if cfg == nil {
 		return lis
@@ -32,11 +45,11 @@ func (s *TCPListener) Accept() (net.Conn, error) {
 	if !ok {
 		// Not a TCPAddr, drop
 		c.Close()
-		return nil, nil
+		return noConn{}, nil
 	}
 	if !s.acl.IPAllowed(addr.IP) {
 		c.Close()
-		return nil, nil
+		return noConn{}, nil
 	}
 	return c, nil
 }