fix: close connections on error paths to prevent resource leaks (#5202)

Fix connection leaks in multiple error paths across client and server:
- server/proxy/http: close tmpConn when WithEncryption fails
- client/proxy: close localConn when ProxyProtocol WriteTo fails
- client/visitor/sudp: close visitorConn on all error paths in getNewVisitorConn
- client/visitor/xtcp: close tunnelConn when WithEncryption fails
- client/visitor/xtcp: close lConn when NewKCPConnFromUDP fails
- pkg/plugin/client/unix_domain_socket: close localConn and connInfo.Conn when WriteTo fails, close connInfo.Conn when DialUnix fails
- pkg/plugin/client/tls2raw: close tlsConn when Handshake or Dial fails

client/proxy/proxy.go

@@ -209,6 +209,7 @@ func (pxy *BaseProxy) HandleTCPWorkConnection(workConn net.Conn, m *msg.StartWor
 	if connInfo.ProxyProtocolHeader != nil {
 		if _, err := connInfo.ProxyProtocolHeader.WriteTo(localConn); err != nil {
 			workConn.Close()
+			localConn.Close()
 			xl.Errorf("write proxy protocol header to local conn error: %v", err)
 			return
 		}

client/visitor/sudp.go

@@ -217,6 +217,7 @@ func (sv *SUDPVisitor) getNewVisitorConn() (net.Conn, error) {
 	}
 	err = msg.WriteMsg(visitorConn, newVisitorConnMsg)
 	if err != nil {
+		visitorConn.Close()
 		return nil, fmt.Errorf("frpc send newVisitorConnMsg to frps error: %v", err)
 	}
 
@@ -224,11 +225,13 @@ func (sv *SUDPVisitor) getNewVisitorConn() (net.Conn, error) {
 	_ = visitorConn.SetReadDeadline(time.Now().Add(10 * time.Second))
 	err = msg.ReadMsgInto(visitorConn, &newVisitorConnRespMsg)
 	if err != nil {
+		visitorConn.Close()
 		return nil, fmt.Errorf("frpc read newVisitorConnRespMsg error: %v", err)
 	}
 	_ = visitorConn.SetReadDeadline(time.Time{})
 
 	if newVisitorConnRespMsg.Error != "" {
+		visitorConn.Close()
 		return nil, fmt.Errorf("start new visitor connection error: %s", newVisitorConnRespMsg.Error)
 	}
 
@@ -238,6 +241,7 @@ func (sv *SUDPVisitor) getNewVisitorConn() (net.Conn, error) {
 		remote, err = libio.WithEncryption(remote, []byte(sv.cfg.SecretKey))
 		if err != nil {
 			xl.Errorf("create encryption stream error: %v", err)
+			visitorConn.Close()
 			return nil, err
 		}
 	}

client/visitor/xtcp.go

@@ -211,6 +211,7 @@ func (sv *XTCPVisitor) handleConn(userConn net.Conn) {
 		muxConnRWCloser, err = libio.WithEncryption(muxConnRWCloser, []byte(sv.cfg.SecretKey))
 		if err != nil {
 			xl.Errorf("create encryption stream error: %v", err)
+			tunnelConn.Close()
 			tunnelErr = err
 			return
 		}
@@ -373,6 +374,7 @@ func (ks *KCPTunnelSession) Init(listenConn *net.UDPConn, raddr *net.UDPAddr) er
 	}
 	remote, err := netpkg.NewKCPConnFromUDP(lConn, true, raddr.String())
 	if err != nil {
+		lConn.Close()
 		return fmt.Errorf("create kcp connection from udp connection error: %v", err)
 	}