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

pkg/plugin/client/tls2raw.go

@@ -62,11 +62,13 @@ func (p *TLS2RawPlugin) Handle(ctx context.Context, connInfo *ConnectionInfo) {
 
 	if err := tlsConn.Handshake(); err != nil {
 		xl.Warnf("tls handshake error: %v", err)
+		tlsConn.Close()
 		return
 	}
 	rawConn, err := net.Dial("tcp", p.opts.LocalAddr)
 	if err != nil {
 		xl.Warnf("dial to local addr error: %v", err)
+		tlsConn.Close()
 		return
 	}
 

pkg/plugin/client/unix_domain_socket.go

@@ -54,10 +54,13 @@ func (uds *UnixDomainSocketPlugin) Handle(ctx context.Context, connInfo *Connect
 	localConn, err := net.DialUnix("unix", nil, uds.UnixAddr)
 	if err != nil {
 		xl.Warnf("dial to uds %s error: %v", uds.UnixAddr, err)
+		connInfo.Conn.Close()
 		return
 	}
 	if connInfo.ProxyProtocolHeader != nil {
 		if _, err := connInfo.ProxyProtocolHeader.WriteTo(localConn); err != nil {
+			localConn.Close()
+			connInfo.Conn.Close()
 			return
 		}
 	}