Scanning port 10247 lead to tcp connection 502 error (#9815)

* fix tcp 502 error

* fix tcp 502 error for parse tcp  backend data

* fix tcp 502 error for parse tcp  backend data

Author: lijiecm

rootfs/etc/nginx/lua/tcp_udp_configuration.lua

@@ -1,5 +1,6 @@
 local ngx = ngx
 local tostring = tostring
+local cjson = require("cjson.safe")
 -- this is the Lua representation of TCP/UDP Configuration
 local tcp_udp_configuration_data = ngx.shared.tcp_udp_configuration_data
 
@@ -37,6 +38,14 @@ function _M.call()
     return
   end
 
+  local _, backends_err = cjson.decode(backends)
+
+  if backends_err then
+    ngx.log(ngx.ERR, "could not parse backends data: ", backends_err)
+    return
+  end
+
+
   local success, err_conf = tcp_udp_configuration_data:set("backends", backends)
   if not success then
     ngx.log(ngx.ERR, "dynamic-configuration: error updating configuration: " .. tostring(err_conf))