update

@@ -67,22 +67,23 @@ end
 
 local args=ngx.req.get_uri_args()
 local method=args["method"]
+
+-- make sure upstream exist
+local upstream = args["upstream"]
+if  upstream == nil  or  upstream == '' then
+  ngx.exit(400)
+  ngx.log(ngx.ERR, "request params is error. upstream is null")
+end
+
 if method == "list" then
-  if not args["upstream"] then
-    ngx.exit(400)
-    ngx.log(ngx.ERR, "request params is error. upstream is null")
-  else
-    local u_name = args["upstream"]
-    list(u_name)
-  end
+    list(upstream)
 elseif(method=="down" or method=="up") then
-  local upstream=args["upstream"]
   local backup=args["backup"]=="true" and true or false
   local id=tonumber(args["id"])
   local down= method=="down" and true or false
   local t={}
   ngx.header["Content-type"]="application/json;charset=utf-8"  
-  if (not upstream) or (not id) then
+  if not id then
     ngx.exit(400)
     ngx.log(ngx.ERR, "request params is error. upstream or id is null")
   else