bug fix for below:

---------

...cal/openresty-1.9.15.1/nginx/conf/lua/limit_api_flow.lua: in function 'rate_limit'
	...cal/openresty-1.9.15.1/nginx/conf/lua/limit_api_flow.lua:98: in function <...cal/openresty-1.9.15.1/nginx/conf/lua/limit_api_flow.lua:1>, client: 122.96.43.103, server: api.yoho.cn, request: "GET /?udid=3fdfe1237c2186ac4431b314f6d47cc9&method=resources.simple.pice&udid=3fdfe1237c2186ac4431b314f6d47cc9&method=resources.simple.pice HTTP/1.1", host: "api.yoho.cn"
2019/03/21 15:09:30 [error] 19621#0: *406564387 lua entry thread aborted: runtime error: ...cal/openresty-1.9.15.1/nginx/conf/lua/limit_api_flow.lua:85: attempt to concatenate local 'req_uri_method' (a table value)
stack traceback:

@@ -6,14 +6,35 @@ local cjson = require "cjson"
 local default_err_code=9999991
 local default_err_msg="系统正忙,请稍后重试!"
 
-function get_req_param(req_param)        
-  local method = ngx.var.request_method
-  if "GET" == method then
-    return ngx.req.get_uri_args()[req_param]
-  else
-    ngx.req.read_body()
-    return ngx.req.get_post_args()[req_param]
+function get_req_param(req_param)  
+  local ret = nil      
+  local args = nil
+  local err = nil
+  local http_req_method = ngx.var.request_method
+  if "GET" == http_req_method then
+      args, err = ngx.req.get_uri_args()
+  elseif "POST" == http_req_method  then
+       ngx.req.read_body()
+       args, err = ngx.req.get_post_args()
   end
+  --- make sure this is some params
+  if not args then
+    ngx.say("failed to get args: ", err)
+    return nil
+  end
+
+  -- the value may be table, like: /test?foo=bar&bar=baz&bar=blah
+   for key, val in pairs(args) do
+         if key == req_param then
+             if type(val) == "table" then
+              ret =  val[0] or val[1]
+             else
+              ret = val
+             end
+         end
+    end
+
+  return ret
 end
 
 function  get_req_uri()