Adds url with formatted params in widgets

Addresses #4915

scripts/lua/rest/v1/get/datasource/datasource.lua

@@ -8,6 +8,7 @@ package.path = dirs.installdir .. "/scripts/lua/modules/datasources/?.lua;" .. p
 
 local json = require "dkjson"
 local rest_utils = require "rest_utils"
+local template = require "resty.template"
 -- Import the classes library.
 local classes = require "classes"
 
@@ -118,6 +119,25 @@ end
 
 -- ##############################################
 
+-- @brief Returns instance metadata, which depends on the current instance and parsed_params
+function datasource:get_metadata()
+   local res = {}
+
+   -- Render a url with submitted parsed_params
+   if self.meta.url then
+      local url_func = template.compile(self.meta.url, nil, true)
+      local url_rendered = url_func({
+	    params = self.parsed_params,
+      })
+
+      res["url"] = url_rendered
+   end
+
+   return res
+end
+
+-- ##############################################
+
 -- @brief Transform data according to the specified transformation
 -- @param data The data to be transformed
 -- @param transformation The transformation to be applied

scripts/lua/rest/v1/get/datasource/interface/packet_distro.lua

@@ -33,6 +33,11 @@ packet_distro.meta = {
    params = {
       "ifid" -- validated according to http_lint.lua
    },
+   -- A URL possibly formatted with parsed_params sent via REST
+   url = "/lua/if_stats.lua?ifid={{ params.ifid }}&page=packets",
+   -- Possibly add placeholders to replace keys and values, e.g., 
+   -- k is the `k` in the response data, v is the `v` in the response data
+   -- url = "/lua/if_stats.lua?ifid={{ params.ifid }}&page=packets&key=__k__&value=__v__",
 }
 
 -- ##############################################
@@ -57,6 +62,8 @@ packet_distro.labels = {
 function packet_distro:init()
    -- Call the parent constructor
    self.super:init()
+
+   self.datasource_key_str = datasource_keys[datasource.ds_type]
 end
 
 -- #######################################################