Add system stats REST endpoint. Load disk space utilzation via AJAX (fix #3421)

scripts/lua/rest/get/system/stats.lua

@@ -0,0 +1,28 @@
+--
+-- (C) 2013-20 - ntop.org
+--
+
+dirs = ntop.getDirs()
+package.path = dirs.installdir .. "/scripts/lua/modules/?.lua;" .. package.path
+
+require "lua_utils"
+local json = require ("dkjson")
+local page_utils = require("page_utils")
+local tracker = require("tracker")
+local storage_utils = require("storage_utils")
+
+if not isAllowedSystemInterface() then
+   sendHTTPContentTypeHeader('text/html')
+   page_utils.print_header()
+   dofile(dirs.installdir .. "/scripts/lua/inc/menu.lua")
+   print("<div class=\"alert alert-danger\"><img src=".. ntop.getHttpPrefix() .. "/img/warning.png>"..i18n("error_not_granted").."</div>")
+   return
+end
+
+sendHTTPContentTypeHeader('application/json')
+
+local stats = ntop.systemHostStat()
+stats.epoch = os.time()
+stats.storage = storage_utils.storageInfo()
+
+print(json.encode(stats, nil))