Implements a lua endpoint to send alerts to syslog

Implements #1973
Implements #1954

scripts/lua/modules/alert_endpoints/syslog.lua

@@ -0,0 +1,52 @@
+--
+-- (C) 2018 - ntop.org
+--
+
+require "lua_utils"
+local json = require "dkjson"
+
+local syslog = {}
+
+syslog.DEFAULT_SEVERITY = "info"
+syslog.EXPORT_FREQUENCY = 1 -- 1 second, i.e., as soon as possible
+
+function syslog.dequeueAlerts(queue)
+   local notifications = ntop.lrangeCache(queue, 0, -1)
+
+   if not notifications then
+      return {success = true}
+   end
+
+   -- Separate by severity and channel
+   local alerts_by_types = {}
+
+   for _, json_message in ipairs(notifications) do
+      local notif = alertNotificationToObject(json_message)
+
+      alerts_by_types[notif.entity_type] = alerts_by_types[notif.entity_type] or {}
+      alerts_by_types[notif.entity_type][notif.severity] = alerts_by_types[notif.entity_type][notif.severity] or {}
+      table.insert(alerts_by_types[notif.entity_type][notif.severity], notif)
+   end
+
+   for entity_type, by_severity in pairs(alerts_by_types) do
+      for severity, notifications in pairs(by_severity) do
+	 -- Most recent notifications first
+	 for _, notif in pairsByValues(notifications, notification_timestamp_rev) do
+	    local msg = formatAlertNotification(notif, {nohtml = true,
+							show_severity = true,
+							show_entity = true})
+
+
+	    local syslog_severity = alertLevelToSyslogLevel(notif.severity)
+	    ntop.syslog(msg, syslog_severity)
+	 end
+      end
+   end
+
+   -- Remove all the messages from queue on success
+   ntop.delCache(queue)
+
+   return {success = true}
+end
+
+return syslog