Implement alert_endpoints and http_lint plugin extensions

Alert endpoints can now be loaded via custom plugins.
It's now possible to extend the http_lint parameters with custom parameters and validators.

scripts/plugins/syslog_alert_endpoint/alert_endpoints/syslog.lua

@@ -0,0 +1,117 @@
+--
+-- (C) 2018 - ntop.org
+--
+
+require "lua_utils"
+local json = require "dkjson"
+local alert_consts = require "alert_consts"
+
+local syslog = {}
+
+syslog.DEFAULT_SEVERITY = "info"
+syslog.EXPORT_FREQUENCY = 1 -- 1 second, i.e., as soon as possible
+syslog.prio = 300
+
+-- ##############################################
+
+function syslog.isAvailable()
+   return(ntop.syslog ~= nil)
+end
+
+-- ##############################################
+
+function syslog.dequeueAlerts(queue)
+   local notifications = ntop.lrangeCache(queue, 0, -1)
+
+   if not notifications then
+      return {success = true}
+   end
+
+   local syslog_format = ntop.getPref("ntopng.prefs.syslog_alert_format")
+   if isEmptyString(syslog_format) then
+      syslog_format = "plaintext"
+   end
+
+   -- Separate by severity and channel
+   local alerts_by_types = {}
+
+   for _, json_message in ipairs(notifications) do
+      local notif = json.decode(json_message)
+      if notif.alert_entity then
+         alerts_by_types[notif.alert_entity] = alerts_by_types[notif.alert_entity] or {}
+         alerts_by_types[notif.alert_entity][notif.alert_severity] = alerts_by_types[notif.alert_entity][notif.alert_severity] or {}
+         table.insert(alerts_by_types[notif.alert_entity][notif.alert_severity], notif)
+      end
+   end
+
+   for _, by_severity in pairs(alerts_by_types) do
+      for severity, notifications in pairs(by_severity) do
+        severity = alertSeverityRaw(severity)
+
+	 -- Most recent notifications first
+	 for _, notif in pairsByValues(notifications, notification_timestamp_rev) do
+	    local syslog_severity = alert_consts.alertLevelToSyslogLevel(severity)
+
+	    local msg
+
+	    if syslog_format == "plaintext" then
+	       -- prepare a plaintext message
+	       msg = formatAlertNotification(notif, {nohtml = true,
+						     show_severity = true,
+						     show_entity = true})
+	    else -- syslog_format == "json" then
+	       -- send out the json message but prepare a nice
+	       -- message
+	       notif.message  = formatAlertNotification(notif, {nohtml = true,
+								show_severity = false,
+								show_entity = false})
+	       msg = json.encode(notif)
+	    end
+
+	    ntop.syslog(msg, syslog_severity)
+	 end
+      end
+   end
+
+   -- Remove all the messages from queue on success
+   ntop.delCache(queue)
+
+   return {success = true}
+end
+
+-- ##############################################
+
+function syslog.printPrefs(alert_endpoints, subpage_active, showElements)
+   print('<thead class="thead-light"><tr><th colspan="2" class="info">'..i18n("prefs.syslog_notification")..'</th></tr></thead>')
+
+   local alertsEnabled = showElements
+   local elementToSwitch = {"row_syslog_alert_format"}
+
+   prefsToggleButton(subpage_active, {
+     field = "toggle_alert_syslog",
+     pref = alert_endpoints.getAlertNotificationModuleEnableKey("syslog", true),
+     default = "0",
+     disabled = alertsEnabled == false,
+     to_switch = elementToSwitch,
+   })
+
+   local format_labels = {i18n("prefs.syslog_alert_format_plaintext"), i18n("prefs.syslog_alert_format_json")}
+   local format_values = {"plaintext", "json"}
+
+   if ntop.getPref(alert_endpoints.getAlertNotificationModuleEnableKey("syslog")) == "0" then
+     alertsEnabled = false
+   end
+
+   multipleTableButtonPrefs(subpage_active.entries["syslog_alert_format"].title,
+       subpage_active.entries["syslog_alert_format"].description,
+       format_labels, format_values,
+       "plaintext",
+       "primary",
+       "syslog_alert_format",
+       "ntopng.prefs.syslog_alert_format", nil,
+       nil, nil, nil, alertsEnabled)
+end
+
+-- ##############################################
+
+return syslog