Alerts changes

NOTE: database schema changed. Existing alerts will be lost.

- Unified engaged and closed tables
- Simplified hosts engaged alert counters handling: periodically set by lua
- Removed alert engine and replaced with alert periodicity
- Now engage is implicitly derived from the alert end timestamp and periodicity
- New alerts_api.lua to easily emit alerts
- Removed past alerts counter aggregation by hash
- Alert notifications for non-flow alerts are now removed from C and triggered by lua

scripts/lua/modules/alert_endpoints_utils.lua

@@ -0,0 +1,148 @@
+--
+-- (C) 2013-19 - ntop.org
+--
+
+local alert_endpoints = {}
+
+package.path = dirs.installdir .. "/scripts/lua/modules/alert_endpoints/?.lua;" .. package.path
+
+-- ##############################################
+
+-- NOTE: order is important as it defines evaluation order
+local ALERT_NOTIFICATION_MODULES = {
+   "custom", "nagios", "slack", "webhook"
+}
+
+if ntop.syslog then
+   table.insert(ALERT_NOTIFICATION_MODULES, 1, "syslog")
+end
+
+if ntop.sendMail then -- only if email support is available
+   table.insert(ALERT_NOTIFICATION_MODULES, 1, "email")
+end
+
+-- ##############################################
+
+function alert_endpoints.getAlertNotificationModuleEnableKey(module_name, short)
+   if module_name == "syslog" and ntop.getPref("ntopng.prefs.alerts_syslog") ~= "" then
+      -- For backward compatibility
+      if short then
+	 return "alerts_syslog"
+      else
+	 return "ntopng.prefs.alerts_syslog"
+      end
+   end
+
+   local short_k = "alerts." .. module_name .. "_notifications_enabled"
+
+   if short then
+      return short_k
+   else
+      return "ntopng.prefs." .. short_k
+   end
+end
+
+-- ##############################################
+
+function alert_endpoints.getAlertNotificationModuleSeverityKey(module_name, short)
+   local short_k = "alerts." .. module_name .. "_severity"
+
+   if short then
+      return short_k
+   else
+      return "ntopng.prefs." .. short_k
+   end
+end
+
+-- ##############################################
+
+local function getEnabledAlertNotificationModules()
+   local notifications_enabled = ntop.getPref("ntopng.prefs.alerts.external_notifications_enabled")
+   local has_alerts_disabled = (ntop.getPref("ntopng.prefs.disable_alerts_generation") == "1")
+
+   if not notifications_enabled or has_alerts_disabled then
+      return {}
+   end
+
+   local enabled_modules = {}
+
+   for _, modname in ipairs(ALERT_NOTIFICATION_MODULES) do
+      local module_enabled = ntop.getPref(alert_endpoints.getAlertNotificationModuleEnableKey(modname))
+      local min_severity = ntop.getPref(alert_endpoints.getAlertNotificationModuleSeverityKey(modname))
+      local req_name = modname
+
+      if module_enabled == "1" then
+         local ok, _module, j = pcall(require, req_name)
+
+         if not ok then
+            traceError(TRACE_ERROR, TRACE_CONSOLE, "Error while importing alert notification module " .. req_name)
+
+            -- the traceback
+            io.write(_module)
+         else
+	    if isEmptyString(min_severity) then
+	       min_severity = _module.DEFAULT_SEVERITY or "warning"
+	    end
+
+            enabled_modules[#enabled_modules + 1] = {
+               name = modname,
+               severity = min_severity,
+               export_frequency = tonumber(_module.EXPORT_FREQUENCY) or 60,
+               export_queue = "ntopng.alerts.modules_notifications_queue." .. modname,
+               ["module"] = _module,
+            }
+         end
+      end
+   end
+
+   return enabled_modules
+end
+
+-- ##############################################
+
+local modules = nil
+
+local function loadModules()
+  if modules == nil then
+    modules = getEnabledAlertNotificationModules()
+  end
+
+  return(modules)
+end
+
+-- ##############################################
+
+function alert_endpoints.dispatchNotification(message, json_message)
+   loadModules()
+
+   for _, m in ipairs(modules) do
+      if message.severity >= alertSeverity(m.severity) then
+         ntop.rpushCache(m.export_queue, json_message, MAX_NUM_PER_MODULE_QUEUED_ALERTS)
+      end
+   end
+end
+
+-- ##############################################
+
+function alert_endpoints.processNotifications(now, periodic_frequency)
+  loadModules()
+
+  -- Process export notifications
+  for _, m in ipairs(modules) do
+    if force_export or ((now % m.export_frequency) < periodic_frequency) then
+
+       local rv = m.module.dequeueAlerts(m.export_queue)
+
+       if not rv.success then
+          local msg = rv.error_message or "Unknown Error"
+
+          -- TODO: generate alert
+          traceError(TRACE_ERROR, TRACE_CONSOLE, "Error while sending notifications via " .. m.name .. " module: " .. msg)
+       end
+    end
+  end
+end
+
+-- ##############################################
+
+return(alert_endpoints)