Reworks plugin loading and structure

Implements #4358

scripts/plugins/examples/example/alert_endpoints/example.lua

@@ -0,0 +1,78 @@
+--
+-- (C) 2019-20 - ntop.org
+--
+
+require "lua_utils"
+local json = require "dkjson"
+local alert_consts = require("alert_consts")
+
+local example = {
+  conf_params = {
+  },
+  conf_template = {
+    plugin_key = "example_alert_endpoint",
+    template_name = "example_endpoint.template"
+  },
+  recipient_params = {
+  },
+  recipient_template = {
+    plugin_key = "example_alert_endpoint",
+    template_name = "example_recipient.template"
+  },
+}
+
+-- How often this script will be called (in seconds)
+example.EXPORT_FREQUENCY = 5
+
+-- The minimum severity for an alert in order to be exported by this endpoint
+-- example.DEFAULT_SEVERITY = "warning"
+
+-- This determines the invocation priority of this endpoint.
+-- Higher priority endpoints are invoked first for the alert export.
+example.prio = 500
+
+-- ##############################################
+
+-- Each endpoint has a dedicated redis queue for the alerts. This function
+-- is called every EXPORT_FREQUENCY seconds and should check the alerts
+-- queue for alerts and possibly export them.
+
+-- @brief Process the pending alerts notifications from the queue
+-- @params recipient the recipient information and configuration, including the queue name
+-- @param budget the number of items to export (or number of external calls in batch mode)
+-- @return {success = true} on success,
+-- {success = false, error_message = "Some error description here"} on failure
+function example.dequeueRecipientAlerts(recipient, budget)
+  local exported = 0
+
+  while exported < budget do
+    local json_alert = ntop.lpopCache(recipient.export_queue)
+
+    if not json_alert then
+      break
+    end
+
+    local alert = json.decode(json_alert)
+
+    -- Print the alert on the console.
+    tprint(alert)
+
+    -- Can filter the alerts based on some criteria
+    if (alert.action == "engage") then
+      if (alert_consts.alertTypeRaw(alert.type) == "alert_threshold_cross") and
+            (alert.alert_key == "min_active_local_hosts") then
+
+        -- Export the alert, e.g. by running a custom bash script
+        --os.execute("/tmp/my_script.sh")
+      end
+    end
+
+    exported = exported + 1
+  end
+
+  return {success=true}
+end
+
+-- ##############################################
+
+return example