Reworks plugin loading and structure

Implements #4358

scripts/plugins/examples/flow_logger/user_scripts/flow/flow_logger.lua

@@ -0,0 +1,73 @@
+--
+-- (C) 2019-20 - ntop.org
+--
+
+local user_scripts = require("user_scripts")
+
+-- Script state
+local f = nil
+
+local script = {
+  -- Script category
+  category = user_scripts.script_categories.system, 
+
+  -- This module is disabled by default
+  default_enabled = false,
+
+  -- The default configuration of this script
+  default_value = {
+    log_mode = "console", -- console | file
+    log_file = "/tmp/flows_log",
+  },
+
+  -- See below
+  hooks = {},
+
+  -- Allow user script configuration from the GUI
+  gui = {
+    -- Localization strings, from the "locales" directory of the plugin
+    i18n_title = "alerts_dashboard.flow_logger",
+    i18n_description = "alerts_dashboard.flow_logger_descr",
+
+    -- TODO: draw config gui
+  }
+}
+
+-- #################################################################
+
+function script.teardown()
+  if(f ~= nil) then
+    -- Close the log file
+    f:close()
+    f = nil
+  end
+end
+
+-- #################################################################
+
+-- Defines an hook which is executed every time a procotol of a flow is detected
+function script.hooks.protocolDetected(now, conf)
+  local line = string.format("%s %s\n", os.date("%d/%b/%Y %X"), shortFlowLabel(flow.getInfo()))
+
+  if(conf.log_mode == "file") then
+    if(f == nil) then
+      local err
+
+      f, err = io.open(conf.log_file, "a")
+
+      if(f == nil) then
+	traceError(TRACE_ERROR, TRACE_CONSOLE, err)
+      end
+    end
+
+    if(f ~= nil) then
+      f:write(line)
+    end
+  else
+    print(line)
+  end
+end
+
+-- #################################################################
+
+return script