Diameter Lua Service

Introduction

The DiameterLuaService is a service for initiating Lua scripts running within the LogicApp.

The DiameterLuaService receives messages from one or more instances of the DiameterApp which is configured to receive Diameter Requests from an external client.

The DiameterLuaService communicates with the DiameterApp using the DIAMETER-S-… messages.

Configuring DiameterLuaService

The DiameterLuaService is configured within a LogicApp.

    <?xml version="1.0" encoding="utf-8"?>
    <n2svcd>
      ...
      <applications>
        ...
        <application name="Logic" module="LogicApp">
          <include>
            <lib>../apps/logic/lib</lib>
          </include>
          <parameters>
            ...
          </parameters>
          <config>
            <services>
              <service module="DiameterApp::DiameterLuaService" libs="../apps/diameter/lib" script_dir="/var/lib/n2svcd/logic/diameter"/>
            </services>
            <agents>
              ...
            </agents>
          </config>
        </application>
        ...
      </application>
      ...
    </n2svcd>

In addition to the Common LogicApp Service Configuration, note the following specific attribute notes, and service-specific attributes.

Under normal installation, the following service attributes apply:

Script Selection (Diameter Request)

Script selection is not configured. The script name is simply the Diameter message name received in the request.

e.g. an inbound request for message Credit-Control-Request will map to a script name of Credit-Control-Request, which will be satisfied by a file named Credit-Control-Request.lua in any of the directories configured as lua_script_dir in the LogicApp.

Refer to the LogicApp configuration for more information on directories, library paths, and script caching parameters.

Script Global Variables

Scripts run with this service have access to the Common LUA Service Global Variables.

There are no service-specific global variables.

Script Entry Parameters (Diameter Request)

The Lua script must be a Lua chunk such as the following:

local n2svcd = require "n2.n2svcd"

local diameter = ...

n2svcd.debug ("Echo Supplied Diameter Inputs:")
n2svcd.debug_var (diameter)

-- Echo back all of the received AVPs with Result-Code appended.
diameter.avps.insert ({ name = "Result-Code", value = 2001 })

return diameter.avps

The chunk will be executed with a single diameter entry parameter which is an object with the following attributes:

Script Return Parameters (Diameter Response)

The Lua script is responsible for determing the Diameter Response which will be sent back in reply to the original Diameter Request.

The simplest way to do this is by the return value given back to the service at the end of script execution.

The script return value should be an array of AVPs, where each array entry has the following attributes:

Example (returning Diameter Response arguments):

local n2svcd = require "n2.n2svcd"

local diameter = ...

return {
    { name = "Custom-1", value = 789 },
    { name = "Result-Code", value = 2001 }
}

Note that returning nil in this case would cause an empty Diameter response to be returned, which is very unlikely to be a satisfactory behavior.

Note that the Diameter Lua script is responsible for adding the Result-Code AVP, along with all other AVPs.

The DiameterLuaService API

The Diameter Service API can be loaded as follows.

    local diameter_service_api = require "n2.n2svcd.diameter_service"

It is not necessary to load the Diameter Service API if you are only using the simple response mechanism described above. It is only required if you wish to use any of the extended features described below.

.response

When a Lua Script needs to perform extended processing, it may wish to send an early Diameter response before the script completes. This can be done with the response method on the Diameter Service API. This method also allows the script to use a non-default response message name.

The response method takes the following parameters.

The response method returns true.

[Fragment] Example (Early Response with failure Result-Code):

    ...
    diameter_service_api.response ({ name = "Result-Code", value = 5030 })
    ...
    [post-processing after Diameter transaction is concluded]
    ...

    return nil

A chunk should return nil after an early response. The actual return result is ignored in this scenario.