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ENUM DNS Lua Service

Introduction

The ENUM DNS Lua service is used for initiating Lua scripts running within the N2SVCD LogicApp.

The service receives a DNS query operation from an instance of the N2SVCD DnsServerApp configured to receive DNS messages from an external client.

During the transaction, the service communicates with the DnsServerApp using the DNS-S-REQUEST and DNS-S-RESPONSE messages.

Configuration

The ENUM DNS Lua service is configured within an N2SVCD LogicApp. A simple configuration might be:

<?xml version="1.0" encoding="utf-8"?>
<n2svcd>
  ...
  <applications>
    ...
    <application name="Logic"
                 module="LogicApp">
      ...
        <parameters>
            ...
            <parameter name="script_key_opcode_0" value="dns_query"/>
        </parameters>
      <config>
        <services>
          <service module="DnsServerApp::DnsLuaService"
                   libs="../apps/dns_s/lib;../../n2sns/lua/lib"
                   lua_lib_path="../lua/lib/?.lua;../../n2sns/lua/lib/?.lua;../../n2sns/lua/3rdparty/?.lua"
                   script_dir="../../n2sns/lua/svc"/>
        </services>
        <agents>
          ...
          <agent module="DBApp::DBLuaAgent"
                 libs="../apps/db/lib"/>
        </agents>
      </config>
    </application>
    ...
  </application>
  ...
</n2svcd>

Note that the DNS opcode 0 script must be overridden using DNS Lua Service parameter configuration to the service script name dns_query with the following parameter:

            <parameter name="script_key_opcode_0" value="dns_query"/>

In addition to the Common LogicApp Service Configuration, the following service attributes apply under a normal installation:

Attribute	Type	XML Type	Description
`module`	String	Attribute	[Required] The service module type. Must be set to `DnsServerApp::DnsLuaService`
`libs`	String	Attribute	[Required] The location of the service module. Must include N2SVCD DNS libraries, e.g. `../apps/dns_s/lib`
`lua_lib_path`	String	Attribute	[Required] The location of the Lua libraries. Must include N2SVCD common and N2SNS common and third-party libraries, i.e. `../lua/lib/?.lua;../../n2sns/lua/lib/?.lua;../../n2sns/lua/3rdparty/?.lua`
`script_dir`	String	Attribute	[Required] The directory containing the scripts used by this service. In a standard N2SVCD installation, this must be `../../n2sns/lua/svc`

Script Selection

The script to be executed for requests is determined by the N2SVCD DnsServerApp.

For all received DNS query requests, this will be query.lua.

Script Global Variables

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

The following service-specific global variables are available:

Variable	Type	Description
`DB_APP_ROUTE`	String	The [database application route][../../../../n2svcd/technical_guide/logic/agents/db_agent.html#dbi_select_route] to use when querying the N2SVCD DNS database. (Default: `nil`, use default application route)
`EDR_STREAM_KEY`	String	A non-default EDR stream key to use when writing EDRs.
`TTL`	Integer	The TTL value to return for each DNS answer in a successful query response. (Default: 30)
`NAPTR_SEND_FLAGS`	String	A (case-insensitive) whitelist of provisioned flags to return in DNS NAPTR responses. Any other flags provisioned against a DNS record will not be silently removed. (Default: `adsu`)
`NO_MATCH_CODE`	Integer	Sets the response code to use when no record for the query can be found. (Default: `3`, no such domain)