DPML Accessors

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DPML Accessor

Accessors can be implemented using declarative DPML scripting.

To create a DPML-based accessor you will:

Write the accessor in DPML.
Expose the script as an accessor.

Write the Accessor

Due to the design specification of DPML, an accessor implemented in DPML can only support SOURCE requests. Also, since DPML has no native operations a DPML scripted accessor is always a composite of other accessor calls.

For example, here's a DPML script which logs into, and sends an SMS text message via a service provider gateway.

<idoc>
  <seq>
    <!--
      Register logon crendentials in an HTTP state resource
    -->
    <instr>
      <type>new</type>
      <uri>active:httpState</uri>
      <credentials>ffcpl:/resources/SMSGatewayCredentials.xml</credentials>
      <target>var:state</target>
    </instr>
    <!--
      Style the "message" argument this accessor/script
      received using some Message to SMS transform
    -->
    <instr>
      <type>XSLT</type>
      <operand>this:param:message</operand>
      <operator>ffcpl:/resources/stlyeMessageToSMS.xsl</operator>
      <target>var:message</target>
    </instr>
    <!--
      Post the message
    -->
    <instr>
      <type>httpPost</type>
      <url>https://www.mySMSGateway.com/sendMessage</url>
      <state>var:state</state>
      <message>var:message</message>
      <target>this:response</target>
    </instr>
    <!--
      Transform the SMSGateway response to something
      useful as the accessor's response.
    -->
    <instr>
      <type>XSLT</type>
      <operand>this:response</operand>
      <operator>ffcpl:/resources/styleMessageSentResponse.xsl</operator>
      <target>this:response</target>
    </instr>
  </seq>
</idoc>

Expose the Accessor

Once written, export the accessor's URI interface from the module and then rewrite requests on that interface to an invocation of the script by its language runtime.

We can expose this as a service active:SMSMessageService as follows.

In your module export section add an entry...

<export>
    ...
    
  <uri>
    <match>active:SMSMessageService.*</match>
  </uri>
    ...

</export>

In your module's mapping section add a rewrite rule which maps requests for active:SMSMessageService to the DPML runtime with the sms-message.idoc script.

<mapping>
    ...
    
  <rewrite>
    <match>active:SMSMessageService(.*)</match>
    <to>active:dpml+operand@ffcpl:/path/to/sms-message.idoc$1</to>
  </rewrite>
    ...

</mapping>

That's it. Your module now provides an accessor active:SMSMessageService - it is irrelevant to the user that this service is implemented by the execution of a DPML script.

[Note: to ensure the script gets executed by the active:dpml runtime your module must import the ext-dpml module and any accessor libraries used by the script.]