Rule based invocation of ICAP services using IRML

March 2002

A Rule based framework for invoking ICAP services is proposed in [4] The rules are to be specified as XML data (using the IRML specification).

The following is the DTD for IRML:
<!ELEMENT rulemodule    (owner, protocol, rule+)>
<!ELEMENT owner         (name, id)>
   <!ELEMENT name          (#PCDATA)>
   <!ELEMENT id            (#PCDATA)>
<!ELEMENT protocol      (#PCDATA)>
<!ELEMENT rule          (property | action)+>
   <!ELEMENT property      (property | action)+>
   <!ELEMENT action        (#PCDATA)>
<!ATTLIST owner         class (content provider |
                                         access provider | client) #REQUIRED>
<!ATTLIST rule          processing-point   (1|2|3|4)      #REQUIRED>
<!ATTLIST property      name               CDATA          #REQUIRED>
<!ATTLIST property      matches            CDATA          #REQUIRED>
<!ATTLIST property      case-sensitive     (yes|no)   #DEFAULT "no">

An example IRML file is shown below:

<?xml version="1.0"?>
<rulemodule>
# Rule for sending the right GIF (For pocket PC)
# Note the nested condition checks
<owner class="ISP">
   <name>Geetha Manjunath</name>
   <id>23242</id>
</owner>
<protocol>http</protocol>
   <rule processing-point="4">
    <property name="User-Agent" matches="*CE*">
      <property name="Request-Path" matches=".*hotspot_long.gif">
          <action>WinCEImage?</action>
      </property>
    </property>
   </rule>

# Rule for translating to French based on Client Id
<owner class="client">
    <name> Venky </name>
    <id>23242</id>
</owner>
<protocol>http</protocol>
   <rule processing-point="4">
      <property name="Client-Id" matches=".*@hpl.hp.com">
         <action>translatePl</action>
      </property>
   </rule>
</rulemodule>

Steps for modifying the rules of invocation:

    1.Author a new proxylet (optional).
           Define a subclass of HTTPProxylet, and override its methods.
           Use the API in modules HttpProxyletRequest and HttpProxyletResponse
    2.Modify icap_server/irml/rules.xml appropriately
    3.Translate the IRML file to Python code
           a) Set up PYTHONPATH
                  cd icap_server
                  . setup
           b) cd icap_server/irml
           c) make install
    4.Restart ICAP server
            ./start_icap.py

References

[1] The ICAP forum at http://www.i-cap.org/
[2] The OPES forum at http://www.ietf-opes.org/
[3] "Proxylet Local Execution Environment Local Binding", IETF Draft. http://www.ietf-opes.org/documents/draft-walker-opes-proxylet-java-binding-01.txt
[4] IRML: A Rule Specification Language for Intermediary Services, IETF Draft, http://www.ietf-opes.org/documents/draft-beck-opes-irml-00.txt
[5] Squid Web Proxy , http://www.squid-cache.org/
[6] Medusa Server, http://www.nightmare.com/medusa/
[7] A Python based ICAP Server http://icap-server.sourceforge.net
[8] Project page, http://sf.net/projects/icap-server

Contact Info

For any comments or feedback on this code or project, please feel free to write to:
geetham@india.hp.com
Geetha Manjunath
Technical Consultant,
Hewlett Packard India Software Operations Ltd.
INDIA.

This project is sponsored by Hewlett Packard Labs.