Resource-Oriented Computing with NetKernel

Appendix F. Examples and Solutions

Example—Limiter

A Limiter endpoint takes care of unwanted side effects in a space.^[43]

Setup

Consider the following rootspace definition:

<rootspace 
  name="Limiter Demo - Services"
  public="true"
  uri="urn:org:netkernelbook:chapter2:limiter:services">
  <fileset>
    <regex>res:/etc/system/SimpleDynamicImportHook.xml</regex>
  </fileset>
  
  <fileset>
    <regex>res:/limiterdemo/(.*)</regex>
    <rewrite>res:/resources/$1</rewrite>
  </fileset>
</rootspace>

The functionality of this rootspace could be described as providing access to anything in the resources directory.

With the following content for SimpleDynamicImportHook.xml, that means you provide access to anything in the resources directory to the whole wide world.^[44]

<connection>
  <type>HTTPFulcrum</type>
</connection>

Let us also create a couple of things in the resources directory. First, there’s a file limiter_demo_allowed.txt:

http://periodicvideos.com/
http://www.sixtysymbols.com/

There’s also a file limiter_demo_not_allowed.xml.

<general>
  <password>ThisIsThePasswordIUseEverywhere</password>
</general>

The issue

http://localhost:8080/limiterdemo/limiter_demo_not_allowed.xml

The solution

<rootspace name="Limiter Demo - Services" public="true" uri="urn:org:netkernelbook:chapter2:limiter:services"> <fileset> <regex>res:/etc/system/SimpleDynamicImportHook.xml</regex> </fileset> <fileset> <regex>res:/limiterdemo/(.*)</regex> <rewrite>res:/resources/$1</rewrite> </fileset> <endpoint> <prototype>Limiter</prototype> <grammar>res:/limiterdemo/ ...