Sunday, December 30, 2012

PAW - Using other Languages with CGI

This post is about using other languages apart from BeanShell and PHP. PAW includes a CGI Handler to execute scripts by using the Common Gateway Protocol (CGI). This handler is also used by the PHP plugin to call the CGI version of PHP. The handler is defined inside the file PAW_HOME/conf/handler.XML. Instead of using PHP we will use Perl to create a simple web page.

Finding the Executable Path

First thing to do is to install the SL4A and Perl APK from the Android Scripting Project: After installing the APKs and extracting Perl it's time to find out where the Perl executable is located. One way to do it is to execute the Perl interpreter and to use a terminal emulator and run the ps command. In the case of Perl the executable is located here: /data/data/com.googlecode.perlforandroid/files/perl/perl

CGI Configuration

Now it's time to edit the PAW handler configuration. Open the file PAW_HOME/conf/handler.XML and add the following lines below the Basic Auth Handler configuration:
 <handler status="active">
    <name>Perl CGI  Handler</name>
    <description>Perl CGI  Handler</description>
    <files />
      <param name="perlCgiHandler.class" value="org.paw.handler.AndroidCgiHandler" />
      <param name="perlCgiHandler.root" value="[PAW_HOME]/html" />
      <param name="perlCgiHandler.suffix" value=".pl" />
      <param name="perlCgiHandler.runwith" value="/data/data/com.googlecode.perlforandroid/files/perl/perl" />
      <param name="perlCgiHandler.sl4a" value="true" />
      <param name="perlCgiHandler.ENV_TMPDIR" value="[PAW_HOME]/tmp" />
Let's have a look at the parameters. The class parameter defines the handler to use. In our case this is the CGI Handler. The next parameter is the root parameter which specifies the directory the scripts are located. Subdirectories are also included. The suffix parameter defines the filename extension for the scripts. The runwith parameter is the most important one, it defines the location of the CGI binary. If the sl4a is set to true the environment variables AP_HOST and AP_PORT are set. Because this information is read from logcat entries, SL4A should be started right before the startup of PAW. Otherwise it might not possible for the handler to extract the SL4A configuration. The last parameter sets the TMPDIR environment variable. All parameters starting with ENV_ are used to set environment variables. Now the PAW configuration is complete and we can start to write a test CGI script.

The CGI Script

We will create a test CGI script inside the PAW_HOME/html directory called The test script looks like this:
print "Content-type: text/html\n\n";

print "Hello world!\n";
After starting PAW and entering the URL http://<ip-address>:8080/ into the address bar of the browser the following text should be displayed:
Hello world!


The Android Scripting Project offers many more interpreters. It should be possible use many of them together with PAW, as long as you can get them to work from the command line.