Shrinkwrap Software
with Perl, PAR and SOAP

Chris Dolan

MediaLandscape Software

cdolan@cpan.org

Properties of shrinkwrap

→

• Easy to install
• Feels self-contained
• Easy to launch
• Has a GUI

Contrast traditional Perl software

Can't locate Foo.pm in @INC (@INC contains: /usr/lib/perl5/site_perl/5.8.6
/usr/lib/perl5/site_perl
/usr/lib/perl5/5.8.6 ...

• Many prerequisites to install
• Files scattered all over system
• Run from command line...
• ... or web browser

A solution in two parts

• PAR makes Perl monolithic
• SOAP lets you separate engine from interface

Part I: PAR

PAR to the rescue

What is PAR? Perl Archive Toolkit!

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• A ZIP archive of Perl files, analogous to Java's JAR
• Can include additional library files
  (e.g. libjpeg.so)
• Killer feature: Self-extracting executables

PAR example

% pp -o MyProgram MyProgram.pl
% ./MyProgram

PAR's pp program finds all of the dependencies in your program via Module::ScanDeps then zips those files into an archive and prepends an executable header (including libperl).

For Windows, add the --gui flag if you want to avoid the console window.

How PAR works

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At runtime, the PAR executable unzips itself into a temp directory and loads the libperl dynamic library. The @INC is modified to look in the temp directory first. PAR then finds the main .pl file and runs it.

Because libperl is embedded, this works even on computers where Perl is not installed.

Advanced PAR Usage

Add extra libraries:
% pp -l /sw/lib/libjpeg.62.dylib -o jpegmunger jpegmunger.pl

Exclude runtime features:
% pp -X Foo::Plugin::Advanced -o foo_lite foo.pl

Exclude unneeded functionality:
% pp -X DBD::mysql -o sqllite_browser sqllite_browser.pl

Disadvantages of PAR

• Large files ("Hello, world!" is 2.7 MB)
• Slow to start up the first time
• Hard to get the dependencies right for complex applications.
  Use pp -M Foo::Bar or:

sub hints_for_PAR {
   require Encode::Unicode;
   require LWP::Protocol::https;
   require URI::https;
}

Don't worry, Module::ScanDeps is improving

Part II: SOAP

The problem: GUI?

Perl does have GUI toolkits: Tk, Wx, Qt, GTK, CamelBones. But most GUIs are developed in other languages. Why?

• IDE tools
• Speed?
• Appearance
• Skill sets
• Legacy...

A solution: modularize!

• Write the GUI in a language well-endowed for GUI development:
  • Cocoa
  • Flash
  • Java
  • .NET
  • HTML
  • XUL
• Write the engine in Perl
• Launch both at runtime and share the work.
  But how do they talk?

SOAP cleans your interfaces

What is SOAP? Simple Object Access Protocol

• Call methods in other programs
• Talks via HTTP
• Messages are XML
• Cross-platform, cross-language

Client – Server

↔

SOAP

↔

If you can write a CGI service, you can write a SOAP service.

When your GUI application launches, it attempts to contact the server. If the connection fails, it forks and execs the server.

The GUI is stateful, the engine is stateless (or less stateful), just like in the web paradigm.

An example

MediaLandscape Converter

• Windows application to convert Windows Media presentations to Flash
• Required to be pretty
• Required to coordinate hours of video conversions
• Required to talk to a MySQL database

Solution: Flash GUI, Perl server, C++ engine

Nuts & Bolts

How do you implement the solution?

• Define the API, e.g.:
  • List presentations in the database
  • Query the available output skins
  • Submit a convert job
• Stub out the server methods
• Write a trivial command-line client
  (hint: Test::More!)
• Get a designer to paint a pretty GUI

Another example

MediaLandscape Presenter

• Mac application to capture video-narrated presentations
• Uses QuickTime, Net::VNC, VGA hardware, HTTP::Server::Simple and Time::HiRes
• Emits Flash, H.264, MPEG4, PDF, HTML

Solution: Cocoa GUI, 6 PAR exes, Perl glue

More advantages of SOAP

✓

• Can move server to another computer easily
  One line change in a WSDL file
• Strict division of labor
• Can write multiple GUIs (maybe Lite vs. Pro)

Disadvantages of SOAP

☓

• Harder to coordinate multiple programs (what if one crashes?)
• Some firewalls trigger even on 127.0.0.1
• Harder to write a WSDL file than a .h file
• SOAP::Lite is one of the most impenetrable modules on CPAN (but is remarkably powerful)

Summary

Shrinkwrap software requires technologies that simplify yet beautify the experience for the user. PAR and SOAP help Perl to accomplish that by:

• Encapsulating the best of CPAN without complex installation
• Letting Perl do what it does best and leaving the rest to other languages