Chapter 6. Packaging and Installing Applications-P1
The previous chapters covered the basic parts of building an application.
Now that you've seen how to create an application with XUL, CSS, and
JavaScript that can be used on your local computer, we will show you how
to turn your program into something that can be installed by other users.
This chapter discusses the technologies Mozilla provides for packaging and
installing applications.
Until your project is packaged for distribution, it can't be fully considered a
finished application (unless it was designed to work only on the computer
where it was created). Making your application distributable, installable, and
registrable allows others to use what you have created.
This chapter is divided into four main sections. It starts with a quick
overview of the basics of packaging and installing applications. The second
section provides details about how to get your application packaged and
described so that Mozilla recognizes what it is. The next section specifies
how to put your package into a cross-platform installation file that can be
installed over the Web onto other machines. The last section provides tips
for customizing how your application will look once it is installed.
6.1. Packaging and Installing Overview
Several different pieces comprise Mozilla's distribution technology. In fact,
Mozilla may have a few more moving parts than other packaging systems
because it needs a way to package and install new software uniformly across
several different platforms. Figure 6-1
shows the major components of
Mozilla's packaging system outlined in black.
Figure 6-1. Mozilla packaging components

As you can see in Figure 6-1
, the Cross-Platform Installer (XPI), pronounced
zippy or X-P-I, is the archive format used to distribute Mozilla applications.
The XPI file contains a script that downloads and installs the application.

to the installation
registerChrome(
PACKAGE | DELAYED_CHROME, // chrome switch
(i.e., type)
getFolder("Chrome","xFly.jar"), // destination of
package
"content/xFly/"); // location of
manifest in package
if (0 == getLastError( )) // if there have
been no errors:
performInstall( ); // install
"xfly.jar"
else // otherwise
cancelInstall( ); // cancel the
installation.
The installation process requires a few different steps. First an installation
must be initialized. Then the software to be installed is added to the
specified target directory. Finally, packages in the installation are registered.
At this point, the application is installed on a user's computer.
When you install new packages or Mozilla-based software, the chrome
registry on the Mozilla side brokers the deal -- reading the manifest,
executing the installation script(s), and updating the package information
that it maintains internally (storing this information using RDF).
The relationship of the packaging, installation, and registration -- and all
pieces involved -- may seem a little complex and idiosyncratic at first, but
bear with it. The upshot of this powerful but somewhat diffuse packaging
technology is that you can bundle your software, put it on a server, and have
users install it by simply clicking a link on a web page when using Mozilla.
It is possible to use this packaging system to bundle any sort of application
or extension to an existing Mozilla application. You can install a XPI that

section
later in this chapter for more information about XPI install files).
6.2.1.1. Theme package manifests
Example 6-2
shows a manifest for a new theme to be installed in Mozilla. It
is simple because it describes only one type of package, the "fly skin," and
the existing component it interacts with, the communicator -- the default
Mozilla browser (the syntax and structure is the same for all manifests,
however). The manifest says, in effect, this is what I have here (the metadata
about the theme -- its name, a description, etc.), and this is what it affects
(the list of chrome:packages to which the theme should be applied).
Example 6-2. Simple theme package manifest
<?xml version="1.0"?>
<RDF:RDF xmlns:RDF=" />rdf-syntax-ns#"

xmlns:chrome="
<!-- List all the skins being supplied by this
theme -->
<RDF:Seq about="urn:mozilla:skin:root">
<RDF:li resource="urn:mozilla:skin:flyskin/1.0"
/>
</RDF:Seq>

<!-- Fly Skin Information -->
<RDF:Description
about="urn:mozilla:skin:flyskin/1.0"
chrome:displayName="Fly Skin"
chrome:author="frillies"
chrome:description="shimmering, purple/black,
hairy">


chrome:previewURL=" />n-DE.gif">
<chrome:packages>
<RDF:Seq about="urn:mozilla:locale:en-
DE:packages">
<RDF:li resource="urn:mozilla:locale:en-
DE:communicator"/>
<RDF:li resource="urn:mozilla:locale:en-
DE:editor"/>
<RDF:li resource="urn:mozilla:locale:en-
DE:global"/>
<RDF:li resource="urn:mozilla:locale:en-
DE:messenger"/>
<RDF:li resource="urn:mozilla:locale:en-
DE:navigator"/>
</RDF:Seq>
</chrome:packages>
</RDF:Description>
</RDF:RDF>
Note that in Example 6-3
's package manifest, all major components are
affected by this new locale package. When the package is installed and the
manifest is read, the chrome registry is made aware of a German language
pack that it can use to display German in the interface of each Mozilla
component.
contents.rdf Type Manifests
Package manifests are an area where Mozilla browser itself may not be the
best model for learning about the best application development practice.
Mozilla is such a large and modular application that it uses several manifests
instead of one application-wide manifest.rdf file.