conceptual architecture of firefox 6.0 rob staalduinen 06009513 katie tanner 06060742 gordon krull...
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Conceptual Architecture of Firefox 6.0
Rob Staalduinen 06009513 Katie Tanner 06060742 Gordon Krull 06003108 James Brereton 06069736
By Fully Optimized eXperience (FOX)
What is Firefox?
A free, open source web browser
Developed and managed by the Mozilla corporation
Has approximately 25% of worldwide usage share of web browsers as of September 2011
Moved to a rapid release cycle in 2011 releasing a new version every 1 to 2 months
Research Overview
Began by reading reference architecture for web browsers provided in the paper “A Case Study in Architectural Analysis: The Evolution of the Modern Web Browser” by Alan Grosskurth and Michael W. Godfrey
We did general research on Firefox as a whole before isolating different subsystems
Then did in-depth research on each subsystem and began mapping out the architecture
Important sources of Documentation Mozilla Developers Network (MDN) Mozilla Wiki
Conceptual Architecture
Initially, we were expecting a layered architecture for Firefox
Within the layers, we expected that the distinct components were implemented in an object oriented architectural style
We were surprised to see that many of the elements of the lower layers were combined with the upper layer
Conceptual Architecture with Reference Architecture
Image source: Figure 3 from “A Case Study in Architectural Analysis: The Evolution of the Modern Web Browser” by Alan Grosskurth and Michael W. Godfrey
XUL & XULRunner
XUL = XML UI Language Firefox’s user interface is not hardwired into the application,
but loaded from a separate UI description. XUL is the language in which these UI descriptions are built.
Based on XML (extensible markup language) Used to communicate data between applications
XULRunner Runtime package that can be used to bootstrap XUL &
XPCOM applications such as Firefox Its goal is to facilitate development and deployment of
internet applications Includes mechanisms for installing, upgrading, and
uninstalling Firefox
Data Persistence
Session Store API Makes it possible for extensions to easily save and
restore data across Firefox sessions Key scenario in which supporting this feature can be
crucial for an extension: Firefox 2 and up lets users undo the closing of tabs
Implemented using the nsISessionStore interface
nsISessionStore: provides a means for extensions and other code to store data in associations with browser sessions, tabs and windows
nsISessionStartup: handles session restore process
Data Persistence
Storage (mozStorage) Is a SQLite database API It is available to trusted callers, meaning extensions and
Firefox components only
DOM Storage Designed to provide larger, securer, and easier-to-use
alternative to storing information in cookies A means through which string key/value pairs can be
securely stored and later retrieved for use Useful because there are no good browser-only methods
exist for persisting reasonable amounts of data for any period of time
Allows for “working offline” for extended periods of time
Gecko
Primarily it is the Browser Engine and Rendering Engine
Gecko lies at the heart of the Firefox Conceptual Architecture
Uses an Object-Orientated Architecture to implement the different components
Has support for many different standards
Through evolution from previous versions, Gecko now contains more than just the tools to render pages but also contains things such as: Networking and Security Libraries JavaScript Interpreter XML Parser (Expat) is now a library in the HTML Parser
Gecko Conceptual Architecture
Gecko Components
Document Parser (HTML & XML Parser) Parses both the HTML code and XML code and passes it on to the
Content Model for further use
Style System The Style System contains the CSS Parser and is responsible for
getting the CSS data from Necko and parsing it before sending it to the frame constructor
Platform-Specific Rendering and Widgets Acts as a Library for the frame constructor to call upon specifics of
the platform the browser is running on using the GTK+/X11 libraries before passing it on to the UI
Image Library Interacts with Necko in order to retrieve image data before
sending it to the Frame Constructor
Gecko Components
Content Model Interacts with the various components of
Gecko, DOM Storage to gather all the data needed before sending it to the frame constructor
Frame Constructor Carries out the task of piece together all the
information and actually from the rendered web page before sending it back to the UI through the Platform-Specific Rendering subsystem
SpiderMonkey
SpiderMonkey, contained within Gecko, is Firefox’s JavaScript engine, written in C/C++
Its components are a compiler, interpreter, 2 just-in-time (JIT) compilers, a decompiler, garbage collection, and a standard library
Also contains a few public APIs
Necko
Necko is the main networking library for Mozilla Firefox
This library is platform independent, allowing Firefox to be versatile, true to its open source nature
Necko itself is split into a layered architecture, with a pipe-and-filter style flow of execution
It relies heavily on the XPCOM library, and uses the NSS library for its network security
Necko Conceptual Architecture
NSS & PSM
NSS Network Security Services Set of libraries, APIs, utilities and documentation
designed to support cross-platform development of security-enabled client and server applications
PSM Personal Security Manager Consists of a set of libraries that perform
cryptographic operations on behalf of a client application
Built on top of NSS
XPCOM
XPCOM = Cross-Platform Component Object Module Breaks up large software projects into modular
components, which are reassembled at runtime Provides tools and libraries that enable the loading
and manipulation of these components
XPCOM provides the means of accessing the Gecko library functionality and embedding or extending Gecko
This modular programming benefits the reuse, updates, performance, and maintenance of software
GTK+/X11 Libraries
GTK+ and X11 are used to create Graphical User Interfaces (GUIs) on multiple platforms
Form the Display Backend of the Architecture
They are used by Gecko (specifically the Frame Constructor) to provide platform specific data
The User Interface (XUL) calls upon the libraries along with Gecko to display the page in the format for each platform
Rendering a cached webpage
(Sequence Diagram)
NeckoGecko SpiderMonkey Display Backend Data PersistenceUI
Check for cached page(found)
Send page to Javascript interpreter
Send page to Display Backend to be rendered
Summary
Firefox overall is implemented in a layered architectural style with Gecko containing most of the subsystems
Gecko uses an Object Oriented Architecture to organize and implement the components needed to render web pages
Necko is now within Gecko along with the security protocols it relies on.
The documentation was largely out-of-date or incomplete which made extracting the architecture difficult, due to the nature of open-source projects
Resources
https://developer.mozilla.org/en/Mozilla_Application_Framework_in_Detail
https://developer.mozilla.org/en/Necko
https://developer.mozilla.org/en/Necko_Architecture
http://www.w3counter.com/globalstats.php
https://developer.mozilla.org/en/Creating_XPCOM_Components/An_Overview_of_XPCOM
https://developer.mozilla.org/En/SpiderMonkey/Internal
https://developer.mozilla.org/en/DOM/Storage
https://developer.mozilla.org/en/Session_store_API
https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsISessionStore
https://developer.mozilla.org/en/XPCOM_Interface_Reference/nsISessionStartup
https://developer.mozilla.org/en/XUL_Tutorial/Persistent_Data
https://developer.mozilla.org/en/NSS
http://www.mozilla.org/projects/security/pki/nss/
https://developer.mozilla.org/en/NSS_FAQ
http://www.mozilla.org/projects/security/pki/psm/
https://wiki.mozilla.org/Gecko:Home_Page
https://wiki.mozilla.org/Gecko:Overview
https://developer.mozilla.org/en/Gecko_FAQ
http://research.cs.queensu.ca/home/emads/teaching/readings/emse-browserRefArch.pdf
http://www.gtk.org/
https://developer.mozilla.org/en/Gecko_Embedding_Basics
http://xkcd.com/198/
https://wiki.mozilla.org/Firefox/Roadmap
http://www.x.org/wiki/