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Gettin into WebKit o en source ro ect

Yael Aharon

Principal SW Engineer

Nokia

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Open source is no joke

April 1st, 2004. A senior manager visited

our office in Burlington with a message: We are going to adopt an open source

browser engine for Nokia devices,

replacing the in-house engine. At the time, we knew nothing about open

source.

April fools day ?

But this was no joke.

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Open source is no free ride either

Our choice was to use the WebKit open

source project. Soon after, a few technical details came

up.

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If the glove doesnt (perfectly) fit - I

WebKit was designed for the desktop,

where memory allocations hardly ever fail. But in Nokia devices, sometimes they do.

the browser when memory allocations fail.

The last thing we wanted in a project thisbig, was to add error handling in everysingle file.

What to do?

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If the glove doesnt (perfectly) fit - II

Thats when our memory manager was

born. Instead of modifying thousands of files,

we identified a handful of key places to

check the level of available memory in thesystem, and handle failure gracefully.

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If the glove doesnt (perfectly) fit - III

WebKit is loaded with features.

But our in-house browser included somenon-standard extensions.

Unable to drop these features, and unableto convince WebKit to add these features,we found an architectural design that willkeep these features in our product, withlittle to no changes in WebKit code.

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Be special

What makes a product stand out, when it

relies on open source project? Our innovative engineers came up with

many ideas.

The graphical history was a great idea,adopted by competitors too.

Page overview was another one. Allows

viewing the whole page on a small screen. Double tree rendering not so great idea.

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Source control is a religion

When adopting an open source project,

comes the question of which sourcecontrol system to use. Ours, or theirs?

For a while, we used a combination of.

Not productive!

Got to pick whats best for the engineers.

Easy to write automated scripts to movethe modified files from one source controlsystem to another.

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When to branch?

It is really important to choose the optimal time

for branching. We branched right away, thinking it would be

easier to maintain a snapshot of WebKit.

webkit.org.

But soon enough, our branched code becameoutdated, and it takes a lot of effort to catch-up.

We plan to start working directly in the WebKittrunk, and branch only towards releases.

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The review

For an open source project to succeed, it

must be policed very tightly. WebKit has a very rigorous review

process.

ne, some mes more an one rev ewer,would review your patch from manyaspects, and provide feedback.

Becoming a reviewer is a merit basedprocess.

You must prove yourself first.

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When every space counts - I

Who likes coding conventions and guidelines?

We all have our prefered way for indenting andnaming and doing things.

In a big open source project, lack of coding.

Messy code leads to sloppiness and that leadsto

When we started working with WebKit, we had a

hard time adjusting to the projects codingconventions.

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When every space counts - II

In fact, one reason for rejecting our

patches used to be wrong indentations. But once we got used to it, we saw the

benefits consistent, professional grade

code.

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Continuous testing

Bad or buggy code can bring a project

down, and fast. WebKits policy requires every patch to

either include new automated tests, or

explain why new tests are not needed. Automated tools are running thousands of

automated tests before every commit, so

regression can be caught immediately.

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Whats in it for me?

Working in an open source project has

challenges, so why would engineers buy-in?

Working on a big project gives engineers

the opportunity to collaborate and networkwith colleagues, working for othercompanies.

Engineers get to see their work being usedin many more products.

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Way ahead

The WHATWG (Web Hypertext Application

Technology Working Group) is adding many newand interesting features to HTML 5.

Of course, we want them in our products.

,and implement the new features in WebKit. Butthen we would get the features in THEIR priorityorder, and with THEIR interpretation.

So dont wait for someone else to do the work.Jump in, participate!

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