JS-ctypes

With the unavailability of XulRunner in Ubuntu Oneiric and the possible removal of it from other distro, we decided to switch to js-ctypes components. The main reason is that our code won't be tied to a XR version (which are released every 6 weeks) as components are. It also has some side-advantages

JS-ctypes

ctypes is a Foreign Function Interface which is available in several languages. It allows one to call C functions (of a library) from Javascript or Python or other language supporting it. It doesn't require specific C code. It just calls arbitrary functions.

Porting

Porting Kiwix components to js-ctypes requires a lot of work so we decided to incorporate other changes. Porting a component consist of the following:

1. Rewrite the C++ component into a C++ library with no mozilla dependency.
2. Write a C++ program testing the C++ API.
3. Write a C Wrapper around the C++ API.
4. Write a C program testing the C Wrapper/API.
5. Write a JS module interfacing with js-ctypes and the C wrapper.
6. Fix existing JS code (gui.js, etc) to use the JS module.

Rewrite the C++ component into a C++ library

The main rule here is to remove Mozilla dependency. It is very important to remove it completely otherwise it's a waste of time. Advantages of removing MOZ dep:

• We build a shared/static lib which is not a component.
• We don't need the mozilla stack to build it (ease Windows, and other system setup like arm)
• We don't need an every-release recompile of our code
• We don't even need to release anything to have it work with newer XR.
• We can use it to build a Kiwix UI with webkit (for example on Android). We'll code all component code and just need a new UI.
• We can use the same code for kiwix-serve
• We could use it to create a Kiwix server instead of a kiwix-http-server (allow one to administer the server library using a Web UI)
• We can then split kiwix code with components code and have a kiwix-libs package.

Writing this library is quite easy. It's mostly a copy-paste of the component code then cleaning.

Note: The goal is to replace the component but until all components are ported, we'll have a duplication of the code in the tree. We need to port-back every addition to the comonent to the new library until it replaces the component completely.

• C++ Component code example
• C++ library example

Rules to embrace/respect:

1. nsAString is replaced with string
2. nsACString is replaced with char *
3. nsIURI is replaced with string and code adapted consequently.
4. No more retVal nor NS_OK. Methods uses return type (bool mostly)
5. Keep case on method names.
6. don't add features while you port to keep it understandable and revert-able.

The component uses no header file (it is generated from IDL at compile time and is really verbose) so you also need to write it manually. header file example.

Remaining work

• unicode