Interrupt-Driven

This article tries to explain how you can extend Webif^2 with your own functionality. I am myself new to Webif^2. The reason i am writing this article is to get acquainted enough with the code so i can decide if i would like to use it to create some NAS specific functionality.

Webif^2 runs on devices with some severe CPU and memory limits. Given that using one of the mainstream web development platforms was apparently off the table. Instead a combination of shell/awk and sed is used to generate dynamic content. Basically the way your father would have done it back in the days (given that there had been a web to develop for…) Having done some work with Ruby on Rails recently i am not too excited by this prospect but lets see how it goes.

My first goal is to have some pages which are displaying friendly greeting messages. These pages should be grouped into a new category in the main menu. I assume that you have checked out a copy of webif^2. All path references are relative to trunk/package/webif/.

Step1: Adding a new category.

files/www/cgi-bin/webif/.categories contains the entries of the main menu. We just add our entry here (”Test”).

If you now reload your web browser you should see a new category “Test”. The next step will be to add content to this category.

Step2: Putting content into the new category.

I add the file test-hello.sh in files/www/cgi-bin/webif. The name of the file doesn’t matter but the convention seems to be to name it $(category)-$(name).sh.

Webif^2 uses an interpreter called Haserl. It will parse html files and execute the shell fragments it finds enclosed by <? … ?> (basically like it is done by php/jsp/…). The documentation for it can be found here.

The first line tells the linux kernel which interpreter to use when trying to execute this file (webif-page is the actual haserl program). The lines 02 to 09 contain the actual program that will generate our page. 03 pulls in webif.sh which is a library containing the functions we will use. 05 calls the header function (found in webif.sh). It will generate the html header, the head section of page and also the main- and sub-menu. $SCRIPT_NAME is set by haserl. On line 07 we say “hello” to openWrt. The only thing left now is to finish the page. To accomplish this we call the footer function (also found in webif.sh). This function will generate the content you see in the bottom section (”Apply Changes”, “Clear Changes”, …). It will also close the HTML document.

The last three lines contain a strange HTML comment. Lets have a closer look. When the main menu is generated webif^2 scans all files in files/www/cgi-bin/webif/ having the .sh extensions, looking for this special marker. The marker tells it to put an entry “Hello” into the category “Test”. The number can be used to allow a non-alphabetical ordering of the entries. The entry with the lowest number comes first. It will also be the page being selected by default of you click on the category.

So far so good. Next time we try to use some forms.