Generating XHTML MP (WAP 2.0) Pages From PHP

Maybe you guys know that I've been working on a service called MyWapBlog.com which lets peoples create/manage mobile blogs using their mobile phones. In the course of the development I've learnt great deal about mobile websites and their dynamic generation, and I'm sharing a bit of it here in this post.

How do you generate dynamic (X)HTML Pages using PHP? Simple:

Hello

echo date('h:i A, j-M-y'); ?>

And if you look at XHTML MP pages, their source look like the following:

...

...

So you see these pages have a different document type and some other differences. So will the following code work and generate a valid WAP 2.0 page?:

Hello

echo date('h:i A, j-M-y'); ?>

The answer is “NO”? Why? Because XHTML MP pages needs to be served with a different Content-Type than what is generated by .PHP files. Normally when you runa s PHP script and it outputs something, the content is served with Content-Type: text/html

What is Content-Type?

It is a header (information about a particular resource) returned to browser when it requests something from a server. When you request an image, the server return the image with the header image/png, image/jpeg etc. letting the browser know how the returned content is to be interpreted.

PHP scripts can return contents of any type (using the header() function), from text to images and PDFs to ZIPs. And therfore if we want to generate XHTML MP pages, it can even do that without doubt.

So what we need to do is, just change the above code a bit adding a new line at the top so that the whole code look like the following:

("Content-type: application/vnd.wap.xhtml+xml; charset=UTF-8");?>















Hello

echo date('h:i A, j-M-y'); ?>

This will tell the browser that the content we are going to serve is of the type XHTML MP. We always use the charset UTF-8 for these pages, which is also told to the requesting browser.

Now the big question is, why we didn't do this for normal HTML pages. Why didn't we have to tell the browser that content is of the type “text/html” when it was so? Because PHP does it for us! Yes whenever we output anything from PHP scripts, the PHP interpreter outputs the default header (text/html) automatically. Just as the PHP interpreter finds anything in the script that needs to be output, it first generates a header, the outputted content follows. For example in the first script, the very first line (very first character “<”) needs to be output to the browser. So before that, the PHP interpreter sends a content type header (default – text/html).

Therefore, when we had to output our content with a different header we had to make sure that it is done before PHP does it automatically. Two headers cannot be valid.

This is it for this post, do check back soon for more new posts. Till then, good bye!