man Html2Wml (1): Program that can convert HTML pages to WML pages

     _____________          _____________ 
    |    deck     |        |   deck #1   |
    |  _________  |        |  _________  |
    | | card #1 | |        | |  card   | |
    | |_________| |        | |_________| |
    |  _________  |        |_____________|
    | | card #2 | |        
    | |_________| |             . . .
    |  _________  |        
    | |   ...   | |         _____________
    | |_________| |        |   deck #n   |
    |  _________  |        |  _________  |
    | | card #n | |        | |  card   | |
    | |_________| |        | |_________| |
    |_____________|        |_____________|

      WML document           WML document
    sliced by cards        sliced by decks

What this means is that Html2Wml generates several WML documents. In CGI mode, only the appropriate deck is sent, selected by the id given in parameter. If no id was given, the first deck is sent.

Note on size calculation

Currently, Html2Wml estimates the size of the card on the fly, by summing the length of the strings that compose the WML output, texts and tags. I say ``estimates'' and not ``calculates'' because computing the exact size would require many more calculations than the way it is done now. One may objects that there are only additions, which is correct, but knowing the exact size is not necessary. Indeed, if you compile the WML, most of the strings of the tags will be removed, but not all.

For example, take an image tag: `<img src="images/dog.jpg" alt="Photo of a dog">'. When compiled, the string `"img"' will be replaced by a one byte value. Same thing for the strings `"src"' and `"alt"', and the spaces, double quotes and equal signs will be stripped. Only the text between double quote will be preserved... but not in every cases. Indeed, in order to go a step further, the compiler can also encode parts of the arguments as binary. For example, the string `"http://www."' can be encoded as a single byte (`8F' in this case). Or, if the attribute is `href', the string `href="http://' can become the byte `4B'.

As you see, it doesn't matter to know exactly the size of the textual form of the WML, as it will always be far superior to the size of the compiled form. That's why I don't count all the characters that may be actually written.

Also, it's because I'm quite lazy ;-)

Why compiling the WML deck?

If you intent to create real WML pages, you should really consider to always compile them. If you're not convinced, here is an illustration.

Take the following WML code snipet:

    <a href='http://www.yahoo.com/'>Yahoo!</a>

It's the basic and classical way to code an hyperlink. It takes 42 bytes to code this, because it is presented in a human-readable form.

The WAP Forum has defined a compact binary representation of WML in its specification, which is called ``compiled WML''. It's a binary format, therefore you, a mere human, can't read that, but your computer can. And it's much faster for it to read a binary format than to read a textual format.

The previous example would be, once compiled (and printed here as hexadecimal):

    1C 4A 8F 03 y a h o o 00 85 01 03 Y a h o o ! 00 01

This only takes 21 bytes. Half the size of the human-readable form. For a Wap device, this means both less to download, and easier things to read. Therefore the processing of the document can be achieved in a short time compared to the tectual version of the same document.

There is a last argument, and not the less important: many Wap devices only read binary WML.

ACTIONS

Actions are a feature similar to (but with far less functionalities!) the SSI (Server Side Includes) available on good servers like Apache. In order not to interfere with the real SSI, but to keep the syntax easy to learn, it differs in very few points.

Syntax

Basically, the syntax to execute an action is:

    <!-- [action param1="value" param2='value'] -->

Note that the angle brackets are part of the syntax. Except for that point, Actions syntax is very similar to SSI syntax.

Available actions

Only few actions are currently available, but more can be implemented on request.

include

: Description
Includes a file in the document at the current point. Please note that Html2Wml doesn't check nor parse the file, and if the file cannot be found, will silently die (this is the same behavior as SSI).

Parameters
`virtual=url' --- The file is get by http.
`file=path' --- The file is read from the local disk.

fsize

: Description
Returns the size of a file at the current point of the document.

Parameters
`virtual=url' --- The file is get by http.
`file=path' --- The file is read from the local disk.

Notes
If you use the file parameter, an absolute path is recommend.

skip

: Description
Skips everything until the first `end_skip' action.

Generic parameters

The following parameters can be used for any action.

for=output format: This paramater restricts the action for the given output format. Currently, the only available format is "`wml'" (when using `html2chtml' the format is "`chtml'").

Examples

If you want to share a navigation bar between several WML pages, you can `include' it this way:

    <!-- [include virtual="nav.wml"] -->

Of course, you have to write this navigation bar first :-)

If you want to use your current HTML pages for creating your WML pages, but that they contains complex tables, or unecessary navigation tables, etc, you can simply `skip' the complex parts and keep the rest.

    <body>
    <!--[skip for="wml"]-->
    unecessary parts for the WML pages
    <!--[end_skip]-->
    useful parts for the WML pages
    </body>

LINKS RECONSTRUCTION

The links reconstruction engine is IMHO the most important part of Html2Wml, because it's this engine that allows you to reconstruct the links of the HTML document being converted. It has two modes, depending upon whether Html2Wml was launched from the shell or as a CGI.

When used as a CGI, this engine will reconstructs the links of the HTML document so that all the urls will be passed to Html2Wml in order to convert the pointed files (pages or images). This is completly automatic and can't be customized for now (but I don't think it would be really useful).

When used from the shell, this engine reconstructs the links with the given templates. Note that absolute URLs will be left untouched. The templates can be customized using the following syntax.

Templates

HREF Template: This template controls the reconstruction of the `href' attribute of the `A' tag. Its value can be changed using the ---hreftmpl option. Default value is `"{FILEPATH}{FILENAME}{$FILETYPE =~ s/s?html?/wml/o; $FILETYPE}"'.
Image Source Template: This template controls the reconstruction of the `src' attribute of the `IMG' tag. Its value can be changed using the ---srctmpl option. Default value is `"{FILEPATH}{FILENAME}{$FILETYPE =~ s/gif|png|jpe?g/wbmp/o; $FILETYPE}"'

Syntax

The template is a string that contains the new URL. More precisely, it's a Text::Template template. Parameters can be interpolated as a constant or as a variable. The template is embraced between curcly bracets, and can contain any valid Perl code.

The simplest form of a template is `{PARAM}' which just returns the value of PARAM. If you want to do something more complex, you can use the corresponding variable; for example `{"foo $PARAM bar"}', or `{join "_", split " ", PARAM}'.

You may read the Text::Template manpage for more information on what is possible within a template.

If the original URL contained a query part or a fragment part, then they will be appended to the result of the template.

Available parameters

URL: This parameter contains the original URL from the `href' or `src' attribute.
FILENAME: This parameter contains the base name of the file.
FILEPATH: This parameter contains the leading path of the file.
FILETYPE: This parameter contains the suffix of the file.

This can be resumed this way:

  URL = http://www.server.net/path/to/my/page.html
                             ------------^^^^ ----
                                 |        |     \
                                 |        |      \
                              FILEPATH FILENAME FILETYPE

Note that `FILETYPE' contains all the extensions of the file, so if its name is index.html.fr for example, `FILETYPE' contains "`.html.fr'".

Examples

To add a path option:

    {URL}$wap

Using Apache, you can then add a Rewrite directive so that URL ending with `$wap' will be redirected to Html2Wml:

    RewriteRule  ^(/.*)\$wap$  /cgi-bin/html2wml.cgi?url=$1

To change the extension of an image:

    {FILEPATH}{FILENAME}.wbmp

PROXY SUPPORT

Html2Wml uses LWP built-in proxy support. It is activated by default, and loads the proxy settings from the environment variables, using the same variables as many others programs. Each protocol (http, ftp, etc) can be mapped to use a proxy server by setting a variable of the form `PROTOCOL_proxy'. Example: use `http_proxy' to define the proxy for http access, `ftp_proxy' for ftp access. In the shell, this is only a matter of defining the variable.

For Bourne shell:

    $ export http_proxy="http://proxy.domain.com:8080/"

For C-shell:

    % setenv http_proxy "http://proxy.domain.com:8080/"

Under Apache, you can add this directive to your configuration file:

    SetEnv http_proxy "http://proxy.domain.com:8080"

but this has the default that another CGI, or another program, can use this to access external ressources. A better way is to edit Html2Wml and fill the option `proxy-server' with the appropriate value.