WAP/WML interfaces
part of the ArsDigita Community System
by Andrew Grumet
The Big Picture
We want to make site content available to wireless devices like cell
phones. The prototypical application is a WAP-accessible phone
directory which lets you look up a phone number by keying in the first
few letters of the person's name or email address, and then serves up
the number providing a link to call that number.
The Medium-Sized Picture
A WAP device connects to a gateway which issues HTTP requests on
behalf of the device. No modifications of the web server itself are
needed---content is served over HTTP---but new headers and markup are
needed. Pages are built according to the Wireless Markup
Language DTD, proposed and maintained by the WAP Forum.
Besides learning new syntax, the major considerations when building
WAP pages are:
- Page flow: WAP devices typically have small
screens without much room for information. Rather than requiring that
a slow request be made for each page, WML provides a mechanism for
transmitting several discrete page views, or cards, in a single
document, or deck. There are also provisions for passing
state information (i.e. variables) between cards in deck (and possibly
between different decks).
- Verbosity: Small displays mean you don't have
room for lengthy explanations.
- Applications: You can help the phone do nifty stuff like dial phone numbers thanks to the WTAI Specification.
- Code reuse: There's no absolute way to get around
the pain of managing parallel sets of pages. If nothing else, you'll
want to serve up less content to smaller screens and perhaps
more to larger screens. But there are ways to minimize the
pain by separating content from presentation (insert favorite X*
acronym here).
The Gory Details
- User login is handled by cookies in the usual way.
- To save the user a bit of typing at login time we provide
autocompletion of the email address using a default domain if the
user's input lacks an @ (see wap_default_email_domain)
- We build a top level index for wap services in /wap/i.wap, which
should ultimately integrate with the module registry to
dynamically build a page of available services.
- All wap services will live under the /wap directory (subject to
change).
- The /admin directory contains tools for managing a list of known
WAP user agents, which can help you determine what type of device is
knocking at your door.
- Documented procedures: see wap-defs section of ACS API documentation
Note for programmers who have worked with the
ACS-3.3 version:As of ACS-3.4, wap_begin_output
and wap_begin_output_no_cache return a string to the
caller, rather than writing directly to the connection.
This change was made so that we can return the WML document with
a single call to ns_return, in keeping with 3.4 standards.
The Steps
To add wap services to your module:
- Add a link to your service in the top level page at /wap/i.wap
(this needs to be integrated with the module registry).
- Learn to code WML. You might want to read the
WML specification.
- For logic, make use of the API functions in wap-defs. Useful
procs: util_guess_doctype,
wap_maybe_redirect_for_registration,
wap_returnredirect,
wml_return
- For debugging, you may want to run a WAP-enabled browser on your PC.
These can be downloaded from
Alternatively, the telnet method works quite well too.
Parameters
[ns/server/yourservername/acs/wap]
; do we serve the generated /wap/index page or something
; else from the file system? This should be the FULL PATH relative
; to page root.
SpecialIndexPage=/wap/i.wap
; how long between lookups of the known user agent list?
WapUserAgentDbRefresh=300
; where to import user-agents strings from
WapImportSiteURL=http://wap.colorline.no/wap-faq/useragents.php3
; what tcl procedure to use to parse the data returned
; from the page listed above
WapImportParseProc=wap_import_parse
; how long between http GET's?
WapImportRefreshTimeout=120
; how many characters in the User-Agent string
; should we compare against?
WapUAStringCompareLength=4
; are we doing HTML browser-based debugging?
WapHTMLDebugMode=0
; to save typing when logging in
WapDefaultEmailDomain=arsdigita.com
More
aegrumet@arsdigita.com