We have moved – Please update your bookmarks!

We have moved the site to mobdev.tknerr.de, please update your bookmarks!

How To Make J2ME Apps Work for the WAP Flat, Part II (Example: Google Maps Mobile)

Last week I posted a tool to “make J2ME apps work with the o2 WAP Flat”. All the magic it does is inserting some HTTP headers into a fully compiled (and often obfuscated) J2ME application.

Some users asked how to get the .jar and .jad files of the J2ME application to your desktop PC in order to patch them with the o2 WAP Flat Patcher. There are many possibilities to accomplish this, but here’s my recommendation:

1. Use your J2ME devices native browser to download the application. For example, visit http://www.google.com/gmm to get the latest version of Google Maps Mobile. It is important to use the devices native browser because most J2ME apps are tailored for a specific device — and the native browser uniquely identifies the device using its User-Agent and Profile headers. In my case this leads me to a site which says “Download Google Maps for Nokia 6630” and links to the appropriate .jad file (note: the .jad file is a plain text file and contains amongst others the location of the .jar file).
2. A caveat of my Nokia 6630’s native browser is that I can not download .jad files. When I click the link above, it will directly install the application. But this is ok, since the browser will download and store both files on the device before installation. Just go ahead and install the application (we will reinstall the patched version later).
3. Now find the Google Maps Mobile .jar and .jad files on your devices file system. On my Symbian OS based Nokia smartphone the installed J2ME apps reside in a subfolder of either “C:/System/MIDlets” (if installed to phone memory) or “E:/System/MIDlets” (if installed to memory card). Navigate to this location and copy the .jar and .jad files to your Desktop PC, e.g. via Bluetooth or USB cable (note: you may need to use FExplorer, a pimped file explorer, to access these locations and copy the files).
4. Once you have the .jar and .jad files on the desktop, use the o2 WAP Flat Patcher to patch the files.
5. Copy the patched files back to the device, but DO NOT overwrite the files in “E:/System/MIDlets”. Just save them to a convenient location, e.g. “E:/myapps/”. Then use the devices native file manger to navigate to “E:/maypps/” and click the patched .jad file. This will trigger the installation of the patched Google Maps Mobile (note: this won’t work with FExplorer, as FExplorer v1.15 does not recognize .jad files). If you already installed the unpatched application (see step 2), you don’t need to uninstall first — you can safely overwrite/replace the existing version.

o2 WAP Flat Patcher – version 0.1

The o2 WAP Flat Patcher is a Java program which “patches” J2ME applications for the o2 WAP flatrate. What it actually does is adding the required User-Agent and X-WAP-Profile header (see previous posts) to the application. You don’t need the application’s sourcecode, and it doesn’t matter whether the J2ME app has been obfuscated or not – the WAP Flat Patcher takes care of the magic. It uses the bytecode engineering technique I described previously.

In order to run it, you need to have Java 1.4 or higher and Sun’s Java Wireless Toolkit installed.

Specify the Java and WTK directory, then pick your J2ME application (preferably the .jad file, but you can specify the .jar file also if there is no .jad) and hit the “Start” button. The WAP Flat Patcher will then do the ‘magic’ and the J2ME app should work with the o2 WAP Flat afterwards. I would be glad to hear some feedback if it worked for you.

Either get the sources from Google code and build it yourself, or download the binary release as an executable jar.

It should fix any J2ME application that communicates via HTTP. Here’s a list of applications that have I have successfully tested with:

• Google Maps Mobile
• alltunes.mobile (Java Version)

UPDATE: more “patchable” applications reported by users:

• mobber
• Colibry
• Papla (HTTP Version)
• Opera Mini

How To Make J2ME Apps Work for the WAP Flat

Because I am a big fan of networked J2ME applications, such as Google Maps Mobile, I want to use them with my WAP flatrate. The downside is that the WAP flat requires some special HTTP headers to be set, otherwise the HTTP requests get blocked by their gateway – and most of the J2ME apps don’t have these headers.

So what can you do?

If the application is open source, fine. Go ahead, add the headers to the sourcecode and recompile. With closed source applications, e.g. Google Maps Mobile, it gets a little tricky. Here are the basic steps you need to do:

1. download j2me app (.jar + .jad)
2. extract class files from .jar file
3. decompile (*)
4. search decompiled classes for networking code
5. add special http headers to networking code
6. recompile changed classes
7. preverify changed classes
8. update .jar file with changed classes
9. update .jad file if necessary

(*) note: obfuscation and preverification of class files makes it hard to decompile the j2me app with a decompiler such as JAD Decompiler (http://www.kpdus.com/jad.html). It results in decompilation errors and thus you can not recompile the code, as the sources are full of errors.

Because the standard decompile/change/recompile procedure does not work if decompilation fails, the only way to add the required HTTP headers is to modify the application’s bytecode directly without decompiling the class files. For this purpose you could use the javassist bytecode engineering API (http://www.csg.is.titech.ac.jp/~chiba/javassist/):

if (m.getClassName().equals(“javax.microedition.io.Connector”) && m.getMethodName().equals(“open”)) { m.replace(“{“ + “$_ = $proceed($$);” + “$_.setRequestProperty(\”User-Agent\”,\”Profile/MIDP-2.0 Configuration/CLDC-1.0\”);” + “$_.setRequestProperty(\”X-WAP-Profile\”,\”foo\”);” + “}”); }

powered by Java2html

The snippet above sets the User-Agent and X-WAP-Profile header directly after each call to Connector.open(). “$_ = $proceed($$)” inserts the original call to Connector.open(), with “$_” being the returned value (an object of type HttpConnection in this case) and “$$” being the parameters (the URL of the server in this case). After the connection has been opened, we use the returned HttpConnection object (“$_”) to set the User-Agent and X-WAP-Profile headers. See the complete source code here.

For more information about the javassist library you might want to check out their javassist tutorial or this article from IBM developerworks.

o2 WAP Flat – Required HTTP Headers

As I’ve already posted in the o2 WAP Flat Basics, you can use any HTTP(S) services — as long as your application sends some special HTTP headers. Most J2ME application don’t, thus they don’t work with the WAP flat. However, here’s what you need to consider if want your application to work with the WAP flat:

HTTP header requirements:
According to their terms and conditions you may only download contents originally designed to be displayed on a WAP browser. They try to emforce this by filtering the requests based on the User-Agent and Profile HTTP headers. For example, the headersof a real-world Nokia phone’s browser will pass the proxy:

• User-Agent: Nokia6600/1.0 (4.03.24) SymbianOS/6.1 Series60/2.0 Profile/MIDP-2.0 Configuration/CLDC-1.0
• X-WAP-Profile: nds.nokia.com/uaprof/N6600r100.xml

The generic User-Agent header of a J2ME apps will pass the gateway too, but you have to add a Profile or X-WAP-Profile (either one works, presence is sufficient) header:

• User-Agent: Profile/MIDP-2.0 Configuration/CLDC-1.1
• Profile: foo

Desktop browsers are usually blocked because a) of a filtered User-Agent and b) missing Profile / X-WAP-Profile header. I have not said would not be possible to change these headers…

More resources:
For more details about the o2 WAP Flat and which mobile browsers / applications are supported see the FAQ on telefon-treff.de or Andi’s WAP Flat FAQ (sorry, german only). Stay tuned for an upcoming post on how to modify J2ME apps to make them work with the o2 WAP flat!

o2 WAP Flat Basics

Mobile operator o2 Germany offers a WAP flatrate (“Surf & E-Mail-Pack“) for your mobile phone at a cost of 5€/month. Despite the name, not only WAP traffic but also HTTP is allowed to pass their gateway. It is not ultra-fast, but hey, it gives you everywhere access to the net (as long as it is WAP or HTTP(S)) along with a real flatrate for a reasonable price! Although nothing new (it exists since 2004 afaik), it deserves a quick introduction. Enough said, here are the details:

Quick facts:
– Supported protocols: HTTP, HTTPS, WTP, WSP
– Speed: GPRS 56kbps, UMTS (limited to) 64kbps
– Unlimited traffic for 5€/month
– max. filesize for downloads: 5MB

Configuration:
– Bearer: packet data
– Access Point (APN): wap.viaginterkom.de
– WAP 2.0 Proxy (HTTP): 195.182.114.52:8080
– WAP 2.0 Proxy (HTTPS): 195.182.114.52:8080
– WAP 1.x Proxy (WTP): 195.182.114.52:9201
– WAP 1.x Proxy (WSP): 195.182.114.52:9203
– No username/password authentication (leave empty)

If you want to do me a favor, please click the banner on the right before ordering 🙂