Thursday, August 31, 2006

MobileServer preview

If you have been reading these posts lately you know that I am working on getting a peer to peer scenario to work with my remote data access tools. This will allow two PDAs to synchronize data just by getting close to one another within the 32 feet required by Bluetooth.

Right now this is working over Wi-Fi and Bluetooth serial COM ports (no support for sockets in the Widcomm stack, alas).

The thing that has been missing from the picture is the server code. I started by providing a standalone native application to serve a TCP / IP sockets connection. Later I split the server feature and put it in a separate DLL. The latest change was to move all that code to the device server DLL (RemSqlCe.dll) and to expose an API for the sockets server. After adding the serial port server I started writing a very simple managed code class library for users to integrate in their own applications.

This class library allows the consuming application to create a server, configure, start, stop, query its status and dispose of it. The above picture shows an instance of the sample MobileServer application running two servers on an HP iPAQ 2210 serving two different desktop PCs, one via Wi-Fi and the other via a Bluetooth COM port.

Now I have to add Bluetooth server abilities to this little beast and this means supporting both the Microsoft stack and the popular Widcomm stack (that's why I'm using the 2210). The server will be able to expose its services (either COM or sockets) via enumeration in order to make ad-hoc device pairing easier.

I expect to release the device client very soon with some P2P samples ready to run.

Monday, August 21, 2006

SQL Mobile over Bluetooth

Well, not yet what you might expect but I just finished the first version of a serial communications Pipe. This allows you to connect to a Bluetooth-enabled device through a virtual COM port as I just did with my laptop (with Targus USB Bluetooth dongle and the standard Microsoft stack) and my iPAQ 2210 (a very reliable beast with the Broadcom stack).

Nothing automatic here - I just configured a serial link between the devices and wrote the serial code to glue them both. I am ashamed to say that this was not a swift experience because my years as a mobile developer led me to overlook some of the finer points of desktop development, namely overlapped IO. Yes, porting the device code to the desktop did not quite work as I expected. Nothing at all, really. After researching into the overlapped IO mechanism, it was quite easy to set up the internal threading and queueing to simulate a RAPI Pipe over a serial port.

Next steps? 1 - Port the client code to the mobile device so you can access another devices SQL CE / Mobile databases over a Bluetooth COM port. 2 - Add support for the Microsoft stack so a device will be able to identify which partners can serve SQL Mobile data and connect via sockets. 3 - Add support for the Broadcom stack. From what I have seen, there is no sockets support in the Broadcom stack. 4 - Why not infrared?

Friday, August 18, 2006

SQL Mobile Peer to Peer

My first P2P experience with SQL Mobile has just happened: using my iPAQ 2210 with a SanDisk SD Wi-Fi card was able to connect via a wireless network to my i-mate K-Jam, open a local SQL Mobile database and enumerate all tables.

This is especially cool because I am not using revolutionary new technology - I just adapted what I had been using in my products a long time ago. Let's see a little history.

When I first shipped Data Port Wizard almost two years ago, the device component DLL (RemSqlCe.dll) was only a RAPI streamed server. Soon I understood that I could adapt the same stream code and build more transports on top of it and the TCP/IP single-threaded server came about in almost no time. In its first incarnation the server resided in a separate device DLL file, but it was not a very pratical solution. The next release of DesktopSqlCe will have a new version of RemSqlCe.dll with the socket server code included as well as a CF (1.0 and 2.0) sample that shows how to use it. And this is what I used on the K-Jam for the server.

The client uses an adapted version of the desktop's dssce.dll and Primeworks.DesktopSqlCe.dll. (In a future version, these DLL files will change their names to better reflect what they do.) This is how I was able to quickly produce pwdclice.dll (dssce.dll device version) and the new Primeworks.Data.Client.dll (Primeworks.DesktopSqlCe.dll device version). I ported the code for both DLL files in about one day (cool, huh?).

Now, besides being able to open a local device connection I can also open a TCP/IP client connection to a server device. Et voilá: P2P! Shipping in September, but I'm open to send the early builds to anyone willing to test the code.

Three final thoughts:

Why should you want to have a local connection on your device? After all, that is why you make a reference to System.Data.SqlServerCe in your application, right? Well, can you connect to either SQL CE 2.0 and SQL Mobile with the same data provider using the same application code? And can you remotely connect to another device just by changing connection properties? Now you can!

And why not add socket server code to the LocSqlCe.dll, the RemSqlCe.dll desktop counterpart? This would be a very easy way to set up a client server scenario over the internet...

On the issue of pluggable data streams, why not a virtual COM port over Bluetooth as well? Can I sync my sdf with yours via Bluetooth?

Stay tuned!

Thursday, August 10, 2006

How do I know the database version of an sdf file?

Have you ever wondered how to detect the SQL engine version of an SDF file? Here is an answer.

Monday, August 07, 2006

DesktopSqlCe redistributables updated

The redistributable files of DesktopSqlCe (LocSqlCe.dll and RemSqlCe.dll) have been updated to version 1.46.1620. This code corrects a SQL command parameter length verification bug.