While programming Bluetooth data transmission routines I've come across an encoding issue at Symbian. The task was to send and receive Unicode strings encoded in UTF-16. The data was moved by RSocket class.

The thing is, the RSocket's read and write methods are taking the 8 bit descriptors only (representing the binary data), so we need to convert the 8 bit descriptors to 16 bit and vice versa. 
For example, we need to receive some UTF-16 string in Russian language from the server and display it on screen.

Some documents here suggest several solutions on converting descriptors, but they don't work as needed. Let me explain why.

The two common methods of conversion are:

1. To use Copy() method of first the descriptor to copy contents of the second one.

Example:


As a result, the contents of buf8 descriptor would not be simply copied to buf16, but each character would be expanded to 16 bits.
So the string “Hello” would become something like “_H_E_L_L_O” after expanding.




Image 1 – Example of how the Copy() method works, and what we actually need.

On the contrary, when converting the 16 bit descriptor to an 8 bit descriptor, the contents of the first would be collapsed. 

That is a behavior of Copy() method.

2. The second method is to use a CnvUtfConverter class provided in Symbian.

Example:


This method will convert between the Unicode and UTF-8. That is again is not what I needed. What I need is the conversion between the descriptor classes themselves but not transforming their contents, that should stay without any change.

Solving

So to read the Unicode string presented in binary format from socket and display it on screen, we need to convert the descriptor's body (8 bit descriptor to 16 bit descriptor) but not the descriptor's contents.

Here is a method on how can it be done.
To pass the descriptor's contents from the descriptor of one type to another, we have to copy contents somehow. I chose the memcpy() function. If you find a better (or safer) way, please submit it here. 
Example:

Copy the contents of 8 bit descriptor to the 16 bit one.
(without memory allocation routines)




This works smoothly for S60 3rd FP1, both emulator and Nokia E90 device.

I wrote the CBinaryConverter class that has two methods, doing these operations. It is attached to this post.

Example of using CBinaryConverter class:





Screenshot of the application, that controls Juke Box holding songs in English and Russian languages over Bluetooth:




Download the source code

Download zip package:
BinaryConverter_class.zip

Or view directly:

 

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Cheers
Konstantine