Re: hidapi: does not retrieve serial number of device on macos x

[Folkert v. H. <fo...@va...>]

>> I ported clewarecontrol to hidapi and all runs fine on linux.
>> On macos x, though, it doesn't show the serial number. This is rather
>> essential as it is needed to distinguish what device to control when you
>> have multiple connected.
>> The hidtest program included in hidapi doesn't show the serial either:
>
>> The serial number ought to be 900705 (decimal) or DBE61 (hex).
>
> It's worth noting that the serial number is a string descriptor,
> containing a Unicode string, UTF-16 encoded. Sticking random bytes in it
> may be causing the UTF-16 parser in the Apple kernel/libraries to bail
> somewhere. That's my first guess since it seems to work for others.

The code of the (original) cleware c++ library does:

                                        int strInc = (s[1] == 0) ? 2 : 1 ;
                                        for ( ; *s ; s+=strInc) {
 // unicode byte 2 == 0
                                                if (*s >= '0' && *s <= '9')
                                                        SerNum =
SerNum * 16 + *s - '0' ;
                                                else if (*s >= 'A' && *s <= 'F')
                                                        SerNum =
SerNum * 16 + *s - 'A' + 10 ;
                                                }

So I think that some use plain ascii while others may use UTF-16 (with
high byte set to 0x00).