The Windows HID api always expects to receive a fixed size buffer
(corresponding to the largest report supported by the device). Therefore
the hidapi library internally pads the buffer with zeros to the expected
size, but apparently it also returns the size of the padded buffer! As a
workaround the number of bytes is limited to the actual size.
The hidapi read and write functions return a negative value if an error
occurs. Those negative values should not be returned to the caller as
the actual number of bytes (or used in the logging). The value is reset
to zero instead.
The hidapi library requires that the first byte contains the report ID.
For devices which support only a single report, the report ID byte
should be zero. The remaining bytes contain the actual report data.
Now, when hidapi uses libusb internally, it strips the zero report ID
byte again before passing the data to libusb. Thus in order to remain
compatible with the hidapi based implementation, our libusb based
implementation should do the same.
On Mac OS X, libusb doesn't work for USB HID devices. We can use the
hidapi library instead. Although the hidapi library supports Linux and
Windows too, we keep using libusb there to avoid the extra dependency.
