Function get_device_id

backend/usb-libusb.c:1073–1134

 */

static int				/* O - 0 on success, -1 on error */
get_device_id(usb_printer_t *printer,	/* I - Printer */
              char          *buffer,	/* I - String buffer */
              size_t        bufsize)	/* I - Number of bytes in buffer */
{
  size_t	length;				/* Length of device ID */


  if (libusb_control_transfer(printer->handle,
			      LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_ENDPOINT_IN |
			      LIBUSB_RECIPIENT_INTERFACE,
			      0, printer->conf,
			      (printer->iface << 8) | printer->altset,
			      (unsigned char *)buffer, bufsize, 5000) < 0)
  {
    *buffer = '\0';
    return (-1);
  }

 /*
  * Extract the length of the device ID string from the first two
  * bytes.  The 1284 spec says the length is stored MSB first...
  */

  length = (((unsigned)buffer[0] & 255) << 8) | ((unsigned)buffer[1] & 255);

 /*
  * Check to see if the length is larger than our buffer or less than 14 bytes
  * (the minimum valid device ID is "MFG:x;MDL:y;" with 2 bytes for the length).
  *
  * If the length is out-of-range, assume that the vendor incorrectly
  * implemented the 1284 spec and re-read the length as LSB first,..
  */

  if (length > bufsize || length < 14)
    length = (((unsigned)buffer[1] & 255) << 8) | ((unsigned)buffer[0] & 255);

  if (length > bufsize)
    length = bufsize;

  if (length < 14)
  {
   /*
    * Invalid device ID, clear it!
    */

    *buffer = '\0';
    return (-1);
  }

  length -= 2;

 /*
  * Copy the device ID text to the beginning of the buffer and
  * nul-terminate.
  */

  memmove(buffer, buffer + 2, length);