2015-08-08 22:18 GMT-03:00 Paul Cornelius <paul.cornel...@vuemetrix.com>: > OK I see. > > I thought I had the latest release (1.0.0.a2), which I got from > sourceforge. I got to there by following the link on > http://walac.github.io/pyusb/. Also I searched exhaustively for anyone > reporting this bug before diving into the pyusb internals. What did I do > wrong? >
The point is that this change was not released yet. When you find a bug, it is better to check against git HEAD to see if it happens in the latest code. > Thanks, > Paul Cornelius > > On 8/8/2015 12:00 PM, Wander Lairson Costa wrote: >> Hi, >> >> Notice the code the get_string has changed: >> https://github.com/walac/pyusb/blob/master/usb/util.py#L295-L340 >> >> 2015-08-08 1:14 GMT-03:00 Paul Cornelius <paul.cornel...@vuemetrix.com>: >>> I found a bug in usb.util.py in the function get_string. This function was >>> failing with an "Overflow" error on my Windows 8.1 machine, using Python 3.3 >>> and libusb-1.0. >>> >>> If this function is called with the default value for langid (None), it >>> first makes a call to get_descriptor to obtain a list of languages supported >>> by the device. This second parameter of this function call is the size of >>> the reply buffer, which was equal to 1024. But a comment in the libusb-1.0 >>> source (descriptor.c, function libusb_get_string_descriptor_ascii) reads: /* >>> Some devices choke on size > 255 */. >>> >>> And it seems to be true. When I changed the get_descriptor function call to >>> reduce the buffer size parameter to 255 the error disappeared. I also >>> thought it would be good to limit the size of any buffer passed to >>> get_string. My modified function now reads as follows: >>> >>> def get_string(dev, length, index, langid = None): >>> r"""Retrieve a string descriptor from the device. >>> >>> dev is the Device object to which the request will be >>> sent to. >>> >>> length is the length of string in number of characters. >>> >>> index is the string descriptor index and langid is the Language >>> ID of the descriptor. If langid is omitted, the string descriptor >>> of the first Language ID will be returned. >>> >>> The return value is the unicode string present in the descriptor. >>> """ >>> from usb.control import get_descriptor >>> if langid is None: >>> # Asking for the zero'th index is special - it returns a string >>> # descriptor that contains all the language IDs supported by the >>> device. >>> # Typically there aren't many - often only one. The language IDs are 16 >>> # bit numbers, and they start at the third byte in the descriptor. See >>> # USB 2.0 specification section 9.6.7 for more information. >>> # >>> # Note from libusb 1.0 sources (descriptor.c) >>> buf = get_descriptor( >>> dev, >>> 255, >>> DESC_TYPE_STRING, >>> 0 >>> ) >>> assert len(buf) >= 4 >>> langid = buf[2] | (buf[3] << 8) >>> >>> lenstr = length * 2 + 2 >>> if lenstr > 255: >>> raise ValueError("String buffer length too long") >>> buf = get_descriptor( >>> dev, >>> length * 2 + 2, # string is utf16 + 2 bytes of the >>> descriptor >>> DESC_TYPE_STRING, >>> index, >>> langid >>> ) >>> return buf[2:].tostring().decode('utf-16-le') >>> >>> Paul Cornelius >>> >>> ------------------------------------------------------------------------------ >>> >>> _______________________________________________ >>> pyusb-users mailing list >>> pyusb-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/pyusb-users >>> >> >> > > > ------------------------------------------------------------------------------ > _______________________________________________ > pyusb-users mailing list > pyusb-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/pyusb-users -- Best Regards, Wander Lairson Costa ------------------------------------------------------------------------------ _______________________________________________ pyusb-users mailing list pyusb-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/pyusb-users
