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?
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
