This may be good to be indexed in the libusbx mailing list as well.
Whole thread:
http://libusb.6.n5.nabble.com/FreeBSD-libusb-missing-libusb-get-descriptor-td5689243.html
Regards,
Xiaofan
---------- Forwarded message ----------
From: Peter Stuge <pe...@stuge.se>
Date: Mon, May 7, 2012 at 10:47 PM
Subject: Re: FreeBSD libusb missing libusb_get_descriptor()
To: libusb-de...@lists.sourceforge.net
Xiaofan Chen wrote:
> > Maybe you want to import some of those checks
> > for the input parameters to this function.
>
> Thanks. Indeed the check may be good.
>
> Let's see Peter's view on this.
Mh, I actually don't think so. I'll explain:
> FreeBSD's implementation:
> 296 int
> 297 libusb_get_string_descriptor(libusb_device_handle *pdev,
> 298 uint8_t desc_index, uint16_t langid, unsigned char *data,
> 299 int length)
> 300 {
> 301 if (pdev == NULL || data == NULL || length < 1)
> 302 return (LIBUSB_ERROR_INVALID_PARAM);
Checking pdev and data is consistently not done in libusb - if you
pass garbage then you get a crash. libusb wants to be thin.
The USB 2.0 spec doesn't say that wLength=0 is invalid, so I think we
should let that go down to the device if for whatever reason someone
requests it.
> 304 if (length > 65535)
> 305 length = 65535;
libusb-1.0 casts to uint16_t, which also truncates the value. The
real error is that the API doesn't use uint16_t for the length, but
that can't be fixed until next API.
> 307 /* put some default data into the destination buffer */
> 308 data[0] = 0;
I'd rather not do this either, I don't think it's libusb's business
to mess with the data, and 0 for descriptor length doesn't make so
much sense.. The return value needs to be checked, and this is just
one special case of the sync API, where the actual length is never
available anyway. :\
> 1369 int LIBUSB_CALL
> libusb_get_string_descriptor_ascii(libusb_device_handle *dev,
> 1370 uint8_t desc_index, unsigned char *data, int length);
This function could very well need some love, and actually it would
be nice to do something more intelligent than only support ASCII
contents, such as libusb_get_string_descriptor_utf8(), but it could
also be nice to offer an API which ties nicely into some or many
different character set conversion libraries..
//Peter
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