[pyusb-users] [PATCH] Limit get_string() length to string descriptor length

[Tormod V. <lis...@gm...>]

From: Tormod Volden <deb...@gm...>

Use the length as reported by the first byte of the descriptor.
Otherwise (at least for some backend/kernel combinations) the buffer
length provided by the user would be used instead, and NUL characters
would be appended to the returned string.

This also makes the legacy getString() function compatible with
pyusb 0.4.

Signed-off-by: Tormod Volden <deb...@gm...>
---

Hi,
Another patch, originally to fix legacy compatibility issues but
probably makes sense for "native" use as well.

It could be discussed whether get_descriptor() should be fixed instead
to only return the number of bytes defined by the descriptor itself, in
which case this patch would not be needed. That would be more intrusive
though.

On the other hand it seems that this bug does not appear on all my
systems although I am pretty sure pyusb and libusb versions are the
same, so I wonder if the different linux kernel versions make up for
the difference. In any case, this patch should not hurt.

Best regards,
Tormod


 usb/util.py |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/usb/util.py b/usb/util.py
index 1f8cee3..bb8fc65 100644
--- a/usb/util.py
+++ b/usb/util.py
@@ -224,7 +224,7 @@ def get_string(dev, length, index, langid = None):
     dev is the Device object to which the request will be
     sent to.
 
-    length is the length of string in number of characters.
+    length is the maximum length of the 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
@@ -257,4 +257,4 @@ def get_string(dev, length, index, langid = None):
                 index,
                 langid
             )
-    return buf[2:].tostring().decode('utf-16-le')
+    return buf[2:buf[0]].tostring().decode('utf-16-le')
-- 
1.7.0.4