window.get_wm_name() is empty but not in window.get_property() equivalent #212

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1. benoit-pierre

   added

   bug

   on Dec 2, 2021
2. benoit-pierre commented on Dec 2, 2021

   

   benoit-pierre

   on Dec 2, 2021

   Member

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   I can reproduce with Chromium.

   From looking at XGetWindowProperty's documentation:

   If the specified property exists but its type does not match the specified
   type, XGetWindowProperty returns the actual property type to actual_type_return,
   the actual property format (never zero) to actual_format_return, and the property
   length in bytes (even if the actual_format_return is 16 or 32) to bytes_after_return.
   It also ignores the delete argument. The nitems_return argument is empty.

   …it looks like our implementation of Window.get_full_property is wrong and should
   call get_property again with the correct type if the previous attempt returned
   a different type than asked for and bytes_after is not zero:

    Xlib/xobject/drawable.py | 22 +++++++++++++---------
    1 file changed, 13 insertions(+), 9 deletions(-)
   
   diff --git i/Xlib/xobject/drawable.py w/Xlib/xobject/drawable.py
   index c36a973..f79a7dc 100644
   --- i/Xlib/xobject/drawable.py
   +++ w/Xlib/xobject/drawable.py
   @@ -470,17 +470,21 @@ def get_property(self, property, property_type, offset, length, delete = 0):
    
        def get_full_property(self, property, property_type, sizehint = 10):
            prop = self.get_property(property, property_type, 0, sizehint)
   -        if prop:
   -            val = prop.value
   -            if prop.bytes_after:
   -                prop = self.get_property(property, property_type, sizehint,
   -                                         prop.bytes_after // 4 + 1)
   -                val = val + prop.value
   -
   -            prop.value = val
   +        if not prop:
   +            return None
   +        if not prop.bytes_after:
                return prop
   +        val = prop.value
   +        if prop.property_type == property_type:
   +            offset = sizehint
   +            sizehint = prop.bytes_after // 4 + 1
            else:
   -            return None
   +            assert not val
   +            property_type = prop.property_type
   +            offset = 0
   +        prop = self.get_property(property, property_type, offset, sizehint)
   +        prop.value = val + prop.value
   +        return prop
    
        def get_full_text_property(self, property, property_type=X.AnyPropertyType, sizehint = 10):
            prop = self.get_full_property(property, property_type,

   👍React with 👍3Reacted by Heraldo, Jessica and Andre Vallestero
3. MestreLion commented on Jan 23, 2023

   

   MestreLion

   on Jan 23, 2023

   More actions

   If the property_type parameter in Python is meant as a sort of "filter" to specify what the returned property should be, then I believe repeating the request with a different type would be the wrong approach to the problem.

   A better fix, IMHO, is to drop the Xatom.STRING argument when calling get_full_property in Window.get_wm_name() (and similar methods such as get_wm_icon_name). I wonder why it is using it instead of the default X.AnyPropertyType.
4. MestreLion commented on Jan 23, 2023

   

   MestreLion

   on Jan 23, 2023

   Last edited by MestreLion

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   get_full_property() should not change a caller's argument: in case of an inconsistency between the requested and the obtained type it should either raise an exception or just return the obtained property as-is (bytes_left included) and let the caller handle the inconsistency. Otherwise, what's the point of the property_type parameter?
5. MestreLion commented on Jan 23, 2023

   

   MestreLion

   on Jan 23, 2023

   More actions

   In other words: the meaning (and usefulness) of property_type in both Window.get_property() and Window.get_full_property() is debatable (IMHO both should be hard-coded to X.AnyPropertyType (= 0)), but in this case the bug is in Windows.get_wm_name() and friends for specifying the wrong type (or for specifying a type at all).