BadDataError when trying to rename a window

[Nathanaël]

I would like to rename a window, but I can't. This is an example with getActiveWindow().

#!/usr/bin/python

from ewmh import EWMH
ewmh = EWMH()

# get the active window
win = ewmh.getActiveWindow()

title = "newtitle"
print 'data length:', len(title)

# set the name
ewmh.setWmName(win, title)

# flush request
ewmh.display.flush()

Logs:

<class 'Xlib.protocol.request.QueryExtension'>
data length: 8
Traceback (most recent call last):
  File "test_2.py", line 15, in <module>
    ewmh.setWmName(win, title)
  File "/usr/local/lib/python2.7/dist-packages/ewmh/ewmh.py", line 136, in setWmName
    self._setProperty('_NET_WM_NAME', name, win)
  File "/usr/local/lib/python2.7/dist-packages/ewmh/ewmh.py", line 321, in _setProperty
    ev = protocol.event.ClientMessage(window=win, client_type=self.display.get_atom(_type), data=(dataSize, data))
  File "/usr/lib/python2.7/dist-packages/Xlib/protocol/rq.py", line 1531, in __init__
    self._binary = self._fields.to_binary(*(), **keys)
  File "/usr/lib/python2.7/dist-packages/Xlib/protocol/rq.py", line 1138, in to_binary
    return self.to_binary(*varargs, **keys)
  File "<string>", line 2, in to_binary
  File "/usr/lib/python2.7/dist-packages/Xlib/protocol/rq.py", line 704, in pack_value
    % (value, ))
Xlib.protocol.rq.BadDataError: Wrong data length for FixedPropertyData: (8, 'newtitle')

[Victor Adam]

This is easily fixed by padding the desired title to the required length:

title += "\0" * (20 - len(title))

Maybe setWmName could be changed to do this automatically:

diff --git a/ewmh/ewmh.py b/ewmh/ewmh.py
index 1302ae6..da149ef 100644
--- a/ewmh/ewmh.py
+++ b/ewmh/ewmh.py
@@ -133,6 +133,7 @@ class EWMH:

                :param win: the window object
                :param name: desired name"""
+               name += '\0' * (20 - len(name))
                self._setProperty('_NET_WM_NAME', name, win)

        def setWmVisibleName(self, win, name):

[Nathanaël]

Ok, thanks, there is no error with your fix... But it doesn't rename the window.

I don't really understand why the length title needs to be fixed to 20 chars.

setWmName is not intended to rename windows.

According to pyewmh sources, setWmName() refers to the _NET_WM_NAME proterty, which is, according to the EWMH specs, should rename a window:

The Client SHOULD set this to the title of the window in UTF-8 encoding. If set, the Window Manager should use this in preference to WM_NAME.

[Victor Adam]

See X11’s documentation, D.5. The ClientMessage event's format:

char data.b[20] (read/write DATA : MAX 20 byte)
If the data is smaller than 20 byte, all data other than available data must be 0.

Python’s Xlib implementation accordingly sets ClientMessage to use a fixed data size of 20:

class ClientMessage(rq.Event):
# ...
                         rq.FixedPropertyData('data', 20)