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  1. JDK
  2. JDK-6961123

setWMClass fails to null-terminate WM_CLASS string

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    • Subcomponent:
    • Resolved In Build:
      b105
    • CPU:
      generic
    • OS:
      solaris

      Backports

        Description

        While debugging a port of the classic xwininfo command from the libX11 to libxcb
        API's, I noted that the class info shown for some java windows contained bogus
        extra characters on the end.

        For instance, while the Xlib version of xwinfo showed:
            0x5400010 "FocusProxy": ("Focus-Proxy-Window" "FocusProxy") 1x1+-1+-1 +1313+1

        the xcb version showed:
            0x5400010 "FocusProxy": ("Focus-Proxy-Window" "FocusProxyFra1") 1x1+-1+-1 +1313+1

        Digging into this, I discovered that Xlib was hiding a bug in Java. Xlib always
        adds a trailing '\0' byte to property strings, while xcb does not. This exposes
        that Java is not including the trailing '\0' when setting the WM_CLASS string - from
        XBaseWindow.java:

            void setWMClass(String[] cl) {
                if (cl.length != 2) {
                    throw new IllegalArgumentException("WM_CLASS_NAME consists of exactly two strings");
                }
                XToolkit.awtLock();
                try {
                    XAtom xa = XAtom.get(XAtom.XA_WM_CLASS);
                    xa.setProperty8(getWindow(), cl[0] + '\0' + cl[1]);
                } finally {
                    XToolkit.awtUnlock();
                }
            }

        But the ICCCM specifies that unlike most window properties, which are not null
        terminated, the WM_CLASS is a special case that must be null terminated:

            Note that WM_CLASS strings are null-terminated and, thus, differ from the
            general conventions that STRING properties are null-separated.
            This inconsistency is necessary for backwards compatibility.

        (BTW, the error message for the IllegalArgumentException seems to have an extra
         "_NAME" on the end of the property name.)

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                • Assignee:
                  omajid Omair Majid
                  Reporter:
                  alanc Alan Coopersmith
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