[Zope] [ANSWER] 500 error with IE on login

[Gregory Dudek]

This presents a longwindeded solution to a problem I posted here. I
think I may not be unique in having this problem.

Problem: A while back I posted a question here regarding a problem I was
having with login screens.  Specifically, users using
MSIE on Windows were getting a "Server Error" page 
saying "The page cannot be displayed" (error 500)
instead of my login page. The login folder product I was using
was the Generic User folder product (GUF)
but I am almost certain the problem afflicts
other user folder products like Extensible User Folder.
I am running zope 2.4

It turns out the problem is unique to MSIE (Internet Explorer)
on the windows platform.  As far as I know it does not occur with
any other browser including mozilla, netscape (even on Windows)
or even the Mac version of MSIE
(Thanks due to complaw@hal-pc.org from this list in helping run tests).
It seems to happen with version 5.5 and version 6.0 of MSIE but not on 
every machine -- differences might be a subversion/patch issue.

Explanation (mainly due to Oliver Bleutgen via this list):
the 500 error is generated by zope and appears in the page header.
It's part of the mechanism for catching an access violation that
leads to a request for login.  The problem is that when MSIE sees this
error it does not display the rest the login page that follows, but
substitutes it's own internally generated page instead.

Solutions / Work-around: There are 2 solutions, one based on users
changing their preferences the second a code-hack to zope itself.

First the easy but sub-optimal work-around:
If the user turns off "friendly" error messages in their browser the
intercept by internally generated pages can be avoided.  Of course, forcing
the user to do this is ugly.

For a page
I made giving detailed user-level instructions, see the following:
  http://abatonix.dyn.dhs.org/mudcritters/windowsLoginProblem

A once-only pointer to this message is generated by the following
DTML on my home page ( http://www.mudcritters.com ):

<dtml-if "(AUTHENTICATED_USER.getUserName()=='Anonymous User')">
       <dtml-if "(_.string.find(REQUEST.get('HTTP_USER_AGENT'),'Windows')>=0)
              and (_.string.find(REQUEST.get('HTTP_USER_AGENT'),'MSIE')>=0)">
    <center>
    <dtml-if "REQUEST.has_key('MSIEwarning')">
        <font  color=#FF7f30>
    <dtml-else>
        <font size=-1>(Once-only obnoxious mega-sized message.)</font><br>
        <font size=+5 color="ff0000">
        <dtml-call "RESPONSE.setCookie('MSIEwarning', AUTHENTICATED_USER, 
                        expires=(ZopeTime() + 365).rfc822(),path='/' )"> 
    </dtml-if>
    WARNING:   As a user of Internet Explorer on Windows, to 
    login properly <a href="windowsLoginProblem"> click here.</font>
    </a>
    </center>
</dtml-if><dtml-else></dtml-if>


Alternate solution: I modified zope not to give a 500 
error as a default in such cases.  Then things work fine with all
browsers and nobody has to muck with any preferences.
I actually think the 500 error in inappropriate in this case so
I removed it.  The code hack may have other
side-effects although since most browsers ignore the 500 error I
think it should be OK and it runs fine for me.

  In line 240 of lib/python/HTTPResponse.py (in the
zope directory) change the lines:
        if type(status) is types.StringType:
            status=lower(status)
        if status_codes.has_key(status): status=status_codes[status]
        else: status = 500
        self.status=status
to read:
        if type(status) is types.StringType:
            status=lower(status)
        if status_codes.has_key(status): status=status_codes[status]
        else: status = 200
        # GD changed above from 500 as a hack
        self.status=status

Sorry this is so long, but I wanted to save the next poor soul
who gets bitten by this.

Greg Dudek
http://www.cim.mcgill.ca/~dudek