[jira] Commented: (MODPYTHON-98) wrong handler supplied to req.add_handler() generates error

["Graham Dumpleton (JIRA)" <ji...@apache.org>]

    [ http://issues.apache.org/jira/browse/MODPYTHON-98?page=comments#action_12359850 ] 

Graham Dumpleton commented on MODPYTHON-98:
-------------------------------------------

A related note against this issue with req.add_handler(), if you errornously do something like:

  def accesshandler(req):
    apache.log_error("accesshandler")
    req.add_handler("PythonHandler","")
    req.add_handler("PythonHandler","example::handler_2")
    return apache.OK

Ie., register the handler as an empty string, it doesn't complain, and further it stops any latter handlers being executed at all.

As far as I can tell at the moment this is because of a check in the HandlerDispatch member function of the Callback class in mod_python.apache. Ie.,

            while hlist.handler:

Normally hlist.handler would be Python None object for the end of the list and that is why it would stop in that case. Where you register an empty string it has the same effect of stopping iteration as it doesn't explicitly qualify the check as being for None object.

If one wanted to ensure that errors occurred whenever possible to highlight problems, it may be better to write the check as:

           while hlist.handler is not None:

That way if the string is set to empty by mistake, your would get an exception later on of:

  Mod_python error: "PythonHandler "

  Traceback (most recent call last):

    File "/System/Library/Frameworks/Python.framework/Versions/2.3/lib/python2.3/site-packages/mod_python/apache.py", line 287, in HandlerDispatch
      log=debug)

    File "/System/Library/Frameworks/Python.framework/Versions/2.3/lib/python2.3/site-packages/mod_python/apache.py", line 468, in import_module
      f, p, d = imp.find_module(parts[i], path)

  ImportError: No module named

You would have to realise the problem was the empty module name it tried to load, but at least it generates an exception rather than silently ignoring the remainder of the registered handlers.

> wrong handler supplied to req.add_handler() generates error
> -----------------------------------------------------------
>
>          Key: MODPYTHON-98
>          URL: http://issues.apache.org/jira/browse/MODPYTHON-98
>      Project: mod_python
>         Type: Bug
>   Components: core
>     Versions: 3.2, 3.1.4
>     Reporter: Graham Dumpleton

>
> The documentation for req.add_handler() states:
>   Note: There is no checking being done on the validity of the handler name. If you pass this function an invalid handler it will simply be ignored.
> In other words, get the name of the handler wrong and it is supposed to just ignore it. This is not actually the case, instead it will generate an exception when it goes to process the handler:
>   Mod_python error: "PythonHandler example::handler_3"
>   Traceback (most recent call last):
>     File "/System/Library/Frameworks/Python.framework/Versions/2.3/lib/python2.3/site-packages/mod_python/apache.py", line 291, in HandlerDispatch
>       arg=req, silent=hlist.silent)
>     File "/System/Library/Frameworks/Python.framework/Versions/2.3/lib/python2.3/site-packages/mod_python/apache.py", line 538, in resolve_object
>       raise AttributeError, s
>   AttributeError: module '/Users/grahamd/Sites/add_handler/example.py' contains no 'handler_3'
> This can be seen with .htaccess file of:
>   SetHandler mod_python
>   PythonAccessHandler example
>   PythonHandler example::handler_1
>   PythonDebug On
> and example.py file containing:
>   from mod_python import apache
>   def accesshandler(req):
>     apache.log_error("accesshandler")
>     req.add_handler("PythonHandler","example::handler_3")
>     return apache.OK
>   def handler_1(req):
>     apache.log_error("handler_1")
>     req.content_type = 'text/plain'
>     req.write("HELLO")
>     return apache.OK
>   def handler_2(req):
>     apache.log_error("handler_2")
>     return apache.OK
> Either the documentation is wrong and an exception is desired, or more likely this is an extension of the prior problem with hlist.silent as described as being a problem in other ways in MODPYTHON-46.
> In that case the logic of SILENT/NOTSILENT was the wrong way around and it was fixed by reversing the definitions of the two. In doing this though, it didn't cover cases where a "silent" flag is passed to hlist_new() and hlist_append() in the req_add_handler() function of requestobject.c.
> Specfically, there are calls to hlist_new() and hlist_append() in that function:
>         hlist_append(self->request_rec->pool, self->hlo->head,
>                      handler, dir, 0);
>             hle = hlist_new(self->request_rec->pool, handler, dir, 0);
>             hlist_append(self->request_rec->pool, hle, handler, dir, 0);
> These should be written as:
>         hlist_append(self->request_rec->pool, self->hlo->head,
>                      handler, dir, SILENT);
>             hle = hlist_new(self->request_rec->pool, handler, dir, SILENT);
>             hlist_append(self->request_rec->pool, hle, handler, dir, SILENT);
> If this change were made, the code would then behaves conformant with the documentation as far as being silent, however it highlights a further issue.
> This further issue is that although it is silent when the handler name is wrong, this results in apache.DECLINED being returned for the handler that couldn't be found. Because apache.DECLINED is returned, Apache will try and interpret the URL again and if possible serve up a static file etc.
> For the above example code this then means that if "example.py" was used in the URL, the browser gets back a response of:
>   HELLOfrom mod_python import apache
>   def accesshandler(req):
>     apache.log_error("accesshandler")
>     req.add_handler("PythonHandler","example::handler_3")
>     return apache.OK
>   def handler_1(req):
>     apache.log_error("handler_1")
>     req.content_type = 'text/plain'
>     req.write("HELLO")
>     return apache.OK
>   def handler_2(req):
>     apache.log_error("handler_2")
>     return apache.OK
> That is, the content as returned by handler_1(), followed by the contents of the example.py file.
> If instead the URL wasn't 'example.py' but say 'other.py' with that not existing, get back:
>   HELLO
>   OK
>   The requested URL /~grahamd/add_handler/foo.py was not found on this server.
>   Apache/2.0.51 (Unix) mod_python/3.2.5b Python/2.3 Server at localhost Port 8080
> In some ways, this behaviour suggests that the behaviour whereby it raised an exception was probably a better way of handling the situtation anyway. Thus, maybe the documentation should instead be changed and the code left as is, or at least the 0 arguments changed to be NOTSLIENT to make it more obvious what it is doing.
> The other option is to change the code to use SILENT, but then document the strange things that can result if the specified handler doesn't exist.
> Comments??????

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