HandlerDispatch doesn't treat OK/DECLINED result properly for all phases.
-------------------------------------------------------------------------
Key: MODPYTHON-129
URL: http://issues.apache.org/jira/browse/MODPYTHON-129
Project: mod_python
Type: Bug
Components: core
Versions: 3.2
Reporter: Graham Dumpleton
Todays daily bug report, or is it? ;-)
The Python*Handler documentation says:
"""Multiple handlers can be specified on a single line, in which case they will
be called sequentially, from left to right. Same handler directives can be
specified multiple times as well, with the same result - all handlers listed
will be executed sequentially, from first to last. If any handler in the
sequence returns a value other than apache.OK, then execution of all subsequent
handlers is aborted."""
That is, no matter which phase is being processed, mod_python will stop
processing them if a value other than OK is returned.
Problem is that this isn't how Apache itself treats the result from handlers.
Apache actually implements two different ways for dealing with the result from
the handlers. Which is used depends on which processing phase is occuring. This
is all specified by the Apache magic macro code:
AP_IMPLEMENT_HOOK_RUN_FIRST(int,translate_name,
(request_rec *r), (r), DECLINED)
AP_IMPLEMENT_HOOK_RUN_FIRST(int,map_to_storage,
(request_rec *r), (r), DECLINED)
AP_IMPLEMENT_HOOK_RUN_FIRST(int,check_user_id,
(request_rec *r), (r), DECLINED)
AP_IMPLEMENT_HOOK_RUN_FIRST(int,auth_checker,
(request_rec *r), (r), DECLINED)
AP_IMPLEMENT_HOOK_RUN_ALL(int,access_checker,
(request_rec *r), (r), OK, DECLINED)
AP_IMPLEMENT_HOOK_RUN_FIRST(int,type_checker,
(request_rec *r), (r), DECLINED)
AP_IMPLEMENT_HOOK_RUN_ALL(int,fixups,
(request_rec *r), (r), OK, DECLINED)
What this gobblegook expands to are loops which will stop processing handlers
based on the result.
For the AP_IMPLEMENT_HOOK_RUN_ALL macro, all handlers in the phase will be run
unless one returns something other than OK or DECLINED. Returning OK means that
it did something and it worked okay. Returing DECLINED means that it didn't do
anything at all. In both these cases, it still goes onto the next handler in
that phase. After that it will go onto the next phase.
Returning an error will cause appropriate error response to go back to client
with any other handlers in the phase, as well as later phases being skipped.
Returning DONE is much like returning an error but Apache interprets it as
meaning a complete response was constructed and that it doesn't have to
generate any response.
For the AP_IMPLEMENT_HOOK_RUN_FIRST macro, all handlers will be run only if
they all return DECLINED. In other words, if a handler returns OK it will skip
the following handlers in that phase and then move onto the next phase.
Returning an error or DONE is like above.
In the case of mod_python, what it does doesn't fit into either. It is closer
to behaving like the AP_IMPLEMENT_HOOK_RUN_ALL macro except that it stops
processing further handlers in the phase if DECLINED is returned.
As to what problems this causes, imagine you had registered multiple
authentication handlers which supported different authentication mechanisms.
This is the case where AP_IMPLEMENT_HOOK_RUN_FIRST macro is used. The idea is
that each authentication handler would check the value associated with the
AuthType directive to determine if it should do anything. If it was the
AuthType it implements, if it were a C based handler module, it would returned
DECLINED to indicate it hadn't done anything and that the next handler should
instead be tried. Each handler would thus be called until one handler says that
is for me, says the user is valid and returns OK or returns an error rejecting
it.
If you wanted to write these multiple authentication handlers in Python you
can't do it. This is because the way mod_python works, if you return DECLINED
it would actually skip the remainder of the mod_python declared handlers
whereas you still want them to be executed. Apache would still execute any
other C based handlers in the phase though. The only way to get mod_python to
execute later mod_python handlers in the phase is to return OK, but if you do
that and it happens to be the last handler in the mod_python list of handlers,
it will return OK to Apache and Apache will then think a handler successfully
handled it and not then execute any subsequent C based handlers in that phase.
There are going to be other sorts of problems with phases implemented using
AP_IMPLEMENT_HOOK_RUN_ALL as well, as a handler that validly returns DECLINED
to say it didn't do anything will cause mod_python to skip later mod_python
handlers as well. If it were only C based handlers, that wouldn't be the case.
In summary, it doesn't work how it probably should.
Note that the above relates to phases other than content handler. Still have to
work out what Apache does for content handler phase when there are multiple
handlers for the phase.
No one has probably noticed these problems as no one seems to use mod_python
for implementing these other phases, simply using mod_python as a jumping off
point for content handlers.
--
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see:
http://www.atlassian.com/software/jira
