Sorry, you have missed an important point. I am not suggesting this as
some sort of convoluted alternative to using os.stat() in Python for
when a Python based handlers wants to stat some alternative file.

I am specifically addressing the issue where request_rec->filename is
being updated to affect the outcome of a later handler phase which isn't
even written in Python but C or Perl and which is designed to look at
request_rec->filename and which correspondingly expects that
request_rec->finfo be for the current file mentioned in

The example I gave was:

   def headerparserhandler(req):
       if req.finfo[apache.FINFO_FILETYPE] == apache.APR_DIR:
           if req.uri[-1] == '/':

               req.filename = posixpath.join(req.filename, 'index.html')

               # XXX
               # Need to somehow ensure that req.finfo (actually
               # request_rec->finfo) is updated here to contain
               # apr_stat() result for new value of req.filename.
               # XXX

       return apache.OK

The purpose of this handler is to get around the problem that the
DirectoryIndex directive is effectively broken for mod_python if you use
handlers prior to the content handler phase. Even though a workaround
for a particular issue, updating req.filename and req.finfo is still
a legitimate thing that can be done in C API modules to affect behaviour
of later handlers implemented by other modules. In other words, please
don't judge the example on the basis that it is a workaround for an
Apache problem and say the real change should be to fix Apache's
DirectoryIndex code.

Now as to the handler above, it needs to do two things. The first is to
update request_rec->filename. The new value of this field will then
be consulted by the type checker phase of mod_mime to update the
request_rec->content_type attribute.

The second is that it needs to somehow force the update of the
request_rec->finfo attribute to correspond to the new value of the
request_rec->filename attribute. This then ensures that the file stats
will reflect that it is a file and not a directory.

If this update to request_rec->finfo is not done and it still records
details of the original directory, when the fixup handler of mod_dir is
executed, then it will still think the target of the request is a directory
and will still trigger the broken DirectoryIndex code which is not what
is desired.

Thus, no matter how it is done, whether it be automatic or whether
an explicit function is provided to do it, there needs to be some way
of updating the underlying request_rec->finfo attribute. Saying to
use Python os.stat() is of no use as req.finfo isn't writable, is not the
same structure as what os.stat() returns and isn't a full reflection of
what the underlying request_rec->finfo attribute holds anyway. So,
you couldn't even fake up request_rec->finfo from the result of
os.stat() anyway.

There is therefore two things that need to worked out. The first is
a consensus that there needs to be a way of updating req.finfo to
correspond to new value of req.filename. Second is to work out how
that should be able to be done.

At the moment I get the feeling that you question the need for req.finfo
to be updatable in the first place. I also think saying a stat is expensive
is a red herring as we are talking about a whether specific case here.

In the majority of cases, no one would have a legitimate need to be
modifying req.filename in the first place, so no extra stat is going
to be done, so cost of the stat is not an issue. Where req.filename
is modified though, it would normally follow that a stat should be
done to update req.finfo.

In the above example to workaround DirectoryIndex problem the
outcome is actually more effecient than the alternative, which is to
use req.internal_redirect(). Thus, that one extra stat is performed
is nothing compared to what is saved in avoiding the redirect.

Now of all the code I have seen so far, the only time I have ever seen anyone
modify req.filename is in mod_python.publisher. It updates it so that
req.filename will properly yield the name of the Python code file that
the request mapped against.

Because mod_python.publisher partly uses it as a temporary variable
rather than use a true temporary variable and only assign to it once, an
automatic update of finfo would incur extra cost. But then, except for
one case, mod_python.publisher is doing its own stat of some form after
each assignment anyway, so it could eliminate those and use the
automatically updated finfo. The one case it isn't stating is when it
normalises the path for local OS, which strictly speaking it possibly
shouldn't do as I think Apache might always provide req.filename in
POSIX like format anyway and thus it is breaking that convention.

That mod_python.publisher updates req.filename but not req.finfo
also means that one can't use the mtime stored in req.finfo as input to
req.set_last_modified(). Ie.,set last modified header based on the
modification time of Python code file as stored in req.finfo. If one really
wanted to do it, one would have to stat the file once again to get the
mtime and call req.update_mtime() explicitly.

I could possibly drag up other cases, but hopefully this time I have been
able to more clearly show that there are some legitimate uses for being
able to update req.finfo to reflect newer value of req.filename. If this is
accepted, the question still remains is how to enable that ability.


Grisha wrote ..
> I'm -1 on updating req.finfo when req.filename is updated. I don't have
> the time to explain it in detail, but I think it flows from Graham's 
> explanation below.
> Basically, httpd does a stat() for you, and its result is stored in finfo.
> Why make it any more complicated and magical?
> If you alter req.filename - should that imply another stat()? I don't 
> think so, because the stat() is the most expensive operations in the whole
> request service process and unnecessary stats should be avoided.
> I also don't see any good use case for it. If you need a stat - Python
> provides way for you to do it, there is no need to get httpd involved in
> this process.
> I, of course, may be missing something obvious here, but this is my 
> initial reaction. Let httpd/apr behave the way they behave - there is no
> need to "pythonize" them, especially when the Python standard library 
> provides the same functionality in a "pythonic" way.
> Grisha
> On Sun, 26 Mar 2006, Jim Gallacher wrote:
> > Hi Graham,
> >
> > +1 auto update req.finfo when req.filename changed.
> >
> > Is there a use case where the user might change filename but not want
> finfo 
> > to change? I can't think of one, so let's save the user some work and
> make 
> > their code more robust to boot.
> >
> > A point I'd like to address is your concern about mod_python differing
> from 
> > the Apache C api in implementing certain features. Personally I think
> our 
> > general concern about this is somewhat misguided. I suspect that the
> majority 
> > of our users are more concerned about the "python-ness" of mod_python
> rather 
> > than its "apache-ness", and most would never notice if we deviate slightly
> > from the apache C api. Adding a method or attribute to the request object
> for 
> > example, if it's useful to *our* users, shouldn't be rejected out of
> hand 
> > just because it does not exist in the underlying api.
> >
> > Jim
> >
> > Graham Dumpleton wrote:
> >> Now the mailing list is a bit quiet, I would like to see if I can get
> >> some explicit feedback on some issues related to the inability to update
> >> the req.finfo attribute.
> >> 
> >> Grisha, would be nice if you could respond on this issue and give some
> >> guidance else I fear I'll never be able to progress a solution to this
> >> issue. :-(
> >> 
> >> As explained in:
> >> 
> >>
> >> 
> >> although it is possible to assign a new value to req.filename, there
> is
> >> no way to update req.finfo to the file stats associated with that new
> >> value of req.filename. If one had access to the low level C API this
> >> would normally be achieved using:
> >> 
> >>   apr_stat(&r->finfo, r->filename, APR_FINFO_MIN, r->pool);
> >> 
> >> In mod_python though, there is no way to access the function and affect
> >> that outcome.
> >> 
> >> In mod_perl 1.0 they implemented the behaviour whereby the "finfo"
> >> attribute was automatically updated when the "filename" attribute was
> >> updated by a handler.
> >> 
> >> In mod_perl 2.0 they dropped this though, as they wanted to preserve
> >> the idea that in mod_perl everything behaved exactly like the C API
> >> they were trying to provide a 1 to 1 mapping for. Thus in mod_perl
> >> 2.0 you need to write:
> >> 
> >>   use Apache2::RequestRec ();
> >>   use APR::Finfo ();
> >>   use APR::Const -compile => qw(FINFO_NORM);
> >>   $r->filename($newfile);
> >>   $r->finfo(APR::Finfo::stat($newfile, APR::Const::FINFO_NORM, $r->pool));
> >> 
> >> As mod_python isn't attempting to provide a strict 1 to 1 mapping, it
> >> might be argued that it could do what mod_perl 1.0 did and automatically
> >> updated the "finfo" attribute when "filename" is updated.
> >> 
> >> The only other alternative is to add a new method to the Python request
> >> object for which there isn't strictly speaking a direct equivalent to
> >> in the Apache C API. That is, a method that calls apr_stat() but which
> >> only performs it in relation to the "filename" and "finfo" attributes
> >> in the request object itself and is not a generic routine.
> >> 
> >> Since it isn't likely that mod_python will ever provide a lower level
> >> API for use of finfo related structures and functions and even if it
> >> did they most likely would be distinct to the request object, the name
> >> of the function added to the request object could still be called 
> >> "stat()".
> >> 
> >> Thus mod_python equivalent to what mod_perl 2.0 does would be:
> >> 
> >>   req.filename = newfile
> >>   req.stat()
> >> 
> >> This though doesn't really convey a sense of what it occurring. Thus
> a
> >> more descriptive name would probably be more appropriate. For example:
> >> 
> >>   req.filename = newfile
> >>   req.update_finfo()
> >> 
> >> There is no ap_update_finfo() function now, but if they did later
> >> implement one, this would shadow it and prevent it being added to the
> >> request object if it was pertinent for that be done.
> >> 
> >> The next problem is that apr_stat() actually takes an argument indicating
> >> what fields in the "finfo" attribute should be updated. In mod_perl
> 1.0
> >> the value used when the automatic update was done was APR_FINFO_MIN
> >> which results in type, mtime, ctime, atime, size being updated. In
> >> the documentation for mod_perl 2.0 it suggests use of APR_FINFO_NORM
> >> instead which is described as intended to be used when an atomic unix
> >> apr_stat() is required whatever that means.
> >> 
> >> Important to note though is that is that the ap_directory_walk()
> >> function in Apache which is used to map a URL against a file in the
> >> filesystem uses APR_FINFO_MIN.
> >> 
> >> Now if a function were to be provided, it seems to make sense that it
> >> have a default whereby it uses APR_FINO_MIN, much as would be the case
> >> if the "finfo" attribute were updated automatically when "filename"
> is
> >> updated.
> >> 
> >> Should though a function if provided allow the ability to supply an
> >> alternate for this value so as to be selective as to what attributes
> >> of "finfo" are updated?
> >> 
> >> If it were allowed, have the problem that there are already attributes
> >> in mod_python for:
> >> 
> >>   FINFO_MODE = 0
> >>   FINFO_INO = 1
> >>   FINFO_DEV = 2
> >>   FINFO_NLINK = 3
> >>   FINFO_UID = 4
> >>   FINFO_GID = 5
> >>   FINFO_SIZE = 6
> >>   FINFO_ATIME = 7
> >>   FINFO_MTIME = 8
> >>   FINFO_CTIME = 9
> >>   FINFO_FNAME = 10
> >>   FINFO_NAME = 11
> >>   FINFO_FILETYPE = 12
> >> 
> >> Rather than these being equivalents to the APR constants:
> >> 
> >>   #define     APR_FINFO_LINK   0x00000001
> >>   #define     APR_FINFO_MTIME   0x00000010
> >>   #define     APR_FINFO_CTIME   0x00000020
> >>   #define     APR_FINFO_ATIME   0x00000040
> >>   #define     APR_FINFO_SIZE   0x00000100
> >>   #define     APR_FINFO_CSIZE   0x00000200
> >>   #define     APR_FINFO_DEV   0x00001000
> >>   #define     APR_FINFO_INODE   0x00002000
> >>   #define     APR_FINFO_NLINK   0x00004000
> >>   #define     APR_FINFO_TYPE   0x00008000
> >>   #define     APR_FINFO_USER   0x00010000
> >>   #define     APR_FINFO_GROUP   0x00020000
> >>   #define     APR_FINFO_UPROT   0x00100000
> >>   #define     APR_FINFO_GPROT   0x00200000
> >>   #define     APR_FINFO_WPROT   0x00400000
> >>   #define     APR_FINFO_ICASE   0x01000000
> >>   #define     APR_FINFO_NAME   0x02000000
> >>   #define     APR_FINFO_MIN   0x00008170
> >>   #define     APR_FINFO_IDENT   0x00003000
> >>   #define     APR_FINFO_OWNER   0x00030000
> >>   #define     APR_FINFO_PROT   0x00700000
> >>   #define     APR_FINFO_NORM   0x0073b170
> >>   #define     APR_FINFO_DIRENT   0x02000000
> >> 
> >> which can be bit wise or'd together as the argument to the apr_stat()
> >> function, they are used as positional indexes into the tuple which
> >> mod_python provides as req.finfo. Thus there is a clash on the names.
> >> 
> >> Thus the whole issue gets very messy. :-(
> >> 
> >> Overall, my feeling is that following what mod_perl 1.0 did of updating
> >> the "finfo" attribute when the "filename" attribute is a reasonable
> >> solution for mod_python given its much higher level API. At the moment
> >> I haven't been able to for-see any problems that this might cause.
> >> The question though is whether that it is hidden is too magic?
> >> 
> >> Whatever is done, this missing ability of not being able to update
> >> req.finfo needs to be added. One use for it that I already have is to
> >> get around the DirectoryIndex problems in mod_python caused by Apache's
> >> use of the ap_internal_fast_redirect() function to implement that
> >> feature. The specifics of this particular issue are documented under:
> >> 
> >>
> >> 
> >> One solution I already provided for this was:
> >> 
> >>   def fixuphandler(req):
> >>       if req.finfo[apache.FINFO_FILETYPE] == apache.APR_DIR:
> >>           if req.uri[-1] == '/':
> >>               uri = req.uri + 'index.html'
> >>               if req.args: uri += '?' + req.args
> >>               req.internal_redirect(uri)
> >>               return apache.DONE
> >>       return apache.OK
> >> 
> >> Although, I believe now it is probably better done as HeaderParserHandler
> >> phase. That is before any access, authentication and authorization
> >> checks. Those access checks would instead then only be done once in
> >> the sub request instead of multiple times.
> >> 
> >> If req.finfo were automatically updated when req.filename is updated
> >> then the alternative is to use:
> >> 
> >>   def headerparserhandler(req):
> >>       if req.finfo[apache.FINFO_FILETYPE] == apache.APR_DIR:
> >>           if req.uri[-1] == '/':
> >>               req.filename = posixpath.join(req.filename, 'index.html')
> >>       return apache.OK
> >> 
> >> This is possibly better as it avoids the need to perform an internal
> >> redirect and thus is slightly more efficient. It will only work though
> >> if req.finfo is updated as that will result in the file type changing
> >> from that of a directory to that of a regular file, that value being
> >> later consulted by type handler of mod_mime when setting up the content
> >> type.
> >> 
> >> Another area where it will be important to be able to update req.finfo
> >> is when a map to storage hook is implemented as described in:
> >> 
> >>
> >> 
> >> Without the ability, there would be no point providing the new hook
> as
> >> it wouldn't be possibly to correctly set up the request object for latter
> >> phases without it.
> >> 
> >> Anyway got anything to contribute as to an opinion or otherwise?
> >> 
> >> To summarise the problem, we need a way of updating req.finfo when
> >> req.filename changes. How should this be done?
> >> 
> >> I would like to get this sorted sooner rather than later. This also
> will
> >> not be the last complicated little issue a decision has to be made on,
> >> and I would rather not see a lack of consensus on these issues pushing
> >> delivery of 3.3 further and further into the future. I also would rather
> >> not see us putting them in to the too hard basket for a later release.
> >> 
> >> Feedback much appreciated.
> >> 
> >> Graham
> >> 
> >> 
> >> 
> >

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