Re: ordering output filters
Thanks, Nick & Ben! On Mon, Mar 14, 2011 at 1:31 PM, Nick Kew wrote: > > AP_FTYPE_RESOURCE+1. That also leaves an admin the possibility of > overriding it. I didn't realize these +1/-1 hacks were available for this API. This looks really simple & is the direction I'm leaning. > Why not an insert_filter hook? This is a really good question: I didn't know about this hook. Is there a good place I should go to learn about these hooks myself? Of course, asking this mailing-list has worked really well so far thanks to Ben & yourself & others. And in particular, adding an insert_filter hook sounds a little more complex than the AP_FTYPE_RESOURCE+1 idea. Is there some advantage to using insert_filter hook? -Josh
Re: ordering output filters
On 14 Mar 2011, at 15:54, Joshua Marantz wrote:
> if (mod_includes was enabled in this config) {
>re-insert mod_pagespeed at the end of the AP_FTYPE_RESOURCE chain
>pass the buckets to mod_includes
> }
Not good. Modules are there to serve the server admin, not to enslave him.
In general they shouldn't touch each other (except through public APIs)
nor second-guess a server admin.
In practical terms, what about a third-party module that parses comments?
If includes get special treatment but others don't, you're making things
horribly
confusing for your users.
A traditional but only slightly less ugly hack would be to declare your filter
AP_FTYPE_RESOURCE+1. That also leaves an admin the possibility of
overriding it.
> Or can we, at init time, call server APIs to tweak the filter order? Is
> there any filter that seeks to do that somehow?
You could take a look at how mod_proxy_html inserts mod_xml2enc
if available.
> A third idea is to exploit the fact that INCLUDES adds itself to the output
> chain via
> ap_hook_fixups(include_fixup, NULL, NULL, APR_HOOK_LAST);
> where include_fixup() does ap_add_output_filter("INCLUDES", NULL, r,
> r->connection);
Why not an insert_filter hook?
That would be the right place to go, but then be sure to document exactly
how it works and what other modules will be auto-configured.
--
Nick Kew
Available for work, contract or permanent
http://www.webthing.com/~nick/cv.html
Re: ordering output filters
On Mon, Mar 14, 2011 at 16:54, Joshua Marantz wrote:
> Even in the absence of 'remove_comments', it would be preferable to have
> mod_pagespeed run after mod_includes so that it has an opportunity to
> optimize the included text. The user can achieve this by putting this line
> into his config file:
>
> AddOutputFilter INCLUDES;MOD_PAGESPEED_OUTPUT_FILTER html
>
> But this is not desirable for a couple of reasons. We'd like to force the
> correct order automatically if possible.
> We also have a constraint that mod_pagespeed must run before mod_deflate.
> Actually mod_pagespeed already inserts mod_deflate in the filter-chain to
> run downstream of it:
>
> ap_add_output_filter("DEFLATE", NULL, request, request->connection);
mod_include runs at AP_FTYPE_RESOURCE, mod_deflate at AP_FTYPE_CONTENT_SET.
If you register your filter at AP_FTYPE_RESOURCE + 1 or
AP_FTYPE_CONTENT_SET - 1, it will run after mod_include but before
mod_deflate.
ordering output filters
Hello from mod_pagespeed again.
Our users have identified another incompatibility between standard filters
and mod_pagespeed; this time with mod_includes. In general I think that
mod_pagespeed should run after mod_includes, for a few reasons. But in
particular, mod_pagespeed, in its own html-centric filter architecture, has
a 'remove_comments' filter which strips out any server-side includes if
mod_pagespeed runs prior to mod_includes. While 'remove_comments' is an
optional feature for mod_pagespeed (many web pages would be broken without
mod_pagespeed), many consider it a desirable feature they'd like to turn on.
This is all documented at length in
http://code.google.com/p/modpagespeed/issues/detail?id=182
Even in the absence of 'remove_comments', it would be preferable to have
mod_pagespeed run after mod_includes so that it has an opportunity to
optimize the included text. The user can achieve this by putting this line
into his config file:
AddOutputFilter INCLUDES;MOD_PAGESPEED_OUTPUT_FILTER html
But this is not desirable for a couple of reasons. We'd like to force the
correct order automatically if possible.
The question for this mailing list is how best to achieve that. Should we,
in mod_pagespeed's output filter, have logic that says:
if (mod_includes was enabled in this config) {
re-insert mod_pagespeed at the end of the AP_FTYPE_RESOURCE chain
pass the buckets to mod_includes
}
Or can we, at init time, call server APIs to tweak the filter order? Is
there any filter that seeks to do that somehow?
We also have a constraint that mod_pagespeed must run before mod_deflate.
Actually mod_pagespeed already inserts mod_deflate in the filter-chain to
run downstream of it:
ap_add_output_filter("DEFLATE", NULL, request, request->connection);
Another hack is to have mod_pagespeed introduce a new output filter,
MOD_PAGESPEED_REORDER which would:
remove INCLUDES
remove MOD_PAGESPEED_OUTPUT_FILTER
add INCLUDES
add MOD_PAGESPEED_OUTPUT_FILTER
This seems ugly though because (a) I don't know how to remove a filter by
name and (b) it would wind up adding INCLUDES even if it was not already
registered.
A third idea is to exploit the fact that INCLUDES adds itself to the output
chain via
ap_hook_fixups(include_fixup, NULL, NULL, APR_HOOK_LAST);
where include_fixup() does ap_add_output_filter("INCLUDES", NULL, r,
r->connection);
I suppose mod_pagespeed could set up its own call
to ap_hook_fixups(niod_pagespeed_fixup, NULL, NULL, APR_HOOK_LAST* + 1*);
and add itself as an output filter.
But all of these ideas seem like a hack. Any hints on how to enforce the
output-filter ordering: INCLUDES,MOD_PAGESPEED,DEFLATE in a robust and
clean way, would be greatly appreciated.
-Josh
