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From "Ryan Bloom" <>
Subject RE: [PATCH] AddOutputFiltersbyType
Date Fri, 15 Mar 2002 17:22:05 GMT

> > > The essential feature of this patch is that
> > > ap_add_output_filters_by_type() is called out
> > > of the ap_http_header_filter.
> >
> > You can't solve this problem this way.  The problem here, is that
> > first time down the filter stack, the data won't go through the
> > filters.  Think of what would happen if you had CGI script that
> > text/html, and you had
> >
> > AddOutputFiltersByType INCLUDES text/html.
> >
> > With this patch, it would be possible to miss SSI tags in the first
> > chunk of data.
> Not sure I understand why this is the case.  The call to
> ap_add_output_filters_by_type()
> is being called right before the call to insert the chunked encoding
> filter. If what you
> say is true, then wouldn't the problem exist with the chunked encoding
> filter as well?

Nope.  The thing is that we insert filters in a defined order, specified
by the filter type.  The chunked filter is a protocol filter, so it is
by definition after the HTTP_HEADER filter.  However, the INLCUDES
filter is a RESOURCE filter, so it is by definition before HTTP_HEADER.

> > The only way to do this, is to have a filter at the end of the
> > and CONTENT_SET filter stacks.  That filter would add more filters,
> > then move itself to below those new filters to check if the
> > has changed.
> Yep, I considered this and will implement it if this is what we really
> need to do.

Take a look at my comments above, if they aren't clear, I will try to go
into more detail.  BTW, the hard part about doing this, is that we have
to re-insert the AddOutputFilterByType filter _after_ the new filter
that is being added, and we need to be sure that the new filter actually
sees the content, which is NOT going to be easy to do, because of the
filter order.

In reality, I don't see a good way to implement this feature.


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