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Date: Thu, 2 Apr 2009 14:12:19 +0200
Message-ID: <20170a030904020512w7b25e4bdwc8fc4ef1e4d8ae38@mail.gmail.com>
Subject: Re: About the order of the processing of the http request
From: Sorin Manolache <sorinm@gmail.com>
To: modules-dev@httpd.apache.org
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On Thu, Apr 2, 2009 at 13:28, Xiaobin <xiaobinshe@gmail.com> wrote:
>
> Hi, everyone.
>
> I new to modlue developemnt of the Apache http server, and I have googled
> this question and can't find the answer. Hope you can help me. Thx.
>
> I am confused with the order of the processing of the http request.
>
> Without the input/output filters, the order seems quick clear, when one http
> request comes, it will go through different kinds of hooks  like "map to
> storage", "fixups" and "handler". And we can set some handlers to deal with
> these hooks.
>
> But what's the order after the introduction of the filter mechanism？
>
> When will the input filters begin to work?
> After the handlers of the fixups hook has been called and before the
> handlers of the "handler" hook begin to work?
> Or in some other order?
> And how can we specify the order of the input filters?
>
> And for the output filters, when did they begin to work? Before or after the
> "log transaction" hook ?
> And also how can we specify the order of the output filters?
>
> Thank you very much for your help!

There are several types of filters: network, protocol, connection,
resource (the list is not exhaustive, check util_filters.h in the
apache sources).

The input headers of the request are read after the create_request
hook and before the post_read_request, quick_handler, translate_name,
map_to_storage, header_parser, access_checker, ..., fixups,
insert_filter, and handler hooks.

The output headers of the request are written during the handler execution.

When the headers are read/written, the protocol filters are called.

The resource input/output filters are called only when you explicitly
read/write the body of the request. If you add filters with the
SetInputFilter/SetOutputFilter directives, the filter is added in the
insert_filter hook. This one is called after fixups and before
handler. Thus, you cannot use a filter added with
SetInputFilter/SetOutputFilter before the handler hook.

log_transaction is called after the request was served and the
response was written to the socket and the socket flushed.

If the filters are of the same type, they are run in the order they
were added. If they are of different types, then I think their type
takes precedence, but I am not sure of that. For output filters,
resource filters are called before network filters.

S
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