Conditionally Setting HTTP Response Header

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Hello,

I am looking for some help to set HTTP response headers conditionally. I
have a setup where HTTPD sits in front of Tomcat and proxies requests to it.

*Problem Statement*
Set a Cache-Control max-age directive in the HTTP response header through
HTTPD if it doesn't already exist. In addition if HTTPD after detecting that
the directive is not already set in the response header, it should set one
depending on the response mime-type.

Example:
HTTPD proxies a request to tomcat -> Tomcat processes the request and send
back the response to HTTPD -> HTTPD checks if Cache-Control max-age
directive is set in the response header. If present it does no changes to
the response header and simply forwards the response back to the user.
However, if the Cache-Control max-age directive is not present it sets one
depending on the response mime type (say max-age=900 for text/html and
max-age=1800 for image/gif)
*
*
*System Info*
$ apachectl -version
Server version: Apache/2.2.9 (Unix)
Server built: Sep 12 2008 16:23:39

$ uname -a
SunOS vm-sol10-45 5.10 Generic_127128-11 i86pc i386 i86p

*What I Have Tried*
I have been trying to work with mod_setenvif module to start but have not
made any progress and thus seeking your help.

Any inputs would be highly appreciated.

Regards
Anurag
*
*----------------------------------------------------------- -------
Anurag Kapur
Associate - Technology,
Sapient Corporation.

http://www.linkedin.com/in/anuragkapur

http://www.google.com/profiles/anuragkapur
------------------------------------------------------------ ------

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Hello,

Re: Conditionally Setting HTTP Response Header

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Hi Anurag
I have had the exact same problem and posted in
http://www.gossamer-threads.com/lists/apache/users/382031?pa ge=last
You can use ExpiresDefault/ExpiresByType (this adds both an Expires and
Cache-Control: max-age header to simultaneously support HTTP 1.0 and HTTP
1.1) or use LocationMatch. For example, I could distinguish between static
content requests (requests to *.gif) vs dynamic content requests
(requests to *.jsp or *.do for a Struts application) using the
LocationMatch. I couldn't find a way of using LocationMatch to work with the
content-type of the response, which was what I needed for file download
requests. Nor could I find a way of checking whether the header was set,
before setting it. (I'm still asking the question).
In the end, I have set the values using e.g. servlet filters in my
application code.
thanks, Balj.

On Mon, Mar 15, 2010 at 12:50 PM, Anurag Kapur wrote:

> Hello,
>
> I am looking for some help to set HTTP response headers conditionally. I
> have a setup where HTTPD sits in front of Tomcat and proxies requests to it.
>
> *Problem Statement*
> Set a Cache-Control max-age directive in the HTTP response header through
> HTTPD if it doesn't already exist. In addition if HTTPD after detecting that
> the directive is not already set in the response header, it should set one
> depending on the response mime-type.
>
> Example:
> HTTPD proxies a request to tomcat -> Tomcat processes the request and send
> back the response to HTTPD -> HTTPD checks if Cache-Control max-age
> directive is set in the response header. If present it does no changes to
> the response header and simply forwards the response back to the user.
> However, if the Cache-Control max-age directive is not present it sets one
> depending on the response mime type (say max-age=900 for text/html and
> max-age=1800 for image/gif)
> *
> *
> *System Info*
> $ apachectl -version
> Server version: Apache/2.2.9 (Unix)
> Server built: Sep 12 2008 16:23:39
>
> $ uname -a
> SunOS vm-sol10-45 5.10 Generic_127128-11 i86pc i386 i86p
>
> *What I Have Tried*
> I have been trying to work with mod_setenvif module to start but have not
> made any progress and thus seeking your help.
>
> Any inputs would be highly appreciated.
>
> Regards
> Anurag
> *
> *----------------------------------------------------------- -------
> Anurag Kapur
> Associate - Technology,
> Sapient Corporation.
>
> http://www.linkedin.com/in/anuragkapur
>
> http://www.google.com/profiles/anuragkapur
> ------------------------------------------------------------ ------
>

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Re: Conditionally Setting HTTP Response Header

Thanks Balj.

Unfortunately using a servlet filter will not serve my purpose. In my
system, some requests are proxied from HTTPD to Tomcat while others
are served directly by HTTPD. Thus, I am looking for something in the
HTTPD layer that can check if the header is already set and then take
action accordingly.

I am quite sure SetEnvIf directive in conjunction with Header set
directive can work here. However, I have not managed to get it working
after quite a few tries. Thus I am polling this group to know if
someone has already implemented somthing similar.

Regards


On 3/15/10, Baljeet Nijjhar wrote:
> Hi Anurag
> I have had the exact same problem and posted in
> http://www.gossamer-threads.com/lists/apache/users/382031?pa ge=last
> You can use ExpiresDefault/ExpiresByType (this adds both an Expires and
> Cache-Control: max-age header to simultaneously support HTTP 1.0 and HTTP
> 1.1) or use LocationMatch. For example, I could distinguish between static
> content requests (requests to *.gif) vs dynamic content requests
> (requests to *.jsp or *.do for a Struts application) using the
> LocationMatch. I couldn't find a way of using LocationMatch to work with the
> content-type of the response, which was what I needed for file download
> requests. Nor could I find a way of checking whether the header was set,
> before setting it. (I'm still asking the question).
> In the end, I have set the values using e.g. servlet filters in my
> application code.
> thanks, Balj.
>
> On Mon, Mar 15, 2010 at 12:50 PM, Anurag Kapur wrote:
>
>> Hello,
>>
>> I am looking for some help to set HTTP response headers conditionally. I
>> have a setup where HTTPD sits in front of Tomcat and proxies requests to
>> it.
>>
>> *Problem Statement*
>> Set a Cache-Control max-age directive in the HTTP response header through
>> HTTPD if it doesn't already exist. In addition if HTTPD after detecting
>> that
>> the directive is not already set in the response header, it should set one
>> depending on the response mime-type.
>>
>> Example:
>> HTTPD proxies a request to tomcat -> Tomcat processes the request and send
>> back the response to HTTPD -> HTTPD checks if Cache-Control max-age
>> directive is set in the response header. If present it does no changes to
>> the response header and simply forwards the response back to the user.
>> However, if the Cache-Control max-age directive is not present it sets one
>> depending on the response mime type (say max-age=900 for text/html and
>> max-age=1800 for image/gif)
>> *
>> *
>> *System Info*
>> $ apachectl -version
>> Server version: Apache/2.2.9 (Unix)
>> Server built: Sep 12 2008 16:23:39
>>
>> $ uname -a
>> SunOS vm-sol10-45 5.10 Generic_127128-11 i86pc i386 i86p
>>
>> *What I Have Tried*
>> I have been trying to work with mod_setenvif module to start but have not
>> made any progress and thus seeking your help.
>>
>> Any inputs would be highly appreciated.
>>
>> Regards
>> Anurag
>> *
>> *----------------------------------------------------------- -------
>> Anurag Kapur
>> Associate - Technology,
>> Sapient Corporation.
>>
>> http://www.linkedin.com/in/anuragkapur
>>
>> http://www.google.com/profiles/anuragkapur
>> ------------------------------------------------------------ ------
>>
>

--
Sent from my mobile device

------------------------------------------------------------ ------
Anurag Kapur
Associate - Technology,
Sapient Corporation.

+44 (0) 7514 996 586

http://www.linkedin.com/in/anuragkapur

http://www.google.com/profiles/anuragkapur
------------------------------------------------------------ ------

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Re: Conditionally Setting HTTP Response Header

> I have been trying to work with mod_setenvif module to start but have not
> made any progress and thus seeking your help.

Show us what you have, and what it does.

--
Eric Covener
covener@gmail.com

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Re: Conditionally Setting HTTP Response Header

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I have been trying configurations like the following:

SetEnvIf response Cache-Control !"^max-age*$"
test=ThisShouldDisplayInXwsField
Header append X-ws test

With the above, as a first step I was trying to test if I can detect the
presence of Cach-Control max-age field in the Response header. What I
expected was, if response header had Cache-Control max-age field, then the
X-ws field would show the string 'ThisShouldDisplayInXwsField'. But I could
not see it set even though max-age was present in the header.

I know these are not complete, but I as the first step, I was trying to get
these to work.

-Anurag

On Mon, Mar 15, 2010 at 2:12 PM, Eric Covener wrote:

> > I have been trying to work with mod_setenvif module to start but have not
> > made any progress and thus seeking your help.
>
> Show us what you have, and what it does.
>
> --
> Eric Covener
> covener@gmail.com
>
> ------------------------------------------------------------ ---------
> The official User-To-User support forum of the Apache HTTP Server Project.
> See for more info.
> To unsubscribe, e-mail: users-unsubscribe@httpd.apache.org
> " from the digest: users-digest-unsubscribe@httpd.apache.org
> For additional commands, e-mail: users-help@httpd.apache.org
>
>

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I have been trying configurations like the following:

Re: Conditionally Setting HTTP Response Header

On Mon, Mar 15, 2010 at 10:19 AM, Anurag Kapur wrote:
> I have been trying configurations like the following:
> SetEnvIf response Cache-Control !"^max-age*$"
> test=ThisShouldDisplayInXwsField
> Header append X-ws test

Re-reading OP, it sounds like you just want Expires. I don't think it
blows away existing headers.

I don't think the syntax is right on either one, was this verbatim
from something you tested? Shouldn't this just be:

SetEnvIf Cache-Control .+ cc_set=1
Header set Cache-Control ... env=cc_set


--
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covener@gmail.com

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Re: Conditionally Setting HTTP Response Header

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Below is exactly what I tried:

SetEnvIfNoCase response Cache-Control .+ cc_set=123
Header append X-ws "test" env=cc_set

Expected output: If response does not have Cache-Control set, the X-ws field
should display the text "test".
Actual output: X-ws field did not display the text "test"

Note: I realized the problem with the syntax I was using after you pointed
it out and tried the above after fixing it (I think).

-Anurag

On Mon, Mar 15, 2010 at 2:26 PM, Eric Covener wrote:

> On Mon, Mar 15, 2010 at 10:19 AM, Anurag Kapur
> wrote:
> > I have been trying configurations like the following:
> > SetEnvIf response Cache-Control !"^max-age*$"
> > test=ThisShouldDisplayInXwsField
> > Header append X-ws test
>
> Re-reading OP, it sounds like you just want Expires. I don't think it
> blows away existing headers.
>
> I don't think the syntax is right on either one, was this verbatim
> from something you tested? Shouldn't this just be:
>
> SetEnvIf Cache-Control .+ cc_set=1
> Header set Cache-Control ... env=cc_set
>
>
> --
> Eric Covener
> covener@gmail.com
>
> ------------------------------------------------------------ ---------
> The official User-To-User support forum of the Apache HTTP Server Project.
> See for more info.
> To unsubscribe, e-mail: users-unsubscribe@httpd.apache.org
> " from the digest: users-digest-unsubscribe@httpd.apache.org
> For additional commands, e-mail: users-help@httpd.apache.org
>
>

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Below is exactly what I tried:

Re: Conditionally Setting HTTP Response Header

On Mon, Mar 15, 2010 at 10:59 AM, Anurag Kapur wrot=
e:
> Below is exactly what I tried:
>    SetEnvIfNoCase response Cache-Control .+ cc_set=3D123
>    Header append X-ws "test" env=3Dcc_set
> Expected output: If response does not have Cache-Control set, the X-ws fi=
eld
> should display the text "test".
> Actual output: X-ws field did not display the text "test"
> Note: I realized the problem with the syntax I was using after you pointe=
d
> it out and tried the above after fixing it (I think).
> -Anurag

What is "response" doing there?

SetEnvIfNoCase attribute regex [!]env-variable[=3Dvalue]
[[!]env-variable[=3Dvalue]] ...


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covener@gmail.com

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Re: Conditionally Setting HTTP Response Header

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I saw it used here
http://mail-archives.apache.org/mod_mbox/httpd-dev/200609.mb ox/%3C450543D6.80505@web.turner.com%3E


I thought it is needed to differentiate a field set in the response header
from that in the request header. But after reading the documentation again,
I see it says:
An HTTP request header field (see
RFC2616for more information
about these); for example:
Host, User-Agent, Referer, and Accept-Language. A regular expression may be
used to specify a set of request headers.
http://httpd.apache.org/docs/2.0/mod/mod_setenvif.html#seten vif

Which means I can use only request header fields (Am I right?). However,
what I am looking to do is conditionally set an environment variable based
on the "response" header (not request header), so that I know if I have to
append or unset a certain field in the response header.

Unless I am getting this wrong, is there any other way of doing this?

Thanks
Anurag

On Mon, Mar 15, 2010 at 3:02 PM, Eric Covener wrote:

> On Mon, Mar 15, 2010 at 10:59 AM, Anurag Kapur
> wrote:
> > Below is exactly what I tried:
> > SetEnvIfNoCase response Cache-Control .+ cc_set=123
> > Header append X-ws "test" env=cc_set
> > Expected output: If response does not have Cache-Control set, the X-ws
> field
> > should display the text "test".
> > Actual output: X-ws field did not display the text "test"
> > Note: I realized the problem with the syntax I was using after you
> pointed
> > it out and tried the above after fixing it (I think).
> > -Anurag
>
> What is "response" doing there?
>
> SetEnvIfNoCase attribute regex [!]env-variable[=value]
> [[!]env-variable[=value]] ...
>
>
> --
> Eric Covener
> covener@gmail.com
>
> ------------------------------------------------------------ ---------
> The official User-To-User support forum of the Apache HTTP Server Project.
> See for more info.
> To unsubscribe, e-mail: users-unsubscribe@httpd.apache.org
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>
>

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I saw it used here=A0 tpd-dev/200609.mbox/%3C450543D6.80505@web.turner.com%3E">htt p://mail-archiv=
es.apache.org/mod_mbox/httpd-dev/200609.mbox/%3C450543D6.805 05@web.turner.c=
om%3E=A0

Re: Conditionally Setting HTTP Response Header

On Mon, Mar 15, 2010 at 11:15 AM, Anurag Kapur wrot=
e:
> I saw it used
> here=A0http://mail-archives.apache.org/mod_mbox/httpd-dev/20 0609.mbox/%3C=
450543D6.80505@web.turner.com%3E
> I thought it is needed to differentiate a field set in the response heade=
r
> from that in the request header. But after reading the documentation agai=
n,
> I see it says:
> An HTTP request header field (see RFC2616 for more information about thes=
e);
> for example: Host, User-Agent, Referer, and Accept-Language. A regular
> expression may be used to specify a set of request headers.
> http://httpd.apache.org/docs/2.0/mod/mod_setenvif.html#seten vif
> Which means I can use only request header fields (Am I right?). However,
> what I am looking to do is conditionally set an environment variable base=
d
> on the "response" header (not request header), so that I know if I have t=
o
> append or unset a certain field in the response header.
> Unless I am getting this wrong, is there any other way of doing this?

Not sure, but the code you reference is not in Apache HTTP Server 2.2.x

--=20
Eric Covener
covener@gmail.com

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