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From André Warnier>
Subject Re: Weird problerm accessing request headers from tomcat
Date Fri, 27 May 2011 16:01:28 GMT

I believe that you are making the often-made confusion between "environment values" (or 
variables), and HTTP headers content.
In particular, here :

>>  Apache1 inserts the following variables into the requests it forwards to 
>> Apache1 (I suppose you meant Apache2 here)

No. It does not do that.  It adds some HTTP headers. This is different, see below.

. Apache1 (I suppose you meant Apache2 here) can see them, I have checked that using 
cgi-bin/printenv (some
>> values anonymized):
>> HTTP_X_FORWARDED_SERVER="aaa.bbb.ccc"
Your check does not show that at all. It shows something that is just confusing enough to

get you confused as to what you are seeing. ;-)

But you have excuses for your confusion, because the Apache documentation itself is very 
confusing as to "environment variables".

What the cgi-bin script sees, are indeed "environment values".
These are set by the Apache process (Apache2), just before it executes the cgi-bin script.

So the cgi-bin script sees them in its environment when it runs.

But there is no one-to-one relationship between what Apache finds in HTTP request headers,

and the environment values which it sets for the cgi-bin scripts that it runs.
Apache does "convert" some of the request HTTP header values into cgi-bin environment 
variables, but :
- the name of the environment variable may be different from the corresponding HTTP header

label (you see this yourself above : a HTTP header named "X-forwarded-for:" has been 
passed to the cgi-bin script as the environment value named "HTTP_X_FORWARDED_FOR")
- not all HTTP headers are converted and passed that way
- some environment values passed to the cgi-bin script are not, and never were, HTTP 
headers of the request (for example, the cgi-bin environment values "QUERY_STRING", or 

On the other hand :

When a HTTP proxy server forwards a HTTP request to another HTTP server via the HTTP 
protocol, it forwards *all* the request headers and request content to this other server,

as a HTTP request (otherwise, it would not be a valid HTTP proxy server).  But it cannot 
forward "environment values", because there is no defined way of doing this over the HTTP

protocol. (*)

But now I see your second post, and your problem is in fact much simpler.

By doing this :
h:outputText style="font: bold 14px sans-serif;"
 >                 value="X_FORWARDED_HOST: #{header['X_FORWARDED_HOST']}" />

what you are actually trying to retrieve, is the content of the HTTP request header
"X_FORWARDED_HOST:" (I guess), but this HTTP header does not exist in the request.
What you are giving as a HTTP header name, is actually what the cgi-bin environment value

name was for your cgi-bin.
Which, as I try to explain at long length above, is not the same thing.

So you get back a null, and you think that the header was not there.
But it is there, only under its real HTTP header name.
Try something like
   value="X_FORWARDED_HOST: #{header['X-Forwarded-for']}" />"

(Noise of self-slap on face ?).

(*) However, when the proxy protocol used is AJP (as it is between Apache and Tomcat when

using the mod_jk connector, or the mod_proxy_ajp connector), /then/ some additional values

/can/ be passed along with the request (because the AJP protocol allows that). On the 
Tomcat side, these then appear as "request attributes" which the webapp can retrieve (via

request.getAttribute(name)), but not as "environment values" of the Tomcat process for 

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