SetEnvIfExpr with response header

apache-2.4

I want to set a environment variable when a specific response header has a value.

But when I make this it doesn't set the variable.

Header add X-foo "bar"
<If "resp('X-foo') == 'bar'">
    Header add X-test-foobar "foobarnew"
</If>

It doesn't set the header X-test-foobar.

Maybe I don't have correctly understand how does it should work. I'm not really fluent in apache programming… I think that programming is not sequential in apache environment but I don't know how to set an env variable with the content of the response header.

Thanks for any help,

Best Answer

If may be evaluated too early in Apache's processing to use attributes of the response. The documentation isn't clear and I can't find that elsewhere right now.

But the Header directive is processed late, so it can use the response. You just need to add the expr condition to it:

Header add X-test-foobar "foobarnew" "expr=resp('X-foo') == 'bar'"

Related Solutions

Php – Apache 2.4.7 ignores response header Content-Encoding: identity, instead respects Content-Encoding: none, set by PHP

So, I've managed to solve my issues, by taking into account the assumptions I've outlined in my question, which appear to be correct. But not without a struggle.

On trying to implement it for only PHP-generated content, I ran into some other issues, which I'll describe here:

I initially had the following rewrite rules in my .htaccess:

RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l
RewriteRule ^.*$ - [NC,L]

RewriteRule ^.*$ index.php [NC,L]

With RewriteRule flags, you should be able to set environment variables. So, I figured I should be able to set the E=no-gzip:1 flag on merely the last RewriteRule, by doing:

RewriteRule ^.*$ index.php [NC,E=no-gzip:1,L]

And even though the earlier mentioned

SetEnv no-gzip 1

worked fine, the RewriteRule flag just wouldn't catch on. Then I looked into all sorts of related questions on Stack Overflow, such as this one this one. But they didn't offer satisfactory solutions.

I then momentarily resorted to setting the environment variable from within PHP with apache_setenv( 'no-gzip', 1 );, which did the trick. But that just didn't feel right and also made me wonder why the damn RewriteRule flag wouldn't work just as well.

I then decided to do a var_dump( $_SERVER ), to see whether the RewriteRule flag was actually set, only to be confronted with an old nemesis I had forgotten about:

array(39) {
  ["REDIRECT_no-gzip"]=>
  string(1) "1"
  ["REDIRECT_APP_ENV"]=>
  string(11) "development"
  /* etc. */
}

The damn REDIRECT_ that gets prepended to environment variables when rewriting.

I was under the impression that the L flag on my last RewriteRule should mean stop rewriting, but apparently I had misinterpreted this rule and it's conditions:

RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l
RewriteRule ^.*$ - [NC,L]

Since RewriteRule ^.*$ index.php [NC,E=no-gzip:1,L] rewrites to index.php, which is a regular file (-s), the aforementioned conditions and rule still kick in.

Now that I've changed that rule to

RewriteRule !^index.php - [NC,L]

everything is finally working as desired!

Apache Custom Header with an environment variable

You have to declare which system environment variables you want to be usable with the PassEnv directive

A working example would be:

PassEnv HOSTNAME
Header Set X-Serv %{HOSTNAME}e

Best Answer

Related Solutions

Php – Apache 2.4.7 ignores response header Content-Encoding: identity, instead respects Content-Encoding: none, set by PHP

Apache Custom Header with an environment variable

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