content-length header from php is overwritten !

I'm trying to figure why the Content-Length header of php gets overwritten. This is demo.php

<?php
header("Content-Length: 21474836470");die;
?>

a request to fetch the headers

curl -I http://someserver.com/demo.php
HTTP/1.1 200 OK
Date: Tue, 19 Jul 2011 13:44:11 GMT
Server: Apache/2.2.16 (Debian)
X-Powered-By: PHP/5.3.3-7+squeeze3
Content-Len开发者_开发百科gth: 2147483647
Cache-Control: must-revalidate
Content-Type: text/html; charset=UTF-8

See Content-Length ? It maxes out at 2147483647 bytes, that is 2GB.

Now if modify demo.php like so

<?php
header("Dummy-header: 21474836470");die;
?>

the header is not overwritten.

HTTP/1.1 200 OK
Date: Tue, 19 Jul 2011 13:49:11 GMT
Server: Apache/2.2.16 (Debian)
X-Powered-By: PHP/5.3.3-7+squeeze3
Dummy-header: : 21474836470
Cache-Control: must-revalidate
Content-Type: text/html; charset=UTF-8

Here are the modules loaded

root@pat:/etc/apache2# ls /etc/apache2/mods-enabled/
alias.conf        authz_host.load  dav_fs.load    expires.load  php5.conf    reqtimeout.load  status.conf
alias.load        authz_user.load  dav.load       headers.load  php5.load    rewrite.load     status.load
auth_basic.load       autoindex.conf   dav_lock.load  mime.conf     proxy.conf   setenvif.conf
authn_file.load       autoindex.load   dir.conf       mime.load     proxy_http.load  setenvif.load
authz_default.load    cgi.load         dir.load       negotiation.conf  proxy.load   ssl.conf
authz_groupfile.load  dav_fs.conf      env.load       negotiation.load  reqtimeout.conf  ssl.load

Here is a phpinfo() : http://pastehtml.com/view/b0z02p8zc.html

Apache does support files over 2GB, as I don't have any problem accessing large file directly :

curl -I http://www.someserver.com/somehugefile.zip (5.3 Gig)
HTTP/1.1 200 OK
Date: Tue, 19 Jul 2011 14:00:25 GMT
Server: Apache/2.2.16 (Debian)
Last-Modified: Fri, 15 Jul 2011 08:50:22 GMT
ETag: "301911-1548e4b11-4a817bd63ef80"
Accept-Ranges: bytes
Content-Length: 5713578769
Cache-Control: must-revalidate
Content-Type: application/zip

Here is a uname -a

Linux pat.someserver.com 2.6.38.2-grsec-xxxx-grs-ipv6-32 #1 SMP Fri Apr 15 17:41:28 UTC 2011 i686 GNU/Linux

Hope somebody can help !

cheers

Seems like php cast Content-length to int

Yes it's certainly a 32 bits thing. Well I don't want to tweak PHP, recompile or something, so for the time being, I will check the file size, and if it's over 2GB, I'm not sending the header.

thank you all for your input