First I installed the curl extension for PHP:
$ sudo pacman -S php-curl
$ grep curl /etc/php/php.ini extension=curl.so
Then I installed the PHP PEAR
$ sudo pacman -S php-pear
Having now installed pear, I have also installed PECL, and should now be able to install the php_http extension.
$ pecl install php_http
$ grep http.so /etc/php/php.ini extension=http.so
The http.so is found in the folder /usr/lib/php/moduels/ and latter copied to the folder /usr/lib/http/modules/ .
Now, as far as I know, this should have installed the php_http extension, but when I try to
$req = new HttpRequest();
I get the error
Fatal error: Class 'HttpRequest' not found in /srv/http/webcrawler/nettocrawl.php on line 4