Can't find php_json.h on my Ubuntu machine

I'm trying to install the solr module for PHP, which uses JSON to communicate between the web server and the solr server. While trying to compile solr, it cannot find the header ext/json/php_json.h and when I look, it isn't there. The perplexing thing is that JSON has been included into the version of PHP that is installed on my server (5.2.10-2ubuntu6.7). When I run a php -me command, I see that json is included in the list of modules installed. Any idea what package i开发者_开发知识库s missing that I need to install to get the missing headers?

I decided to make the appropriate directory /usr/include/php5/ext/json and copy the file from the PHP source tree. I got the file from http://svn.php.net/viewvc/php/php-src/tags/php_5_2_10/ext/json/php_json.h?revision=282308&view=markup. Turns out the module requires a newer version of json that what is installed on my server; I'm testing a patch to the module that would work for this old of a PHP installation.