ApachesolrExtension module

I have completed the module and am posting here. The module implements :

• hook_install() and hook_uninstall() which register the variable apachesolr_service_class which is used by apachesolr_get_solr()
• hook_menu() and hook_settings_form() for the update path configuration page
• Drupal_Apache_Solr_Service_Extn.php file which contains the class that overrides _sendRawPost()

A few other findings that may help others :
1. fopen() is not allowed on certain sites if configured. You can use file_put_contents() in that case.
2. Make sure that the directory to which you are writing has write permissions for the Apache / web server user. This is required as Drupal writes the file during cron run.
3. Delete the index or change some content so that apachesolr_index_updated() is invoked. This function builds the index and a series of calls later invokes _sendRawPost()

Next, my solr infrastructure team will copy over the index from the file to the solr server. Will get back with how it goes !