canonicalLink not working on

Hello, I am running zen cart version 1.5.1 with several add on plugins and recently I noticed that my canonicalLink was not working. I'm assuming it's because of some add on either eliminated or created an error on one of the files. Please let me know what files control the canonicalLink so I can see where the error is and fix it.
Thanks

The template basically controls whether or not to display the canonical link. If there is reason to believe that an error is being generated, then this will typically manifest as a white page or a partial white page. But regardless would/should log a myDebug file to the logs directory beginning in ZC 1.5.1. Otherwise try temporarily changing to the default ZC template and see if your canonical link is restored for display.

Tadj Hemingway:

Please let me know what files control the canonicalLink so I can see where the error is and fix it.

/includes/init_includes/init_canonical.php .....is where they are defined

/includes/templates/YOURTEMPLATE/common/html_header.php ....... is where the are output.

Cheers
RodG

Some info just to help me next time I have this problem and can't remember the answer.

I found the $canonicallink was not being generated ...and eventually discovered it was due to viewing the page as ssl (https) BUT HTTP_SERVER was http.

This is trapped by the code in init_canonical:

  case ($request_type == 'SSL' && substr(HTTP_SERVER, 0, 5) != 'https'):
    $canonicalLink = '';

torvista:

Some info just to help me next time I have this problem and can't remember the answer.

I found the $canonicallink was not being generated ...and eventually discovered it was due to viewing the page as ssl (https) BUT HTTP_SERVER was http.

This is trapped by the code in init_canonical:

case ($request_type == 'SSL' && substr(HTTP_SERVER, 0, 5) != 'https'):
$canonicalLink = '';

This appears to have been from an earlier design consideration that https sites/pages would not be indexed, but it is also a reason why the suggestion of the way to implement full site https: is provided in the following FAQ: <https://www.zen-cart.com/content.php?56-how-do-i-enable-ssl-after-i-have-installed-zen-cart>