Add a pre-comment action

[arickmann]

I may have missed this but I was searching for an action that triggers prior to comment handling in wp-comments-post.php to allow the post variables to be altered.

It seems that most spam plugins allow the comment to be added and then roll back instead of preventing the comment entering the database at all.

[fitztrev]

There is a filter: preprocess_comment (applied on line 648 of wp-inc/comment.php)

Also, in the past, I've accomplished what you're trying to do by using the following: ​http://wordpress.pastebin.com/f65e58aa8 But of course, the filter is the better way to do it.