Quick and dirty WordPress plugin to ensure content is served over SSL if no mixed content.

gistfile1.php

<?php
/*
Plugin Name: Force HTTPS
Version: 0.1
Description: Quick and dirty way to ensure content is served over SSL if no mixed content. Removes the "http:" and "https:" from external images embedded in the_content so that SSL can be enabled without the security warning in IE. Redirects to HTTPS if no mixed-content warning will be generated; redirects back to HTTP if it will. Makes use of output buffering. Developed at <a href="http://shepherdinteractive.com/">Shepherd Interactive</a>.
Author: Weston Ruter
Author URI: http://weston.ruter.net/
*/

function wr_force_https_init(){
	if(!is_admin())
		ob_start('wr_force_https_replace');
}
add_action('init', 'wr_force_https_init');


function wr_force_https_replace($response){
	$http_url  = "http://" .  $_SERVER["SERVER_NAME"] . $_SERVER["REQUEST_URI"];
	$https_url = "https://" . $_SERVER["SERVER_NAME"] . $_SERVER["REQUEST_URI"];
	
	$https_response = preg_replace("#http://(" . join('|', array_map('preg_quote', array(
		$_SERVER['HTTP_HOST'],
		'ajax.googleapis.com'
	))) . ")#", '//$1', $response);
	
	$has_http_src = preg_match('{src=.?http:}', $https_response);
	
	if($_SERVER["HTTPS"] == "on") {
		if($has_http_src){
			wp_redirect($http_url);
			exit();
		}
		return $https_response;
	}
	else {
		if(!$has_http_src){
			wp_redirect($https_url);
			exit();
		}
	}
	return $https_response;
}