Allow Linking to Private Posts

nacin-linking-private-posts.php

<?php
/*
 * Plugin Name: Allow Linking to Private Posts
 * Description: Allows direct linking to private posts without authentication.
 * Author: Nacin
 * Version: 0.1-beta
 */

class Nacin_Links_Private_Posts {
	private $restore = null;
	private $comment_on_private = false;
	function __construct() {
		add_filter( 'posts_results', array( &$this, 'post_results' ), 10, 2 );
		add_action( 'pre_comment_on_post', array( &$this, 'pre_comment_on_post' ) );
		add_filter( 'pre_comment_approved', array( &$this, 'pre_comment_approved' ) );
	}

	function post_results( $posts, $wp_query ) {
		// Make sure this is the main query.
		if ( $wp_query !== $GLOBALS['wp_the_query'] )
			return $posts;
		// Need to be a single post, and not the comments feed.
		if ( ! $wp_query->is_single || $wp_query->is_feed )
			return $posts;
		// If the post status is private, fake it.
		if ( $posts[0]->post_status == 'private' ) {
			$posts[0]->post_status = 'publish';
			// Robots noindex, nofollow.
			add_filter( 'pre_option_blog_public', '__return_zero' );
			// Add a little warning.
			add_filter( 'the_content', array( &$this, 'the_content' ), 11 );
			// Restore.
			add_filter( 'the_posts', array( &$this, 'the_posts' ) );
			$this->restore = $posts[0];
		}
		return $posts;
	}

	function the_posts( $posts ) {
		if ( $posts[0] === $this->restore ) {
			$posts[0]->post_status = 'private';
			$this->restore = null;
		}
		return $posts;
	}

	function the_content( $content ) {
		$warning = '<hr/><p><strong>Warning: This post is private.
			It can only be accessed by the URL.</strong></p><hr/>';
		return $warning . $content;
	}

	function pre_comment_on_post( $post_id ) {
		global $post;
		if ( $post->post_status == 'private' ) {
			$this->comment_on_private = true;
			$post->post_status = 'publish';
		}
	}

	function pre_comment_approved( $approved ) {
		if ( $this->comment_on_private )
			$approved = 0;
		return $approved;
	}
}
new Nacin_Links_Private_Posts;