FeedWordPress works well if you want to syndicate content from various sources into a single Wordpress blog. Syndicating comments is, of course, more difficult. I’m finishing up a job for a client who wanted real-time synced comments, and suggested that Disqus might do the trick. I quickly discovered that Disqus is clearly not made to do what I wanted it to do. But, being the cool guy that I am, I hacked something together that is more or less functional.

Here were the requirements: Comments on a blog post needed to be synchronized between the source blogs and the hub blog. Readers had to be able to comment in both places and have the comments sync. While I’d be using Wordpress to create the hub blog, the source blogs would be hosted on various platforms: Tumblr, Typepad, Blogger, self-hosted Wordpress. (The distributed requirement is especially important. If the blogs were all on the same installation of WPMU, the job would be trivial and would not require a third-party solution like Disqus.) Because bloggers would be coming from different platforms, I not only had to be able to accomodate those platforms, but I also had to make sure that the system would work with the platforms’ stock configuration. That is, since I (and, generally speaking, the bloggers) don’t have access to the platform code, all custom modifications need to happen at the hub blog.

I don’t particularly recommend that anyone try to replicate what I’ve done here. But hopefully it will point the way toward what might be a viable third-party system for true comment syncing.

The details

Here’s my strategy with regard to Disqus. If all the source blogs were registered to the same Disqus Comments account (ie corresponding to a single shortname), then they’d all have the same forum_key, which is to say they’d be accessible by the same API request. Thus the strategy is to make Disqus unable to distinguish between API calls from the source blogs (which are, recall, making stock API calls to Disqus) and API calls from the corresponding posts on the hub blog.

I installed the Disqus Comment System plugin for the Wordpress hub blog and registered with the same credentials that would be given to the source blogs. When feeds starting syndicating to the hub blog, however, I found that the comment sections on the source post weren’t matching the comment section on the hub post. The URL for each comment thread’s RSS feed showed me why: Disqus indexes a forum’s comment thread based on some post information that it gets from the client platform, and each platform was formatting the information in a different way.

First problem: The Wordpress Disqus plugin uses a post variable called $thread_meta, which is set in disqus-comment-system/lib/api.php thus:

$thread_meta = $post->ID . ' ' . $post->guid;

Disqus would then create a comment thread based on this string. The problem is that $post->ID is the post ID number for the hub blog, and has nothing to do with the source blog (which, depending on platform, does not include post ids in its API request at all). So the source blog’s thread would be identified as test_post (for example) while the hub blog would be 34_test_post. I replaced the code above with

$thread_meta = $post->guid

which manages to stay pretty consistent across platforms. (NB: The same change has to be made on the source blog version of the Disqus plugin, if the source blog is running a self-hosted installation of Wordpress.)

Second problem: Getting a stable and unique identifier for each post thread is only the first step. You also need to make sure that the identifier is concatenated correctly when the actual API request is made. Disqus comment sections work by loading a piece of Javascript that is concatenated from an API request to disqus.com for the proper thread, then finds the comment section on the post page, and replaces the native comment code with the code returned from disqus.com. But I found (again, by looking at the URL for the RSS feeds) that each platform was making the request a little bit differently. At the end of disqus-comments-system/comments.php, the stock WP plugin reads

<script type="text/javascript" charset="utf-8" src="http://./disqus.js?v=2.0&slug=&pver=">

Through a fair degree of trial and error, I replaced it with a big block of code that figures out (via some metadata created by FeedWordPress) which platform that particular post came from, and then modifies the javascript accordingly:

ID, 'syndication_permalink'); ?>
ID, 'syndication_source'); ?>

<script type="text/javascript" charset="utf-8" src="http://./disqus.js?v=2.0&slug=&pname=wordpress&pver=">

<script type="text/javascript" charset="utf-8" src="http://./disqus.js?v=2.0&slug=&pname=wordpress&pver=">

<script type="text/javascript" charset="utf-8" src="http://./disqus.js?v=2.0&slug=&pver=">

In the first few lines, I do a bit of string manipulation to standardize the post title (ie the unique post identifier from Disqus’s point of view). Then I do some very ugly stuff. Wordpress was converting the em-dash (which was all over the client’s blog) into an ASCII code, which was screwing up the post identifier, so I just str_replaced it out. The next part (with the preg_match) is a bit tricky: in some cases, when Disqus receives requests from two blog posts with the same title (as is the case with the source blog post and the hub blog post), it differentiates between the two by assigning an apparently random two digit number to the second request it gets. Since the syndicated Disqus request will generally be sent after the source blog’s Disqus request (in virtue of its being syndicated), and therefore will be the one to be appended with the two-digit number, I figured I could just look for ‘_xx’ (where xx is a two digit number) at the end of the post title and strip it off. Ugly ugly ugly, but it works. The rest of the code just rearranges the javascript according to which platform the original post comes from, which in some cases requires the addition of source blog name.

With all this in place, I’ve got the following: A blogger posts on, say, his Tumblr blog, where Disqus is enabled. The post is fetched by FeedWordPress on the hub blog, where Disqus is also enabled, with the same user credentials. Then the hacks listed above trick Disqus into thinking that the syndicated post is the very same as the source post, so that the very same comments section is sent to each post. Kind of like magic, when it actually works.

Clearly, though, it would be much, much easier with a system that is built to do what I’m trying to do. That means, in part, having a single system for identifying posts across platforms (some appropriate htmlization of the post name, I presume) and then a single, unified system for making API requests.