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My involvement at NASA inadvertently got web hooks written about on O’Reilly Broadcast yesterday. Kurt Cagle did a nice write-up on his take on web hooks, and it’s possible there will be more coming from Cagle on the topic. Although the post at first seemed pretty framed around syndication and push, the fact that he says things like “server-side mashups” and sees web hooks as a means to “create orchestration of web services” shows he gets the greater significance of this simple mechanism.

I just wanted to cover a few things that were brought up by Cagle and a few others that have written about web hooks recently.

Replacing Syndication

It seems a lot of people see web hooks as an alternative to poll-based feeds and syndication. Although I’ve claimed before that “feeds are not the answer,” it was in context of the vision of pipes for the web. Feeds were not invented for pipelining. They were invented for simple content syndication, and I think they do a pretty good job at that use-case: answering the question, “Hey, what’s new from you?” That said, Cagle seems to be spot on about web hooks and syndication working together.

One of my original arguments for web hooks was that polling sucks. “Hey, what’s new from you?” becomes “Are we there yet? Are we there yet? Are we there yet?” The thing is, web hooks alone don’t let you ask, “What’s new from you?” Nor do they provide a persistent reference to data. Web hook payloads should be ephemeral.

What seems like an obvious solution in this use-case is to provide a feed and a web hook for notifications of updates to the feed. This way you have the feed, which is nice for people that like polling, but also to have a persistent resource on the web for that content stream. And then you have the optional web hook for getting notified of updates, potentially with the updated data so if you don’t want to retrieve the feed, you don’t have to.

There’s a slightly verbose standard spec (as many are) called GetPingd that shows a way you can do this, but I imagine there are simpler approaches. One thing GetPingd points out is that this is all very similar to the ping services for blogs to notify search engines of new content. The missing element of that system is the ability for anybody to subscribe to the notifications. That is part of the essence of web hooks, as Timothy Fitz recently tweeted:

Remember, HTTP callbacks are nothing new. It’s exposing them to the user that makes it a web hook, and that’s where the emergence is.

Anyway, I can understand asking the question, “Will web hooks replace feeds/syndication?” as a thought experiment in trying to understand this new paradigm. But I have to say, after thinking about this for a long time, they won’t. They might replace certain use-cases for feeds, but if feeds were broken enough that web hooks would replace them, it would have happened already.

HTTP vs XMPP

Now this is where we get into some interesting waters. A lot of people bring up good points on both sides. My stance is simply that web hooks are simpler and just as effective for the majority of use-cases, and therefore the obvious winner. There are less pieces, simpler APIs, existing infrastructure, and it’s debatable whether XMPP is inherently any more performant.

You have to consider the use-cases, though. Part of the vision of web hooks is to have a standard HTTP event mechanism for the web. I just don’t see every web service throwing up an XMPP stack along with their HTTP stack. The two can and will work together when necessary, but as Cagle notes, “web hooks in general may be superior for orchestration.” Remember, web hooks are about more than message passing.

Standards

Cagle briefly touched on the standards issue. I’m sure that having a nice standards document would make for great adoption propaganda, and I know quite well the significance of agreed upon conventions in technology. However, I’m not in a hurry to over engineer anything, and I’m not going to assume we’ll know everything about the implications of this mechanism that we can encode them in a document that will either be ignored or adopted by everybody, making it harder to adapt to change. The longer we can put off standardizing, the better.

In the article, Cagle compares it to AJAX, in that the community isn’t very standards oriented. I’m not exactly sure what the AJAX community would benefit from standards. I’m quite happy that AJAX wasn’t limited by a standard to only use XML. There is nothing wrong with options. That’s kind of the whole point of technology: to provide new avenues, options, and choices for empowerment. Tools will always be used however the tool user finds useful, which is not always how the toolmaker intended.

I would much rather provide examples, and rigorously defined patterns of usage and implementation than try to define a standard. When a globally accepted convention is necessary, then we can work one out (with a useful, ideally proven, implementation), but it will probably be about some aspect of web hooks, not the model as whole. I think the biggest aspect ripe for standardization is for machine-friendly announcement of hooks and mechanism for registering callbacks (aka subscribing). But this is not preventing web hooks from being useful, otherwise nobody would be using them already.

3 Comments

  1. Hey thanks for mentioning GetPingd – we’d love to find ways to simplify it – would love your help :)

  2. Some how Cagle still hasn’t fixed the typo I pointed out in my comment 4 days ago. Do some people just not read comments?

    • Mike, he might just be the super busy type. For example, he contacted me to talk more about web hooks and since I responded he has yet to follow up.


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