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Tag Archives: webhooks

Push/callbacks are better than polling.

This should be an easy argument. It’s not just more efficient, it’s more real-time. I once heard something like 40% of delicious.com requests returned 304 Not Modified. I imagine similar numbers for other popular sites. The more real-time you try to be with polling, the worse it gets. Don’t call us, we’ll call you. It’s more efficient.

RPC solutions provide more value than messaging solutions.

Although you can argue that RPC can be powered by messaging, and messaging can be used for RPC, the point is that they are different mindsets. RPC is about triggering code that does something. Messaging is about putting a piece of data in another bucket. When you try to call somebody, you usually don’t want to get their voicemail, right? This analogy goes even further in that, like voicemail, it must be checked on the other end. Messaging just pushes polling somewhere else.

More importantly, the focus on triggering code is central to this value proposition. Generative systems are more valuable than sterile systems. When did the web get interesting? When it became about more than just static content, and code was put in the loop to generate dynamic content. The point is that if you prioritize code to receive a message before humans, you open up many more possibilities.

RPC is about making things happen. Messaging stops short short of that by just moving data around.

HTTP is the defacto RPC protocol.

HTTP is everywhere. There are powerful free servers, clients in every major programming environment, and people know it well. It’s proven and it just works. HTTTP’s simple design also allows it to be extremely versatile. It’s basically the TCP of the application layer.

However, the best thing is that HTTP is RPC. This subtle fact has been true ever since CGI was introduced. We’ve gone through building RPC on top of it with XML-RPC and SOAP, but wisely settled on a form of RPC that’s just HTTP and is even aligned with HTTP semantics: REST.

If HTTP is RPC and HTTP is everywhere, it is our defacto RPC protocol. Especially for web applications that breath HTTP, it almost doesn’t make sense to think of any kind of inter-application communication that isn’t HTTP. Turtles all the way down!

HTTP RPC + Indirection = Webhooks

David Wheeler said, “All problems in computer science can be solved by another level of indirection.” Webhooks, and all callbacks, are about taking a procedure call and performing it on a variable function. This is indirection and this is very powerful. This is why Unix pipes work. STDIN and STDOUT are not hardcoded values, they’re variables that you can control.

Now imagine if all the web applications you used had extension points that you could effectively hook together with any other application. Well, that’s what webhooks are about.

Although it’s not the most compelling story, this blog post is a terribly effective analogy. So effective, non-techies can read it and “get webhooks” … in some cases leading them to rally for webhooks as much as I do! The analogy focuses on a non-computer, real-world analogy based on telephone calls. Then it follows up with a more concrete example that helps explain the possibilities:

A concrete example of a story made possible from webhooks that might be a useful scenario for many of you involves Twitter. Let’s say Twitter supported webhook callbacks for when somebody follows you. Right now you get an email, and from there you can decide what to do manually: follow them back, block them, or do nothing. I used to go out of my way to block users that I knew were spam bots, but now there’s so many it’s not worth the time. And of course I also generally follow back people that I actually know. If Twitter would simply call a script of mine whenever somebody followed me passing along the user ID, I could very easily run this logic in a PHP script or a simple App Engine app. Or perhaps I’d use Scriptlets (ahem, which was made exactly for these kinds of web scripts). It would work like this:

First, use the Twitter API to look up the user from the ID, and grab their name. Then use the Facebook API to check if that name shows up in my list of friends on Facebook. If so, use the Twitter API to follow them back. Otherwise, if they’re following over 1000 users and that number is more than twice the number that’s following them (which is roughly the heuristic I use manually), use the Twitter API to block them. All automatic.

Definitely worth the read, if I do say so myself. It’s also worth pointing people that want a quick understanding of webhooks. What kind of analogies have you come up with?