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Website Integrations #2: oEmbed

Welcome to part 2 of this impromptu miniseries! In this second part of three, I'll be showing you a little about how I set up and tested a simple oEmbed provider for my blog posts - I've seen lots of oEmbed client information out there, but not much in the way of provider (or server) implementations.

If you haven't read part one about the open graph protocol yet, then you might find it interesting.

oEmbed is a bit different to open graph in that instead of throwing a bunch of meta tags into your <head />, you instead use a special <link /> element that points interested parties in the direction of some nice tasty json. Personally, I find this approach to be more sensible and easier to handle - the kind of thing you'd expect from an open standard.

To start with, I took a read of their specification, as I did with open graph. It doesn't have as many examples as I'd have liked, and I had to keep jumping around, but it's certainly not the worst I've seen.

oEmbed is built on the idea of providers (that's me!) and consumers (the programs and website you use). Providers, erm, provide machine-readable information about urls passed to them, and consumers take this information provided to them and display it to the user in a manner they think is appropriate.

To start with, I created a new PHP file to act as my provider over at https://starbeamrainbowlabs.com/blog/oembed.php and took a look at the different oEmbed types available - oEmbed has a type system of sorts, similar to open graph. I decided on link - while a rich would look cool, it would be almost impossible to test with every client out there, and I can't guarantee how the html would be rendered or what space it would have either.

With that decided, I made a list of the properties that I'd need to include in the json response:

Then I looked at the data I'd be getting from the client. It all comes in the form of GET parameters:

With all the information close at hand, I spent a happy hour or so writing code, and ended up with a script that outputs something like this:

{
    "version": "1.0",
    "type": "link",
    "title": "Website Integrations #1: Open Graph",
    "author_name": "Starbeamrainbowlabs",
    "author_url": "https:\/\/starbeamrainbowlabs.com\/",
    "provider_name": "Stardust | Starbeamrainbowlabs' Blog",
    "provider_url": "https:\/\/starbeamrainbowlabs.com\/blog\/",
    "cache_age": 3600,
    "thumbnail_url": "https:\/\/starbeamrainbowlabs.com\/images\/logos\/open-graph.png",
    "thumbnail_width": 300,
    "thumbnail_height": 300
}

(See it for yourself!)

Though the specification includes requirements for satisfying 2 extra GET parameters, maxwidth and maxheight, I chose to ignore them since writing a dynamic thumbnail rescaling script is both rather complicated and requires a not insignificant amount of processing power every time it is used.

After finishing the oEmbed script, I turned my attention to one final detail: The special <link /> tag required for auto-discovery. A quick bit of PHP in the article page renderer adds something like this to the header:

<link rel="alternate" type="application/json+oembed" href="https://starbeamrainbowlabs.com/blog/oembed.php?format=json&url=https%3A%2F%2Fstarbeamrainbowlabs.com%2Fblog%2Farticle.php%3Farticle%3Dposts%252F229-Website-Integrations-1-Open-Graph.html" />

and with that, my oEmbed provider implementation is complete - but it still needs testing! Unfortunately, testing tool for oEmbed are few and far between, but I did manage to find a few:

After testing and fixing a few bugs, my oEmbed provider was complete! Next time, I'll be taking a look at twitter's take on the subject: Twitter cards.

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