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Some People Understand REST and HTTP
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This is a follow-up post to my post here. You probably want to read that first.

UPDATE: Please note that 'REST is over'. 'Hypermedia API' is the proper term now.

A few words on standards versus pragmatism

When I wrote my first post on this topic, I tried to take a stance that would be somewhat soft, yet forceful. Engineering is the art of making the proper trade-offs, and there are times when following specifications is simply not the correct decision. With that said, my motivation for both of these posts is to eradicate some of the ignorance that some developers have about certain areas of the HTTP spec and Fielding's REST paper. If you understand the correct way, yet choose to do something else for an informed reason, that's absolutely, 100% okay. There's no use throwing out the baby with the bathwater. But ignorance is never a good thing, and most developers are ignorant when it comes to the details of REST.

Secondly, while I think that REST is the best way to develop APIs, there are other valid architectural patterns, too. Yet calling non-REST APIs 'RESTful' continues to confuse developers as to what "RESTful" means. I'm not sure what exactly we should call "RESTish" APIs (hey, there we go, hmmm...) but I'm also not under the illusion that I personally will be able to make a huge dent in this. Hopefully you, humble reader, will remember this when dealing with APIs in the future, and I'll have made a tiny dent, though.

So who does understand REST?

As it turns out, there are two companies that you've probably heard of who have APIs that are much more RESTful than many others: Twilio and GitHub. Let's take a look at GitHub first.

GitHub: logically awesome

GitHub's developer resources are not only beautiful, but thorough. In addition, they make use of lots more of REST.

The good

GitHub uses custom MIME types for all of their responses. They're using the vendor extensions that I talked about in my post, too. For example:

application/vnd.github-issue.text+json

Super cool.

Their authentication works in three ways: HTTP Basic, OAuth via an Authentication Header, or via a parameter. This allows for a maximum amount of compatibility across user agents, and gives the user some amount of choice.

Their Pagination uses a header I didn't discuss in part I: the Link header. Here's a link to the reference. Basically, Link headers enable HATEOAS for media types which aren't hypertext. This is important, especially regarding JSON, since JSON isn't hypermedia. More on this at the end of the post. Anyway, so pagination on GitHub:

$ curl -I "https://api.github.com/users/steveklabnik/gists"
HTTP/1.1 200 OK
Server: nginx/1.0.4
Date: Sun, 07 Aug 2011 16:34:48 GMT
Content-Type: application/json
Connection: keep-alive
Status: 200 OK
X-RateLimit-Limit: 5000
X-RateLimit-Remaining: 4994
Link: <https://api.github.com/users/steveklabnik/gists?page=2>; rel="next", <https://api.github.com/users/steveklabnik/gists?page=33333>; rel="last"
Content-Length: 29841

The Link header there shows you how to get to the next page of results. You don't need to know how to construct the URL, you just have to parse the header and follow it. This, for example, is a great way to connect a resource that's not text-based, such as a PNG, to other resources.

The bad

There's really only one place that GitHub doesn't knock it out of the park with their new API, and that's HATEOAS. GitHub's API isn't discoverable, because there's no information at the root:

$ curl -I https://api.github.com/
HTTP/1.1 302 Found
Server: nginx/1.0.4
Date: Sun, 07 Aug 2011 16:44:02 GMT
Content-Type: text/html;charset=utf-8
Connection: keep-alive
Status: 302 Found
X-RateLimit-Limit: 5000
Location: http://developer.github.com
X-RateLimit-Remaining: 4993
Content-Length: 0

Well, at least, this is how they present it. If you ask for JSON:

$ curl -I https://api.github.com/ -H "Accept: application/json"
HTTP/1.1 204 No Content
Server: nginx/1.0.4
Date: Sun, 07 Aug 2011 16:45:32 GMT
Connection: keep-alive
Status: 204 No Content
X-RateLimit-Limit: 5000
X-RateLimit-Remaining: 4991
Link: <users/{user}>; rel="user", <repos/{user}/{repo}>; rel="repo", <gists>; rel="gists"

You do get Links, but you have to construct things yourself. As a user, you get the same thing. It doesn't change the links to point to your repos, it doesn't give you links to anything else that you can do with the API.

Instead, the root should give you a link to the particular resources that you can actually view. Maybe something like this:

$ curl -I https://api.github.com/ -H "Accept: application/json" -u "username:password"
HTTP/1.1 204 No Content
Server: nginx/1.0.4
Date: Sun, 07 Aug 2011 16:45:32 GMT
Connection: keep-alive
Status: 204 No Content
X-RateLimit-Limit: 5000
X-RateLimit-Remaining: 4991
Link: </gists/public>; rel="public_gists", </user/repos>; rel="repos", <gists>; rel="gists"

And a bunch more, for all of the other resources that are available. This would make the API truly discoverable, and you wouldn't be forced to read their gorgeous documentation. :)

Twilio

I've always really enjoyed Twilio. Their API is incredibly simple to use. I once hooked up a little "Text me when someone orders something from my site" script, and it took me about fifteen minutes. Good stuff.

The good

Twilio has got the HATEOAS thing down. Check it out, their home page says that the base URL is "https://api.twilio.com/2010-04-01". Without looking at any of the rest of their docs, (I glanced at a page or two, but I didn't really read them fully yet), I did this:

$ curl https://api.twilio.com/2010-04-01
<?xml version="1.0"?>
<TwilioResponse>
  <Version>
    <Name>2010-04-01</Name>
    <Uri>/2010-04-01</Uri>
    <SubresourceUris>
      <Accounts>/2010-04-01/Accounts</Accounts>
    </SubresourceUris>
  </Version>
</TwilioResponse>

I introduced some formatting. Hmm, okay, Accounts. Let's check this out:

$ curl https://api.twilio.com/2010-04-01/Accounts<?xml version="1.0"?>
<TwilioResponse><RestException><Status>401</Status><Message>Authenticate</Message><Code>20003</Code><MoreInfo>http://www.twilio.com/docs/errors/20003</MoreInfo></RestException></TwilioResponse>

Okay, so I have to be authenticated. If I was, I'd get something like this:

<TwilioResponse>
  <Account>
    <Sid>ACba8bc05eacf94afdae398e642c9cc32d</Sid>
    <FriendlyName>Do you like my friendly name?</FriendlyName>
    <Type>Full</Type>
    <Status>active</Status>
    <DateCreated>Wed, 04 Aug 2010 21:37:41 +0000</DateCreated>
    <DateUpdated>Fri, 06 Aug 2010 01:15:02 +0000</DateUpdated>
    <AuthToken>redacted</AuthToken>
    <Uri>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d</Uri>
    <SubresourceUris>
      <AvailablePhoneNumbers>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/AvailablePhoneNumbers</AvailablePhoneNumbers>
      <Calls>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/Calls</Calls>
      <Conferences>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/Conferences</Conferences>
      <IncomingPhoneNumbers>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/IncomingPhoneNumbers</IncomingPhoneNumbers>
      <Notifications>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/Notifications</Notifications>
      <OutgoingCallerIds>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/OutgoingCallerIds</OutgoingCallerIds>
      <Recordings>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/Recordings</Recordings>
      <Sandbox>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/Sandbox</Sandbox>
      <SMSMessages>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/SMS/Messages</SMSMessages>
      <Transcriptions>/2010-04-01/Accounts/ACba8bc05eacf94afdae398e642c9cc32d/Transcriptions</Transcriptions>
    </SubresourceUris>
  </Account>
</TwilioResponse>

Awesome. I can see my all of the other resources that I can interact with. Other than knowing how to authenticate, I can follow the links from the endpoint, and discover their entire API. Rock. This is the way things are supposed to be.

The bad

This:

$ curl https://api.twilio.com/2010-04-01/Accounts -H "Accept: application/json"
<?xml version="1.0"?>
<TwilioResponse><RestException><Status>401</Status><Message>Authenticate</Message><Code>20003</Code><MoreInfo>http://www.twilio.com/docs/errors/20003</MoreInfo></RestException></TwilioResponse>

Versus this:

$ curl https://api.twilio.com/2010-04-01/Accounts.json
{"status":401,"message":"Authenticate","code":20003,"more_info":"http:\/\/www.twilio.com\/docs\/errors\/20003"}

:/ Returning JSON when your resource ends with '.json' isn't bad, but not respecting the Accept header, even when you return the right MIME type, is just unfortunate.

... and a little Announcement

It seems that this is a topic that people are really interested in. Part I of this article was pretty well-received, and I got lots of great email and feedback from people. It was also made pretty clear by a few people that they want more content from me on this topic.

So I decided to write a book about it. You can check out the site for "Get Some REST", and put in your email address. Then you'll get updated when I start pre-release sales.

So what's in "Get Some REST"? It's going to be a full description of how to build RESTful web applications, from the ground up. Designing your resources, laying out an API, all the details. I'm going to try to keep most of the content language-agnostic, but provide code samples in Rails 3.1, as well.

I plan on writing a bunch of content, and then releasing the book at half-price in beta. Early adopters will be able to get their two cents in, and I'll cover things they still have questions on. It'll be available under a liberal license, in PDF, ePub, all that good stuff.

I've also set up a Twitter account at @hypermediaapis. I'll be tweeting updates about the book, and also other good content related to RESTful design.

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