REST

Kay Ashaolu

REST

Representational State Transfer

Good news, everyone!

  • You already know REST
  • Representations (HTML! but also XML, JSON)
  • State
  • Transfer

History

  • Roy Fielding co-wrote HTTP specs
  • Defined REST in his 2000 PhD dissertations
  • Defined core set of constraints and why they were important

Constraints

  • Client-server: Two separate systems talk to each other through a well defined interface
  • Stateless: No context is stored between requests
  • Cacheable: Clients or intermediaries can cache results, and requests and results can specify caching information

Constraints

  • Layered: Requests can go through intermediaries (proxies)
  • Uniform Interface: The protocol between client and server follows the same rules regardless of the specific application

Client-Server

Pros
  • Browsers don't care what web server is providing representations, or which database is holding data
  • Servers don't care which clients are connecting
Cons
  • Overhead of transferring data
  • Fewer, simpler failure modes

Stateless

Pros
  • Simplifies server design and storage
  • Simplifies request grammar
  • Improves scalability, error recovery
Cons
  • Overhead of transferring client state
  • Not convenient for interactivity at protocol level

Cacheable

Pros
  • Browsers can store CSS and JavaScript
  • Businesses can cache responses, even from external sites
  • Servers can specify how long things should be cached for
Cons
  • Cache invalidation is hard
  • Can't rely on updated resources updating "everywhere"

Uniform Interface

Pros
  • Client and server know how to interact regardless of application hosted
  • Ancestry uses same interface as Yelp
  • Wider variety of clients that can handle multiple applications
Cons
  • For really unique applications, must jam into old paradigms
  • Difficult to optimize for performance of single application

REST is not HTTP

  • Remember HTTP is a transport protocol: a tube!
  • REST is a set of constraints on how to use that tube
  • We could use other tubes, like FTP, SMTP

Web is RESTful

  • Web is build on these ideas
  • Better leverage attained by embracing REST
  • Flexibility, scalability, visibility, simplicity

How to Spot RESTfulness

  • Should think through constraints, but here are some heuristics

Uses HTTP

  • REST is the underlying architectural principle of the web
  • The web primarily uses the HTTP protocol
  • The way browsers interface with web servers is inherently RESTFul if you think about it

Uses HTTP Commands

  • GET, POST, PUT...
  • vs using POST for everything

Uses HTTP response codes

  • 404 Not Found, 200 OK
  • vs. always responding with 200 OK but has an error message

URLs point to resources

  • /blog, /api/messages/34
  • vs. URLs pointing to commands: /api/createBlog, /api/getMessage/34

Representation links

  • A representation links to new possible actions
  • Client only needs to have representation
  • Hypermedia as the engine of application state (HATEOAS)

Example

{
	"business": "http://yelp.com/biz/27",
	"user": "http://yelp.com/user/5",
	"review_text": "..."
}

Counter Example

data = {
	"business_id": 27,
 	"user_id": 5
 	"review_text": "..."
}
requests.get("http://yelp.com/biz/{}".format(data[business_id"]))

Uses headers for meta data

  • Content-Type XML or JSON
  • vs. response has extra meta data in XML

Questions?