ReST vs SOA(P)yawn ...

Instead ... Facts and confused metaphors

for Understanding ReST

Early Web

• Human edited Files / Document Oriented programatic output

• A patchy server opening up access to static files

• Massive Upgrade to Human Knowlege, Communication, and Transparency

• CGI Scripts

• Screen scrapping clients

• Spiders, Robots, and Internet Duct-tape

• Dynamic HTML

• XHTML & XML formats

• CSS

Tech Progress

Roy T. Fielding

Architectural Styles and the Design of Network-based Software Architectures

by Paul Downey

http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm

ReST is not

• A technology

• A set of standards

• COTS software

• A tooth paste

http://www.lostwackys.com/Wacky-Packages/die-cuts/Crust.htm

ReST is• A series of constraints that defines a

specific flavor of system architecture

• Layered

• Client / Server

• Code on Demand

• Client Cache

• Stateless Server

RepresentationaleStateTransfer

ReST is Weak

Poor network latency

Difficult to identify authoritative response

Uniform Interfaces degrade performance

Lacks “mandatory extensions” - must understand

Optimized for course grained transmissions

Hard to customize

ReST is Dope

Low technical barrier to play

General Interfaces

Resource Extensibility

Massively Scalable

Independent Deployment

but also

because of

UnReST

• Cookies - enabled server side session

• Personalization

• Vendor specific extensions

Lastly in his Thesis Fielding identifies these issues with HTTP

Did the masses listen to academia?

A Common Path

SOAP

/Server.do?some=stuff

RPC style

Large ControllersQuery String Param mappers

Form deserializers

Sessions

XML-RPC

Abstract away the network!

A Common Path?• Focus on APIs, distributed transactions, etc

• Procedural code

• Distributed OOP1992 called, it wants it’s

CORBA back ...

ReST Web Services are injectedinto HTTP molds

with gooey Web2.0 filling

RPC usually

http://www.wisconsinhistory.org/whi/fullimage.asp?id=13487

fights the webwith Complexity

ReSTful Web Services?

via Shannon C. on Flickr

Madge!You’re suggesting there’s issues with transporting all my SOAP traffic over POST through one URI?

But won’t I lose transport independence?

Relax, SOAP document literal over HTTP is the most popular.

Yes, but if you add using GET, more endpoints, etc you can have caching for free!

ReST in 90 seconds

• URIs

• Resources

• Representations

• State Transitions

• User agents, intermediaries, and servers

• Uniform Interfaces

Core Concepts

http://flickr.com/photos/68661927@N00/350737025/in/photostream/

URI• Everything has a name

• Excel good C3 = B3 * B2

• Outlook bad - No address for “Last email from RSDG”

• This presentation is available athttp://www.slideshare.net/ozten/slideshows

Resources

• Any “Thing” - concept, event, person

• Anything you would want to point too

• Request or Respose = data + metadata in an envelope with control data

• Explicit request / response - no hidden state

• Easier to load balance

• Easier to troubleshoot

Representations

• A serializable description of a Resource

• Modify resources through representations

• XHTML Microformats

• Industry standard binary formats ( jpg, mpg, etc )

• JSON

• XML ( Atom or custom )

• The resource itself for static files

State Transitions• Links

• link, img, and a tags

• FormsLinks and forms are the hypermedia elements of XHTML. They create the network effect of the web.

Every resource represents a state in your application. State transition aren’t hidden behind an API, but are instead transmitted back in forth in a hypermedia protocol. Client’s can follow these links and be less fragile to future changes. RPC usually lacks links and encourages assumptions about formatting URI or server states.

Hypermedia as the engine of application state

Client / Server

• User Agents

• Web browsers

• HTTP libraries - libwww, libcurl, etc

• Proxies

• Gateways

• Servers

Uniform InterfacesHTTP Method Guarantee # Of Effects

GET, HEAD Safe 0

PUT, DELETE Idempotent 1

POST None ???

Möbius strip via wikipediajpg

So What?

• Stateless Client / Server rules give us

• Client Side Cache

• HTTP 1.1 conditional GET

• Implement Etags, If-Modified-Since

• Real savings time, $, and complexity

Most popular example:

Common Misconceptions

But, Browsers only do GET and POST

• Yep, their horrible ReST clients

• Web Developers use XMLHttpRequest for PUT, DELETE, etc

• Outside of browser, use HttpClient,libwww, or libcurl

• ReST uniform interface means you can tunnel PUT, DELETE over POST or write one off Proxy via cleansweepsupply.com

ReST is just CRUD

• Sure you can expose DB on web

• Too cute and simple right?

HTTP SQL CRUDPOST INSERT Create

GET SELECT Read

PUT UPDATE Update

DELETE DELETE Delete

It’s about favoring protocols and resources over APIs.

Refactor design to use new resources if you run out of HTTP methods

ExampleRequirment: A user can subscribe to an artist feed

ArtistWS.subscribeUserTo( User user, Feed feed )

Artist - GET, PUT, DELETE

Subscription - GET, POST, PUT, DELETE

Feed - GET, PUT, DELETE

User - GET, POST, PUT, DELETE

POST /subscriptions

artist=Art.1234feed=Feed.2345

email=false

Location: http://foo.com/subscription/Sub.3456

OR

We need WSDL for ReST

• Yes, programmers need documentation and a way to discover functionality

• ReST gets for free

• Uniform Interface

• Transparent data and HTTP tools

• Explicit state transitions

• Power of XML - XSD, extensibility, etc

• WSDL tries to hide network, parsing and formating messages, loose typing

• Often WSDL is an afterthought, a verbose format itself, used to generate incredibly verbose SOAP payloads - Yeah tools!

• Doesn’t actually solve the really hard problems, still need other WS-* specs focused on such as transitions or security

• ReST still requires you to document your resources, representations, and other highly application specific details

• URI, Microformats, XSD, hypermedia, etc let ReST clients do this in a lightweight manner

• URITemplates, XHTML 5, etc coming

• besides, WSDL2Foo is bad

WADL

• Don’t agree that WSDL2Foo is bad?

• OKAY, Use WADL

• WSDL like tool

Rare Conceptions

• ReST is nothing more than the web circa 2003

• Human and programatic web both thrive under ReST constraints

• It’s the Data, not the Source, not the API, not the platform

• Mashups and ??? (future emergent techniques) are easier with ReST

Surprise, you’re soaking in it...

Everything we do over HTTP is “ReST”,

but we can build systems that work

with the natural form of the web

Call the police! TheseAPIs are a crime!

ReST isn’t your solution

• If your doing sophisticated mission critical distributed programming with transactions across multiple partners in synergistic fashion

• Use CORBA, EDI, Stateful protocol, etc

• Client and server written in Java? Use RMI, Jini, etc

• Invent a new architecture by applying constraints to derive a solution that works with your problem space ala Chapter 5 of Fielding

Resources

•http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm •http://rest.blueoxen.net/•http://microapps.org/•http://bitworking.org/news/•http://intertwingly.net/blog/•http://www.tbray.org/ongoing/