Gabriele Lanagabriele.lana@gmail.com

REST and Resource Oriented

Architectures

what isREST?

a Protocolan Architecture

a Softwarea Standard

a fancy name for Web Servicesa Buzzword

REST is not

RepresentationalStateTransfer

Roy T. Fielding“Architectural Styles and the Design of Network-based Software Architectures”

Ph.D dissertation, 2000

a Software Architecture Stylea set of Constraints on Component

Interaction that, when obeyed, cause the resulting Architecture to have

certain properties

Roy T. Fielding http://roy.gbiv.com/untangled/2008/on-software-architecture

REST is

?

“Roy Fielding will officially disown most of the RESTful authors and software packages

available. Nobody will care, or worse, somebody looking to make a name for themselves will proclaim that “Roy doesn't really understand

REST”, and they'll be right: Roy doesn't understand what they consider to be REST”

http://dotnet.dzone.com/articles/ted-neward-2009-predictions-20

prediction for 2009

“... the motivation for developing REST was to create an architectural model for how the Web

should work, such that it could serve as the guiding framework for the Web protocol

standards”

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

why?

REST vsSOA vsSOAP vsRPC vsWS-* vs

...

no Silver Bullets

but sometimesREST is better :-)

HTTPOOP

RDB

MS

web applicationsInformation Flow

HTTPOOP

RDB

MSHTTP

HTTP is REST

HTTPOOP

RDB

MS

Impedance Mismatch

HTTPOOP

RDB

MS

AccidentalComplexity

HTTPOOP

RDB

MSHTTP

OOP

RDB

MS

EssentialComplexity

RPC

RPC OOP

RDB

MS

HTTP

HTTPRDB

MSROA

Resource Oriented Architectures

HTTP ROA DATA

maybe not today, but Yes, we Can

REST by Example(Chess)

how to Design aRESTful service

Step by Step

Leonard Richardson & Sam Ruby “RESTful Web Services”, O’Reilly 2007

1. every Resource must be Identified

BoardGame

Position

Move

FileRankPlayer

Square

Knight

Queen

Rook

Pawn Bishop

every Concept in your Domain can

be a Resource

2. design the URIs (Ubiquitous Language)

/position/wqd3,wkd1,bqd7,bkd8

/position/wqd3,wkd1,bqe6,bkf8/d3-d8

/move/wqd3,wkd1,bkf8-wqd8,wkd1,bkf8

/position/initial

/board/4815162342

/position/wqd3,wkd1,bqe6,bkf8

/position/wqd8,wkd1,bqe6,bkf8

move = d3-d8

/player/50298

3. for each Resourceexpose a subset of

the Uniform Interface

GET (Read)POST (Create)PUT (Update)

DELETE (Delete)

Uniform Interface

GET /player/50298 HTTP/1.1

Retrieve informations on identified Resource

Idempotent, should not changethe Resource State

POST /position/wqd3,wkd1,bke8 HTTP/1.1\nmove = d3-d8

POST to let Resources process informations

HTTP/1.1 302 FoundLocation: /position/wqd8,wkd1,bke8

POST /game HTTP/1.1\nwhite = /player/50298 &black = /player/39650

POST to Createnew Resources

HTTP/1.1 201 CreatedLocation: /game/42

PUT /board/4815162342 HTTP/1.1\nposition = /position/wqd3,wkd2,bke8

PUT to UpdateResource Informations

HTTP/1.1 205 Reset Content

PUT /position/wqd3,wkd1,bke8 HTTP/1.1\nposition = /position/wqd3,wkd2,bke8

a Method can benot supported by a Resource

but should not be ignored

HTTP/1.1 405 Method Not Allowed

DELETE /board/4815162342 HTTP/1.1

DELETE tologically Remove

Resources

HTTP/1.1 204 No Content

4. for each Resourcedesign Representations

from and to Client

GET /position/wqd3,wkd2,bke8 HTTP/1.1Accept: text/plain

client/server Content Negotiation(MIME properties)

HTTP/1.1 200 OKContent-Type: text/plain;format=fen\n3k4/8/3q4/8/8/8/8/5K2

GET /position/wqd3,wkd2,bke8 HTTP/1.1Accept: image/png;q=0.8, text/plain;q=0.2

HTTP/1.1 200 OKContent-Type: image/png\nPNG...

client/server Content Negotiation(Preferences)

GET /position/wqd3,wkd2,bke8.png HTTP/1.1Accept: image/png

HTTP/1.1 200 OKContent-Type: image/png\nPNG...

client Explicit Request ofContent-Type

GET /position/wqd3,wkd2,bke8.gif HTTP/1.1Accept: image/gif

HTTP/1.1 406 Not Acceptable

or more friendlyHTTP/1.1 300 Multiple ChoicesContent-Type: application/xml \n<choices><content type=”image/png” uri=”...”>

GET /game/42 HTTP/1.1Accept: application/vnd.dharma.chess

<game> <player role=”white”>/player/1001</player> <player role=”black”>/player/1002</player> <moves> <position>/position/initial</position> </moves></game>

custom Content-Type

wait...what about

plain oldWeb Applications?

GET /game/42 HTTP/1.1Accept: application/xhtml+xml

<html> ... <a rel=”owner” href=”/player/1001”>...</a> ... <ul class=”moves”> <li><image src=”/position/initial.png”/></li> </ul></html>

Semantic Web is not a dream

Tim Berners-Leeon Linked Data

“... almost 20 years ago I wanted to reframe the way we use

informations ... I invented the Word Wide Web ... now is time

for a new reframing...”

Tim Berners-Lee @ http://linkeddata.org

expected behavior of the web

1. Use URIs as names for things2. Use HTTP URIs so that people

can look up those names3. When someone looks up a URI,

provide useful information4. Include links to other URIs, so

that they can discover more things

POST /game/42 HTTP/1.1Content-Type: application/vnd.dharma.chess

Authorization: Basic dXN1cm5hbWU6cG...\n<game> <player>...</player> <moves> <position>/position/initial</position>

<position color=”white”> /position/wra1,wna2,...,wpd4,... </position> </moves></game>

... from and to the Client

5. designtypical flowsanderrorconditions

POST /game/42 HTTP/1.1Content-Type: application/vnd.dharma.chessAuthorization: Basic dXN1...\n<game> <player>...</player> <moves> <position>/position/initial</position>

<position color=”white”> /position/wra1,wna2,...,wpd4,... </position> </moves></game>

white Player make first move

HTTP/1.1 201 CreatedLocation: /game/42/position/2

Response to the white Player

GET /game/42/position/2

HTTP/1.1 301 Moved PermanentlyLocation: /position/wra1,wna2,...,wpd4,...

GET /game/42 HTTP/1.1Authorization: Basic dXN1...\n<game> <player>...</player> <moves>...</player></game>

GET /game/42 HTTP/1.1Authorization: Basic aYR5...\n<game> <player>...</player> <moves>...</player></game>

both Players must GETthe game Representation

POST /game/42 HTTP/1.1Content-Type: application/vnd.dharma.chessAuthorization: Basic aYR5...\n<game> <player>...</player> <moves> <position>/position/initial</position> <position>/position/wra1,wna2,...,wpd4,...</position>

<position color=”black”> /position/wra1,wna2,...,bpd5,... </position> </moves></game>

black Player can make next move

POST /game/42 HTTP/1.1Content-Type: application/vnd.dharma.chessAuthorization: Basic aYR5...\n...

what if black Player try to resend?

HTTP/1.1 409 Conflict

the game Representation isout of date

POST /game/42 HTTP/1.1Content-Type: application/vnd.dharma.chessAuthorization: Basic aYR5...\n...

what if black Player try to move again?

HTTP/1.1 403 Forbidden

the black Player should waitfor the white Player to move

Business Rules could be easilyexpressed through the Resource's

Behavior

POST /position/wqd3,wkd1,bke8 HTTP/1.1\nmove = d3-e8

what if we try to make a wrong move?

HTTP/1.1 404 Not Found

wait...what about

complex UserInterfaces?

what about Gmail

HTTP

?

JS

JS

what about Gmail

what about Gmail

FAQ: cool URIsare RESTful?

OpenSocial/people/{guid}/@all

Collection of all people connected to user {guid}http://www.opensocial.org/Technical-Resources/opensocial-spec-v081/restful-protocol.html

FAQ: REST isstateless?

Statelessness says thatall possible states of the server

are also Resources(Resource State)

FAQ: REST isstateless?

Statelessness says thateach message contains

all the informations necessaryto understand the Request

(Application State)

SERVER

R1

R2

R3R4

CLIENT

Application

State

Resource

State

Representational State Transfer

your application can be Discoverable

your application can be Testable

Testability

HTTP

View Model

Control

too much code untested

HTTP

View Model

Control

Testability

too fragile and unreliableTestability

HTTP

View Model

Control

Testability

HTTP

Board

Game

Player

Position

Move

Js

HTTP

Board

Game

Player

Position

Move

Js

what about the view?Testability

your application can be Composable

your application can be Scalable

...so what Really means (for me) being RESTful?

now the Webcan talk about

chess