REST e Resource Oriented Architectures

REST and Resource Oriented Architectures Gabriele Lana gabriele.lana@gmail.com

what is REST?

REST is not a Protocol an Architecture a Software a Standard a fancy name for Web Services a Buzzword

Representational State Transfer Roy T. Fielding “Architectural Styles and the Design of Network-based Software Architectures” Ph.D dissertation, 2000

REST is a Software Architecture Style a 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

prediction for 2009 “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

why? “... 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

no Silver Bullets REST vs SOA vs SOAP vs RPC vs WS-* vs ...

but sometimes REST is better :-)

web applications Information Flow RDB HTTP OOP MS

HTTP is REST RDB HTTP OOP MS

Impedance Mismatch RDB HTTP OOP MS

Accidental Complexity RDB HTTP OOP MS

Essential Complexity RDB HTTP OOP MS

RDB RPC OOP MS HTTP RPC

Resource Oriented Architectures RDB HTTP ROA MS

maybe not today, but Yes, we Can HTTP ROA DATA

REST by Example (Chess)

how to Design a RESTful service Step by Step Leonard Richardson & Sam Ruby “RESTful Web Services”, O’Reilly 2007

1. every Resource must be Identiﬁed

Pawn Move Bishop Game Player Rank Board Rook File Knight Position Queen Square

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 move = d3-d8 /position/wqd8,wkd1,bqe6,bkf8

/player/50298

3. for each Resource expose a subset of the Uniform Interface

Uniform Interface GET (Read) POST (Create) PUT (Update) DELETE (Delete)

GET /player/50298 HTTP/1.1 Retrieve informations on identiﬁed Resource Idempotent, should not change the Resource State

POST /position/wqd3,wkd1,bke8 HTTP/1.1 n move = d3-d8 HTTP/1.1 302 Found Location: /position/wqd8,wkd1,bke8 POST to let Resources process informations

POST /game HTTP/1.1 n white = /player/50298 & black = /player/39650 HTTP/1.1 201 Created Location: /game/42 POST to Create new Resources

PUT /board/4815162342 HTTP/1.1 n position = /position/wqd3,wkd2,bke8 HTTP/1.1 205 Reset Content PUT to Update Resource Informations

PUT /position/wqd3,wkd1,bke8 HTTP/1.1 n position = /position/wqd3,wkd2,bke8 HTTP/1.1 405 Method Not Allowed a Method can be not supported by a Resource but should not be ignored

DELETE /board/4815162342 HTTP/1.1 HTTP/1.1 204 No Content DELETE to logically Remove Resources

4. for each Resource design Representations from and to Client

GET /position/wqd3,wkd2,bke8 HTTP/1.1 Accept: text/plain HTTP/1.1 200 OK Content-Type: text/plain;format=fen n 3k4/8/3q4/8/8/8/8/5K2 client/server Content Negotiation (MIME properties)

GET /position/wqd3,wkd2,bke8 HTTP/1.1 Accept: image/png;q=0.8, text/plain;q=0.2 HTTP/1.1 200 OK Content-Type: image/png n PNG... client/server Content Negotiation (Preferences)

GET /position/wqd3,wkd2,bke8.png HTTP/1.1 Accept: image/png HTTP/1.1 200 OK Content-Type: image/png n PNG... client Explicit Request of Content-Type

GET /position/wqd3,wkd2,bke8.gif HTTP/1.1 Accept: image/gif HTTP/1.1 406 Not Acceptable or more friendly HTTP/1.1 300 Multiple Choices Content-Type: application/xml n <choices><content type=”image/png” uri=”...”>

GET /game/42 HTTP/1.1 Accept: 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 old Web Applications?

GET /game/42 HTTP/1.1 Accept: 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-Lee on 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 things 2. Use HTTP URIs so that people can look up those names 3. When someone looks up a URI, provide useful information 4. Include links to other URIs, so that they can discover more things

POST /game/42 HTTP/1.1 Content-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. design typical ﬂows and error conditions

POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: 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 Created Location: /game/42/position/2 Response to the white Player GET /game/42/position/2 HTTP/1.1 301 Moved Permanently Location: /position/wra1,wna2,...,wpd4,...

GET /game/42 HTTP/1.1 Authorization: Basic dXN1... n <game> <player>...</player> <moves>...</player> </game> GET /game/42 HTTP/1.1 Authorization: Basic aYR5... n <game> <player>...</player> <moves>...</player> </game> both Players must GET the game Representation

POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: 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/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic aYR5... n ... what if black Player try to resend? HTTP/1.1 409 Conflict the game Representation is out of date

POST /game/42 HTTP/1.1 Content-Type: application/vnd.dharma.chess Authorization: Basic aYR5... n ... what if black Player try to move again? HTTP/1.1 403 Forbidden the black Player should wait for the white Player to move

POST /position/wqd3,wkd1,bke8 HTTP/1.1 n move = d3-e8 what if we try to make a wrong move? HTTP/1.1 404 Not Found Business Rules could be easily expressed through the Resource's Behavior

wait... what about complex User Interfaces?

what about Gmail

what about Gmail JS HTTP ? JS

what about Gmail

FAQ: cool URIs are 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 is stateless? Statelessness says that all possible states of the server are also Resources (Resource State)

FAQ: REST is stateless? Statelessness says that each message contains all the informations necessary to understand the Request (Application State)

Representational State Transfer Application State R3 R4 R2 R1 CLIENT SERVER Resource State

your application can be Discoverable

your application can be Testable

Testability View Model Control HTTP

Testability too much code untested View Model Control HTTP

Testability too fragile and unreliable View Model Control HTTP

Testability Player Board Position Game Move Js HTTP

Testability what about the view? Player Board Position Game Move Js HTTP

your application can be Composable

your application can be Scalable

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

now the Web can talk about chess

REST e Resource Oriented Architectures

by GrUSP on Jun 07, 2009

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