on being restful

On being RESTfulFabio Mancinelli

fm@fabiomancinelli

An introduction to the REST architectural style...

A different way of looking atService Oriented Computing

What is this talk about?

An introduction to the REST architectural style...

A different way of looking atService Oriented Computing

What is this talk about?

...and some ideas to foster discussion forfinding new research directions! ☺

A RESTless worldAlso known as “Service Oriented

Architecture”

Classic SOA

• Web-services

• WSDL

• SOAP

• UDDI Service provider

Servicerequester

Servicebroker

Register Search

Request

Classic SOA

• Web-services

• WSDL

• SOAP

• UDDI Service provider

Servicerequester

Servicebroker

Register Search

Request

WSDL WSDL

SOAP

Web Service

UDDI

Web(?) services“Definition: A Web service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format (specifically WSDL). Other systems interact with the Web service in a manner prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.”

[W3C, http://www.w3.org/TR/ws-arch/#whatis]

http://www.w3.org/TR/ws-arch/#

http://www.w3.org/TR/ws-arch/#

WSDL

XML description of the service interface

SOAP

• Was “Simple Object Access Protocol”, sometimes referred as SOA-Protocol

• Simply an XML-based messaging protocol used mainly as an RPC protocol

UDDI

• Universal Description, Discovery and Integration

• Platform-independent, XML-based registry for business services

• Accessible via SOAP, provides WSDLs (... and other complementary information)

The WS-* hell• WS-Policy

• WS-PolicyAssertions

• WS-PolicyAttachment

• WS-SecurityPolicy

• WS-Discovery

• WS-Introspection

• WS-Metadata Exchange

• WS-Resource Framework

• WS-Eventing

• WS-Addressing

• WS-Enumeration

• WS-Transfer

• WS-I Basic Profile

• WS-I Basic Security Profile

• WS-BPEL

• WS-CDL

• WS-Security

• WS-Secure Conversation

• WS-Security Policy

• WS-Trust

• WS-Federation

• WS-Federation Active Requestor Profile

• WS-Federation Passive Requestor Profile

• WS-Reliable Messaging

• WS-Reliability

• WS-Atomic Transaction

• WS-Business Activity

• WS-Notification

• WS-Eventing

• WS-Management

• WS-Management Catalog

• WS-Resource Transfer

The RESTful sideAlso known as “The Web”

2000

@PHDThesis{REST, Author = {Roy Thomas Fielding}, Title = {Architectural styles and the design of network-based software architectures}, Year = {2000}, Publisher = {University of California, Irvine},}

What is REST?

• REpresentational State Transfer

• An architectural style for distributed hypermedia systems

• A Uniform-Layered-Client-Cache-Stateless-Server with Code on Demand architectural style [Fielding2000, Figure 5-8]

What is REST?

What is REST?

• Data elements• Resources and identifiers

• Representations

• Metadata

• Control data

• Connectors• Client

• Server

• Cache

• Resolver

• Tunnel

• Components• User agent

• Origin server

• Gateway

• Proxy

Data elements

• Resources (and resource identifiers)“Any concept that might be the target of author’s hypertext”, addressable by well defined resource identifiers and associated to one or more representations

• RepresentationsA machine-understandable description of the current resource state; typically a sequence of bytes in a well defined format known as the media-type

• MetadataAdditional data used to provide additional information about a representation, that cannot be extrapolated from the representation itself

• Control dataInformation describing the purpose of a message exchanged between components

Connectors• Client connector

Initiates communication and performs requests

• Server connectorListens for connections and replies to requests

• Cache connectorAssociated to a client or server connector, saves replies to requests for a later usage

• ResolverTranslates resource identifiers to network addresses for the actual communication

• TunnelRelays communication across communication boundaries

Components

• User agentUses a client connector to perform requests and is the final recipient of responses

• Origin serverUses a server connector for processing requests and providing responses. It is the source of resource representations and is the entity governing their state

• ProxyAn intermediary entity selected by a client for performance enhancement, data translation, etc.

• GatewayAn intermediary entity imposed by the network or by the origin server with similar functions as a proxy

REST and the Web

• URLs provide a consistent and accepted naming scheme for addressing resources

• HTTP provides the uniform interface for accessing resources

• Standard formats provide widely understood representations

Web Data Elements

REST data element Web instantiation

Resource identifier URL

Representation HTML, JPG, ...

Representation medatada Media-type, last-modification time

Control data if-modified-since, cache-control

Web ConnectorsREST connector Web instantiation

Client libwww, libwww-perl

Server libwww, Apache API

Cache Browser cache, Akamai

Resolver Bind (DNS)

Tunnel SOCKS, SSL

Web Components

REST component Web instantiation

Origin server Apache httpd, Microsoft IIS

User agent Firefox, IE, Safari, ...

Gateway Squid, CGI, ...

Proxy CERN proxy, Gauntlet

A twisted perspectiveFrom interfaces to resources

REST Key principles

• Addressability

• Uniform interface

• Stateless communication

• Hypermedia As The Engine Of Application State

Addressability

• Using resource URIs to expose interesting part of system data and state

• All the pages talking about me: http://www.google.com/search?q=Fabio+Mancinelli

• Introduces nice properties (e.g., easy communication, bookmarking, caching, chaining...)

http://www.google.fr/search?q=Fabio+Mancinelli




Uniform interface

• A single interface is used to access and manipulate resources

• Well defined semantics

• HTTP is the uniform interface to the webVerb (method) Semantics Property

GET Retrieve a representation Safe + Idempotent

PUT Store a representation Idempotent

DELETE Delete a resource Idempotent

POST Problems here! A backdoor/mismatch

Uniform interface

API1

API3

API2

APIn

Uniform interface

Uniform interface

Twisted!

OrderManagementService

+ getOrders()+ submitOrder()+ getOrdersForCustomers()+ updateOrder()+ addOrderItem()+ cancelOrder() CustomerManagementService

+ getCustomers()+ addCustomer()+ getCustomerDetail()+ updateCustomer()+ deleteCustomer()

[Example taken from http://www.infoq.com/articles/rest-introduction by Stefan Tilkov]

http://www.infoq.com/articles/rest-introduction


Twisted!

[Example taken from http://www.infoq.com/articles/rest-introduction by Stefan Tilkov]

HTTP

GETPUTPOSTDELETE

/orders

GET - List all ordersPUT POST - Add new orderDELETE

/orders/{id}

GET - Get order detailsPUT - Update orderPOST - Add itemDELETE - Cancel order

/customers

GET - List all customersPUT - Update customerPOSTDELETE - Delete customer

/customers/{id}

GET - Get customer detailPUT - Update customerPOSTDELETE - Delete customer

/customers/{id}/orders

GET - Get all orders for customerPUTPOST - Add orderDELETE - Cancel all customer orders



Statelessness

• No conversational state: every request carries all the information needed to its fulfillment

• Implies that every possible server state is exposed as a resource

HATEOAS (!)

• Addressability enables clients to follow links to “next states”

• http://www.google.fr/search?q=Fabio+Mancinelli&start=2

http://www.google.fr/search?q=Fabio+Mancinelli&start=10




Prior artA sense of déjà vu?

Unix

(Almost) Everything is a file

Unix

(Almost) Everything is a file

Uniform interface

+ read()+ write()

Pipes

for i in $(seq 13830 21829); do egrep "^From:" $i | awk '{print $2 $3}'; done | sort | uniq -c | sort -nr | head -n15

[Extract the Top-15 most active people on the eclipse.newcomer newsgroup during the last yearhttp://eclipsewebmaster.blogspot.com/2008/02/newcomer-newsgroups-top-15.html]

http://eclipsewebmaster.blogspot.com/2008/02/newcomer-newsgroups-top-15.html%5D

http://eclipsewebmaster.blogspot.com/2008/02/newcomer-newsgroups-top-15.html%5D

/dev and /proc

• Make a backup image of the whole disk:cat /dev/hda > backup.img

• Play music: cat music.mp3 > /dev/audio

• Record voice:cat /dev/audio > mytalk.wav

• Change system settings: echo “0” > /proc/sys/net/ipv4/ip_forward

Pervasively RESTfulBringing REST everywhere

A “Pervasive Web”

• From objects providing services to resources representing things (...and their state)

• Applying REST principles to the pervasive world

• Make pervasive contexts be part of “The Web” and not running on top of it.

The vision

Expose the “pervasive hardware” RESTfully

The visionGET ptp://room/light

PTP/1.0 200 OKContent-type: text/xml<state> off</state>

The visionPUT ptp://room/lightContent-type: text/xml<state> on</state>

PTP/1.0 200 OK

Challenges

• KISS: Keep It Sweet & Simple!

• New architectures and protocols (extensions) for being pervasively RESTful: Is “The Web” enough?

• Reconcile pervasive world’s peculiar characteristics with a RESTful setting

• Overcoming REST limitations

Conclusions

• No conclusions yet... That’s the beginning!

Questions?

• WDYT? Does it make sense?

on being restful

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