REST – Theory vs Practicejaoo.dk/dl/jaoo-aarhus-2009/slides/MikeAmundsen_and_SubbuAllam… · REST as Explained 1. Identify resources 2. Give a URI to every resource 3. Design representations

10/06/2009 1

REST–TheoryvsPractice

SubbuAllamarajuMikeAmundsen

AbouttheSpeakers

  SubbuAllamaraju  Architect,Yahoo!  Webservicesstandards/practicesatYahoo!  Builtwebportals,andweb/WSservices(SOAPkind)frameworks(BEASystems)

  MikeAmundsen  IndependentConsultant  .NET  Long‐timeRESTafarian

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RESTfulWebServicesCookbookO’Reilly,March2010

Objectives

  RESTissetofconstraintsandnotrules  Knowinglyrelaxconstraints  Workwiththeplumbing  Applysoundsoftwareengineering

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RESTasExplained

1.  Identifyresources2.  GiveaURItoeveryresource3.  Designrepresentationsforresources4.  Operateusingauniforminterface5.  Usehypermediaastheengineofapplication

state

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AddressBook1.0

BuildaRESTfuladdressbook

GET /user/subbu/address/{id}Host: ex.org

200 OK ...PUT /user/subbu/address/{id}Host: ex.orgIf-Match: xyz

200 OK ...

POST /user/subbu/address-bookHost: ex.org

201 Created ...

Address Collection Resource

Address Resource

DELETE /user/subbu/address/{id}Host: ex.orgIf-Match: xyz

200 OK ...

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<address> <link rel=“http://ex.org/rel/person” href=“http://ex.org/mike”/> <street>...</street> <city>...</city> ...</address>

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<address-book> <link rel=“http://ex.org/rel/owner” href=“http://ex.org/subbu”/> <link rel=“next” href=“http://ex.org/subbu/address-book?p=2/”/> <address>...</address> <address>...</address> ...</address-book>

GET /user/subbu/address/{id}Host: ex.org

200 OK ...PUT /user/subbu/address/{id}Host: ex.orgIf-Match: xyz

200 OK ...

POST /user/subbu/address-bookHost: ex.org

201 Created ...


Address Resource

DELETE /user/subbu/address/{id}Host: ex.orgIf-Match: xyz

200 OK ...

ResourcesURIs

Uniforminterface

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✔

✔

✔

<address> <link rel=“http://ex.org/rel/person” href=“http://ex.org/subbu”/> <street>...</street> <city>...</city> ...</address>

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<address-book> <link rel=“self” href=“http://ex.org/subbu/address-book”/> <link rel=“next” href=“http://ex.org/subbu/address-book?p=2/”/> <address>...</address> <address>...</address> ...</address-book>

4 Representations

5 Applicationstate

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Visibility

StatelessInteractions

UniformInterface

Self‐Describing

HTTPgoodies–caching,optimisticconcurrency,conneg,monitoring,analytics+others

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AddressBook1.1

[UC]Supportaddressbooksyncformobileusers

GET /user/subbu/address-book

ForeachaddressinthecollectionComparelocalcopy

PUT if different

DELETE if missing

POST if new


Address Resource


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Visibility

SeparationofconcernsNetworkefficiency

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POST /user/subbu/address-book/mergeHost: ex.orgContent-Length: xxxContent-Type: application/xml;charset=UTF-8

<address-book> <address>...</address> <address>...</address> ...</address-book>

303 See OtherLocation: http://ex.org/user/subbu/address-book

BetterMerge

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POST /user/subbu/address-book/mergeHost: ex.orgContent-Type: application/xml;charset=UTF-8

<address-book> <address>...</address> <address>...</address> ...</address-book>

303 See OtherLocation: http://ex.org/user/subbu/address-book

? Reducedvisibility

✔ Betterseparationofconcerns

✔ Efficientnetworkuse

NetworkEfficiency

SeparationofConcerns

AtomicityandConcurrency

Protocol‐levelVisibility

Infrastructuresupport

Tradeoffs

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TakeaStepBack

1.EverythingattheendofaURIisaresource

Some“things”

“person”, “address book”

andsomenon‐“things”

“merge address book”, “reserve”, “cancel”, “compute distance”, “reimage the virtual machine”

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2.UsePOSTwhenindoubt

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GET Safe +IdempotentPUT Unsafe +IdempotentDELETE Unsafe +IdempotentPOST Unsafe +Non‐Idempotent

AllbetsareoffwithPOSTPOSTlimitsdamage

3.Don’ttunnelusingPOST

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POST /address-book

Mergeanaddressbook?Fixduplicates?Orsomethingelse?

Tunneling=Backtodarkages

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ProxyServer

WebServer

Browser(JSClient)

Dev:“WeshouldfindawaytomakeREST'faster'and/orprovidebatchingsupport”

Thisisnota“pedantic”pointofview

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ProxyServer

WebServer

Browser(JSClient)

Batch“endpoint”

POST /batchHost: ex.orgContent-Length: xxxContent-Type: application/xml;charset=UTF-8

<batch> <request method=“PUT” uri=“/addr”>...</request> <request method=“GET” uri=“/poi”>...</request> <request method=“GET” uri=“/deals”>...</request> </batch>

Abenignsolution?

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WebServer

Browser(JSClient)

ProxyServer

WebServer

Browser(JSClient)

BadGuy

Batch“endpoint”

ProxyServer

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POST /updateAddressGetPoiDealsHost: ex.orgContent-Length: xxxContent-Type: application/xml;charset=UTF-8

<address> ...</address>

CreateapplicationspecificresourceswithdistinctURIs

POST /batchHost: ex.orgContent-Length: xxxContent-Type: application/xml;charset=UTF-8

<batch>...</batch>✗

✓

4.BecreativewithURIs

FixedandknownURIs(CoolURIs)http://ex.org/user/subbu

ResourceswithmanyURIshttp://ex.org/user/1234/profile;t=3231231dasdhttp://ex.org/user/1234/profile;t=3da8432stgs

EphemeralURIs(UncoolURIs)http://ex.org/act/4567/status;t=rfdsf3adsd23dashttp://ex.org/act/transfer?f=12&t=32&sig=a359d72d424cbd913686435bc6e7e372

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5.IDsarenotbad,butURIsarebetter

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Howmuch“hyper”media?Shouldyoucare?

PerformanceLoosecoupling

Separationofconcerns

Appcomplexity

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<album>

<photoid=“1234”>...</photo>

<photoid=“5678”>…</photo></album>

<albumxml:base=“http://ex.org”>

<photo>

<linkhref=“/photo/1234”/>...</photo>

<photo>

<linkhref=“/photo/5678”/>...

</photo>

</album>

Bad?

Good?

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Scheduleinterview

Enterfeedback

Hire

Nohire

Enterreferencechecks

Candidate

Candidate

Candidate

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GET /transfer/token?from=1234&to=5678Host: ex.org

200 OK Content-Type: application/xml;charset=UTF-8

<token> <link rel=“http://ex.org/rels/transfer” href=“http://ex.org/transfer;9ihrdsadas”/> <from> <balance>...</balance> </from> <to> <balance>...</balance> </to> </token>

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URIdecoupling *****

Applicationflow *****

Opaqueapplicationstate *****

6.Managingconcurrency

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GET /subbu/address/1

200 OK Date: Mon, 28 Sep 2009 14:30:53 GMT Etag: “8cf498a1ca3ceb67fe50d401d4759e34” Last-Modified: Mon, 28 Sep 2009 01:30:53 GMT Cache-Control: public,max-age=3600

<address>...</address>

PUT /subbu/address/1If-Unmodified-Since: Mon, 28 Sep 2009 14:30:53 GMTIf-Match: “8cf498a1ca3ceb67fe50d401d4759e34”

412 Precondition Failed

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GET /acct/1234

200 OK ETag: "f091aae21b44c71:6b9" Content-Type: application/xml;charset=UTF-8

<account> ... </address>

GET /acct/5678

...

POST /transferHost: ex.orgContent-Type: application/x-www-form-urlencoded

amount=1000&from=1234&to=5678...

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GET /acct/1234

200 OK ETag: "f091aae21b44c71:6b9" Content-Type: application/xml;charset=UTF-8

<account> ... </address>

GET /acct/5678

...

POST /transferHost: ex.orgContent-Type: application/x-www-form-urlencoded

amount=1000&from=1234&to=5678...

✗ Noconcurrencycontrol

GET /transfer/token?from=1234&to=5678Host: ex.org

200 OK Content-Type: application/xml;charset=UTF-8

<token> <link rel=“http://ex.org/rels/transfer” href=“http://ex.org/transfer;9ihrdsadas”/> <from> <balance>...</balance> </from> <to> <balance>...</balance> </to> </token>

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POST /transfer/token;9ihrdsadasHost: ex.orgContent-Type: application/x-www-form-urlencoded

amount=1000

201 Created Location: http://ex.org/transfer/1234 Content-Type: application/xml;charset=UTF-8

<transfer> <created>2009‐09‐30T15:00:00Z</created> <from> <balance>...</balance> </from> <to> <balance>...</balance> </to> </transfer>

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✔ Concurrencycontrol

7.Cachingisnotperfect

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HTTPServerCacheClient Data

Ideal–perfectlyvisible

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Otherapps

HTTPServerCacheClient

Data

Data

Data

Client

CacheClient Cache

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Everyrowisaresource

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Overlappingdata

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Someresourcesarelikehomepages

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Noconditionalreads

Nowritesonoverlappingresources

Acceptstaleness

Conclusion

  Focusontradeoffs  Relaxconstraintsjudiciously,butnotaccidentallyorbyignorance

  PutHTTPanditsplumbingtogooduse

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8.URIsforExtensibilityandVersioning

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HTTPmethodsarefixed

Newheadersmaygetdropped

Plumbingmaynotdifferentiatebetweenmediatypes

URIsareyourbestbet

9.FocusonDesignTimeDiscovery

  Runtimediscoveryworksgreatforbrowsers+humans,notformachineclients

  Developersneeddesign‐timeinformation  LeverageOPTIONSandconventionswheneverpossible

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Developersneeddesign‐timeinfo

  Allresourcesandmethodssupportedforeach  Mediatypesandrepresentationsforrequestsandresponses

  Linkrelations,descriptions,expectedresources,mediatypes

  AnyfixedURIsnotavailablevialinks  QueryparametersforfixedURIs  URItemplatesandtokenparsingrules

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Documents

REST – Theory vs Practicejaoo.dk/dl/jaoo-aarhus-2009/slides/MikeAmundsen_and_SubbuAllam… · REST as Explained 1. Identify resources 2. Give a URI to every resource 3. Design representations