representational state transfer
DESCRIPTION
This presentation aimed to explain what is REST and why it is commonly misunderstood. It focuses on describing REST from scientific point of view, based on Roy`s Fielding dissertation.TRANSCRIPT
Representational State Transfer
Alexei Skachykhin – Software EngineeriTechArt, 2014
The Internet Of Things Explosion of WWW Smart Electronics Web APIs
Painting Style
What painting style is it?
Cubism? Surrealism?
REST
Like painting style, REST is a network architectural styleRepresentational State Transfer
REST
NO SPEC! NO PROTOCOL!
Who coined the term?Roy Fielding
Author of HTTP spec Co-founder of Apache HTTP Server Senior Principal scientist at Adobe
Who else?Mike Amundsen Leonard Richardson
Architectural Style
Architectural style is basically set of constraints, andfollowing them leads to gaining certain
architectural properties (benefits)
Architectural Style
Feature-driven Architectural
Style
Architectural Style
Constraints-driven Architectural Style
Properties of REST
Heterogeny Scalability Evolvability
Visibility Reliability Efficiency
ConstraintsClient-Server Stateless Cacheable
Layered System
Code on Demand
Uniform Interface
Optional constraint
REST Derivation
RR CS LS VM U
$ CSS LCS COD
C$SS LC$SS LCODC$SS REST
uniform interface
programmable
layeredseparated
on-demand
replicated
stateless mobile simplevisible
intermediate
processing
cacheable
reliable shared extensible reusable
scalable multi.org.
Client-Server Separation of concerns Independent development Security is scoped to connections
Benefits
Client-Server
Wouldn`t that mean that Client-Side databases violate REST?
NOT AT ALL ACTUALLY
Client-Server
How does WebRTC fit into REST?IT DOESN`T
Stateless
Each request from client to server must contain all of the information necessary
to understand the request
Stateless
Application State
Resource State
Stateless Simplified Scalability (CAP theorem) Improved Reliability (recover from
failures) Visibility
Benefits
Stateless Performance decrease (repetitive data) Risk of inconsistent app behavior
Disadvantages
Cacheable
Cache constraints require that the data within a response to a request be implicitly or
explicitly labeled as cacheable or non-cacheable
Cacheable Improved efficiency Improved scalability Improved user perceived performance
Benefits
Layered system
Allows an architecture to be composed of hierarchical layers
Layered system Bound complexity Improved scalability (load balancing)
Benefits
Layered system Increased latency User-perceived performance may
degrade
Disadvantages
Code on Demand (Optional)
REST allows client functionality to be extended by downloading and executing
code in the form of applets or scripts
Code on Demand (Optional) Improved extensibility Simplified clients
Benefits
Uniform Interface
Generalized interface between components. All of the components communicate through this interface
Uniform Interface Improved visibility Overall simplicity Implementation decoupled from
services
Benefits
Uniform Interface
BUT!Performance suffers!
Uniform InterfaceIdentification of
resourcesManipulation of
resources through representations
Self-descriptive messages
Hypermedia as the engine of application
state
Uniform InterfaceResources
Resource is any concept that might be target of an author`s hypertext reference
Uniform InterfaceResources
DOCUMENT, IMAGE, PERSON, COLLECTION OF FAVOURITE MOVIES, E.T.C.
Uniform InterfaceResources
resource to set map Static semantics Many-to-Many
Uniform InterfaceResources
Don`t use database schema as a basis for Web API for couple of reasons
API clients care about application semantics not database schema, which is different thing
Changes to the database schema become impossible
Uniform InterfaceResource Identification
Not a word about URL format!It doesn`t matter!
Uniform InterfaceResource Identification
Hardcoded URLs or URL templates is a form of
coupling!
Uniform InterfaceResource Identification
URI Templates (RFC 6570)http://example.org/~{username}/{term:1}/{term}{?
q*,lang} { username: "rodneyrehm", term: "hello world", q: { a: "mars", b: "jupiter“ }, lang: "en" }
+
=http://example.org/~rodneyrehm/h/hello%20world?a=mars&b=jupiter&lang=en
Uniform InterfaceManipulation of resources through representations
A representation is a sequence of bytes, plus representation metadata to describe those bytes. Representation captures the state of
resource.
Uniform InterfaceManipulation of resources through representations
Can be any sequence of bytes Resource can have multiple representations Content negotiation is needed
Uniform InterfaceManipulation of resources through representations
Do I violate REST if I pick HTML as representation
format? NO YOU DON`T
Uniform InterfaceHATEOAS
HATEOAS!Is it a Greek got?
Uniform InterfaceHATEOAS
Hypermedia as the engine of application state!
Uniform InterfaceHATEOAS
You already know about Application State, right?
At least I told you 10 minutes ago :)
Uniform InterfaceHATEOAS
Hypermedia connects resources to each other, and describes their
capabilities in machine-readable ways
Uniform InterfaceHATEOAS
What to do next?
Uniform InterfaceHATEOAS
What to do next?
{ "appnews": { "appid": 440, "newsitems": [{ "gid": "3189986872441392984", "title": "Team Fortress 2 Update Released", "url": "http://store.steampowered.com/news/13634/", "is_external_url": false, "author": "Valve", "feedlabel": "Product Update", "date": 1402535460, "feedname": "steam_updates“ }] }}
Uniform InterfaceHATEOAS
“Hypermedia connects resources to each other, and describes their capabilities in machine-readable
ways”
- Roy Fielding
Uniform InterfaceHATEOAS
Most of the “RESTful” Web APIs are not RESTful, because of lack of
hypermedia
Uniform InterfaceHATEOAS
Decoupling between client and server Resilience to API changes Enhanced usability (no hardcode and doc issues)
Why hypermedia is important for Web APIs?
Uniform InterfaceHypermedia Aware Media Types
Siren – generic hypermedia format
{ "class": ["owner", "vip"], "properties": { "name": "Kevin“ }, "entities": [ { "rel": ["https://rels.x.io/dog"], "href": https://api.x.io/dogs/1 } ], "actions": [ { "name": "adopt", "method": "POST", "href": "https://api.x.io/owners/1/dogs", "fields": [{ "name": "dog-name", "type": "text" }] } ], "links": [ { "rel": ["self"], "href": "https://api.x.io/owners/1" } ] }
LinkLink Relation
Uniform InterfaceHypermedia Aware Media Types
SIREN, HAL, COLLECTION+JSON, JSON-LD, HYDRA, OData, AtomPub, HTML
W3C Spec
Uniform InterfaceHATEOAS
Not a word about URL format!It doesn`t matter!
Uniform InterfaceHATEOAS
Hardcoded URLs or URL templates is a form of
coupling!
REST Flavor“REST is software design on the scale of decades:
every detail is intended to promote software longevity and independent evolution. Many of the
constraints are directly opposed to short-term efficiency”
- Roy Fielding
HTTP only?REST is not bound to HTTPOther implementations are: CoAP, Waka
Richardson Maturity ModelNot only verbs but all HTTP facilities
Richardson Maturity Model
Don`t reinvent the wheel, stick with capabilities of application protocol of your choice (HTTP
mostly)HTTP Verbs, Status Codes, Headers
REST Religion
REST is not a religion! Treat it as a reference network architecture of the Web
LinksRoy`s Fielding dissertation: http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm
API Academy:http://www.apiacademy.co/
Parse.com https://parse.com/
Hypertext Driven API: http://roy.gbiv.com/untangled/2008/rest-apis-must-be-hypertext-driven
