Rest and the WCF Web API

REST and the WCF Web API
Getting started with REST services and the WCF Web API
Maurice de Beijer

Objectives
What are REST services
Why REST instead of SOAP
The WCF Web API framework
The next webinar on the 25th of October is about creating HTML5/JavaScript clients for REST services

What are REST services
Representational State Transfer
A way of creating web services
Not using the WS-* SOAP specifications
All about resources
Not about calling functions, RPC
Embraces HTTP
Not just a way of getting data across the wire
Leverages the structure of the Internet
URLS
MIME Media Types
HTTP Methods
Caching
Security

The origin of REST
Architectural Styles and the Design of Network-based Software Architectures
By Roy Thomas Fielding
Chapter 5
One of the authors of the HTTP specification

Why are REST services popular
Almost every platform supports consuming them
All you need is an HTTP client stack
Many services are build around resources
CRUD style
Enables very scalable services
Build around the technology that powers the Internet

The WCF Web API framework
On CodePlex
http://wcf.codeplex.com/wikipage?title=WCF%20HTTP
Use NuGet from within Visual Studio 2010
http://nuget.org/
Current version 0.5
Much better than the original WCF support for REST
But doesn’t replace it

The resource URL
The URL is the key to a resource
http://bookshop.com/books (The collection of books)
http://bookshop.com/books/12345(An individual book)
A given URL always returns the same resource
Deleting one resource doesn’t change the URL of another resource
But a resource can have multiple URL’s
http://bookshop.com/orders/12345
http://bookshop.com/customers/12345/orders/12345

Different request/response formats
Uses standard HTTP MIME Media Types
http://www.iana.org/assignments/media-types/index.html
Content Negotiation
The client specifies a list of acceptable media types
The server chooses the best supported media type to return
XML
Good general purpose data format
JSON
Optimised for usage with JavaScript clients
Custom formats
Use one of the many IANA types
Define your own
Normally prefixed with vnd.
Example: application/vnd.wordperfect

HTTP Status codes
Tell the client application what happened
Successful 2xx
200 OK
201 Resource created
Redirection 3xx
301 Moved Permanently
Client Error 4xx
400 Bad request
404 Not found
Server Error 5xx
500 Internal Server Error
503 Service Unavailable

HTTP GET Method
No side effects
Can retrieve it as often as you like
Allows for caching
Request may never get to the server
Makes the web as scalable as it is
Use Accept header to specify the acceptable media type
Multiple types are supported
Examples:
Accept: application/xml
Accept: application/json
Accept: image/jpeg, image/*; q=0.5

Other HTTP Methods
POST
Creates new resource
Returns the URL to the created resource
PUT or PATCH
Replaces/updates resource
Idempotent
PATCH only replaces a part of the resource
DELETE
Removes resource
Idempotent

Microformats
Enable a much smarter client application
Embed allowed actions with a resource
Client can update the UI based on the resource
OData is a good example
Based on AtomPub
http://www.odata.org
Roll your own
Or reuse an existing one from IANA
Set the content-type
Use your own application/vnd.xxx

Rest is not perfect
No metadata
Little tooling in Visual Studio 2010
It’s harder than it seems
There is no official REST standard
There are many strong opinions about what is REST and what is not

Usefull resources
Essential Windows Communication Foundation 4 Training
http://www.develop.com/training-course/windows-communication-foundation-wcf
Hypertext Transfer Protocol -- HTTP/1.1
http://tools.ietf.org/html/rfc2616
The Atom Syndication Format
The Atom Publishing Protocol
Open Data Protocol (OData)
http://www.odata.org
WCF Web API Contrib
http://webapicontrib.codeplex.com
Fiddler
http://www.fiddler2.com

Summary
REST is all about resources
CRUD actions
REST embraces HTTP and the web
HTTP isn’t just a means of moving bits
REST services are a good way to build scalable services
Build on the infrastructure of the web
REST allows for very flexible services
You control every part of the message

Rest and the WCF Web API

by Maurice Beijer

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