An Introduction into the Web API

Brad Genereaux | @integratorbrad | about.me/integratorbrad | hcintegrations.ca

Web Developers P2P : February 2014

Housekeeping

• About Me - Brad Genereaux– Healthcare and API developer– Integration Architect at Agfa Healthcare– Blogger about all the API things

• Discussion and questions– Ask anytime, or at the end

Topics

• API

• REST

• Security

• Web

• Examples

The API

Application Programming Interface

What is an API?

• Methods to access data and workflow from an application without using the application itself

API Example

vs

Why an API?• Not all users are the same

– Some want:

– Some want / need:

– And their needs and wants are ever shifting

An API Stack

GUI(front-end)

API(middle tier)

Data Sources(back-end)

… sounds like a good framework for Web …

The REST

REpresentational State Transfer

What is REST?

• Architectural style (not a standard!)

• Client server model

• Stateless– Idempotency

• Cacheable

• Layered System

• Uniform interface

Source: https://www.ics.uci.edu/~fielding/pubs/dissertation/fielding_dissertation.pdf

Who RESTs?

• Facebook

• Twitter

• Google

• LinkedIn

• Netflix

• Evernote

• Etc etc

Why REST?

• Scalable

• Fault-tolerant

• Recoverable

• Secure

• Loosely coupled

What do I need to REST?

Clients• Browsers• Mobile Apps• Desktop Apps

Servers• “Capable of HTTP”

– Java-based– .Net-based– PHP– Ruby– Perl– Etc.

Three levels of REST

• Level 1 : Resources

• Level 2 : Verbs

• Level 3 : HATEOAS

Resources, Level 1 REST

• /users

• /users/bob

• /users/bob/tweets

• /users/bob/tweets/1

Verbs, Level 2 REST

• CRUD

What is CRUD?

• Standard database operations:C reateR eadU pdateD elete

Verbs, Level 2 REST

• CRUD• GET /tweets

(as opposed to /givemethetweets)

• POST /tweets (as opposed to /createnewtweet)

• PUT /tweets/1 (as opposed to /updatetweet/1)

• DELETE /tweets/1 (as opposed to /removetweet/1)

RESTful Methods

GET PUT POST DELETE

Collection URI(such as http://a.com/items/)

List the items in the collection and some metadata about the items

Replace the entire collection with another collection

Create a new entry in the collection, and return the reference

Delete all the items in the collection

Element URI(such as http://a.com/items/17)

Retrieve a specific item in the collection

Replace a specific item in the collection; if it doesn't exist, create it

Not generally used

Delete the specific item in the collection

• There are other methods less used (HEAD, OPTIONS, PATCH) for other purposes• Representations of an item are specified by the media type (MIME type)

Source: http://en.wikipedia.org/wiki/Representational_state_transfer

HATEOAS, Level 3 REST

• Hypermedia as the engine of application state

"ids" : [ 12345678, 87654321, 11223344]

"links": [ { "rel": "UserInfo", "href": "https://.../user/12345678" }, { "rel": "Tweets", "href": "https://.../tweet/87654321" }, { "rel": "Messages", "href": "https://.../msgs/11223344" }]

Data Formats (XML and JSON)

XML (135 characters):<tweets> <tweet type="text" id="1"> <text>REST is great!</text> </tweet> <tweet type="text" id="2"> <text>APIs forever!</text> </tweet></tweets>

JSON (109 characters):{ "tweets": [ {"type": "text", "id": "1", "text": "REST is great!"}, {"type": "text", "id": "2", "text": "APIs forever!"} ]}

XML can be validated (XML Schema), stylized (XSL), traversed (XPath), queried (XQuery), transformed (XSLT), and namespaced

JSON is easier

What makes for good REST?

• Self-documenting• Nouns in path, verbs by HTTP• Complexity under the “?”

– i.e., /tweets/?contains=API

• Errors use HTTP error code mechanism

• As simple as possible, but no simpler

REST Alternatives

• SOAP (simple object access protocol)

• Javascript

• XML-RPC

• See discussion at http://www.slideshare.net/jmusser/j-musser-apishotnotgluecon2012

Important : Know your TTFHW (Time to First Hello World) !

API Worst Practices

10. Poor error handling 9. Ignoring HTTP rules 8. Exposing your underlying data model 7. Security complexity 6. Unexpected release cycles 5. Poor developer experience 4. Expecting an MVC to give you a great API 3. Assuming if you build it, they will come 2. Inadequate support 1. Poor documentation

Source: http://www.slideshare.net/jmusser/j-musser-apishotnotgluecon2012

The Security

Authentication and Authorization

• Authentication : Who

• Authorization : What they are allowed to do

• Not your job, but your responsibility

Security Frameworks

• OAuth– Authorizing services

• OpenID– Facebook, Google

• LDAP– Enterprise authentication

Application Security Threats

Input Validation Session Management

Authentication Cryptography

Authorization Exception Management

Configuration Management

Parameter Manipulation

Sensitive Information Auditing and Logging

Source: http://en.wikipedia.org/wiki/Application_security

SQL Injection

Consider the following pseudo-code:String topic = request.getParameter(“topic");SQLCommand sql = new SQLCommand("select * from tweets where topic like ‘" + topic + "%’")

So what happens if the parameter is:– API– REST– h3ck0rz’; drop table tweets; --

Source: http://xkcd.com/327/

The Web

Client-side Access to REST

HTML5 + CSS

• “HyperText Markup Language”– Characterized by the DOM (document object model) Completely

ubiquitous across the Internet<html> <body> <h1>Hello World</h1> </body></html>

• “Cascading Style Sheets”– Allows for advanced stylization of content– Example:

.giant { font-size: 72px; color: blue;}

JavaScript

• Multi-paradigm weakly-typed scripting language• Used most often hand-in-hand with HTML• Not Java, at all (syntax based on C)• Example:

alert (“Hello World!”);• Able to manipulate the DOM and interact with the

browser environment

AJAX

• “Asynchronous JavaScript and XML”• Group of technologies that allow for robust client

interactions without reloading web pages– HTML and CSS for presentation– DOM for display and interaction of data– XML for data interchange– XMLHttpRequest for asynchronous communication– JavaScript to bring these technologies together

• AJAX is the key to consuming REST

jQuery

• “jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development.”

• Example:

$(“#h1”).html(“Hello World!”);• jQuery tests against many browser platforms and solves

a lot of the problems that supporting many platforms introduces

Calling REST with jQuery

• Use an AJAX Call$.ajax({type : "GET",url : "http://a.com/tweets",data : {"contains" : "API"},dataType : "json",success : function(data){ alert ("Results: " + data);}

});

Verb

Query parameters

Resource

Media type

Tips

• Use “curl” to simulate calls from your command line

• Use Chrome debug tools or Firebug to watch traffic and test your Javascript

• Use libraries – no need to reinvent the wheel

Other Frameworks

• UI Frameworks (Bootstrap, Foundation)

• MVC Frameworks (Angular, Backbone)

• Tooling (Yeoman, Lineman)

• Documentation (Apiary, Swagger)

• No shortage of options

The Examples

Some REST API Examples

• Facebook

• Twitter

• If This, Than That

• Twilio

• Demo

Facebook Graph API• Every object has an ID:

• Objects can be searched:

• Objects can be updated:

Twitter REST API

If This, Then That

• API Integration Website - http://ifttt.com/

Twilio

Demo

Need more REST?

• Programmable Webhttp://programmableweb.comJohn Musser’s presentations: http://www.slideshare.net/jmusser

• Crafting Interfaces that Developers Love http://offers.apigee.com/api-design-ebook-rr/

• API Craft Google Group https://groups.google.com/forum/#!forum/api-craft

Discussion - Questions