Presentation on introducing Web APIs to Communitech P2P Web Developers group on Feb 20, 2014

1. An Introduction into
the Web API
Brad Genereaux | @integratorbrad | about.me/integratorbrad | hcintegrations.ca
Web Developers P2P : February 2014

2. 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

3. Topics
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•
•
•
•
API
REST
Security
Web
Examples

4. The API
Application Programming Interface

5. What is an API?
• Methods to access data and workflow
from an application without using the
application itself

6. API Example
vs

7. Why an API?
• Not all users are the same
– Some want:
– Some want / need:
– And their needs and wants are ever shifting

8. An API Stack
GUI
(front-end)
API
(middle tier)
Data Sources
(back-end)

9. … sounds like a good framework
for Web …

10. The REST
REpresentational State Transfer

11. What is REST?
• Architectural style (not a standard!)
• Client server model
• Stateless
– Idempotency
• Cacheable
• Layered System
• Uniform interface

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

13. Who RESTs?
•
•
•
•
•
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Facebook
Twitter
Google
LinkedIn
Netflix
Evernote
Etc etc

14. Why REST?
•
•
•
•
•
Scalable
Fault-tolerant
Recoverable
Secure
Loosely coupled

15. What do I need to REST?
Clients
• Browsers
• Mobile Apps
• Desktop Apps
Servers
• “Capable of HTTP”
–
–
–
–
–
–
Java-based
.Net-based
PHP
Ruby
Perl
Etc.

16. Three levels of REST
• Level 1 : Resources
• Level 2 : Verbs
• Level 3 : HATEOAS

17. Resources, Level 1 REST
•
•
•
•
/users
/users/bob
/users/bob/tweets
/users/bob/tweets/1

18. Verbs, Level 2 REST
• CRUD

19. What is CRUD?
• Standard database operations:
C reate
R ead
U pdate
D elete

20. 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)

21. RESTful Methods
GET
Collection URI
(such as
http://a.com/items/)
Element URI
(such as
http://a.com/items/17)
PUT
POST
DELETE
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
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

22. 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"
}
]

23. 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

24. 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

25. REST Alternatives
• SOAP (simple object access protocol)
• Javascript
• XML-RPC
• See discussion at
http://www.slideshare.net/jmusser/j-musser-ap

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

27. API Worst Practices
Source: http://www.slideshare.net/jmusser/j-musser-apishotnotgluecon2012
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

28. The Security

29. Authentication and Authorization
• Authentication : Who
• Authorization : What they are allowed to
do
• Not your job, but your responsibility

30. Security Frameworks
• OAuth
– Authorizing services
• OpenID
– Facebook, Google
• LDAP
– Enterprise authentication

31. Application Security Threats
Input Validation
Authentication
Session Management
Cryptography
Authorization
Exception Management
Configuration
Management
Parameter Manipulation
Sensitive Information
Auditing and Logging
Source: http://en.wikipedia.org/wiki/Application_security

32. 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/

33. The Web
Client-side Access to REST

34. 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;
}

35. JavaScript
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•
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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

36. 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

37. 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

38. Calling REST with jQuery
Verb
• Use an AJAX Call
Resource
$.ajax({
type : "GET",
url : "http://a.com/tweets",
data : {"contains" : "API"},
dataType : "json",
success : function(data){
alert ("Results: " + data);
}
});
Query
parameters
Media type

39. 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

40. Other Frameworks
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UI Frameworks (Bootstrap, Foundation)
MVC Frameworks (Angular, Backbone)
Tooling (Yeoman, Lineman)
Documentation (Apiary, Swagger)
• No shortage of options

41. The Examples

42. Some REST API Examples
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Facebook
Twitter
If This, Than That
Twilio
Demo

43. Facebook Graph API
• Every object has an ID:
• Objects can be searched:
• Objects can be updated:

44. Twitter REST API

45. If This, Then That
•
API Integration Website - http://ifttt.com/

46. Twilio

47. Demo

48. Need more REST?
• Programmable Web
http://programmableweb.com
John 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

49. Discussion - Questions