Cocoaheads Berlin March 12th 2009 About implementing an API wrapper for a OAuth protected Web API in Objective-C for Mac and iPhone. http://github.com/soundcloud/cocoa-api-wrapper

1. The SoundCloud API
Cocoa Wrapper
How to build a connection framework for an
OAuth protected RESTful Web-API
Wednesday, March 18, 2009

2. Agenda
1.Introduction
The SoundCloud API
2.Challenges
Problems we solved
3.Try it!
Integrating SoundCloud sharing to your app
Wednesday, March 18, 2009

3. The SoundCloud API
Wednesday, March 18, 2009

4. The SoundCloud API
• RESTful
Resource based
•
User, Track, Comment, ...
•
HTTP based
•
GET, PUT, POST, DELETE
•
Data representation in JSON, XML
•
Wednesday, March 18, 2009

5. The SoundCloud API
• RESTful
Resource based
•
User, Track, Comment, ...
•
HTTP based
•
GET, PUT, POST, DELETE
•
Data representation in JSON, XML
•
• OAuth protected
Wednesday, March 18, 2009

6. REST Example
• Resource: Tracks
Resource Method
/tracks GET, POST
/tracks/{track_id} GET, PUT, DELETE
• Creating a new Track
POST /tracks
• curl -u joey:hairspray
'http://api.sandbox-soundcloud.com/tracks'
-F track[asset_data]=@step_by_step.aif
-F track[title]=Superstitious
Response
• < HTTP/1.1 201 Created
< Location: http://api.sandbox-soundcloud.com/tracks/13
Wednesday, March 18, 2009

7. OAuth
Wednesday, March 18, 2009

8. OAuth
• Token based API authentication + authorization
Exchange tokens rather than login & password
•
Authorization on server side
•
Wednesday, March 18, 2009

9. OAuth
• Token based API authentication + authorization
Exchange tokens rather than login & password
•
Authorization on server side
•
• Client applications registered on server
Consumer key + secret
•
Wednesday, March 18, 2009

10. OAuth
• Token based API authentication + authorization
Exchange tokens rather than login & password
•
Authorization on server side
•
• Client applications registered on server
Consumer key + secret
•
• HTTP requests signed by authorized tokens
Wednesday, March 18, 2009

11. OAuth
• Token based API authentication + authorization
Exchange tokens rather than login & password
•
Authorization on server side
•
• Client applications registered on server
Consumer key + secret
•
• HTTP requests signed by authorized tokens
• Tokens can be revoked
Wednesday, March 18, 2009

12. Challenges
Wednesday, March 18, 2009

13. Challenges
1.Nice code
Wednesday, March 18, 2009

14. Challenges
1.Nice code
2.Integrating OAuth
Signing API requests
•
Implementing the token authorization
•
Wednesday, March 18, 2009

15. Challenges
1.Nice code
2.Integrating OAuth
Signing API requests
•
Implementing the token authorization
•
3.Posting large (80+Mb) data to the server
Memory issues & upload progress
•
Wednesday, March 18, 2009

16. Challenges
1.Nice code
2.Integrating OAuth
Signing API requests
•
Implementing the token authorization
•
3.Posting large (80+Mb) data to the server
Memory issues & upload progress
•
4.Sending requests asynchronously
Wednesday, March 18, 2009

17. Challenges
1.Nice code
2.Integrating OAuth
Signing API requests
•
Implementing the token authorization
•
3.Posting large (80+Mb) data to the server
Memory issues & upload progress
•
4.Sending requests asynchronously
5.Cross platform Xcode project (3 platforms)
Wednesday, March 18, 2009

18. 1. Nice code
Wednesday, March 18, 2009

19. 1. Nice code
• Meant for 3rd party developers
Few classes that are easy to understand
•
Stable interface
•
Wednesday, March 18, 2009

20. 1. Nice code
• Meant for 3rd party developers
Few classes that are easy to understand
•
Stable interface
•
• API might change
Not implementing model or controller logic
•
Just implementing communication layer
•
JSON / XML parsing is up to the developer
•
Wednesday, March 18, 2009

21. Architecture
Client AppDelegate Some Client Controller
Authentication
API Delegate
Delegate
Wednesday, March 18, 2009

22. Architecture
Client AppDelegate Some Client Controller
Authentication
API Delegate
Delegate
SoundCloud API
Wednesday, March 18, 2009

23. Architecture
Client AppDelegate Some Client Controller
Authentication
API Delegate
Delegate
SoundCloud API
SoundCloud API
Configuration
Wednesday, March 18, 2009

24. Architecture
Client AppDelegate Some Client Controller
Authentication
API Delegate
Delegate
SoundCloud API
SoundCloud API
Configuration
Wednesday, March 18, 2009

25. 2. Integrating OAuth
Wednesday, March 18, 2009

26. 2. Integrating OAuth
• Problems
Signing Requests
•
Implementing token authorization
•
Wednesday, March 18, 2009

27. 2. Integrating OAuth
• Problems
Signing Requests
•
Implementing token authorization
•
• Solution to signing
Using OAuthConsumer reference implementation
•
Added keychain support for Mac & iPhone (& Simulator)
•
Replaced crypto algorithms
•
Wednesday, March 18, 2009

28. OAuth token flow
Client Application SoundCloud
Wednesday, March 18, 2009

29. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Getting unauthorized token
request token
Wednesday, March 18, 2009

30. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Wednesday, March 18, 2009

31. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL
authorization via browser
Wednesday, March 18, 2009

32. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL User logs in
authorization via browser
+ authorizes token
Wednesday, March 18, 2009

33. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL User logs in
authorization via browser
+ authorizes token
Redirecting to
callback URL with
custom URL scheme
Wednesday, March 18, 2009

34. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL User logs in
authorization via browser
+ authorizes token
Redirecting to
callback URL with
Application is triggered
custom URL scheme
by URL scheme
Wednesday, March 18, 2009

35. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL User logs in
authorization via browser
+ authorizes token
Redirecting to
callback URL with
Application is triggered
custom URL scheme
by URL scheme
App initiates exchange
Step 3
of request token
Exchanging tokens
Wednesday, March 18, 2009

36. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL User logs in
authorization via browser
+ authorizes token
Redirecting to
callback URL with
Application is triggered
custom URL scheme
by URL scheme
App initiates exchange
Step 3
of request token
Exchanging tokens
Generating
access token
Wednesday, March 18, 2009

37. OAuth token flow
Client Application SoundCloud
Step 1 Asking for request
Generating
Getting unauthorized token
request token request token
Step 2 Sent user to browser
Obtaining user with token in URL User logs in
authorization via browser
+ authorizes token
Redirecting to
callback URL with
Application is triggered
custom URL scheme
by URL scheme
App initiates exchange
Step 3
of request token
Exchanging tokens
Generating
access token
Step 4 Stores access token
Storing access token
for further usage
Wednesday, March 18, 2009

38. 3.Large files
• Audio files are large!
60 min recording is very large, even compressed
•
• The problem with lage files
iPhone memory limits
•
Upload progress not supported by NSURLConnection
•
• The solution: NSInputStream
Be aware!! Not easy to subclass
•
Wednesday, March 18, 2009

39. Post Body Stream
• Data transfered as multipart
• SCPostBodyStream as wrapper around array of stream parts
• Stream parts
NSString, NSURL (file URL), NSData
•
• Upload progress by counting bytes in read method
Wednesday, March 18, 2009

40. 4.Asynchronous Communication
Wednesday, March 18, 2009

41. 4.Asynchronous Communication
Connection
Your Class
Connection
Connection Management
Data fetching
Request generation
Connection
Wednesday, March 18, 2009

42. 4.Asynchronous Communication
Connection
SoundCloud API
Connection
Connection Management
Data fetching
Request generation
Connection
Wednesday, March 18, 2009

43. 4.Asynchronous Communication
Connection
SoundCloud API
Your Class
Connection
Lean & Mean Connection Management
Data fetching
Request generation
Connection
Wednesday, March 18, 2009

44. 4.Asynchronous Communication
OAuth
Connection
SoundCloud API
Your Class
Connection
Lean & Mean Connection Management
Data fetching
Request generation
Connection
Uploads
Wednesday, March 18, 2009

45. 5. Cross platform Xcode project
Wednesday, March 18, 2009

46. 5. Cross platform Xcode project
• Targets
Framework for Mac
•
Fat static library for iPhone Device & Simulator
•
Wednesday, March 18, 2009

47. 5. Cross platform Xcode project
• Targets
Framework for Mac
•
Fat static library for iPhone Device & Simulator
•
• Problems
Only one Base SDK per project
•
Base SDK defines which frameworks are allowed
•
Wednesday, March 18, 2009

48. 5. Cross platform Xcode project
• Targets
Framework for Mac
•
Fat static library for iPhone Device & Simulator
•
• Problems
Only one Base SDK per project
•
Base SDK defines which frameworks are allowed
•
• Solution
Manually linking frameworks
•
Wednesday, March 18, 2009

49. 5. Cross platform Xcode project
• Targets
Framework for Mac
•
Fat static library for iPhone Device & Simulator
•
• Problems
Only one Base SDK per project
•
Base SDK defines which frameworks are allowed
•
• Solution
Manually linking frameworks
•
Wednesday, March 18, 2009

50. Try it !
Wednesday, March 18, 2009

51. Try it !
• Licensed under Apache License
You‘re free to use it
•
Can be integrated into closed projects
•
Just mention us somewhere
•
Wednesday, March 18, 2009

52. Try it !
• Licensed under Apache License
You‘re free to use it
•
Can be integrated into closed projects
•
Just mention us somewhere
•
• Wrapper comes with iPhone and Mac demo projects
Wednesday, March 18, 2009

53. Try it !
• Licensed under Apache License
You‘re free to use it
•
Can be integrated into closed projects
•
Just mention us somewhere
•
• Wrapper comes with iPhone and Mac demo projects
Lets see some code!
Wednesday, March 18, 2009

54. Further reading
Wednesday, March 18, 2009

55. Further reading
• The repository
http://github.com/soundcloud/cocoa-api-wrapper/
•
Wednesday, March 18, 2009

56. Further reading
• The repository
http://github.com/soundcloud/cocoa-api-wrapper/
•
• On OAuth
http://oauth.net
•
http://fireeagle.yahoo.net/developer/documentation/
•
http://code.google.com/p/oauth/
•
Wednesday, March 18, 2009

57. Further reading
• The repository
http://github.com/soundcloud/cocoa-api-wrapper/
•
• On OAuth
http://oauth.net
•
http://fireeagle.yahoo.net/developer/documentation/
•
http://code.google.com/p/oauth/
•
• Twitter: @stigi, @gernot, @soundcloud
Wednesday, March 18, 2009

58. Further reading
• The repository
http://github.com/soundcloud/cocoa-api-wrapper/
•
• On OAuth
http://oauth.net
•
http://fireeagle.yahoo.net/developer/documentation/
•
http://code.google.com/p/oauth/
•
• Twitter: @stigi, @gernot, @soundcloud
• Of course: http://www.soundcloud.com
Wednesday, March 18, 2009