A super-quick and high-level introduction to the principles of REST, prepared for the AusPost SAP development team

1. REST A Super-Quick Introduction

2. REpresentationalStateTransfer

3. Say What???

4. Apply ‘Web’ Principles to A2A Integration Problems

5. Remember the OSI Stack? http://en.wikipedia.org/wiki/Osi_stack

6. So what?

7. REST uses HTTP as the Application Protocol! Not (just) as the transport

8. How does that work?

9. Standard Verbs The HTTP Spec give you the verbs to use: GET PUT POST DELETE HEAD OPTIONS PATCH TRACE http://en.wikipedia.org/wiki/HTTP#Request_methods

10. SOAP Doesn’t… getAccountCustomerByInternalId searchCustomerByBasicData updateSalesProspectStatusByPartnerSalesRepresentativeBasicData_sync Everything works via HTTP POST (i.e. uses HTTP as the dumb transport)

11. Status Codes The HTTP Spec give you the verbs to use: 200 OK 302 Moved Permanently 404 Not Found 406 Method Not Allowed 418 I’m a Teapot … http://en.wikipedia.org/wiki/List_of_HTTP_status_codes

12. SOAP Doesn’t… <SOAP-ENV:Faultxmlns:sqlsoapfaultcode="http://schemas.microsoft.com/sqlserver/2004/SOAP/SqlSoapFaultCode"> <faultcode>SOAP-ENV:Client</faultcode> <faultstring>There was an error in the incoming SOAP request packet: Client, InvalidXml</faultstring> <faultactor>http://schemas.microsoft.com/sqlserver/2004/SOAP</faultactor> <detail xmlns:SOAP-1_2-ENV="http://www.w3.org/2003/05/soap-envelope"> <SOAP-1_2-ENV:Code> <SOAP-1_2-ENV:Value>SOAP-1_2-ENV:Sender</SOAP-1_2-ENV:Value> <SOAP-1_2-ENV:Subcode> <SOAP-1_2-ENV:Value>sqlsoapfaultcode:InvalidXml</SOAP-1_2-ENV:Value> </SOAP-1_2-ENV:Subcode> </SOAP-1_2-ENV:Code> <SOAP-1_2-ENV:Reason> <SOAP-1_2-ENV:Text xml:lang="en-US">There was an error in the incoming SOAP request packet: Sender, InvalidXml</SOAP-1_2-ENV:Text> </SOAP-1_2-ENV:Reason> <SOAP-1_2-ENV:Node>http://MyServer:80/sql</SOAP-1_2-ENV:Node> <SOAP-1_2-ENV:Role>http://schemas.microsoft.com/sqlserver/2004/SOAP</SOAP-1_2-ENV:Role> <SOAP-1_2-ENV:Detail> <sqlresultstream:SqlMessagexsi:type="sqlmessage:SqlMessage"> <sqlmessage:Class>16</sqlmessage:Class> <sqlmessage:LineNumber>0</sqlmessage:LineNumber> <sqlmessage:Message>XML parsing: line 3, character 0, incorrect document syntax</sqlmessage:Message> <sqlmessage:Number>9422</sqlmessage:Number> <sqlmessage:Source>Microsoft-SQL/9.0</sqlmessage:Source> <sqlmessage:State>1</sqlmessage:State> </sqlresultstream:SqlMessage> </SOAP-1_2-ENV:Detail> </detail> </SOAP-ENV:Fault>

13. So What’s Wrong with that?

14. So What’s Wrong with that? Suboptimal

15. Scalability HTTP GET is the most optimised piece of code on the planet! Easily cached to support millions of clients Defined semanticsHTTP = Application Protocol Everyone knows how to do a GET Everyone knows how to behave

16. We Exchange Representations

17. Representations? The server can store its data/objects in whatever way it likes The clients can store the same stuff differently We serialise that into Representations

18. Less Abstract… A Website is a Representation of the server’s database, code, etc. Clients don’t care how the server stores it, as long as it understands the Representation

19. State Transfer?

20. State is Transferred between Server and Client Not just kept at the Server!

21. Client requests Shopping Cart Server sends HTML page with items and links Client’s move Client clicks “Check Out” Server sends HTML page with Total Amount Client’s move Client clicks “Pay” Server sends HTML page with “Thank You” and we’re done!

22. Notice Something?

23. The Client Drives the Interaction Responsible for moving forward Or not! The server guides the client forward (with ‘Check Out’, ‘Pay’ links) The client is responsible for completing the process If the client stops, the server doesn’t care!

24. And…

25. Everything has a URL

26. So it’s like the Web! …Just for Machines

27. Restbucks works with whisky too ;-) http://www.infoq.com/articles/webber-rest-workflow

28. So, the Formal Principles:

29. REST Principles Identify Resources (URLs) Manipulate Resources through Representations Self-Descriptive Messages HATEOAS http://www.infoq.com/articles/rest-introduction

30. HypertextAsTheEngineOfApplicationState

31. In other words: Linking Things TogetherDriving the Process via Links Like the ‘Check Out’ link!

32. …and some Constraints: Client-Server Stateless Cacheable Layered System Uniform Interface Duh! = scalable = scalable load balancers, proxies HTTP verbs & codes

33. Finally: http://geekandpoke.typepad.com/geekandpoke/2009/11/service-calling-made-easy-part-1.html

35. More Resources: http://en.wikipedia.org/wiki/REST http://www.infoq.com/rest http://www.infoq.com/articles/webber-rest-workflow http://www.infoq.com/minibooks/emag-03-2010-rest (Excellent FREE eBook) CD108 from 2010 TechEd https://www.ibm.com/developerworks/webservices/library/ws-restful/