1 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Some Details

2 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Asynchronous Operations Assembling applications from micro-services is “cool” But, getting a response to a GET or PUT might take a while –The action implementation requires talking to other micro-services, which in turn talk to other micro-services. –You need to assume that calls are occurring over a network. –Some operations take a little while, e.g. a complex DB query. –Some micro-services are inherently asynchronous, e.g. because they are people –PUT …/account/21 with some data has an implementation –That sends and to Bob who has to make sure the account data is OK –And sends an “approved” or “not approved” response –Before the original PUT can return success or failure Holding the “connection” while a long task is running is icky –Consumes resources and may block other calls due to limits on active requests –Network are unreliable, and connections break. This can result in really icky –My PUT failed. I will try again. –Failed again. I will try again. –… …

3 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Asynchronous Operation

4 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Implementation Observations Define a collection /QueuedResponses –A client can call …/QueuedResponses/21 to get a specific response. –You already know how to do this for …/staff, …/stores –The data format in the table is {id, status, JSONString}, where JSONString is the response you would have received for a synchronous request. A simple implementation would be writing a façade –Accept request –Create new table entry with status = “in progress” –Return 202 and URL –Call the actual implementation –Update the database table entry with the JSON result Most application platforms have middleware approaches to support registering callbacks, threads, etc. The implementation would typically –Invoke some long running action, e.g. DB query, workflow process and register a callback –The callback implementation updates the entry in the response table.

5 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Example Considerations Service Endpoint –Endpoint –Endpoint Encryption Requests and Authentication –Request Headers –Request Timestamps –Request Authentication –Response Headers Resources –Resource Requests –Resource Representation –Resource Methods –Synchronous Operations –Asynchronous Operations –Success Response Codes –Failure Response Codes Resource Data Types –Atomic Types –Complex Type - Object or Structure –Resource Relationships –Resource References Pagination –Through HTTP Link Header –Syntax and Example of Pagination Link Header –Consistency Across Page Requests Versioning –Version Header –Version URI Saying “REST is not enough You have to define a set of patterns/ conventions of URLs, headers, …

6 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Headers – Some Choices I Made HTTP Request HeaderValueMandatory auth-timestamp:The current POSIX time.Yes auth-key: The user or client’s unique API KEY. Yes auth-signature: The HMAC-SHA256 digest for the request. Yes api-version:(Optional) API version stringNo Accept: (Optional) application/xml or application/json No Nonce:One time UUID to enable idempotency/duplicate detection

7 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Response Codes OperationHTTP RequestHTTP Response Codes Supported READGET OK with message body OK no message body OK with partial message body CREATEPOST Resource created (Operation Complete) Resource accepted (Operation Pending) UPDATEPUT Accepted (Operation Pending) Success (Operation Complete) DELETE Accepted (Operation Pending) Success (Operation Complete) Examples of Link Headers in HTTP response: Link: ;rel=monitor;title="update profile" Link: ;rel=summary;title=”access report” 202 means Your request went asynch. The HTTP header Link is where to poll for rsp.

8 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Failure Response Code ErrorResponse Code Invalid Parameter400 - Invalid parameter Authentication401 - Authentication failure Permission Denied403 - Permission denied Not Found404 - Resource not found Invalid Request Method405 - Invalid request method Internal Server Error500 - Internal Server Error Service Unavailable503 - Service Unavailable

9 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Assignment 1

10 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Setup Form teams –If you have already formed your team, –Give your team a “name.” –Elect a leader. If you cannot elect a leader using Rock-Paper-Lizard-Scissors-Spock, or something similar. –The leader sends me an of the form “Our team is the Bobcats Bobcats, dff9, Ferguson, Donald, Bobcats, js2001, Smith, John, Bobcats, gw1031, Washington, George, –If you have not formed your teams, –Why not? –I think maybe 2 people sent s saying they do not have a team. –I will form teams randomly at the break. Perform the following computation –Form a set that is all of the team members UNIs without the text prefix. –Choose the smallest number in the set, which we will call x –Compute N = x MOD 3 –If –N = 0, your team’s datamodel is Customer Data –N = 1, your team’s datamodel is Movie Information –N = 2, your team’s datamodel is Business –N = 3, you do not know what MOD means

11 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns The Project Setup –You may pick any language, runtime, framework, DB, … you want. –You will create a database “schema” for you model and populate with sample data –You do not need to rigorously adhere to “table” and “column” names Implement a REST service for your information model with –A resource representation for each “type” in the model, e.g. store, staff –GET, PUT, POST and DELETE operations for each “type” –Navigable relationships, e.g. …/store/manager –All PUT operations must implement an asynchronous response, e.g. Receive request, response accepted with link to rsp, sleep(x),update the response –Implement a template based query language, e.g. –…/humans?q=“iq=50&hairColor=red” with only “=“ operators –That returns the collection elements with fields equal to the input –Pagination –Projection: –GET …/humans?fields=“iq,shoeSize” returns –PUT contains a JSON object with the fields to update

12 © Donald F. Ferguson, All rights reserved.Modern Internet Service Oriented Application Development – Lecture 2: REST Details and Patterns Grading The grade for the project is based on –Top-Level Design Spec –Demo –Code review Top-Level Design Spec structure –Introduction –Uniform Resource Representation: –How your API surfaces each of the concepts –A couple of examples –Implementation technology you used –Implementation –How you implemented each of the concepts –A couple of examples –Issues Due dates –Your design document is due 06-February –We will do code reviews and demos via eMeetings the week of 09-February Do not panic! I will help you if you are confused/unsure. Just do the best you can. I will provide feedback on the first version. Do not panic!