The ASP.NET Web API for Beginners

W. Kevin Hazzard

Richardson Maturity Model

martinfowler.com/articles/richardsonMaturityModel.html

The Web API Experience

• Solid resource-orientation• HTTP method support• Content negotiation• Open-ended formatting• Model-binding• Minimal platform

dependencies• Test friendly

Level 3

Level 2

Level 1

Level 0

H A T E O A S

Hypermedia As

The Engine Of

ApplicationState

H A T E O A S

Web API Architecture

Web API Processing Architecture

controller

message

hostingHttpRequestM

essa

ge

Http

ResponseMess

age

HTTP Request

GET /index.html HTTP/1.1Accept: text/htmlAccept-Encoding: gzip, deflateAccept-Language: en-USUser-Agent: Mozilla/5.0Connection: Keep-Alive

HttpRequestMessage

• In System.Net.Http namespace• Properties:

oContent – HttpContentoHeaders – HttpRequestHeadersoMethod – HttpMethodo Properties – IDictionary<string, object>oRequestUri – Uri

Request Extensions• CreateErrorResponse – many overloads• CreateResponse – many overloads• GetClientCertificate• GetProperty<T>• GetQueryNameValuePairs• GetUrlHelper

These are in System.Net.Http.dll.

HTTP Response

HTTP/1.1 200 OKCache-Control: private, max-age=0Content-Type: text/html; charset=utf-8Vary: Accept-EncodingDate: Thu, 31 Dec 2015 23:59:59 GMTContent-Length: 41309Connection: keep-aliveSet-Cookie: XYZ=123; domain=.me.com; path=/

...

HttpResponseMessage

• In System.Net.Http namespace• Properties:

oContent – HttpContentoHeaders – HttpResponseHeaderso IsSuccessStatusCode – booloReasonString – stringoRequestMessage – HttpRequestMessageo StatusCode – HttpStatusCode

Key Attributeso HttpGeto HttpPosto HttpPuto HttpPatcho HttpDeleteo HttpHeado HttpOptions

o AcceptVerbso Authorizeo AllowAnonymouso NonActiono FromBodyo FromUrio Queryable

Example OneCreate a Simple Controller to Fetch Person Entities

Add OData Query Syntax Support

Example One Summary

• Implement a basic controller with a actions• Demonstrate controller selection by convention• Discuss controller selection by attribution• Implement OData query parameters and

demonstrate

Example TwoAdd WebApiTestClient to the Project and ConfigureTurn Documentation Comments on and Configure

Cross-Cutting Concerns

HttpMessageHandler class:

protected abstract Task<HttpResponseMessage> SendAsync( HttpRequestMessage request, CancellationToken token);

DelegatingHandler

Derives fromHttpMessageHandler

Chains handlers togetherin the order youadd them

Chained Handlers

Server

MessageHandle

rA

Message

HandlerB

Dispatch

Message

HandlerSendAsync SendAsync SendAsync

Example ThreeImplement an Authorization Key Handler

Example Three Summary

• Implement an application key handler• Discuss the invocation of the InnerHandler• Demonstrate the creation and return of an error

response• Discuss why throwing exceptions will always

return an HTTP 500 (Internal Server Error) result• Demonstrate using the request object to create

the error response instead• Attach the handler to the pipeline• Debug with Help & Test

Possible Uses• Implementing a cache manager• Implementing an AAA scheme• Capturing pay-per-call data• Recording statistics• Logging and tracing• Inserting custom request and response headers• Performing message compression or encryption• Transforming messages

Testing Web API• Faking context with ASMX and WCF is difficult• Too many platform dependencies

o ASP.NET produces an HttpContexto WFC produces an OperationContext

• Typically requires a running host

Example FourAdd Tests

Example Four Summary

• Add test fixtures• Demonstrate Arrange, Act, Assert pattern• Call controller action without HttpRequestMethod• Call controller action with HttpRequestMethod

Contacting Kevinwkhazzard@gmail.com@KevinHazzard

blogs.captechconsulting.commanning.com/hazzard