Workshop Refit & Polly

Jacob Duijzer, January 2018

Refit

Refit: The automatic type-safe REST library for .NET Core, Xamarin and .NET

public interface IRemoteApi
{
	[Get("/posts")]
	Task<IEnumerable<Post>> GetAllPostsAsync();

	[Post("/posts")]
	[Headers("Authorization: Bearer")]
	Task<Post> AddPostAsync([Body]Post post);

	[Delete("/posts/{id}")]
	[Headers("Authorization: Bearer")]
	Task DeletePostByIdAsync(int id);
}

Refit - sample code

var remoteApi = RestService
	.For<IRemoteApi>("http://localhost:3000");


var posts = await remoteApi.GetAllPostsAsync();

var singlePost = await remoteApi.GetPostByIdAsync(1);

Refit - Scenario 1

Simple api calls

Refit - Scenario 2

Logging

Refit - Scenario 3

Authenticated api calls

Polly

Policies:

• Retry
• CircuitBreaker
• Timeout
• Bulkhead Isolation
• Cache
• Fallback
• PolicyWrap

Polly - sample code

// Retry multiple times, calling an action on each retry
// with the current exception, retry count and context
// provided to Execute()
var _retryPolicy = Policy.Handle<SomeExceptionType>()
	.Retry(3, (exception, retryCount, context) =>
	{
    	// do something to prevent the next exception
	});

await _retryPolicy.ExecuteAsync(
	remoteApi.GetAllPostsAsync()
);

Polly - Scenario 1

Retry

Polly - Scenario 2

Fallback

Polly - Scenario 3

CircuitBreaker

Polly - Scenario 4

Retry with fallback

Polly - Scenario 5

CircuitBreakerWithRetryAndFallBack

HttpClientHandler

• MSDN Documentation
• Scott Hanselmans post With REFIT

Polly - Unit testing

Alternatives - Flurl

C#!
// Flurl will use 1 HttpClient instance per host
var person = await "https://api.com"
    .AppendPathSegment("person")
    .SetQueryParams(new { a = 1, b = 2 })
    .WithOAuthBearerToken("my_oauth_token")
    .PostJsonAsync(new
    {
        first_name = "Claire",
        last_name = "Underwood"
    })
    .ReceiveJson<Person>();

• Flur.io
• Blog post

Alteratives - DalSoft.RestClient

C#!
var config = new Config().UseFormUrlEncodedHandler();

dynamic restClient = new RestClient("https://jsonplaceholder.typicode.com", config);
var user = new User { name="foo", email="[email protected]" };

//POST name=foo&[email protected]  https://jsonplaceholder.typicode.com/users/1
result = await client
  .Headers(new { ContentType = "application/x-www-form-urlencoded" })
  .User(1)
  .Post(user);

• Blogpost
• Github

Setup sample project

https://github.com/jacobduijzer/RefitPollyWorkshop

• Get the source from GitHub
• in folder src/api: npm install
• in the folder src/api: npm run start
• configure & run the console app

Links

• Sample repository
• Refit
• Polly
• JSON Server
• Presentation created from markdown with Marp