README.md

Http.Resilience

Http.Resilience adds fault tolerance to any HTTP request. It can be used together with C# HttpClient, WebRequest or any other HTTP client. Transient network failures are automatically catched and a configurable number of retries is issued.

Download and Install Http.Resilience

This library is available on NuGet: https://www.nuget.org/packages/Http.Resilience Use the following command to install Http.Resilience using NuGet package manager console:

PM> Install-Package Http.Resilience

You can use this library in any .NET Standard or .NET Core project.

API Usage

HttpRetryHelper provides easy-to-use Invoke and InvokeAsync methods which support configurable retry behavior - not only for the wellknown HttpClient but also for other http clients such as WebRequest or WebClient. HttpRetryHelper is equipped with some good-practice retry logic but it also exposes configurability via HttpRetryOptions.

Recover from transient network failure

The following sample demonstrates a simple HTTP request using HttpClient. HttpRetryHelper is used to wrap httpClient.GetAsync(...). Whenever GetAsync(...) fails due to a transilient network failure, HttpRetryHelper attempts to recover the problem by repeatedly calling InvokeAsync.

var httpClient = new HttpClient();
var requestUri = "https://quotes.rest/qod?language=en";

var httpRetryHelper = new HttpRetryHelper(maxRetries: 3);

try
{
    var httpResponseMessage = await httpRetryHelper.InvokeAsync(async () => await httpClient.GetAsync(requestUri));
    var jsonContent = await httpResponseMessage.Content.ReadAsStringAsync();

    Console.WriteLine($"{jsonContent}");
}
catch (Exception ex)
{
    Console.WriteLine($"{ex.Message}");
}

Recover from unsuccessful HTTP status code

Retries can be configured using the RetryOnException delegate. If Invoke/Async throws an exception, we can intercept it with RetryOnException((ex) => ...) and return a bool value to indicate whether we want to retry the particular HTTP request (true=retry, false=do not retry).

var httpClient = new HttpClient();
var requestUri = "https://quotes.rest/qod?language=en";

var httpRetryOptions = new HttpRetryOptions();
httpRetryOptions.MaxRetries = 4;

var httpRetryHelper = new HttpRetryHelper(httpRetryOptions);
httpRetryHelper.RetryOnException<HttpRequestException>(ex => { return ex.StatusCode == HttpStatusCode.ServiceUnavailable; });

try
{
    var httpResponseMessage = await httpRetryHelper.InvokeAsync(async () => await httpClient.GetAsync(requestUri));
    var jsonContent = await httpResponseMessage.Content.ReadAsStringAsync();

    Console.WriteLine($"{jsonContent}");
}
catch (Exception ex)
{
    Console.WriteLine($"{ex.Message}");
}

Retry based on returned result

Retries can also be carried out if a particular result is returned by Invoke/InvokeAsync. RetryOnResult delegate allows to evaluate the returned result and indicate if a retry is necessary (true=retry, false=do not retry).

var httpClient = new HttpClient();
var requestUri = "https://yourapi/token/refresh";

var httpRetryOptions = new HttpRetryOptions();
httpRetryOptions.MaxRetries = 4;

var httpRetryHelper = new HttpRetryHelper(httpRetryOptions);
httpRetryHelper.RetryOnResult<RefreshTokenResult>(r => r.Error != "invalid_grant");

try
{
    var refreshTokenResult = await httpRetryHelper.InvokeAsync(async () => await httpClient.PostAsync(requestUri, ...));
    
    // ...
}
catch (Exception ex)
{
    Console.WriteLine($"{ex.Message}");
}

License

This project is Copyright © 2023 Thomas Galliker. Free for non-commercial use. For commercial use please contact the author.