PoliNorError.Extensions.Http 0.1.1

The library provides an outgoing request resiliency pipeline for HttpClient, using policies from the PoliNorError library.

Key Features

• Provides the ability to create a pipeline to handle typical transient HTTP failures (including the HttpRequestException exception).
• Flexible transient failure filter for the final DelegatingHandler in the pipeline for the response.
• Additionally, custom failure status codes or categories can be added to the final handler filter.
• Other exception types (besides HttpRequestException) can also be included in the final handler filter.
• Inclusion in the outer handler filter of any Exception type thrown by the inner handler is also supported.
• Both typed and named HttpClient, as well as IHttpClientFactory, can be used.
• Targets .NET Standard 2.0.

Usage

1. Configure typed or named HttpClient:

services.AddHttpClient<IAskCatService, AskCatService>((sp, config) =>
	{
		...
		config.BaseAddress = new Uri(settings.BaseUri);
		...
	})...

, where AskCatService is a service that implements IAskCatService, with HttpClient or IHttpClientFactory injected.

2. Use the library's IHttpClientBuilder.WithResiliencePipeline extension method and configure the pipeline of DelegatingHandlers by using the AddPolicyHandler method with the policy you want to apply in this handler:

services.AddHttpClient<IAskCatService, AskCatService>((spForClient, client) =>
	{
			...
	})
	.WithResiliencePipeline((pb) => 
		pb
		.AddPolicyHandler(PolicyJustCreated)
		.AddPolicyHandler((IServiceProvider sp) => funcThatUsesServiceProviderToCreatePolicy(sp))
		...
	)

Or use the WithResiliencePipeline method overload that includes an additional context parameter:

services.AddHttpClient<IAskCatService, AskCatService>((spForClient, client) =>
	{
			...
	})
	.WithResiliencePipeline<SomeContextType>((pb) => 
		pb
		.AddPolicyHandler((SomeContextType ctx, IServiceProvider sp) => 
			funcThatUsesContextAndServiceProviderToCreatePolicy(ctx, sp))

		.AddPolicyHandler((IServiceProvider sp) => funcThatUsesServiceProviderToCreatePolicy(sp))
		...
	, context)

, where

• pb - represents the pipeline builder.
• PolicyJustCreated - a policy from the PoliNorError library.
• funcThatUsesServiceProviderToCreatePolicy - Func that uses the IServiceProvider to create a policy.
• funcThatUsesContextAndServiceProviderToCreatePolicy - Func that uses the IServiceProvider and context to create a policy.

3. When you want to complete the pipeline, call the AsFinalHandler method for the last added handler and configure HttpErrorFilter to filter transient http errors and/or any non-successful status codes or categories:

services.AddHttpClient<IAskCatService, AskCatService>((sp, config) =>
	{
			...
	})
	.WithResiliencePipeline((pb) => 
		pb
		...
		.AddPolicyHandler(PolicyForFinalHandler)
		//Adds transient http errors to the response handling filter.
		.AsFinalHandler(HttpErrorFilter.HandleTransientHttpErrors())
		...
	)

Additionally, you can include custom failure status codes or categories in the final handler filter:

		...
		.AsFinalHandler(HttpErrorFilter.HandleHttpRequestException()
			//Also adds 5XX status codes to the response handling filter.
			.OrServerError())
		...

You can also include in the filter any exception type thrown by an inner handler:

		...
		.AsFinalHandler(HttpErrorFilter.HandleTransientHttpErrors())
		//Include 'SomeExceptionFromNonPipelineHandler' exceptions in the filter 
		//when thrown by a non-pipeline handler (in this case).
		.IncludeException<SomeExceptionFromNonPipelineHandler>()
		...

4. In a service that uses HttpClient or HttpClientFactory, wrap the call to HttpClient in a catch block that handles the special HttpPolicyResultException exception. If the request was not successful, examine the HttpPolicyResultException properties in this handler for details of the response:

try
{
	...
	using var response = await _client.GetAsync(uri, token);
	...
}
catch (OperationCanceledException oe)
{
	...
}
catch (HttpPolicyResultException hpre)
{
	//If the response status code matches the handling filter status code:
	if (hpre.HasFailedResponse)
	{
		//For example, log a failed status code.
		logger.LogError("Failed status code: {StatusCode}.", hpre.FailedResponseData.StatusCode);
	}
}
catch (Exception ex)
{
	...
}