10. ASP .Net core - Fundamentals - Make an HTTP request

This series is a collection of knowledge about ASP .NET Core. It just is my notes.

Part 1: Startup file.

Part 2: DI.

Part 3: Middleware.

Part 4: Host and Servers.

Part 5: Configurations.

Part 6: Environment.

Part 7: Logs.

Part 8: Error Handling.

Part 9: Routing.

Part 11: Static files.

Part 12: Authentication and Authorization.

Part 13: CORS.

This part shows us some ways to make an HTTP request against a web service/ web api.

1. Issues when using HttpClient:

• Socket exhaustion
• DNS changes not reflecting

To get more information concerning these issues, you can read this article.

2. Solution in .NET Core is:

• use IHttpClientFactory
• Some consumption patterns:

    2.1 Basic usage:

            - Add HttpClient to the services container

public void ConfigureServices(IServiceCollection services)

{

services.AddHttpClient();

// Remaining code deleted for brevity.

            - Use Dependency Injection to use IHttpClientFactory.CreateClient()

public BasicUsageModel(IHttpClientFactory clientFactory)

{

_clientFactory = clientFactory;

}

....

var client = _clientFactory.CreateClient();

    2.2. Named clients:

            - Add HttpClient to services:

services.AddHttpClient("github", c =>

{

c.BaseAddress = new Uri("https://api.github.com/");

// Github API versioning

c.DefaultRequestHeaders.Add("Accept", "application/vnd.github.v3+json");

// Github requires a user-agent

c.DefaultRequestHeaders.Add("User-Agent", "HttpClientFactory-Sample");

});

            - Create clients

var client = _clientFactory.CreateClient("github");

    2.3. Typed Client:

• It's similar to create a new service class that wraps HttpClient

    2.4. Generated clients: used in combination with the third party

3. Configure HttpMessageHandler

• Can be used in case you want to control the configuration of  the inner HttpMessageHandler
• An example is to bypass SSL Server Certificate
• Use the extension method: ConfigurePrimaryHttpMessageHandler to create and configure

public void ConfigureServices(IServiceCollection services)

{

services.AddHttpClient("configured-inner-handler")

.ConfigurePrimaryHttpMessageHandler(() =>

{

return new HttpClientHandler()

{

AllowAutoRedirect = false,

UseDefaultCredentials = true

};

});

services.AddHttpClient(ONPREMISEHTTPCLIENT)

.ConfigurePrimaryHttpMessageHandler(() =>

{

return new HttpClientHandler()

{

ServerCertificateCustomValidationCallback = (_, __, ___, ____) => true

};

});

• Header propagation

References:

https://docs.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-5.0

https://www.rahulpnath.com/blog/are-you-using-httpclient-in-the-right-way/