HttpClientFactory in ASP NET Core 2.1

ASP.NET Core 2.1 ships with a factory for HttpClient called HttpclientFactory. This factory allows us to no longer care about the lifecycle of the HttpClient by leaving it to the framework. Today we will see few ways of instantiating clients:

1. Default client
2. Typed client
3. Named client

1. Default client

To use the factory, we start first by registering it to the service collection with .AddHttpClient() which is an extension coming from Microsoft.Extensions.Http.

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();
    
    services.AddHttpClient();
}

This gives us access to the IHttpClientFactory which we can inject and using it, we can create a HttpClient.

[HttpPost]
public async Task<ActionResult<string>> PostDefaultClient([FromServices]IHttpClientFactory factory, [FromBody] ValueDto value)
{
    var client = factory.CreateClient();
    client.BaseAddress = new System.Uri("http://localhost:5100");
    var result = await client.PostAsJsonAsync("api/values", value);
    return await result.Content.ReadAsStringAsync();
}

Notice here that we have set the client.BaseAddress from the controller endpoint. If we have multiple places where we want to use the HttpClient, a more appropriate way would be to configure it before hand.

2. Typed client

Typed clients provide us a way to configure base address and default headers for the request of our HttpClient while mainting type safety using a class which we create. To use it, we register it from .AddHttpClient<T>:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddHttpClient<MyTypeClient>(client =>
    {
        client.BaseAddress = new Uri("http://localhost:5100");
    });
}

The extensions takes an action as parameter allowing us to specify a base address. Make sure to only specify the root address as any URI will be discarded. As we can see here, we need to specify a type which is our own client, MyTypedClient, who will receive an HttpClient configured by the Action argument in AddHttpClient<T>(...).

public class MyTypedClient
{
    private HttpClient _client;

    public MyTypedClient(HttpClient client)
    {
        _client = client;
    }

    public async Task<string> Post(Dto value)
    {
        var result = await _client.PostAsJsonAsync("api/values", value);
        return await result.Content.ReadAsStringAsync();
    }
}

Here we simply create one function to handle a post of data and use the HttpClient with PostAsJsonAsync to post the value. Next from our controller endpoint, we can inject our own client MyTypedClient and use it.

[HttpPost]
public async Task<ActionResult<string>> Post([FromServices]MyTypedClient client, [FromBody] Dto value)
{
    return await client.Post(value);
}

3. Named client

The last way to get a HttpClient is to use named clients. Instead of passing a type, we use the overload specifying a name for the client:

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddHttpClient("my-named-client", client =>
    {
        client.BaseAddress = new Uri("http://localhost:5100");
    });
}

Next in the controller, we inject the IHttpClientFactory which allows us to instantiate a client using the CreateClient factory function by specifying the name of the configuration we want to use.

[HttpPost]
public async Task<ActionResult<string>> Post([FromServices]IHttpClientFactory factory, [FromBody] Dto value)
{
    var result = await factory.CreateClient("my-named-client").PostAsJsonAsync("api/values", value);
    return await result.Content.ReadAsStringAsync();
}

And that concludes today’s post on how to use the new HttpClientFactory, see you next time!