HttpClient

✅ What is HttpClient?

HttpClient is a built-in class in .NET used to send HTTP requests and receive HTTP responses from web APIs.

---

✅ Why is it used?

You use HttpClient to:

• 🔗 Call external APIs or services

• 📥 Get data from a URL (like JSON)

• 📤 Send data (like POST, PUT requests)

• 🌐 Communicate over the internet (HTTP/HTTPS)

---

✅ Simple Example:

var client = new HttpClient();
var response = await client.GetStringAsync("https://api.example.com/data");
Console.WriteLine(response);

---

✅ Why Not Use new HttpClient() Directly?

Using new HttpClient() in every request can cause:

• Socket exhaustion (sockets are not released quickly).

• Hard-to-test code.

• No built-in support for resilience libraries like Polly.

---

🔧 1. IHttpClientFactory (Basic Usage)

✅ Best for:

• Creating HttpClient instances on demand.

• Having control over how the client is configured at runtime.

💡 Example:

Startup.cs / Program.cs

builder.Services.AddHttpClient();

Usage in a service:

public class MyService
{
    private readonly IHttpClientFactory _httpClientFactory;
 
    public MyService(IHttpClientFactory httpClientFactory)
    {
        _httpClientFactory = httpClientFactory;
    }
 
    public async Task<string> GetDataAsync()
    {
        var client = _httpClientFactory.CreateClient();
        return await client.GetStringAsync("https://api.example.com/data");
    }
}

---

🏷️ 2. Named HttpClient

✅ Best for:

• Calling multiple APIs with different configurations.

• Centralizing configs (like base address, headers).

💡 Example:

Startup.cs / Program.cs

builder.Services.AddHttpClient("GitHubClient", client =>
{
    client.BaseAddress = new Uri("https://api.github.com/");
    client.DefaultRequestHeaders.UserAgent.ParseAdd("HttpClientFactory-Sample");
});

Usage:

var client = _httpClientFactory.CreateClient("GitHubClient");
var response = await client.GetStringAsync("/users/octocat");

---

👨‍💻 3. Typed HttpClient

✅ Best for:

• Clean Dependency Injection (DI).

• Testable services.

• Automatically injects preconfigured HttpClient.

💡 Example:

Typed client class:

public class GitHubService
{
    private readonly HttpClient _client;
 
    public GitHubService(HttpClient client)
    {
        _client = client;
        _client.BaseAddress = new Uri("https://api.github.com/");
        _client.DefaultRequestHeaders.UserAgent.ParseAdd("HttpClientFactory-Sample");
    }
 
    public async Task<string> GetUserAsync(string username)
    {
        return await _client.GetStringAsync($"/users/{username}");
    }
}

Register it:

builder.Services.AddHttpClient<GitHubService>();

Usage:

var result = await _gitHubService.GetUserAsync("octocat");

---

🧙 4. Refit (Type-safe REST Client)

✅ Best for:

• Declarative API definitions.

• Auto-generates HTTP logic from interfaces.

• Great with Polly, testability, and clean architecture.

💡 Install:

dotnet add package Refit.HttpClientFactory

Define interface:

public interface IGitHubApi
{
    [Get("/users/{username}")]
    Task<User> GetUserAsync(string username);
}

Register with Refit:

builder.Services.AddRefitClient<IGitHubApi>()
       .ConfigureHttpClient(c => c.BaseAddress = new Uri("https://api.github.com/"));

Usage:

var user = await _gitHubApi.GetUserAsync("octocat");

---

✍ Summary Table

Method	Best For	Factory Access Needed	Testable
IHttpClientFactory	Flexible, low-level usage	✅ Yes	👍
Named HttpClient	Multiple APIs with different settings	✅ Yes	👍
Typed HttpClient	DI-friendly, clean architecture	❌ No	👍👍
Refit	Interface-based, declarative HTTP calls	❌ No (hidden under hood)	👍👍👍