11.2 Making HTTP Requests

Let’s go through making HTTP requests in C# using HttpClient — the standard way to call web APIs or fetch data from the internet.

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📌 1. What is HttpClient?

• HttpClient is a class in System.Net.Http used for:

  • Sending GET, POST, PUT, DELETE requests

  • Communicating with REST APIs

  • Handling HTTP responses asynchronously

• Designed to be reused for multiple requests (avoid creating a new instance per request).

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📌 2. Creating an HttpClient Instance

using System.Net.Http;
 
HttpClient client = new HttpClient();

• For better performance, use a single shared instance:

private static readonly HttpClient client = new HttpClient();

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📌 3. Making a GET Request

using System;
using System.Net.Http;
using System.Threading.Tasks;
 
async Task GetExample()
{
    string url = "https://jsonplaceholder.typicode.com/todos/1";
    HttpResponseMessage response = await client.GetAsync(url);
 
    if (response.IsSuccessStatusCode)
    {
        string content = await response.Content.ReadAsStringAsync();
        Console.WriteLine(content);
    }
}

• GetAsync() → sends a GET request

• ReadAsStringAsync() → reads response body

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📌 4. Making a POST Request

using System.Net.Http;
using System.Text;
using System.Text.Json;
 
var data = new { title = "New Task", completed = false };
string json = JsonSerializer.Serialize(data);
 
HttpContent content = new StringContent(json, Encoding.UTF8, "application/json");
HttpResponseMessage response = await client.PostAsync("https://jsonplaceholder.typicode.com/todos", content);
 
string result = await response.Content.ReadAsStringAsync();
Console.WriteLine(result);

• StringContent wraps the JSON payload

• Specify encoding and media type (application/json)

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📌 5. Handling Other HTTP Methods

await client.PutAsync(url, content);    // Update resource
await client.DeleteAsync(url);         // Delete resource
await client.PatchAsync(url, content); // Partial update (needs extension method or custom HttpMethod)

• Supports all standard HTTP verbs

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📌 6. Setting Headers

client.DefaultRequestHeaders.Add("Authorization", "Bearer your_token_here");
client.DefaultRequestHeaders.Accept.Add(
    new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json")
);

• Useful for authentication, API keys, or content negotiation

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📌 7. Disposing HttpClient

• Avoid frequent creation/disposal to prevent socket exhaustion

• Prefer long-lived instances or use IHttpClientFactory in ASP.NET Core

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📌 8. Summary Table

Feature	Description
Class	HttpClient (System.Net.Http)
GET request	GetAsync(url)
POST request	PostAsync(url, HttpContent)
Read response	response.Content.ReadAsStringAsync()
Set headers	DefaultRequestHeaders.Add()
Best practice	Reuse HttpClient instance, use async/await

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✅ Tip:

• Always use async methods (GetAsync, PostAsync) to keep your app responsive.

• For ASP.NET Core apps, consider IHttpClientFactory to manage HttpClient lifetimes efficiently.