How do I make a HEAD request with HttpClient (C#)?

In C#, you can use the HttpClient class to make various types of HTTP requests, including a HEAD request. To perform a HEAD request, you'll use the SendAsync method with an HttpRequestMessage where the Method property is set to HttpMethod.Head.

Here's a simple example on how to make a HEAD request with HttpClient:

using System;
using System.Net.Http;
using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        // Create an instance of HttpClient
        using (HttpClient client = new HttpClient())
        {
            // Create an HttpRequestMessage with HttpMethod.Head
            using (HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Head, "http://example.com"))
            {
                // Send the HEAD request asynchronously
                using (HttpResponseMessage response = await client.SendAsync(request))
                {
                    // Ensure we got a successful response
                    if (!response.IsSuccessStatusCode)
                    {
                        Console.WriteLine("Error: " + response.StatusCode);
                    }
                    else
                    {
                        // Process the response headers (if needed)
                        Console.WriteLine("Headers: ");
                        foreach (var header in response.Headers)
                        {
                            Console.WriteLine($"{header.Key}: {string.Join(", ", header.Value)}");
                        }
                    }
                }
            }
        }
    }
}

In this example, a HEAD request is sent to http://example.com. A HEAD request is similar to a GET request, except that it doesn't return the body of the response. It's often used to retrieve the headers from a resource without needing to download the entire content, which can be useful for checking things like content type, content length, or whether a resource exists.

When using the HttpClient for multiple requests, it's important to reuse the same instance of HttpClient for the lifetime of your application, rather than creating a new instance for each request. This is because each HttpClient instance may allocate system resources (like sockets), and creating numerous instances without properly disposing them can lead to resource exhaustion issues. The example above uses a using block to ensure that the HttpClient and other resources are properly disposed of after use.