Is it possible to cancel an ongoing request with HttpClient (C#)?

Yes, it is possible to cancel an ongoing request using HttpClient in C#. To do this, you can use a CancellationToken. A CancellationToken is part of the .NET's System.Threading namespace and can be used to signal that an operation should be canceled.

Here's a step-by-step guide to using a CancellationToken with HttpClient:

1. Create a CancellationTokenSource (CTS). This object is responsible for creating and managing a CancellationToken.
2. Pass the CancellationToken from the CTS to the HttpClient method you're using (GetAsync, PostAsync, SendAsync, etc.).
3. To cancel the request, call the Cancel method on the CancellationTokenSource. This will signal to the HttpClient that the operation should be canceled.

Below is an example demonstrating how to use a CancellationToken with HttpClient in C#:

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

class Program
{
    static async Task Main()
    {
        using var httpClient = new HttpClient();
        using var cts = new CancellationTokenSource();

        // Optionally, you can set a timeout for the cancellation:
        // cts.CancelAfter(TimeSpan.FromSeconds(10));

        try
        {
            // Make an asynchronous GET request
            HttpResponseMessage response = await httpClient.GetAsync("http://example.com", cts.Token);

            // You can check if cancellation was requested
            cts.Token.ThrowIfCancellationRequested();

            // Read response content if the request was not canceled
            string content = await response.Content.ReadAsStringAsync();
            Console.WriteLine(content);
        }
        catch (TaskCanceledException)
        {
            Console.WriteLine("The request was canceled.");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"An error occurred: {ex.Message}");
        }
    }
}

// Somewhere else in your application, you can cancel the request by calling:
// cts.Cancel();

In this example, the HttpClient.GetAsync method is passed the CancellationToken from the CancellationTokenSource (cts.Token). If the Cancel method on the CancellationTokenSource is called before the request completes, the TaskCanceledException will be thrown, and the catch block will handle it by printing "The request was canceled." to the console.

One common use case for cancellation is when implementing a timeout for an HTTP request. The CancellationTokenSource can be configured to cancel the token after a certain period using the CancelAfter method, as commented out in the example.

It's good practice to always pass a CancellationToken to asynchronous methods when possible, as it provides a way to control and abort operations that may otherwise run indefinitely.