What is the difference between HttpClient (C#) and WebClient in C#?

HttpClient and WebClient are both classes in C# that are used to send HTTP requests and receive HTTP responses from a resource identified by a URI. However, they are designed for different use cases and have different capabilities.

HttpClient:

• Introduced in .NET Framework 4.5. It is a modern, more flexible, and highly extensible class that is recommended for new development.
• Async Support: HttpClient is designed with async/await support in mind, which means it is optimized for tasks that involve asynchronous programming and can help avoid blocking the calling thread.
• Lifetime Management: It is intended to be instantiated once and re-used throughout the life of an application. This is because HttpClient is built on top of HttpMessageHandler, which is meant to be reused to maintain HTTP connections (when possible) and reduce the overhead of connection establishment.
• Request/Response Classes: HttpClient uses HttpRequestMessage and HttpResponseMessage for constructing and processing HTTP messages, which provides more control over the request/response.
• Headers Management: It provides better support for setting and reading HTTP headers.
• Extensibility: HttpClient can be extended with custom message handlers (derived from DelegatingHandler) that can intercept and modify requests and responses.
• Performance: It is generally more performant, especially when making many requests over time, because it is able to re-use connections via the underlying HttpMessageHandler.

Here is an example of using HttpClient:

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

public class HttpClientExample
{
    public static async Task Main()
    {
        using (var httpClient = new HttpClient())
        {
            HttpResponseMessage response = await httpClient.GetAsync("http://example.com/");
            if (response.IsSuccessStatusCode)
            {
                string content = await response.Content.ReadAsStringAsync();
                Console.WriteLine(content);
            }
        }
    }
}

WebClient:

• Introduced in .NET Framework 2.0. It is an older class that was designed to be a simple way to perform operations like downloading or uploading data to and from a web resource.
• Synchronous and Asynchronous Support: WebClient provides methods for both synchronous and asynchronous operations, but it does not natively support async/await.
• Lifetime Management: WebClient is designed to be instantiated as needed and is typically used for a single operation or a small number of operations. It is not optimized for re-use across requests, which can lead to less efficient connection management.
• Request/Response Classes: WebClient does not expose HTTP request and response messages directly. Instead, it provides simple methods such as DownloadString, UploadString, etc.
• Headers Management: Headers can be set via the Headers property, but there is less flexibility compared to HttpClient.
• Extensibility: WebClient is less extensible and does not support custom message handlers.
• Deprecation: WebClient is considered to be deprecated and might not be available in future versions of .NET. It is still available in .NET Framework but is not included in .NET Core and later versions.

Here is an example of using WebClient:

using System;
using System.Net;

public class WebClientExample
{
    public static void Main()
    {
        using (var webClient = new WebClient())
        {
            string content = webClient.DownloadString("http://example.com/");
            Console.WriteLine(content);
        }
    }
}

In summary, HttpClient is the preferred class for HTTP communication in modern C# applications due to its support for asynchronous programming, efficient connection management, and extensibility. It should be used for new developments, whereas WebClient is considered a legacy class and should be avoided in new projects.