Deciding between HttpClient and WebClient

HttpClientFactory

It's important to evaluate the different ways you can create an HttpClient, and part of that is understanding HttpClientFactory.

https://docs.microsoft.com/en-us/dotnet/architecture/microservices/implement-resilient-applications/use-httpclientfactory-to-implement-resilient-http-requests

This is not a direct answer I know - but you're better off starting here than ending up with new HttpClient(...) everywhere.

When it comes to ASP.NET apps I still prefer WebClient over HttpClient because:

1. The modern implementation comes with async/awaitable task-based methods
2. Has smaller memory footprint and 2-5 times faster (other answers already mention that)
3. It's suggested to "reuse a single instance of HttpClient for the lifetime of your application". But ASP.NET has no "lifetime of application", only lifetime of a request. The current guidance for ASP.NET 5 is to use HttpClientFactory, but it can only be used via dependency injection. Some people want a simpler solution.
4. Most importantly, if you're using one singleton instance of HttpClient through the lifetime of the app like MS suggests - it has known issues. For example the DNS caching issue - HttpClient simply ignores the TTL and caches DNS "forever". There are workarounds, however. If you'd like to learn more about the issues and confusion with HttpClient just read this comment at Microsoft GitHub.

Perhaps you could think about the problem in a different way. WebClient and HttpClient are essentially different implementations of the same thing. What I recommend is implementing the Dependency Injection pattern with an IoC Container throughout your application. You should construct a client interface with a higher level of abstraction than the low level HTTP transfer. You can write concrete classes that use both WebClient and HttpClient, and then use the IoC container to inject the implementation via config.

What this would allow you to do would be to switch between HttpClient and WebClient easily so that you are able to objectively test in the production environment.

So questions like:

Will HttpClient be a better design choice if we upgrade to .Net 4.5?

Can actually be objectively answered by switching between the two client implementations using the IoC container. Here is an example interface that you might depend on that doesn't include any details about HttpClient or WebClient.

/// <summary>
/// Dependency Injection abstraction for rest clients. 
/// </summary>
public interface IClient
{
    /// <summary>
    /// Adapter for serialization/deserialization of http body data
    /// </summary>
    ISerializationAdapter SerializationAdapter { get; }

    /// <summary>
    /// Sends a strongly typed request to the server and waits for a strongly typed response
    /// </summary>
    /// <typeparam name="TResponseBody">The expected type of the response body</typeparam>
    /// <typeparam name="TRequestBody">The type of the request body if specified</typeparam>
    /// <param name="request">The request that will be translated to a http request</param>
    /// <returns></returns>
    Task<Response<TResponseBody>> SendAsync<TResponseBody, TRequestBody>(Request<TRequestBody> request);

    /// <summary>
    /// Default headers to be sent with http requests
    /// </summary>
    IHeadersCollection DefaultRequestHeaders { get; }

    /// <summary>
    /// Default timeout for http requests
    /// </summary>
    TimeSpan Timeout { get; set; }

    /// <summary>
    /// Base Uri for the client. Any resources specified on requests will be relative to this.
    /// </summary>
    Uri BaseUri { get; set; }

    /// <summary>
    /// Name of the client
    /// </summary>
    string Name { get; }
}

public class Request<TRequestBody>
{
    #region Public Properties
    public IHeadersCollection Headers { get; }
    public Uri Resource { get; set; }
    public HttpRequestMethod HttpRequestMethod { get; set; }
    public TRequestBody Body { get; set; }
    public CancellationToken CancellationToken { get; set; }
    public string CustomHttpRequestMethod { get; set; }
    #endregion

    public Request(Uri resource,
        TRequestBody body,
        IHeadersCollection headers,
        HttpRequestMethod httpRequestMethod,
        IClient client,
        CancellationToken cancellationToken)
    {
        Body = body;
        Headers = headers;
        Resource = resource;
        HttpRequestMethod = httpRequestMethod;
        CancellationToken = cancellationToken;

        if (Headers == null) Headers = new RequestHeadersCollection();

        var defaultRequestHeaders = client?.DefaultRequestHeaders;
        if (defaultRequestHeaders == null) return;

        foreach (var kvp in defaultRequestHeaders)
        {
            Headers.Add(kvp);
        }
    }
}

public abstract class Response<TResponseBody> : Response
{
    #region Public Properties
    public virtual TResponseBody Body { get; }

    #endregion

    #region Constructors
    /// <summary>
    /// Only used for mocking or other inheritance
    /// </summary>
    protected Response() : base()
    {
    }

    protected Response(
    IHeadersCollection headersCollection,
    int statusCode,
    HttpRequestMethod httpRequestMethod,
    byte[] responseData,
    TResponseBody body,
    Uri requestUri
    ) : base(
        headersCollection,
        statusCode,
        httpRequestMethod,
        responseData,
        requestUri)
    {
        Body = body;
    }

    public static implicit operator TResponseBody(Response<TResponseBody> readResult)
    {
        return readResult.Body;
    }
    #endregion
}

public abstract class Response
{
    #region Fields
    private readonly byte[] _responseData;
    #endregion

    #region Public Properties
    public virtual int StatusCode { get; }
    public virtual IHeadersCollection Headers { get; }
    public virtual HttpRequestMethod HttpRequestMethod { get; }
    public abstract bool IsSuccess { get; }
    public virtual Uri RequestUri { get; }
    #endregion

    #region Constructor
    /// <summary>
    /// Only used for mocking or other inheritance
    /// </summary>
    protected Response()
    {
    }

    protected Response
    (
    IHeadersCollection headersCollection,
    int statusCode,
    HttpRequestMethod httpRequestMethod,
    byte[] responseData,
    Uri requestUri
    )
    {
        StatusCode = statusCode;
        Headers = headersCollection;
        HttpRequestMethod = httpRequestMethod;
        RequestUri = requestUri;
        _responseData = responseData;
    }
    #endregion

    #region Public Methods
    public virtual byte[] GetResponseData()
    {
        return _responseData;
    }
    #endregion
}

Full code

HttpClient Implementation

You can use Task.Run to make WebClient run asynchronously in its implementation.

Dependency Injection, when done well helps alleviate the problem of having to make low level decisions upfront. Ultimately, the only way to know the true answer is try both in a live environment and see which one works the best. It's quite possible that WebClient may work better for some customers, and HttpClient may work better for others. This is why abstraction is important. It means that code can quickly be swapped in, or changed with configuration without changing the fundamental design of the app.

BTW: there are numerous other reasons that you should use an abstraction instead of directly calling one of these low-level APIs. One huge one being unit-testability.

I have benchmarked between HttpClient, WebClient, and HttpWebResponse, and then called the REST Web API.

And the results:

Call REST Web API Benchmark

---------------------Stage 1  ---- 10 Request

{00:00:17.2232544} ====>HttpClinet
{00:00:04.3108986} ====>WebRequest
{00:00:04.5436889} ====>WebClient

---------------------Stage 1  ---- 10 Request--Small Size
{00:00:17.2232544}====>HttpClinet
{00:00:04.3108986}====>WebRequest
{00:00:04.5436889}====>WebClient

---------------------Stage 3  ---- 10 sync Request--Small Size
{00:00:15.3047502}====>HttpClinet
{00:00:03.5505249}====>WebRequest
{00:00:04.0761359}====>WebClient

---------------------Stage 4  ---- 100 sync Request--Small Size
{00:03:23.6268086}====>HttpClinet
{00:00:47.1406632}====>WebRequest
{00:01:01.2319499}====>WebClient

---------------------Stage 5  ---- 10 sync Request--Max Size

{00:00:58.1804677}====>HttpClinet
{00:00:58.0710444}====>WebRequest
{00:00:38.4170938}====>WebClient

---------------------Stage 6  ---- 10 sync Request--Max Size

{00:01:04.9964278}====>HttpClinet
{00:00:59.1429764}====>WebRequest
{00:00:32.0584836}====>WebClient

WebClient Is faster

var stopWatch = new Stopwatch();

stopWatch.Start();
for (var i = 0; i < 10; ++i)
{
    CallGetHttpClient();
    CallPostHttpClient();
}

stopWatch.Stop();

var httpClientValue = stopWatch.Elapsed;

stopWatch = new Stopwatch();

stopWatch.Start();
for (var i = 0; i < 10; ++i)
{
    CallGetWebRequest();
    CallPostWebRequest();
}

stopWatch.Stop();

var webRequesttValue = stopWatch.Elapsed;

stopWatch = new Stopwatch();

stopWatch.Start();
for (var i = 0; i < 10; ++i)
{
    CallGetWebClient();
    CallPostWebClient();
}

stopWatch.Stop();

var webClientValue = stopWatch.Elapsed;

//-------------------------Functions

private void CallPostHttpClient()
{
    var httpClient = new HttpClient();
    httpClient.BaseAddress = new Uri("https://localhost:44354/api/test/");
    var responseTask = httpClient.PostAsync("PostJson", null);
    responseTask.Wait();

    var result = responseTask.Result;
    var readTask = result.Content.ReadAsStringAsync().Result;
}

private void CallGetHttpClient()
{
    var httpClient = new HttpClient();
    httpClient.BaseAddress = new Uri("https://localhost:44354/api/test/");
    var responseTask = httpClient.GetAsync("getjson");
    responseTask.Wait();

    var result = responseTask.Result;
    var readTask = result.Content.ReadAsStringAsync().Result;
}

private string CallGetWebRequest()
{
    var request = (HttpWebRequest)WebRequest.Create("https://localhost:44354/api/test/getjson");

    request.Method = "GET";
    request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;

    var content = string.Empty;

    using (var response = (HttpWebResponse)request.GetResponse())
    {
        using (var stream = response.GetResponseStream())
        {
            using (var sr = new StreamReader(stream))
            {
                content = sr.ReadToEnd();
            }
        }
    }
    return content;
}

private string CallPostWebRequest()
{
    var apiUrl = "https://localhost:44354/api/test/PostJson";

    HttpWebRequest httpRequest = (HttpWebRequest)WebRequest.Create(new Uri(apiUrl));
    httpRequest.ContentType = "application/json";
    httpRequest.Method = "POST";
    httpRequest.ContentLength = 0;

    using (var httpResponse = (HttpWebResponse)httpRequest.GetResponse())
    {
        using (Stream stream = httpResponse.GetResponseStream())
        {
            var json = new StreamReader(stream).ReadToEnd();
            return json;
        }
    }
    return "";
}

private string CallGetWebClient()
{
    string apiUrl = "https://localhost:44354/api/test/getjson";

    var client = new WebClient();

    client.Headers["Content-type"] = "application/json";

    client.Encoding = Encoding.UTF8;

    var json = client.DownloadString(apiUrl);

    return json;
}

private string CallPostWebClient()
{
    string apiUrl = "https://localhost:44354/api/test/PostJson";

    var client = new WebClient();

    client.Headers["Content-type"] = "application/json";

    client.Encoding = Encoding.UTF8;

    var json = client.UploadString(apiUrl, "");

    return json;
}