Send HTTP POST request in .NET

How can I make an HTTP POST request and send data in the body?

There are several ways to perform HTTP GET and POST requests:

Method A: HttpClient (Preferred)

Available in: .NET Framework 4.5+, .NET Standard 1.1+, and .NET Core 1.0+.

It is currently the preferred approach, and is asynchronous and high performance. Use the built-in version in most cases, but for very old platforms there is a NuGet package.

using System.Net.Http;

Setup

It is recommended to instantiate one HttpClient for your application's lifetime and share it unless you have a specific reason not to.

private static readonly HttpClient client = new HttpClient();

See HttpClientFactory for a dependency injection solution.

-
POST

var values = new Dictionary
  {
      { "thing1", "hello" },
      { "thing2", "world" }
  };

  var content = new FormUrlEncodedContent(values);

  var response = await client.PostAsync("http://www.example.com/recepticle.aspx", content);

  var responseString = await response.Content.ReadAsStringAsync();

-
GET

var responseString = await client.GetStringAsync("http://www.example.com/recepticle.aspx");

Method B: Third-Party Libraries

RestSharp

-
POST

var client = new RestClient("http://example.com");
   // client.Authenticator = new HttpBasicAuthenticator(username, password);
   var request = new RestRequest("resource/{id}");
   request.AddParameter("thing1", "Hello");
   request.AddParameter("thing2", "world");
   request.AddHeader("header", "value");
   request.AddFile("file", path);
   var response = client.Post(request);
   var content = response.Content; // Raw content as string
   var response2 = client.Post(request);
   var name = response2.Data.Name;

Flurl.Http

It is a newer library sporting a fluent API, testing helpers, uses HttpClient under the hood, and is portable. It is available via NuGet.

using Flurl.Http;

-
POST

var responseString = await "http://www.example.com/recepticle.aspx"
      .PostUrlEncodedAsync(new { thing1 = "hello", thing2 = "world" })
      .ReceiveString();

-
GET

var responseString = await "http://www.example.com/recepticle.aspx"
      .GetStringAsync();

Method C: HttpWebRequest (not recommended for new work)

Available in: .NET Framework 1.1+, .NET Standard 2.0+, .NET Core 1.0+. In .NET Core, it is mostly for compatibility -- it wraps HttpClient, is less performant, and won't get new features.

using System.Net;
using System.Text;  // For class Encoding
using System.IO;    // For StreamReader

-
POST

var request = (HttpWebRequest)WebRequest.Create("http://www.example.com/recepticle.aspx");

  var postData = "thing1=" + Uri.EscapeDataString("hello");
      postData += "&thing2=" + Uri.EscapeDataString("world");
  var data = Encoding.ASCII.GetBytes(postData);

  request.Method = "POST";
  request.ContentType = "application/x-www-form-urlencoded";
  request.ContentLength = data.Length;

  using (var stream = request.GetRequestStream())
  {
      stream.Write(data, 0, data.Length);
  }

  var response = (HttpWebResponse)request.GetResponse();

  var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

-
GET

var request = (HttpWebRequest)WebRequest.Create("http://www.example.com/recepticle.aspx");

  var response = (HttpWebResponse)request.GetResponse();

  var responseString = new StreamReader(response.GetResponseStream()).ReadToEnd();

Method D: WebClient (Not recommended for new work)

This is a wrapper around HttpWebRequest. Compare with HttpClient.

Available in: .NET Framework 1.1+, NET Standard 2.0+, and .NET Core 2.0+.

In some circumstances (.NET Framework 4.5-4.8), if you need to do a HTTP request synchronously, WebClient can still be used.

using System.Net;
using System.Collections.Specialized;

-
POST

using (var client = new WebClient())
  {
      var values = new NameValueCollection();
      values["thing1"] = "hello";
      values["thing2"] = "world";

      var response = client.UploadValues("http://www.example.com/recepticle.aspx", values);

      var responseString = Encoding.Default.GetString(response);
  }

-
GET

using (var client = new WebClient())
  {
      var responseString = client.DownloadString("http://www.example.com/recepticle.aspx");
  }

Stack Overflow Q#4015324, score: 2733