Cómo hacer una petición web HTTP POST

Hay varias formas de realizar peticiones HTTP GET y POST:

Método A: HttpClient (Preferido)

Se trata de una envoltura alrededor de HttpWebRequest. Comparar con WebClient.

Disponible en: .NET Framework 4.5+, .NET Standard 1.1+, .NET Core 1.0+.

Actualmente el enfoque preferido. Asíncrono. Versión portátil para otras plataformas disponible a través de NuGet.

using System.Net.Http;

Setup

Es recomendable instanciar un HttpClient para toda la vida de tu aplicación y compartirlo.

private static readonly HttpClient client = new HttpClient();

Ver HttpClientFactory para una solución de Inyección de Dependencia.

• POST

    var values = new Dictionary
    {
    { "cosa1", "hola" },
    { "cosa2", "mundo" }
    };
  
    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");

Método B: Bibliotecas de terceros

RestSharp

Biblioteca probada para interactuar con las APIs REST. Portátil. Disponible a través de NuGet.

Flurl.Http

Una biblioteca más reciente que cuenta con una API fluida y ayudantes de prueba. HttpClient bajo el capó. Portátil. Disponible a través de NuGet.

    usando Flurl.Http;

• POST

    var responseString = await "http://www.example.com/recepticle.aspx"
        .PostUrlEncodedAsync(new { cosa1 = "hola", cosa2 = "mundo" })
        .ReceiveString();

• GET

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

Método C: HttpWebRequest (No se recomienda para trabajos nuevos)

Disponible en: .NET Framework 1.1+, .NET Standard 2.0+, .NET Core 1.0+

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("hola");
        postData += "&thing2=" + Uri.EscapeDataString("mundo");
    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();

Método D: WebClient (No se recomienda para trabajos nuevos)

Esta es una envoltura alrededor de HttpWebRequest. Comparar con HttpClient.

Disponible en: .NET Framework 1.1+, NET Standard 2.0+, .NET Core 2.0+

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");
    }

Petición GET simple

using System.Net;

...

using (var wb = new WebClient())
{
    var response = wb.DownloadString(url);
}

Petición POST simple

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

...

using (var wb = new WebClient())
{
    var data = new NameValueCollection();
    data["username"] = "myUser";
    data["password"] = "myPassword";

    var response = wb.UploadValues(url, "POST", data);
    string responseInString = Encoding.UTF8.GetString(response);
}

MSDN tiene un ejemplo.

using System;
using System.IO;
using System.Net;
using System.Text;

namespace Examples.System.Net
{
    public class WebRequestPostExample
    {
        public static void Main()
        {
            // Create a request using a URL that can receive a post. 
            WebRequest request = WebRequest.Create("http://www.contoso.com/PostAccepter.aspx");
            // Set the Method property of the request to POST.
            request.Method = "POST";
            // Create POST data and convert it to a byte array.
            string postData = "This is a test that posts this string to a Web server.";
            byte[] byteArray = Encoding.UTF8.GetBytes(postData);
            // Set the ContentType property of the WebRequest.
            request.ContentType = "application/x-www-form-urlencoded";
            // Set the ContentLength property of the WebRequest.
            request.ContentLength = byteArray.Length;
            // Get the request stream.
            Stream dataStream = request.GetRequestStream();
            // Write the data to the request stream.
            dataStream.Write(byteArray, 0, byteArray.Length);
            // Close the Stream object.
            dataStream.Close();
            // Get the response.
            WebResponse response = request.GetResponse();
            // Display the status.
            Console.WriteLine(((HttpWebResponse)response).StatusDescription);
            // Get the stream containing content returned by the server.
            dataStream = response.GetResponseStream();
            // Open the stream using a StreamReader for easy access.
            StreamReader reader = new StreamReader(dataStream);
            // Read the content.
            string responseFromServer = reader.ReadToEnd();
            // Display the content.
            Console.WriteLine(responseFromServer);
            // Clean up the streams.
            reader.Close();
            dataStream.Close();
            response.Close();
        }
    }
}