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How to send a POST request in .NET using C#

How to send a POST request in .NET using C#

Richard C.

—

The Problem

In C#, how do you send an HTTP POST request to a URL?

Let’s take a simple example you can run in a terminal with curl to a test site, and see if we can recreate it in .NET:

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curl -X POST https://httpbin.org/post -H "Content-Type: application/json" -d '{"name":"Alice"}'

# Result returned by httpbin.org:
{
  "args": {},
  "data": "{\"name\":\"Alice\"}",
  "files": {},
  "form": {},
  "headers": {
    "Accept": "*/*",
    "Content-Length": "16",
    "Content-Type": "application/json",
    "Host": "httpbin.org",
    "User-Agent": "curl/7.81.0",
    "X-Amzn-Trace-Id": "Root=1-6571815c-1743cbd01a39a04a466fd1ab"
  },
  "json": {
    "name": "Alice"
  },
  "origin": "5.157.13.3",
  "url": "https://httpbin.org/post"
}

The Solution

Microsoft recommends using the HttpClient for web requests.

Here’s a C# example that has the same result as the curl command above:

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using System;
using System.Collections.Generic;
using System.Net.Http; // for HttpClient
using System.Threading.Tasks;

public class Program
{
    public static async Task Main()
    {
        using var client = new HttpClient();
        var values = new Dictionary<string, string> { { "name", "alice" } };
        var content = new FormUrlEncodedContent(values);
        var response = await client.PostAsync("https://httpbin.org/post", content);
        var responseString = await response.Content.ReadAsStringAsync();
        Console.WriteLine(responseString);
    }
}

We use an asynchronous Main method, instead of the traditional public static void Main(). This allows us to use await so our app can do other work while waiting for a response from the website.

Your app should only have one instance of HttpClient, to use as few network resources as possible. Every class in your app can share a single HttpClient. Here we are also instantiating HttpClient with a using statement so that .NET immediately frees its network resources when it is no longer in use.

To make the request, we create a dictionary with whatever POST key-value pairs we want to send and use the client’s PostAsync method to send the encoded data. The response is returned as a string, which we print.

How to Write Less Code

If you prefer a more fluent or functional style of coding with fewer temporary variables, you can refactor this function as:

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using var client = new HttpClient();
var data = new FormUrlEncodedContent(new Dictionary<string, string> { { "name", "alice" } });
var responseString = await client.PostAsync("https://httpbin.org/post", data)
    .Result
    .Content
    .ReadAsStringAsync();
Console.WriteLine(responseString);

How to Make a GET Request

Here’s how to make a GET request instead of a POST:

Click to Copy
using System;
using System.Net.Http;
using System.Threading.Tasks;

public class Program
{
    public static async Task Main()
    {
        using var client = new HttpClient();
        var response = await client.GetAsync("https://httpbin.org/get");
        var responseString = await response.Content.ReadAsStringAsync();
        Console.WriteLine(responseString);
    }
}

/* Response:
{
  "args": {},
  "headers": {
    "Host": "httpbin.org",
    "X-Amzn-Trace-Id": "Root=1-65718c3b-35fba5f01f87156337c46655"
  },
  "origin": "40.112.208.75",
  "url": "https://httpbin.org/get"
}
*/

We have only removed code from the POST request example, and changed PostAsync to GetAsync.

How to Convert Objects To and From JSON to Send Requests

If you want to serialize and deserialize .NET objects to JSON strings to transfer them in HTTP requests, you can use Microsoft’s JsonSerializer class. We have a simple example of this in this article.

You can also use the shortcut package System.Net.Http.Json. It provides two methods to read and write JSON:

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var data = new Person(Id: 1, Name: "Alice");
var response = await httpClient.PostAsJsonAsync("data", data);
var todo = await response.Content.ReadFromJsonAsync<Person>();

Further Reading

Read Microsoft’s detailed documentation on the HttpClient class here. It explains how to catch timeout exceptions and check status codes.

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