.NET: Simplest way to send POST with data and read response

Question

To my surprise, I can't do anything nearly as simple as this, from what I can tell, in the .NET BCL:

byte[] response = Http.Post
(
    url: "http://dork.com/service",
    contentType: "application/x-www-form-urlencoded",
    contentLength: 32,
    content: "home=Cosby&favorite+flavor=flies"
);

This hypothetical code above makes an HTTP POST, with data, and returns the response from a Post method on a static class Http.

Since we're left without something this easy, what's the next best solution?

How do I send an HTTP POST with data AND get the response's content?

Bjorn

This actually worked perfectly for me... stickler.de/en/information/code-snippets/… – Outofdoor

Answer 1

   using (WebClient client = new WebClient())
   {

       byte[] response =
       client.UploadValues("http://dork.com/service", new NameValueCollection()
       {
           { "home", "Cosby" },
           { "favorite+flavor", "flies" }
       });

       string result = System.Text.Encoding.UTF8.GetString(response);
   }

You will need these includes:

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

If you're insistent on using a static method/class:

public static class Http
{
    public static byte[] Post(string uri, NameValueCollection pairs)
    {
        byte[] response = null;
        using (WebClient client = new WebClient())
        {
            response = client.UploadValues(uri, pairs);
        }
        return response;
    }
}

Then simply:

var response = Http.Post("http://dork.com/service", new NameValueCollection() {
    { "home", "Cosby" },
    { "favorite+flavor", "flies" }
});

Ardyce

If you want more control over the HTTP headers, you could attempt the same using HttpWebRequest and reference RFC2616 (w3.org/Protocols/rfc2616/rfc2616.txt). Answers from jball and BFree follow that attempt. – Ardyce

This example doesn't actually read the response, which was an important part of the original question! – Mehala

To read the response, you can do string result = System.Text.Encoding.UTF8.GetString(response). This is the question where I found the answer. – Fritter

This method will no longer work if you're trying to build a Windows Store app for Windows 8.1, as WebClient isn't found in System.Net. Instead, use Ramesh's answer and look into the usage of "await." – Gatling

I'm gonna plus-one this, but you should include @Fritter comment about reading the response to improve your answer. – Testicle

Nice working solution, but I would like to add that Microsoft implemented the HttpClient class, a newer api that has some benefits over the WebClient class. – Melon

Answer 2

Using HttpClient: as far as Windows 8 app development concerns, I came across this.

var client = new HttpClient();

var pairs = new List<KeyValuePair<string, string>>
    {
        new KeyValuePair<string, string>("pqpUserName", "admin"),
        new KeyValuePair<string, string>("password", "test@123")
    };

var content = new FormUrlEncodedContent(pairs);

var response = client.PostAsync("youruri", content).Result;

if (response.IsSuccessStatusCode)
{


}

Paucity

Also works with a Dictionary<String, String>, which makes it cleaner. – Sanative

BEST ANSWER EVER.. Oh thank the lords, thank you I love you. I have been struggling.. 2 FREAKNG WEEKS.. you should see all my posts. ARGHH ITS WORKING, YEHAAA <hugs> – Ablate

Note that, when possible, you should not use .Result with Async calls - use await to ensure your UI thread will not block. Also, a simple new[] will work as well as the List; Dictionary may clean up the code, but will reduce some HTTP functionality. – Elongation

Nowadays (2016) this one is the best answer. HttpClient is newer than WebClient (most voted answer) and has some benefits over it: 1) It has a good async programming model being worked on by Henrik F Nielson who is basically one of the inventors of HTTP, and he designed the API so it is easy for you to follow the HTTP standard; 2) It is supported by the .Net framework 4.5, so it has some guaranteed level of support for the forseeable future; 3) It also has the xcopyable/portable-framework version of the library if you want to use it on other platforms - .Net 4.0, Windows Phone etc... – Melon

how to send files with httpclient – Yoko

Thanks dude, I've literally never worked with APIs in Dotnet before with backend C# code anyway. I literally sat down tried this, because it looked simple, accurate and concise. Worked first time(having never touched Web APIs in Dotnet before). You're a star! Much better than any documentation I can find out there. – Dianetics

Answer 3

Use WebRequest. From Scott Hanselman:

public static string HttpPost(string URI, string Parameters) 
{
   System.Net.WebRequest req = System.Net.WebRequest.Create(URI);
   req.Proxy = new System.Net.WebProxy(ProxyString, true);
   //Add these, as we're doing a POST
   req.ContentType = "application/x-www-form-urlencoded";
   req.Method = "POST";
   //We need to count how many bytes we're sending. 
   //Post'ed Faked Forms should be name=value&
   byte [] bytes = System.Text.Encoding.ASCII.GetBytes(Parameters);
   req.ContentLength = bytes.Length;
   System.IO.Stream os = req.GetRequestStream ();
   os.Write (bytes, 0, bytes.Length); //Push it out there
   os.Close ();
   System.Net.WebResponse resp = req.GetResponse();
   if (resp== null) return null;
   System.IO.StreamReader sr = 
         new System.IO.StreamReader(resp.GetResponseStream());
   return sr.ReadToEnd().Trim();
}

Wolfy

Answer 4

private void PostForm()
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://dork.com/service");
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";
    string postData ="home=Cosby&favorite+flavor=flies";
    byte[] bytes = Encoding.UTF8.GetBytes(postData);
    request.ContentLength = bytes.Length;

    Stream requestStream = request.GetRequestStream();
    requestStream.Write(bytes, 0, bytes.Length);

    WebResponse response = request.GetResponse();
    Stream stream = response.GetResponseStream();
    StreamReader reader = new StreamReader(stream);

    var result = reader.ReadToEnd();
    stream.Dispose();
    reader.Dispose();
}

Gnash

Answer 5

Personally, I think the simplest approach to do an http post and get the response is to use the WebClient class. This class nicely abstracts the details. There's even a full code example in the MSDN documentation.

http://msdn.microsoft.com/en-us/library/system.net.webclient(VS.80).aspx

In your case, you want the UploadData() method. (Again, a code sample is included in the documentation)

http://msdn.microsoft.com/en-us/library/tdbbwh0a(VS.80).aspx

UploadString() will probably work as well, and it abstracts it away one more level.

http://msdn.microsoft.com/en-us/library/system.net.webclient.uploadstring(VS.80).aspx

Hernandes

+1 I suspect there's a bunch of ways to do this in the framework. – Wolfy

Answer 6

Given other answers are a few years old, currently here are my thoughts that may be helpful:

Simplest way

private async Task<string> PostAsync(Uri uri, HttpContent dataOut)
{
    var client = new HttpClient();
    var response = await client.PostAsync(uri, dataOut);
    return await response.Content.ReadAsStringAsync();
    // For non strings you can use other Content.ReadAs...() method variations
}

A More Practical Example

Often we are dealing with known types and JSON, so you can further extend this idea with any number of implementations, such as:

public async Task<T> PostJsonAsync<T>(Uri uri, object dtoOut)
{
    var content = new StringContent(JsonConvert.SerializeObject(dtoOut));
    content.Headers.ContentType = MediaTypeHeaderValue.Parse("application/json");

    var results = await PostAsync(uri, content); // from previous block of code

    return JsonConvert.DeserializeObject<T>(results); // using Newtonsoft.Json
}

An example of how this could be called:

var dataToSendOutToApi = new MyDtoOut();
var uri = new Uri("https://example.com");
var dataFromApi = await PostJsonAsync<MyDtoIn>(uri, dataToSendOutToApi);

Solanaceous

Answer 7

I know this is an old thread, but hope it helps some one.

public static void SetRequest(string mXml)
{
    HttpWebRequest webRequest = (HttpWebRequest)HttpWebRequest.CreateHttp("http://dork.com/service");
    webRequest.Method = "POST";
    webRequest.Headers["SOURCE"] = "WinApp";

    // Decide your encoding here

    //webRequest.ContentType = "application/x-www-form-urlencoded";
    webRequest.ContentType = "text/xml; charset=utf-8";

    // You should setContentLength
    byte[] content = System.Text.Encoding.UTF8.GetBytes(mXml);
    webRequest.ContentLength = content.Length;

    var reqStream = await webRequest.GetRequestStreamAsync();
    reqStream.Write(content, 0, content.Length);

    var res = await httpRequest(webRequest);
}

Unanimous

What is httpRequest? Its giving me an error "Does not exist". – Southerly

Answer 8

You can use something like this pseudo code:

request = System.Net.HttpWebRequest.Create(your url)
request.Method = WebRequestMethods.Http.Post

writer = New System.IO.StreamWriter(request.GetRequestStream())
writer.Write("your data")
writer.Close()

response = request.GetResponse()
reader = New System.IO.StreamReader(response.GetResponseStream())
responseText = reader.ReadToEnd

Farro

Answer 9

Here is an example from .net 7:

Note that httpClient.PostAsJsonAsync is an extension method. This means you must add System.Net.Http.Json to your project, and then use it using System.Text.Json; or you will get a compile error.

Also note that this example instantiates an httpClient for every request. This is NOT recommended. This practice forces a new connection on every call, which requires a new https handshake. Instead, use a singleton or static instance. See the docs for full details on how to correctly implement this, or see my video here: https://youtu.be/BA1e_ez8fwI?si=Tt0ppiIxoVOX57mA

var roomRequest = new RoomRequest() { EndDate = DateTime.Now.AddHours(2) };
RoomRequestResponse roomRequestResponse;

var apiKey = await this.DataStore.GetAppSetting("whereby-api");
HttpClient client = new HttpClient();

client.DefaultRequestHeaders.Authorization
             = new AuthenticationHeaderValue("Bearer", apiKey.Value);
var response = await client.PostAsJsonAsync("https://api.whereby.dev/v1/meetings", roomRequest);

string jsonString = await response.Content.ReadAsStringAsync();


RoomRequestResponse? returnValue=
    JsonSerializer.Deserialize<RoomRequestResponse>(jsonString);

Janssen