Sending HTTP POST with System.Net.WebClient

Question

Is it possible to send HTTP POST with some form data with System.Net.WebClient?

If not, is there another library like WebClient that can do HTTP POST? I know I can use System.Net.HttpWebRequest, but I'm looking for something that is not as verbose.

Hopefully it will look like this:

Using client As New TheHTTPLib
    client.FormData("parm1") = "somevalue"
    result = client.DownloadString(someurl, Method.POST)
End Using

Endy Tjahjono · Accepted Answer · 2011-11-23T04:32:21.517

67

Based on @carlosfigueira 's answer, I looked further into WebClient's methods and found UploadValues, which is exactly what I want:

Using client As New Net.WebClient
    Dim reqparm As New Specialized.NameValueCollection
    reqparm.Add("param1", "somevalue")
    reqparm.Add("param2", "othervalue")
    Dim responsebytes = client.UploadValues(someurl, "POST", reqparm)
    Dim responsebody = (New Text.UTF8Encoding).GetString(responsebytes)
End Using

The key part is this:

client.UploadValues(someurl, "POST", reqparm)

It sends whatever verb I type in, and it also helps me create a properly url encoded form data, I just have to supply the parameters as a namevaluecollection.

edited Nov 23 '11 at 04:32

answered Nov 22 '11 at 06:55

Endy Tjahjono

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What does `someUrl` refer to?? I'm trying to log in to a website that has a HTML login-form, it doesn't login. The resulted data is as if I'm anonymous. – Shimmy Weitzhandler Jun 12 '13 at 03:41
@Shimmy I haven't tried using webclient on a site that requires login. `someUrl` is URL string, for example `client.UploadValues("http://localhost", "POST", reqparm)`. – Endy Tjahjono Jun 12 '13 at 05:18
can we use this POST request (including the parameters call) with the asynchronous call? – gumuruh Apr 07 '14 at 09:14
It's working fine, thanks for the answer! But when I call `Net.WebClient.UploadValues` method it's start 7 threads and don't stop these. What could I do about this? – kukko Oct 20 '16 at 14:06

score 14 · Answer 2 · answered Nov 22 '11 at 04:47

14

WebClient doesn't have a direct support for form data, but you can send a HTTP post by using the UploadString method:

Using client as new WebClient
    result = client.UploadString(someurl, "param1=somevalue&param2=othervalue")
End Using

answered Nov 22 '11 at 04:47

carlosfigueira

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1

POST - that's the default for `UploadString`. You can also pass the HTTP verb as an optional third parameter. – carlosfigueira Nov 22 '11 at 04:51
2

I guess the form data needs to be escaped: `"param1=" & HttpUtility.UrlEncode("somevalue")` – Endy Tjahjono Nov 22 '11 at 05:08
If the value needs to be escaped, yes. "somevalue" doesn't. As I mentioned, `WebClient` itself doesn't have any form support, you need to create the string yourself. – carlosfigueira Nov 22 '11 at 05:23
Based on your answer, I found UploadValues. Thanks! – Endy Tjahjono Nov 22 '11 at 07:02
Interesting, I didn't know that. Thanks for sharing it :) – carlosfigueira Nov 22 '11 at 14:46
If you use UploadString to post form values make sure to include client.Headers.Add("Content-Type", "application/x-www-form-urlencoded"). – Jeff Widmer Jul 25 '16 at 15:43
uploadvalues of course works at the moment i wrote this comment. But is it possible as well for downloading a file? – gumuruh Jul 19 '18 at 03:58

score 2 · Answer 3 · answered Nov 22 '11 at 07:16

As far as the http verb is concerned the WebRequest might be easier. You could go for something like:

    WebRequest r = WebRequest.Create("http://some.url");
    r.Method = "POST";
    using (var s = r.GetResponse().GetResponseStream())
    {
        using (var reader = new StreamReader(r, FileMode.Open))
        {
            var content = reader.ReadToEnd();
        }
    }

Obviously this lacks exception handling and writing the request body (for which you can use r.GetRequestStream() and write it like a regular stream, but I hope it may be of some help.

question has tag `vb.net` – Gray Programmerz Dec 14 '21 at 09:28 — Gray Programmerz, Dec 14 '21 at 09:28

Sending HTTP POST with System.Net.WebClient

3 Answers3

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