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Empty answer from webclient C#

I'm trying to receive data from compressor, but it's answer is always empty. Here is my code:
WebClient client = new WebClient();
client.Headers[HttpRequestHeader.ContentType]= "application/x-www-form-urlencoded";
string question = "online_pressure";
string URL = "http://10.0.163.51/getVar.cgi";
string answer = client.UploadString(URL, "POST", question);
Console.WriteLine(answer);
When I use this code for another compressor, which different only 2 strings, it works great and I can see answer in console:
string question = "QUESTION=300201";
string URL = "http://10.0.163.50/cgi-bin/mkv.cgi";
Code in VBS works great for both compressors. I can see answer in MsgBox from first and second compressors:
Dim objHTTP
strToSend = "online_pressure"
Set objHTTP = CreateObject("Microsoft.XMLHTTP")
Call objHTTP.Open("POST", "http://10.0.163.51/getVar.cgi", false)
objHTTP.setRequestHeader "Content-Type", "application/x-www-form-urlencoded"
objHTTP.Send strToSend
MsgBox(objHTTP.ResponseText)
HttpRequest code works just for second compressor too:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.ContentLength = data.Length;
StreamWriter requestWriter = new StreamWriter(request.GetRequestStream(), System.Text.Encoding.ASCII);
requestWriter.Write(data);
requestWriter.Close();
try
{
// get the response
WebResponse webResponse = request.GetResponse();
Stream webStream = webResponse.GetResponseStream();
StreamReader responseReader = new StreamReader(webStream);
string response = responseReader.ReadToEnd();
responseReader.Close();
Console.WriteLine(response);
}
catch (WebException we)
{
string webExceptionMessage = we.Message;
}
What I can try else to get data from first compressor in C#?

I compared the three requests in Fiddler 4 and realized that the only difference (apart from some other headers which won't affect behavior) between vbs script and both WebClient
and HttpWebRequest is that, managed API's send the Expect: 100-continue header and vbs script does not.
This can be the issue if the software running on the compressor device does not support this.
Please try the following, which tells the HttpWebRequest to not send this header:
For the HttpWebRequest, you can simply prevent sending this by:
request.ServicePoint.Expect100Continue = false;
Note: For the WebClient, the assignment requires accessing to the HttpWebRequest object used internally, but this has "protected" access modifier and can be worked around.
Before setting this value:
POST http://oguzozgul.com.tr/getVar.cgi HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: oguzozgul.com.tr
Content-Length: 15
Expect: 100-continue
Connection: Keep-Alive
online_pressure
After setting this value:
POST http://oguzozgul.com.tr/getVar.cgi HTTP/1.1
Content-Type: application/x-www-form-urlencoded
Host: oguzozgul.com.tr
Content-Length: 15
Connection: Keep-Alive
online_pressure
I also want to put the vb script request here so you can see other differences as well. The Accept-Encoding and some other headers are also not sent by default:
POST http://oguzozgul.com.tr/getVar.cgi HTTP/1.1
Accept: */*
Content-Type: application/x-www-form-urlencoded
Accept-Language: tr,en-US;q=0.8,en-GB;q=0.7,en;q=0.5,zh-Hans-CN;q=0.3,zh-Hans;q=0.2
UA-CPU: AMD64
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.3; Win64; x64; Trident/7.0; .NET4.0E; .NET4.0C; Tablet PC 2.0; .NET CLR 3.5.30729; .NET CLR 2.0.50727; .NET CLR 3.0.30729; wbx 1.0.0; Zoom 3.6.0; wbxapp 1.0.0)
Host: oguzozgul.com.tr
Content-Length: 15
Connection: Keep-Alive
Pragma: no-cache
online_pressure

WebClient and HttpWebRequest still do not works with this comressor. I tried to add any headers, but no result.
I tried PowerShell and it returns empty response too:
Invoke-WebRequest -Uri http://10.0.163.51/getVar.cgi -Method POST -Body "package_discharge_pressure" -ContentType "application/x-www-form-urlencoded"
Curl not working too, it hangs without errors
curl -i -X POST -H "Content-Type:application/x-www-form-urlencoded" -d "sump_pressure" http://10.0.163.51/getVar.cgi
Javascript and VBS works good. And today I found c# code wich works too
WinHttpRequest req = new WinHttpRequest();
try {
req.Open("POST", "http://10.0.163.51/getVar.cgi", true);
req.SetRequestHeader("Content-Type", "application/x-www-form-urlencoded");
req.Send("sump_pressure");
req.WaitForResponse();
}
catch(Exception ex) {
Console.WriteLine("Error : " + ex.Message.Trim());
}
Console.WriteLine(req.ResponseText);
In visual studio need to make reference to WinHttp

C# Http Request with username

Hello everyone I am currently working on a Post Method of my C# work. As the URL I am going to send request to requires username and password, I have it but I do not know how to include them in my code. How should I insert them into my code?
Here is my request:
Content-Type: multipart/related; boundary="myboundary"
From: 12345678
To: 12345678
Password: my_Password
Username: my_UserName
--myboundary
Content-Type: application/smil
Content-ID: <abc.smil>
Content-Location: abc.smil
Here are my code:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("https://myurl.com");
request.Method = "POST";
request.ContentType = "multipart/related; boundary = myboundary";
WebResponse response = request.GetResponse();
Console.WriteLine(((HttpWebResponse)response).StatusDescription);

Webclient equivalent of CURL command

I am trying to upload a file via a POST to a REST API in a c# winform.
If I run the following command with curl the file is uploaded successfully:
curl.exe -H "Content-type: application/octet-stream" -X POST http://myapiurl --data-binary #C:\test.docx
I have tried using WebClient in my WinForm:
using (var client = new WebClient())
{
client.Headers.Add("Content-Type", "application/octet-stream");
byte[] result = client.UploadFile(url, file);
string responseAsString = Encoding.Default.GetString(result);
tb_result.Text += responseAsString;
}
But I just get a (500) Internal Server.
Checking this with fiddler the following headers are added with CURL:
POST http://myapiurl HTTP/1.1
User-Agent: curl/7.33.0
Host: 10.52.130.121:90
Accept: */*
Connection: Keep-Alive
Content-type: application/octet-stream
Content-Length: 13343
Expect: 100-continue
But checking my WebClient method shows the following:
POST http://myapiurl HTTP/1.1
Accept: */*
Content-Type: multipart/form-data; boundary=---------------------8d220bbd95f8b18
Host: 10.52.130.121:90
Content-Length: 13536
Expect: 100-continue
Connection: Keep-Alive
How can I simulate the CURL command above from my app?

How can I simulate the CURL command above from my app?
Use HttpWebRequest. It offers you more flexibility. As follows:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://myapiurl");
request.Method = "POST";
request.UserAgent = "curl/7.33.0";
request.Host = "10.52.130.121:90";
request.Accept = "Accept=*/*";
request.Connection = "Keep-Alive";
request.ContentType = "application/octet-stream";
request.ContentLength = 13343;
request.Expect = "100-continue";

Multipart/form-data with additional parameters in .net

What is the best way to create post request like this one in .net ?
I try to use HttpClient and MultipartFormDataContent classes but so far I can only be able to upload image. How can i add additional parameter like api key?
POST /services/upload/ HTTP/1.1
Content-Type: multipart/form-data; boundary=---------------------------7d44e178b0434
Host: api.flickr.com
Content-Length: 35261
-----------------------------7d44e178b0434
Content-Disposition: form-data; name="api_key"
3632623532453245
-----------------------------7d44e178b0434
Content-Disposition: form-data; name="auth_token"
436436545
-----------------------------7d44e178b0434
Content-Disposition: form-data; name="api_sig"
43732850932746573245
-----------------------------7d44e178b0434
Content-Disposition: form-data; name="photo"; filename="C:\test.jpg"
Content-Type: image/jpeg
{RAW JFIF DATA}
-----------------------------7d44e178b0434--

Something along the lines of.. in C# + .NET 4.0
Uri uri = new Uri("api.flickr.com");
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = "POST";
//goes into the body. not header
NameValueCollection queryString = HttpUtility.ParseQueryString(string.Empty);
queryString["api_key"] = "7d44e178b0434";
...
object returnValue = null;
try
{
using (var writer = new StreamWriter(request.GetRequestStream()))
{
writer.WriteLine(queryString);
}
returnValue = request.GetResponse();
}
catch (Exception ex)
{
..
}
And if you wanted to add something to the header -
request.Headers.Add("HeaderKEY", somevalue);

Garbled httpWebResponse string when posting data to web form programmatically

I tried to search previous discussion about this issue but I didn't find one, maybe it's because I didn't use right keywords.
I am writing a small program which posts data to a webpage and gets the response. The site I'm posting data to does not provide an API. After some Googling I came up to the use of HttpWebRequest and HttpWebResponse. The code looks like this:
HttpWebRequest httpRequest = (HttpWebRequest)WebRequest.Create("https://www.site.com/index.aspx");
CookieContainer cookie = new CookieContainer();
httpRequest.CookieContainer = cookie;
String sRequest = "SomeDataHere";
httpRequest.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
httpRequest.Headers.Add("Accept-Encoding: gzip, deflate");
httpRequest.Headers.Add("Accept-Language: en-us,en;q=0.5");
httpRequest.Headers.Add("Cookie: SomecookieHere");
httpRequest.Host = "www.site.com";
httpRequest.Referer = "https://www.site.com/";
httpRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:14.0) Gecko/20100101 Firefox/14.0.1";
httpRequest.ContentType = "application/x-www-form-urlencoded";
//httpRequest.Connection = "keep-alive";
httpRequest.ContentLength = sRequest.Length;
byte[] bytedata = Encoding.UTF8.GetBytes(sRequest);
httpRequest.ContentLength = bytedata.Length;
httpRequest.Method = "POST";
Stream requestStream = httpRequest.GetRequestStream();
requestStream.Write(bytedata, 0, bytedata.Length);
requestStream.Flush();
requestStream.Close();
HttpWebResponse httpWebResponse = (HttpWebResponse)httpRequest.GetResponse();
string sResponse;
using (Stream stream = httpWebResponse.GetResponseStream())
{
StreamReader reader = new StreamReader(stream, System.Text.Encoding.GetEncoding("iso-8859-1"));
sResponse = reader.ReadToEnd();
}
return sResponse;
I used firefox's firebug to get the header and data to post.
My question is, when I store and display the response using a string, all I got are garbled characters, like:
?????*??????xV?J-4Si1?]R?r)f?|??;????2+g???6?N-?????7??? ?6?? x???q v ??? j?Ro??_*?e*??tZN^? 4s?????? ??Pwc??3???|??_????_??9???^??#?Y??"?k??,?a?H?Lp?A?$ ;???C#????e6'?N???L7?j#???ph??y=?I??=(e?V?6C??
By reading the response header using FireBug I got the content type of response:
Content-Type text/html; charset=ISO-8859-1
And it is reflected in my code. I have even tried other encoding such as utf-8 and ascii, still no luck. Maybe I am in the wrong direction.
Please advise. A small code snippet will be even better.
Thanks you.

You're telling the server that you can accept compressed responses with httpRequest.Headers.Add("Accept-Encoding: gzip, deflate");. Try removing that line, and you should get a clear-text response.
HttpWebRequest does have built in support for gzip and deflate if you want to allow compressed responses. Remove the Accept-Encoding header line, and replace it with
httpRequest.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate
This will take care of adding the appropriate Accept-Encoding header for you, and handle decompressing the content automatically when you receive it.