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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

use HttpClient to set the Content-Type to "application/json" and add object to the body

I'm trying to create the following post using HttpClient, using postman its working correctly but I cant seem to replicate it in code. I need to set the header Content-Type to application/json and have an object in the body of the post.
POST https://mycompanyurl.com/authenticate
HEADERS
Key: Content-Type, Value: application/json
BODY
{
"username": "someusername",
"password": "somepassword"
}
using (var client = new HttpClient())
{
client.BaseAddress = new Uri("https://companyurl.com");
var serializedObject = JsonConvert.SerializeObject(
new {username = "username", password = "password" });
var request = new HttpRequestMessage(HttpMethod.Post, "authenticate");
request.Content = new StringContent(serializedObject, Encoding.UTF8,"application/json");
var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
var content = await response.Content.ReadAsStringAsync();
}
Using the reverse proxy in fidder I can capture the raw call from postman which works, the rest api returns a result as expected:
POST http://127.0.0.1:8888/v1/authenticate HTTP/1.1 Content-Type: application/json;charset=UTF-8 cache-control: no-cache Postman-Token: 4db8f2dd-cbf0-413c-ad5b-20af0543a31d User-Agent: PostmanRuntime/7.6.0 Accept: / Host: 127.0.0.1:8888 accept-encoding: gzip, deflate content-length: 87 Connection: keep-alive
{"username":"username","password":"password"}
My call from HttpClient and using fiddler is below, This does not work, returns 200 but its not working correctly, data is not being returned, I cant see anything differences in the payload that will make the rest api not respond as expected.
POST http://127.0.0.1:8888/v1/authenticate HTTP/1.1 Content-Type: application/json; charset=utf-8 Host: 127.0.0.1:8888 Content-Length: 87 Expect: 100-continue Connection: Keep-Alive
{"username":"username","password":"password"}

The logic below should generate the same working request signature provided in your example (which was posted as an Answer, please edit your Question instead), and therefore should work:
var clientHandler = new HttpClientHandler
{
AutomaticDecompression = System.Net.DecompressionMethods.GZip | System.Net.DecompressionMethods.Deflate,
AllowAutoRedirect = false
};
using (var client = new HttpClient(clientHandler, true))
{
client.BaseAddress = new Uri("http://127.0.0.1:8888/v1/");
client.DefaultRequestHeaders.Add("cache-control", "no-cache");
client.DefaultRequestHeaders.Add("Postman-Token", "db8f2dd-cbf0-413c-ad5b-20af0543a31d");
client.DefaultRequestHeaders.Add("User-Agent", "PostmanRuntime/7.6.0");
client.DefaultRequestHeaders.Add("Accept", "*/*");
client.DefaultRequestHeaders.ExpectContinue = false;
var serializedObject = JsonConvert.SerializeObject(
new { username = "username", password = "password" }
);
var request = new HttpRequestMessage(HttpMethod.Post, "authenticate")
{
Content = new StringContent(serializedObject, Encoding.UTF8, "application/json")
};
var response = await client.SendAsync(request);
response.EnsureSuccessStatusCode();
var content = await response.Content.ReadAsStringAsync();
}
It will create the following request:
POST http://127.0.0.1:8888/v1/authenticate HTTP/1.1
cache-control: no-cache
Postman-Token: db8f2dd-cbf0-413c-ad5b-20af0543a31d
User-Agent: PostmanRuntime/7.6.0
Accept: */*
Content-Type: application/json; charset=utf-8
Host: 127.0.0.1:8888
Content-Length: 45
Accept-Encoding: gzip, deflate
Connection: Keep-Alive
{"username":"username","password":"password"}
Hope this helps.

How to add access-control-allow-methods to method in C# POST

I am trying to sending a POST to a java web-service with my windows phone app using this c# code:
using (var client = new HttpClient())
{
client.DefaultRequestHeaders.Accept.Add(new
MediaTypeWithQualityHeaderValue("application/json"));
var requestContent = new StringContent(json);
requestContent.Headers.ContentType = new
MediaTypeWithQualityHeaderValue("application/json");
var response = await client.PostAsync(requestUri, requestContent);
//...
}
but I am getting a 400 Bad Request and sending this header:
POST [myreq] HTTP/1.1
Content-Type: application/json
Content-Length: 340
Accept-Encoding: identity
Accept: application/json
User-Agent: NativeHost
Host: [myhost]
Connection: Keep-Alive
Pragma: no-cache
and the only difference that I see from a valid similar (to the same web service) android java request is this line in my header:
access-control-allow-methods=[POST]
How to include this access-control-allow-methods with C#?

for future help
client.DefaultRequestHeaders.Add("Access-Control-Allow-Methods", "POST");

C# WebClient HTTP Basic Authentication Failing 401 with Correct Credentials

I'm trying to automate configuring a wireless router's SSID and Password via c# webclient. The router has no API that I know of. It's an unbranded chinese router. The web config seems to be the only option for configuration. It uses http-basic-authentication (you browse to the IP address of the router and get a generic dialog asking for username and password).
I've used Wireshark to get the headers and form fields that the http-post requests use when I manually update the SSID and Password (two separate forms). I then attempted to use webclient to emulate those post requests.
Here is a snippet of code that I am using to attempt to save a new SSID (NameValueCollection is defined elsewhere):
private const string FORM_SSID = "http://192.168.1.2/formWlanSetup.htm";
private const string REF_SSID = "http://192.168.1.2/formRedirect.htm?redirect-url=wlbasic.htm&wlan_id=0";
private NameValueCollection mFields = HttpUtility.ParseQueryString(string.Empty, Encoding.ASCII);
public string SaveConfigResponse()
{
try
{
using (WebClient wc = new WebClient())
{
wc.Headers[HttpRequestHeader.Accept] = "text/html, application/xhtml+xml, */*";
wc.Headers[HttpRequestHeader.Referer] = REF_SSID;
wc.Headers[HttpRequestHeader.AcceptLanguage] = "en-US";
wc.Headers[HttpRequestHeader.UserAgent] = "Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko";
wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
wc.Headers[HttpRequestHeader.AcceptEncoding] = "gzip, deflate";
wc.Headers[HttpRequestHeader.Host] = "192.168.1.2";
wc.Headers[HttpRequestHeader.Connection] = "Keep-Alive";
wc.Headers[HttpRequestHeader.ContentLength] = Encoding.ASCII.GetBytes(mFields.ToString()).Length.ToString();
wc.Headers[HttpRequestHeader.CacheControl] = "no-cache";
string credentials = Convert.ToBase64String(Encoding.ASCII.GetBytes(config_user + ":" + config_pass));
wc.Headers[HttpRequestHeader.Authorization] = string.Format("Basic {0}", credentials);
//wc.Credentials = new NetworkCredential("admin", "admin");
return Encoding.ASCII.GetString(wc.UploadValues(FORM_SSID, "POST", mFields));
}
}
catch (Exception ex)
{
return ex.Message;
}
}
This results in an http-status-code-401 not authorized response. Is what I'm trying to do just impossible?
UPDATE
Here are the HTTP headers of both the browser post/response and the WebClient post/response. Again, I tried to match what I saw the browser posting as well as I could with my WebClient post.
Browser:
POST /formWlanSetup.htm HTTP/1.1
Accept: text/html, application/xhtml+xml, */*
Referer: http://192.168.1.2/formRedirect.htm?redirect-url=wlbasic.htm&wlan_id=0
Accept-Language: en-US
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
Content-Type: application/x-www-form-urlencoded
Accept-Encoding: gzip, deflate
Host: 192.168.1.2
Content-Length: 524
Connection: Keep-Alive
Cache-Control: no-cache
Authorization: Basic YWRtaW46YWRtaW4=
HTTP/1.1 302 Found
Location: wlbasic.htm
Content-Length: 183
Date: Thu, 23 Oct 2014 18:18:27 GMT
Server: eCos Embedded Web Server
Connection: close
Content-Type: text/html
Transfer-Encoding: chunked
Cache-Control: no-cache
WebClient:
POST /formWlanSetup.htm HTTP/1.1
Accept-Language: en-US
Accept-Encoding: gzip, deflate
Cache-Control: no-cache
Authorization: Basic YWRtaW46YWRtaW4=
Accept: text/html, application/xhtml+xml, */*
Content-Type: application/x-www-form-urlencoded
Referer: http://192.168.1.2/formRedirect.htm?redirect-url=wlbasic.htm&wlan_id=0
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko
Host: 192.168.1.2
Content-Length: 524
Connection: Keep-Alive
HTTP/1.1 401 Not Authorized
WWW-Authenticate: Basic realm="AP"
Date: Thu, 23 Oct 2014 18:18:41 GMT
Server: eCos Embedded Web Server
Connection: close
Content-Type: text/html
Transfer-Encoding: chunked
Cache-Control: no-cache
Again, that was all gleaned from Wireshark. I'm not very familiar with Wireshark, but I was able to get this far. If I knew how to properly extract the raw packet data and pastebin it, I would.
Important New Observations
The Wireshark captures of the post packets from both Browser and WebClient obviously differ in the order of the headers. I don't know how significant that might or might not be, though, as the data for each header is clearly the same.
One stark difference between the packets that I noticed is that Wireshark reports the Browser packet to be significantly larger than the WebClient packet. Looking at the itemized view, I couldn't find any obvious differences. I assume posting raw data for comparison would reveal a lot, but again, I don't really know how to do that.
I had a bewildering revelation. Despite the response clearly stating '(401) Unauthorized', the post is in fact being accepted by the router! Driving in to the router's web config after my WebClient post shows that the settings were accepted and saved.
That last one is a biggie. I find myself in a situation where I can get my config to save with a WebClient post, but I have to ignore a 401 response in order to do so. Obviously, this is far from ideal. So close, yet so far!
FINAL UPDATE (RESOLUTION)
I've solved the issue of failing basic authentication, though not with WebClient. I used the suggestion from #caesay and went with HttpWebRequest (together with WebResponse). My form posts result in redirects, so I had to allow for that.
This is essentially what I went with:
private bool ConfigureRouter()
{
bool passed = false;
string response = "";
HttpWebRequest WEBREQ = null;
WebResponse WEBRESP = null;
// Attempt to POST form to router that saves a new SSID.
try
{
var uri = new Uri(FORM_SSID); // Create URI from URL string.
WEBREQ = HttpWebRequest.Create(uri) as HttpWebRequest;
// If POST will result in redirects, you won't see an "OK"
// response if you don't allow those redirects
WEBREQ.AllowAutoRedirect = true;
// Basic authentication will first send the request without
// creds. This is protocol standard.
// When the server replies with 401, the HttpWebRequest will
// automatically send the request again with the creds when
// when PreAuthenticate is set.
WEBREQ.PreAuthenticate = true;
WEBREQ.AuthenticationLevel = System.Net.Security.AuthenticationLevel.MutualAuthRequested;
// Mimic all headers known to satisfy the request
// as discovered with a tool like Wireshark or Fiddler
// when the form was submitted from a browser.
WEBREQ.Method = "POST";
WEBREQ.Accept = "text/html, application/xhtml+xml, */*";
WEBREQ.Headers.Add("Accept-Language", "en-US"); // No AcceptLanguage property built-in to HttpWebRequest
WEBREQ.UserAgent = USER_AGENT;
WEBREQ.Referer = REF_SSID;
WEBREQ.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
WEBREQ.KeepAlive = true;
WEBREQ.Headers.Add("Pragma", "no-cache"); // No Pragma property built-in to HttpWebRequest
// Use a cached credential so that the creds are properly
// submitted with subsequent redirect requests.
CredentialCache creds = new CredentialCache();
creds.Add(uri, "Basic", new NetworkCredential(config_user, config_pass));
WEBREQ.Credentials = creds;
// Submit the form.
using (Stream stream = WEBREQ.GetRequestStream())
{
SSID ssid = new SSID(ssid_scanned); // Gets predefined form fields with new SSID inserted (NameValueCollection PostData)
stream.Write(ssid.PostData, 0, ssid.PostData.Length);
}
// Get the response from the final redirect.
WEBRESP = WEBREQ.GetResponse();
response = ((HttpWebResponse)WEBRESP).StatusCode.ToString();
if (response == "OK")
{
StatusUpdate("STATUS: SSID save was successful.");
passed = true;
}
else
{
StatusUpdate("FAILED: SSID save was unsuccessful.");
passed = false;
}
WEBRESP.Close();
}
catch (Exception ex)
{
StatusUpdate("ERROR: " + ex.Message);
return false;
}
return passed;
}

Is what I'm trying to do just impossible?
No, its not impossible. I have had many headaches with web scraping like this over the years because some web servers are picky, and your router interface is likely a custom web server implementation that isnt as forgiving as apache or iis.
I would do a wireshark capture and get the raw packet data that chrome sends (w/ payload etc), and then do the same capture for your application. Make sure the packets are as similar as you can get them. If you still have issues, post the packet captures to pastebin or something so we can have a look.
EDIT::
Instead of using the limited WebClient API, try using some lower level items, I wonder if the following code will work for you:
var uri = new Uri("http://192.168.1.2/formWlanSetup.htm");
var cookies = new CookieContainer();
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uri);
request.CookieContainer = cookies;
request.ServicePoint.Expect100Continue = false;
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko";
request.Referer = "http://192.168.1.2/formRedirect.htm?redirect-url=wlbasic.htm&wlan_id=0";
request.Credentials = new NetworkCredential(config_user, config_pass);
request.PreAuthenticate = true;
var response = request.GetResponse();
var reader = new StreamReader(response.GetResponseStream());
string htmlResponse = reader.ReadToEnd();

PostAsJsonAsync POST variables don't arrive at Flight PHP REST server

I have a Flight PHP REST server set up.
At 1 end point it expects POST data and based on one of the POST data it retrieves some data from the database and returns it as JSON.
When I use the Postman REST extension in Chrome I see the correct result. But when I do the call using my C# application the returned json is null because the $_POST seems empty.
This is my Flight index.php:
Flight::route('POST /getText', function(){
// Create a new report class:
$reportText = new ReportText;
$theText = $reportText->ParsePost($_POST);
if ($theText == null)
{
echo null;
}
else
{
echo json_encode($theText);
}
});
This is my ParsePost:
public function ParsePost($PostDictionary)
{
$textArray = null;
foreach ($PostDictionary as $key => $value)
{
if (!empty($value))
{
list($tmp, $id) = explode("_", $key);
$text = $this->geFooWithText($id);
$textArray[$key] = "bar";
}
}
return $textArray;
}
This is my C# part:
private static async Task RunAsyncPost(string requestUri)
{
using (var client = new HttpClient())
{
// Send HTTP requests
client.BaseAddress = new Uri("myUrl");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
try
{
// HTTP POST
var response = await client.PostAsJsonAsync(requestUri, new { question_8 = "foo", question_9 = "bar" });
response.EnsureSuccessStatusCode(); // Throw if not a success code.
if (response.IsSuccessStatusCode)
{
var json = await response.Content.ReadAsStringAsync();
if (string.IsNullOrEmpty(json))
{
throw new ArgumentNullException("json", #"Response from the server is null");
}
var dictionary = JsonConvert.DeserializeObject<Dictionary<string, string>>(json);
foreach (var kvp in dictionary)
{
Debug.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
}
}
}
catch (HttpRequestException e)
{
// Handle exception.
Debug.WriteLine(e.ToString());
throw;
}
}
}
This is the response from Postman:
{
"question_8": "foo",
"question_9": "bar"
}
It seems I'm missing something in my call using C#.
[Update]
In this post (Unable to do a HTTP POST to a REST service passing json through C#) the same problem seems to appear.
Using Fiddler was suggested.
Using Postman and x-www-form-urlencoded:
POST http://myHost/api/getText HTTP/1.1
Host: myHost
Connection: keep-alive
Content-Length: 29
Cache-Control: no-cache
Origin: chrome-extension://fdmmgilgnpjigdojojpjoooidkmcomcm
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.111 Safari/537.36
Content-Type: application/x-www-form-urlencoded
Accept: */*
Accept-Encoding: gzip,deflate
Accept-Language: nl-NL,nl;q=0.8,en-US;q=0.6,en;q=0.4
question_8=foo&question_9=bar
Using Postman and form-data:
POST http://myHost/api/getText HTTP/1.1
Host: myHost
Connection: keep-alive
Content-Length: 244
Cache-Control: no-cache
Origin: chrome-extension://fdmmgilgnpjigdojojpjoooidkmcomcm
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/38.0.2125.111 Safari/537.36
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryvb4wmaP4KooT6TFu
Accept: */*
Accept-Encoding: gzip,deflate
Accept-Language: nl-NL,nl;q=0.8,en-US;q=0.6,en;q=0.4
------WebKitFormBoundaryvb4wmaP4KooT6TFu
Content-Disposition: form-data; name="question_8"
foo
------WebKitFormBoundaryvb4wmaP4KooT6TFu
Content-Disposition: form-data; name="question_9"
bar
------WebKitFormBoundaryvb4wmaP4KooT6TFu--
Using my C#-application:
POST http://myHost/api/getText/ HTTP/1.1
Accept: application/json
Content-Type: application/json; charset=utf-8
Host: myHost
Content-Length: 50
Expect: 100-continue
Connection: Keep-Alive
{"question_8":"foo","question_9":"bar"}
The C# application is sending it clearly in a different way.

I've found the problem.
Because I use client.PostAsJsonAsync() the POST data is send as json, as you can see in Fiddler.
PHP doesn't expects the POST data to be in json format.
To read that data I need to use $data = file_get_contents('php://input'); in my PHP file.
Now I have my keys and values and can I continue. It looks like PHP needs a $_JSON variable ;)