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Can't get web html code: System.Net.WebException: 'The remote server returned an error: (403) Forbidden.

My problem is that I can't get specific website html code and I get this error:
'System.Net.WebException: 'The remote server returned an error: (403) Forbidden.'
My code is simple:
using (WebClient client = new WebClient())
{
string htmlCode = client.DownloadString("http://isbnsearch.org/isbn/");
MessageBox.Show(htmlCode);
}
When I try using other website like Google everything works perfectly, but with this website I can't reach it.
Is there any solution to fix this?
Thanks

well as you dont have access to isbnsearch.org, so you can just catch the error and avoid your app break down, but can not solve it.
using (WebClient client = new WebClient())
{
try
{
string htmlCode = client.DownloadString("http://isbnsearch.org/isbn/");
MessageBox.Show(htmlCode);
}
catch (Exception e)
{
MessageBox.Show(e.Message);
}
}

Found solution to get over this error:
string url = "https://www.isbnsearch.org/";
using (HttpClient client = new HttpClient())
{
using (HttpResponseMessage response = client.GetAsync(url).Result)
{
using (HttpContent content = response.Content)
{
string result = content.ReadAsStringAsync().Result;
MessageBox.Show(result);
}
}
}

Webclient POST 405 Error in API

I've written some code a while back that handles POST requests. Suddenly it stopped working whilst I changed nothing in either the API (It still works fine with postman) nor the C# code. But I get a 405 error (method not allowed) when I run my code.
The login method:
public byte[] logInViaAPI(string email, string password)
{
var response = APIHandler.Post("http://myurlhere", new NameValueCollection() {
{ "email", email },
{ "password", password },
});
return response;
}
This is my POST method:
public static byte[] Post(string uri, NameValueCollection pairs)
{
byte[] response = null;
try
{
using (WebClient client = new WebClient())
{
response = client.UploadValues(uri, pairs); //This is where I get my error
}
}
catch (WebException ex)
{
Console.Write(ex);
return null;
}
return response;
}
The error:
An unhandled exception of type 'System.Net.WebException' occurred in
System.dll
Additional information:
The remote server returned an error: (405) Method Not Allowed.
I used HTTP request with post as a source (and some other topics too) but I cant seem to figure out the problem.

Found the answer to my own question: I changed to protocol to HTTPS from HTTP, whilst still using the HTTP url.

Another possible solution is the use SecurityProtocol. Try this before the call:
ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

WebRequest Strange NotFound Error

I have 2 different ASP.NET Core websites: admin and public.
Both running on staging server and on local machine.
I send GET request to different pages to determine execution time of different pages and encountered problem with admin site: all urls on local instance and staging always returns 404 error:
An unhandled exception of type 'System.Net.WebException' occurred in
System.dll
Additional information: The remote server returned an error: (404) Not
Found.
Meanwhile, same requests in browser return html pages normally. Requests through HttpWebRequest to public site always also return 200 Status Code (OK).
Code for request I took here.
I tried to add all headers and cookies from browser request, but it didn't help. Also tried to debug local instance and found that no exceptions thrown while request executed.
Any ideas?

404 is way to generic. The code provided in answer in your link (https://stackoverflow.com/a/16642279/571203) does no error handling - this is brilliant example of how you can get to troubles when you blindly copy code from stackoverflow :)
Modified code with error handling should look like:
string urlAddress = "http://google.com/rrr";
var request = (HttpWebRequest)WebRequest.Create(urlAddress);
string data = null;
string errorData = null;
try
{
using (var response = (HttpWebResponse)request.GetResponse())
{
data = ReadResponse(response);
}
}
catch (WebException exception)
{
using (var response = (HttpWebResponse)exception.Response)
{
errorData = ReadResponse(response);
}
}
static string ReadResponse(HttpWebResponse response)
{
if (response.CharacterSet == null)
{
using (var reader = new StreamReader(response.GetResponseStream()))
{
return reader.ReadToEnd();
}
}
using (var reader = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(response.CharacterSet)))
{
return reader.ReadToEnd();
}
}
So when there is an exception, you'll get not just the status code, but entire response from server in the errorData variable.
One thing to check is proxy - browser can use http proxy while your server client uses none.

How to know if a website/domain is available before loading a webview with that URL

hello I am trying to launch an intent with a webview from a user entered URL, I have been looking everywhere online and I can't find a concrete answer as to how to make sure the website will actually connect before allowing the user to proceed to the next activity. I have found many tools to make sure the URL follows the correct format but none that actually let me make sure it can actually connect.

You can use WebClient and check if any exception is thrown:
using (var client = new HeadOnlyClient())
{
try
{
client.DownloadString("http://google.com");
}
catch (Exception ex)
{
// URL is not accessible.
}
}
You can catch more specific exceptions to make it more elegant.
You can also use custom modification to WebClient to check HEAD only and decrease the amount of data downloaded:
class HeadOnlyClient : WebClient
{
protected override WebRequest GetWebRequest(Uri address)
{
WebRequest req = base.GetWebRequest(address);
req.Method = "HEAD";
return req;
}
}

I would suggest you to use HttpHead for simple request with AndroidHttpClient, but it is deprecated now. You can try to implement HEAD Request by sockets.

You can try to ping the address first.
See this SO question: How to Ping External IP from Java Android

Another option:
Connectivity Plugin for Xamarin and Windows
Task<bool> IsReachable(string host, int msTimeout = 5000);
But, any pre-check that succeeds isn't guaranteed as the very next request might fail so you should still handle that.

Here's what I ended up doing to Check if a Host name is reachable. I was connecting to a site with a self signed certificate so that's why I have the delegate in the ServiceCertificateValidationCallback.
private async Task<bool> CheckHostConnectionAsync (string serverName)
{
string Message = string.Empty;
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(serverName);
ServicePointManager.ServerCertificateValidationCallback += delegate
{
return true;
};
// Set the credentials to the current user account
request.Credentials = System.Net.CredentialCache.DefaultCredentials;
request.Method = "GET";
request.Timeout = 1000 * 40;
try
{
using (HttpWebResponse response = (HttpWebResponse) await request.GetResponseAsync ())
{
// Do nothing; we're only testing to see if we can get the response
}
}
catch (WebException ex)
{
Message += ((Message.Length > 0) ? "\n" : "") + ex.Message;
return false;
}
if (Message.Length == 0)
{
goToMainActivity (serverName);
}
return true;
}

HttpWebRequest-The remote server returned an error: (400) Bad Request

I am getting The remote server returned an error: (400) Bad Request error while running the following code.
I am trying to upload xml file on the http server.
My xml file contains tag for the username,password and domain and when i am trying to connect is manually i am able to connect it,but using same credentials when i am trying to connect it through this code, i am getting 400 Bad Request error.
Please suggest me how to overcome this issue.
Thanks
`
public static void UploadHttp(string xml)
{
string txtResults = string.Empty;
try
{
string url = "http://my.server.com/upload.aspx ";
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
request.KeepAlive = false;
request.SendChunked = true;
request.AllowAutoRedirect = true;
request.Method = "Post";
request.ContentType = "text/xml";
var encoder = new UTF8Encoding();
var data = encoder.GetBytes(xml);
request.ContentLength = data.Length;
var reqStream = request.GetRequestStream();
reqStream.Write(data, 0, data.Length);
reqStream.Close();
WebResponse response = null;
response = request.GetResponse();
var reader = new StreamReader(response.GetResponseStream());
var str = reader.ReadToEnd();
}
catch (WebException ex)
{
if (ex.Status == WebExceptionStatus.ProtocolError)
{
HttpWebResponse err = ex.Response as HttpWebResponse;
if (err != null)
{
string htmlResponse = new StreamReader(err.GetResponseStream()).ReadToEnd();
txtResults = string.Format("{0} {1}", err.StatusDescription, htmlResponse);
}
}
else
{
}
}
catch (Exception ex)
{
txtResults = ex.ToString();
}
}`

Are you sure you should be using POST not PUT?
POST is usually used with application/x-www-urlencoded formats. If you are using a REST API, you should maybe be using PUT? If you are uploading a file you probably need to use multipart/form-data. Not always, but usually, that is the right thing to do..
Also you don't seem to be using the credentials to log in - you need to use the Credentials property of the HttpWebRequest object to send the username and password.

400 Bad request Error will be thrown due to incorrect authentication entries.
Check if your API URL is correct or wrong. Don't append or prepend spaces.
Verify that your username and password are valid. Please check any spelling mistake(s) while entering.
Note: Mostly due to Incorrect authentication entries due to spell changes will occur 400 Bad request.

What type of authentication do you use?
Send the credentials using the properties Ben said before and setup a cookie handler.
You already allow redirection, check your webserver if any redirection occurs (NTLM auth does for sure). If there is a redirection you need to store the session which is mostly stored in a session cookie.

//use "ASCII" or try with another encoding scheme instead of "UTF8".
using (StreamWriter postStream = new StreamWriter(request.GetRequestStream(), System.Text.Encoding.UTF8))
{
postStream.Write(postData);
postStream.Close();
}