Develop Reference

Error Handling for WebRequest & Response

I am currently running a method that takes a string (a domain name) and checks to see if the site is available or not and passes the information into a Domain object I have created. Currently, I am running into an issue where one of the sites is down and is in turn crashing the application. Below is the method:
private Domain GetStatus(string x)
{
string status = "";
WebRequest req = HttpWebRequest.Create("http://www." + x);
WebResponse res = req.GetResponse();
HttpWebResponse response = (HttpWebResponse)res;
if ((int)response.StatusCode > 226 || response.StatusCode == HttpStatusCode.NotFound)
{
status = "ERROR: " + response.StatusCode.ToString();
}
else
{
status = "LIVE";
}
Domain temp = new Domain(x, status);
return temp;
}
Initial thoughts were that the response.StatusCode == HttpStatusCode.NotFound would handle such an error but it is currently crashing on the line WebResponse res = req.GetResponse(); with the following response:
System.Net.WebException: 'The remote name could not be resolved: 'www.DOMAIN.com''

The issue is due to the fact that your own code is raising an exception.
This can be due to the lack of an internet connection, or a dns resolve issue (which could be caused by the remote party).
So, if the remote server throws an error, you'll get HTTP 500 Internal Server Error, if you can't reach it; your code throws an exception and you'll need to handle that.
To fix this, you can use a try/catch block, something like this:
private Domain GetStatus(string x)
{
string status = "";
try
{
WebRequest req = HttpWebRequest.Create("http://www." + x);
WebResponse res = req.GetResponse();
HttpWebResponse response = (HttpWebResponse)res;
if ((int)response.StatusCode > 226 ||
response.StatusCode == HttpStatusCode.NotFound)
{
status = "ERROR: " + response.StatusCode.ToString();
}
else
{
status = "LIVE";
}
}
catch (Exception e)
{
status = "ERROR: Something bad happend: " + e.ToString();
}
Domain temp = new Domain(x, status);
return temp;
}
By the way, the message,
The remote name could not be resolved
indicates that the host cannot be resolved.
Most likely cause is that your internet is down or, the domain is misspelled or the route to the domain is faulty (e.g. on intranet environments).

HttpWebRequest is all about HTTP protocol, which is kind of a agreed upon language.
But if the person on the other end doesn't exists, so how should you expect him to return you an "Hello" for example ?
So StatusCode is really just about if the actual remote site did response, what did the response state was according to the request resource, is it Successful(200) ? Not Found(404) ? Unauthorized(401) and so on.
Exception means, i couldn't reach the site because of many reasons.
StatusCode means the resource you requested has return this response type.
But a more actual check if the site is alive or not, is querying a static page and not getting exception, a more healthy check, will querying a static page, you will always count as being Healthy; meaning will return a 200 OK response.
So it all depends on what LIVE means for you (or the client using it).
Is it the remote host is actually receiving requests, meaning no Exceptions.
Or it actually means, he's able to get requests and returning me a valid StatusCode response that i expect him to return (Healthy).

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;

HttpWebRequest.GetResponse methods throws 404 exception

I want to download one image from url using console application.
I have used following code:
string sourceUrl = "http://i.ytimg.com/vi/pvBnYBsUi9A/default.jpg"; // Not Found
//string sourceUrl = "http://i.ytimg.com/vi/OrxZAN1FZUY/default.jpg"; // Found
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(sourceUrl);
HttpWebResponse response = null;
try
{
response = (HttpWebResponse)request.GetResponse();
}
catch (Exception)
{
}
Above code throws exception in line "response = (HttpWebResponse)request.GetResponse();"
but when I am accessing "http://i.ytimg.com/vi/pvBnYBsUi9A/default.jpg" url in my browser then image will be display.
What I am missing here?

I tried that url "http://i.ytimg.com/vi/pvBnYBsUi9A/default.jpg" in Chrome
developer tools. It also receives a 404, but the response includes the image, which displays.
Your code is not the cause of the exception. The site is returning a 404 and your code gets an exception.
You could write logic to look at the response even if you get a 404 and decide whether to take it anyway, as the browser does.
It looks like you can get the response returned by the site if you catch WebException, which allows you to see the http request status and the response, per the documentation.
Example from the .Net 4.5 doc...
try
{
// Creates an HttpWebRequest for the specified URL.
HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create(url);
// Sends the HttpWebRequest and waits for a response.
HttpWebResponse myHttpWebResponse = (HttpWebResponse)myHttpWebRequest.GetResponse();
if (myHttpWebResponse.StatusCode == HttpStatusCode.OK)
Console.WriteLine("\r\nResponse Status Code is OK and StatusDescription is: {0}",
myHttpWebResponse.StatusDescription);
// Releases the resources of the response.
myHttpWebResponse.Close();
}
catch(WebException e)
{
Console.WriteLine("\r\nWebException Raised. The following error occured : {0}",e.Status);
}
catch(Exception e)
{
Console.WriteLine("\nThe following Exception was raised : {0}",e.Message);
WebException has Response and Status properties. So it looks like the .Net way to deal with this is to catch WebException and determine how to handle based on the status and response content (if necessary).

HttpClient failing in accessing simple website

Here is my code
internal static void ValidateUrl(string url)
{
Uri validUri;
if(Uri.TryCreate(url,UriKind.Absolute,out validUri))
{
using (HttpClient client = new HttpClient())
{
try
{
HttpResponseMessage response = client.Get(url);
response.EnsureStatusIsSuccessful();
}
catch (Exception ex)
{
//exception handler goes here
}
}
}
}
This code when i run it produces this result.
ProxyAuthenticationRequired (407) is not one of the following:
OK (200), Created (201), Accepted (202), NonAuthoritativeInformation
(203), NoContent (204), ResetContent (205), PartialContent (206).
All i want to do is make this code validate whether a given website is up and running.
Any ideas?

This basically means exactly what it says: That you are trying to access the service via a proxy that you are not authenticated to use.
I guess that means your server was reached from the Web Service, but that it was not permitted to access the URL it tried to reach, since it tried to access it through a proxy it was not authenticated for.

It's what EnsureStatusIsSuccessful() does, it throws an exception if status code (returned from web server) is not one of that ones.
What you can do, to simply check without throwing an exception is to use IsSuccessStatusCode property. Like this:
HttpResponseMessage response = client.Get(url);
bool isValidAndAccessible = response.IsSuccessStatusCode;
Please note that it simply checks if StatusCode is within the success range.
In your case status code (407) means that you're accessing that web site through a proxy that requires authentication then request failed. You can do following:
Provide settings for Proxy (in case defaults one doesn't work) with WebProxy class.
Do not download page but just try to ping web server. You won't know if it's a web page or not but you'll be sure it's accessible and it's a valid URL. If applicable or not depends on context but it may be useful if HTTP requests fails.
Example from MSDN using WebProxy with WebRequest (base class for HttpWebRequest):
var request = WebRequest.Create("http://www.contoso.com");
request.Proxy = new WebProxy("http://proxyserver:80/",true);
var response = (HttpWebResponse)request.GetResponse();
int statusCode = (int)response.StatusCode;
bool isValidAndAccessible = statusCode >= 200 && statusCode <= 299;

You are invoking EnsureStatusIsSuccessful() which rightfully complains that the request was not successful because there's a proxy server between you and the host which requires authentication.
If you are on framework 4.5, I've included a slightly enhanced version below.
internal static async Task<bool> ValidateUrl(string url)
{
Uri validUri;
if(Uri.TryCreate(url,UriKind.Absolute,out validUri))
{
var client = new HttpClient();
var response = await client.GetAsync(validUri, HttpCompletionOption.ResponseHeadersRead);
return response.IsSuccessStatusCode;
}
return false;
}

WEbResponse throws 500 Internal server error

I have many times successfully implemented reading data from web pages using technique like this:
WebRequest req = (WebRequest)WebRequest.Create(path);
WebResponse resp = (WebResponse)req.GetResponse(); etc.
.........
However, this time the WebResponse throws an internal error. Otherwise, I can browse the parameter path.
What could be the reason?

I think it could be any number of reasons.
You should try to catch the error and see if you can get any further details from the response. Perhaps try adding the code below and see if that provides any further details:
catch (WebException webex)
{
Console.WriteLine("Unable to perform command: " + req);
String data = String.Empty;
if (webex.Response != null)
{
StreamReader r = new StreamReader(webex.Response.GetResponseStream());
data = r.ReadToEnd();
r.Close();
}
Console.WriteLine(webex.Message);
Console.WriteLine(data);

Probably its not creating the request, WebRequest.Create,
there can be a proxy issue if you are behind any proxy, i got the same problem that my code was unable to connect to any path but it was browsing fine.