I know I can locally, on my filesystem, check if a file exists:
if(File.Exists(path))
Can I check at a particular remote URL?
If you're attempting to verify the existence of a web resource, I would recommend using the HttpWebRequest class. This will allow you to send a HEAD request to the URL in question. Only the response headers will be returned, even if the resource exists.
var url = "http://www.domain.com/image.png";
HttpWebResponse response = null;
var request = (HttpWebRequest)WebRequest.Create(url);
request.Method = "HEAD";
try
{
response = (HttpWebResponse)request.GetResponse();
}
catch (WebException ex)
{
/* A WebException will be thrown if the status of the response is not `200 OK` */
}
finally
{
// Don't forget to close your response.
if (response != null)
{
response.Close();
}
}
Of course, if you want to download the resource if it exists it would most likely be more efficient to send a GET request instead (by not setting the Method property to "HEAD", or by using the WebClient class).
If you want to just copy & paste Justin's code and get a method to use, here's how I've implemented it:
using System.Net;
public class MyClass {
static public bool URLExists (string url) {
bool result = false;
WebRequest webRequest = WebRequest.Create(url);
webRequest.Timeout = 1200; // miliseconds
webRequest.Method = "HEAD";
HttpWebResponse response = null;
try {
response = (HttpWebResponse)webRequest.GetResponse();
result = true;
} catch (WebException webException) {
Debug.Log(url +" doesn't exist: "+ webException.Message);
} finally {
if (response != null) {
response.Close();
}
}
return result;
}
}
I'll keep his observation:
If you want to download the resource, and it exists, it would be more efficient to send a GET request instead by not setting the Method property to "HEAD" or by using the WebClient class.
Below is a simplified version of the code:
public bool URLExists(string url)
{
bool result = true;
WebRequest webRequest = WebRequest.Create(url);
webRequest.Timeout = 1200; // miliseconds
webRequest.Method = "HEAD";
try
{
webRequest.GetResponse();
}
catch
{
result = false;
}
return result;
}
If you are using a unc path or a mapped drive, this will work fine.
If you are using a web address (http, ftp etc) you are better off using WebClient - you will get a WebException if it doesn't exist.
public static bool UrlExists(string file)
{
bool exists = false;
HttpWebResponse response = null;
var request = (HttpWebRequest)WebRequest.Create(file);
request.Method = "HEAD";
request.Timeout = 5000; // milliseconds
request.AllowAutoRedirect = false;
try
{
response = (HttpWebResponse)request.GetResponse();
exists = response.StatusCode == HttpStatusCode.OK;
}
catch
{
exists = false;
}
finally
{
// close your response.
if (response != null)
response.Close();
}
return exists;
}
I had the same problem to solve in asp.net core, I've solved with HttpClient
private async Task<bool> isFileExist(string url)
{
using (HttpClient client = new HttpClient())
{
var restponse = await client.GetAsync(url);
return restponse.StatusCode == System.Net.HttpStatusCode.OK;
}
}
My version:
public bool IsUrlExist(string url, int timeOutMs = 1000)
{
WebRequest webRequest = WebRequest.Create(url);
webRequest.Method = "HEAD";
webRequest.Timeout = timeOutMs;
try
{
var response = webRequest.GetResponse();
/* response is `200 OK` */
response.Close();
}
catch
{
/* Any other response */
return false;
}
return true;
}
WebRequest will waiting long time(ignore the timeout user set) because not set proxy, so I change to use RestSharp to do this.
var client = new RestClient(url);
var request = new RestRequest(Method.HEAD);
request.Timeout = 5000;
var response = client.Execute(request);
result = response.StatusCode == HttpStatusCode.OK;
Thanks for all answers.
And I would like to add my implementation which includes default state when we get errors, for specific cases like mine.
private bool HTTP_URLExists(String vstrURL, bool vResErrorDefault = false, int vTimeOut = 1200)
{
bool vResult = false;
WebRequest webRequest = WebRequest.Create(vstrURL);
webRequest.Timeout = vTimeOut; // miliseconds
webRequest.Method = "HEAD";
HttpWebResponse response = null;
try
{
response = (HttpWebResponse)webRequest.GetResponse();
if (response.StatusCode == HttpStatusCode.OK) vResult = true;
else if (response.StatusCode == HttpStatusCode.NotFound) vResult = false;
else vResult = vResErrorDefault;
}
catch (WebException ex)
{
if (ex.Status == WebExceptionStatus.ProtocolError && ex.Response != null)
{
var resp01 = (HttpWebResponse)ex.Response;
if (resp01.StatusCode == HttpStatusCode.NotFound)
{
vResult = false;
}
else
{
vResult = vResErrorDefault;
}
}
else
{
vResult = vResErrorDefault;
}
}
finally
{
// Don't forget to close your response.
if (response != null)
{
response.Close();
}
}
return vResult;
}
Anoter version with define timeout :
public bool URLExists(string url,int timeout = 5000)
{
...
webRequest.Timeout = timeout; // miliseconds
...
}
This works for me:
bool HaveFile(string url)
{
try
{
using (WebClient webClient = new WebClient())
{
webClient.DownloadString(url);
}
return true;
}
catch (Exception)
{
return false;
}
}
Related
void test() //apply multithreading
{
ThreadPool.SetMaxThreads(int.Parse(TxtThread.Text), int.Parse(TxtThread.Text) + 10);
foreach (string url in list_url)
{
ThreadPool.QueueUserWorkItem(new WaitCallback(CheckFile), url);
}
}
void CheckFile(object url) //incoming url to check files exists or not
{
HttpWebResponse response = null;
foreach (string str in filenameArr)
{
try
{
string strUrlFile2 = UriFile(url.ToString(), str);
response = Com.WebResponse(strUrlFile2);
if (response.StatusCode == HttpStatusCode.OK && response.ContentType.ToLower() != "text/html")
{
}
}
catch (Exception ex)
{
}
finally
{
if (response != null)
{
response.Close();
}
}
}
}
public static HttpWebResponse WebResponse(string strUrlFile) //check method
{
HttpWebRequest req = null;
try
{
//System.GC.Collect();
req = (HttpWebRequest)WebRequest.Create(strUrlFile);
req.Method = "HEAD";
req.Timeout = 100;
req.ProtocolVersion = HttpVersion.Version11;
req.AllowAutoRedirect = false;
req.Accept = "*/*";
req.KeepAlive = false;
HttpWebResponse res = (HttpWebResponse)req.GetResponse();
return res;
}
catch (Exception)
{
return null;
}
}
list_url:url ArrayList
filenameArr:filename dictionary array
Questions：
1、After a while when httprequesting to check telefile several times，task didn't finish.And all threads stopped.
2、When the number of thread pool threads to grow to a certain number, and all sub-thread operation is not the main UI thread, but the program interface slow phenomenon
I have this RIA Service URL:
http://192.168.2.100/MegaSystem/Services/RIAServicesLibraryMain-Web-Version_1_0-DomainService.svc
So I need to validate this URL somehow in the configuration window of the my application.
I use this method to do it:
private bool KickServices(string serviceUrl)
{
bool result = false;
var request = WebRequest.Create(serviceUrl) as HttpWebRequest;
if (request != null)
{
request.ContentType = "application/xml";
request.Method = "GET";
}
if (request != null)
{
var response = request.GetResponse() as HttpWebResponse;
if (response != null && response.StatusCode == HttpStatusCode.OK)
{
result = true;
}
}
return result;
}
The main problem if I use some incorrect URL like
http://192.168.2.100/MegaSystem/Services/RIAServicesLibraryMain-Web-Version_1_0-DomainService_SHIT_SHIT_SHIT.svc
It returns TRUE anyway...
Please help me to find correct way to validate RIA Services URL.
Thank you!
I found good solution:
private bool KickServices(string serviceUrl)
{
bool result = false;
var request = WebRequest.Create(serviceUrl) as HttpWebRequest;
if (request != null)
{
request.ContentType = "application/xml";
request.Method = "GET";
}
if (request != null)
{
var response = request.GetResponse() as HttpWebResponse;
if (response != null && response.StatusCode == HttpStatusCode.OK)
{
string resultContent = null;
Encoding responseEncoding = Encoding.GetEncoding(response.CharacterSet);
using (var sr = new StreamReader(response.GetResponseStream(), responseEncoding))
{
resultContent = sr.ReadToEnd();
if (resultContent.Contains(serviceUrl))
result = true;
}
}
}
return result;
}
In my project I'm using C# app client and tomcat6 web application server.
I wrote this snippet in the C# client:
public bool isServerOnline()
{
Boolean ret = false;
try
{
HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(VPMacro.MacroUploader.SERVER_URL);
req.Method = "HEAD";
req.KeepAlive = false;
HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
if (resp.StatusCode == HttpStatusCode.OK)
{
// HTTP = 200 - Internet connection available, server online
ret = true;
}
resp.Close();
return ret;
}
catch (WebException we)
{
// Exception - connection not available
Log.e("InternetUtils - isServerOnline - " + we.Status);
return false;
}
}
Everytime I invoke this method, I get a new session at server side.
I suppose it's because I should use HTTP cookies in my client. But I don't know how to do that, can you help me?
You must use a CookieContainer and keep the instance between calls.
private CookieContainer cookieContainer = new CookieContainer();
public bool isServerOnline()
{
Boolean ret = false;
try
{
HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(VPMacro.MacroUploader.SERVER_URL);
req.CookieContainer = cookieContainer; // <= HERE
req.Method = "HEAD";
req.KeepAlive = false;
HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
if (resp.StatusCode == HttpStatusCode.OK)
{
// HTTP = 200 - Internet connection available, server online
ret = true;
}
resp.Close();
return ret;
}
catch (WebException we)
{
// Exception - connection not available
Log.e("InternetUtils - isServerOnline - " + we.Status);
return false;
}
}
I'm trying to make a function that checks if a site is online or not, but is having some problem with the timeout. I want to limit it to a max 3 sec, if there is no respons within 3 sec I should see the page as offline.
My try:
class OnlineCheck
{
public static bool IsOnline(string url)
{
try
{
WebClient webclient = new WebClient();
webclient.Headers.Add(HttpRequestHeader.KeepAlive, "1000");
webclient.OpenRead(url);
}
catch { return false; }
return true;
}
}
The WebClient doesn't support timeout. But you can use the HttpWebRequest!
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Endpoint);
request.Timeout=3000;
request.GetResponse();
If you want to check that the site is online, you are not really interested in the content of the page, just that you get a response. To make that more efficient, you should only request the http headers. Here is a quick example on how you could do:
private static IEnumerable<HttpStatusCode> onlineStatusCodes = new[]
{
HttpStatusCode.Accepted,
HttpStatusCode.Found,
HttpStatusCode.OK,
// add more codes as needed
};
private static bool IsSiteOnline(string url, int timeout)
{
HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
{
if (request != null)
{
request.Method = "HEAD"; // get headers only
request.Timeout = timeout;
using (var response = request.GetResponse() as HttpWebResponse)
{
return response != null && onlineStatusCodes.Contains(response.StatusCode);
}
}
}
return false;
}
Use HttpWebRequest rather than WebClient. HttpWebRequest class has a timeout property.
You can try this code:
System.Net.WebRequest r = System.Net.WebRequest.Create("http://www.google.com");
r.Timeout = 3000;
System.Net.WebProxy proxy = new System.Net.WebProxy("<proxy address>");
System.Net.NetworkCredential credentials = new System.Net.NetworkCredential();
credentials.Domain = "<domain>";
credentials.UserName = "<login>";
credentials.Password = "<pass>";
proxy.Credentials = credentials;
r.Proxy = proxy;
try
{
System.Net.WebResponse rsp = r.GetResponse();
}
catch (Exception)
{
MessageBox.Show("Is not avaliable");
return;
}
MessageBox.Show("Avaliable!");
static bool isOnline (string URL)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL);
request.Timeout = 3000;
try
{
WebResponse resp = request.GetResponse();
}
catch (WebException e)
{
if (((HttpWebResponse)e.Response).StatusCode == HttpStatusCode.NotFound)
{
return false;
}
}
return true;
}
public void BuildImg()
{
// The two different images as strings.
string url1 = "http://remoteimage.com/image.jpg";
string url2 = "http://remoteimage.com/image2.jpg";
try
{
// Check to see if url1 exists or not
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url1);
request.Credentials = System.Net.CredentialCache.DefaultCredentials;
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
myImg.Visible = true;
myImg.ImageUrl = url1;
}
catch (Exception ex)
{
// Check to see if url2exists or not
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url2);
request.Credentials = System.Net.CredentialCache.DefaultCredentials;
HttpWebResponse response;
try
{
response = request.GetResponse() as HttpWebResponse;
}
catch (WebException exc)
{
response = exc.Response as HttpWebResponse;
}
// Set myImg to show if url2 exists
myImg.Visible = true;
myImg.ImageUrl = url2;
// If response returns 404, then hide myImg
if (response.StatusCode == HttpStatusCode.NotFound)
{
myImg.Visible = false;
}
}
var arr = new[]
{
"http://example.com/image.jpg",
"http://example.com/image2.jpg"
...
};
myImg.ImageUrl = arr.FirstOrDefault(i => CheckExistence(i));
static bool CheckUrlExistence(string url)
{
try
{
var request = (HttpWebRequest)WebRequest.Create(url);
request.Credentials = CredentialCache.DefaultCredentials;
request.Method = "HEAD";
var response = (HttpWebResponse)request.GetResponse();
return response.StatusCode == HttpStatusCode.OK;
}
catch (Exception ex)
{
var code = ((HttpWebResponse)((WebException)ex).Response).StatusCode; // NotFound, etc
return false;
}