[how-to] Detect if a URL is "alive"

  • Thread starter Thread starter news.microsoft.com
  • Start date Start date
N

news.microsoft.com

I want to make a boolean function to determine if a given URL is "alive",
where 'alive' means it does not result in DNS error, 404 error, or other
common errors.

I am currently using this code, but I'm not sure if it is the best way to do
it:

private bool IsURLAlive (string strURL)
{

WebClient myWebClient = new WebClient();
char[] buf = new char[128];


try
{

Stream myStream = myWebClient.OpenRead(strURL);

StreamReader sr = new StreamReader(myStream);

sr.ReadBlock(buf, 0, 127);

myStream.Close();

}

catch (System.Net.WebException webe)

{

return false;

}

return true;

}



I would like not to use exceptions, because I will be running a loop for,
say, 500 URLs.

Any ideas?

Thanks in advance,

Dan
 
news.microsoft.com said:
I want to make a boolean function to determine if a given URL is "alive",
where 'alive' means it does not result in DNS error, 404 error, or other
common errors.

I am currently using this code, but I'm not sure if it is the best way to do
it:
Click to expand...

<snip>

I don't know of any way of doing this without incurring an exception
other than implementing HTTP yourself.

You're right to be concerned about using exceptions for this kind of
detection, but I wouldn't worry too much about the performance side of
things - the time taken to throw the exception is likely to be
insignificant compared to the time taken to do the DNS lookup etc in
the first place.
 
Thanks, Jon!

Just another question, if I may...

Inside my loop for 500 URLs, I would like to be populating a ListBox,
telling for each URL if it is alive. But is seems the ListBox gets updated
only at the end of the loop.
I remember in old VB we had a "ProcessMessages"(?) procedure. Is there
anything like that I can use?

Dan
 
news.microsoft.com said:
Just another question, if I may...

Inside my loop for 500 URLs, I would like to be populating a ListBox,
telling for each URL if it is alive. But is seems the ListBox gets updated
only at the end of the loop.
I remember in old VB we had a "ProcessMessages"(?) procedure. Is there
anything like that I can use?
Click to expand...

A few suggestions:

1) You should *definitely* not be doing this in the UI thread
2) Your worker thread can (either asynchronously or synchronously)
invoke a delegate on the UI thread to update the UI. You mustn't update
it from the worker thread directly.
3) You might want to consider batching the updates and using
Begin/EndUpdate on the list box

See
http://www.pobox.com/~skeet/csharp/multithreading.html#windows.forms
for the threading aspect of this.
 
Thanks again.

My final version:

public static HttpStatusCode GetURLStatus (string strURL)

{

HttpWebResponse myHttpWebResponse;

try

{

// Create a web request for the given URL.

HttpWebRequest myHttpWebRequest = (HttpWebRequest)
WebRequest.Create(strURL);

// Get the associated response for the above request.

myHttpWebResponse = (HttpWebResponse) myHttpWebRequest.GetResponse();

myHttpWebResponse.Close();

}

catch(WebException we)

{

return ((HttpWebResponse)we.Response).StatusCode;

}


return myHttpWebResponse.StatusCode;

}
 
Back
Top