Image Url validation in asp.net - asp.net

Question

i have images url , i need to check url is responding or not .
For Example :Below i i have written three image url, first two url is not valid only third url is valid .but second and fourth url is responding as valid image
and but there is no image.
http://media.expedia.com/hotels/1000000/90000/84900/84853/84853_744_b.jpg
http://www.iceportal.com/brochures/media/show.aspx?brochureid=ICE19044&did=3073&mtype=3073&type=pic&lang=en&publicid=4175749&resizing=X
http://images.trvl-media.com/hotels/1000000/30000/20400/20313/20313_166_b.jpg
http://www.iceportal.com/brochures/ice/ErrorPages/404.htm?aspxerrorpath=/brochures/media/show_A.aspx
here is my code:
public static bool CheckUrlExists(string url)
{
try
{
Uri u = new Uri(url);
WebRequest w = WebRequest.Create(u);
w.Method = WebRequestMethods.Http.Head;
using (StreamReader s = new StreamReader(w.GetResponse().GetResponseStream()))
{
return (s.ReadToEnd().Length >= 0);
}
}
catch
{
return false;
}
}
with this code i am validating only those url which is showing 404 error,but not those url which showing 'Sorry, requested brochure is temporarily un-published 'or any other type of message.

Answer 1

You will need a more complex logic to validate if the URL points to an image. If a resource is missing from the server or it is otherwise unavailable, you may get a HTTP error like the infamous 404, which will trigger a WebException. However, that is only part of the story.
Your second URL returns HTTP 200, confirming that the resource is there when in fact the resource is missing. What you really get there is a HTML document explaining the resource is not available. This is bad practice, but not without example.
At very least, you should examine the MIME type (Content-Type header, see WebResponse.ContentType) of the resource you test. A content type of image/* suggests an image-type resource. Failing to detect a known MIME type (e.g. if you receive application/octet-stream) you can actually HTTP GET get resource and run image type detection on the downloaded content.

Answer 2

I would suggest using HttpWebRequest and HttpWebResponse to do this, they are sub classes of WebRequest and WebResponse and as such are more granular for what you're trying to achive. The following code works with the example URIs provided
public static bool CheckUrlExists(string url)
{
try
{
Uri u = new Uri(url);
HttpWebRequest w = (HttpWebRequest)WebRequest.Create(u);
w.AllowAutoRedirect = false;
w.Method = WebRequestMethods.Http.Head;
HttpWebResponse response = (HttpWebResponse)w.GetResponse();
return response.StatusCode == HttpStatusCode.OK; //Check http status code
}
catch(WebException ex)
{
return false;
}
}
What's important here is that I'm checking the HttpStatus code. You're catch will already catch the 404s but the problem URIs ultimately lead to a 200 (OK). By setting AllowAutoRedirect to false the HttpWebRequest instance returns a 302 (redirect) status code, instead of following the redirect through to the "Sorry, requested brochure is temporarily un-published." page which is returning 200 (OK). This should serve your purpose.
Also: Catching a WebException will allow you to examine the status code (400+,500+, etc).
Be aware however, that you may be redirected to a new location for the image you're requesting. Taking that you might want to use PeterK's mime type check.