Test to see if an image exists in C#

Question

I am writing a diagnostic page for SiteScope and one area we need to test is if the connection to the file/media assets are accesible from the web server. One way I think I can do this is load the image via code behind and test to see if the IIS status message is 200.

So basically I should be able to navigate to within the site to a folder like this: /media/1/image.jpg and see if it returns 200...if not throw exception.

I am struggling to figure out how to write this code.

Any help is greatly appreciated.

Thanks

Answer 1

Just use HEAD. No need to download the entire image if you don't need it. Here some boilerplate code.

HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create("url");
request.Method = "HEAD";

bool exists;
try
{
    request.GetResponse();
    exists = true;
}
catch
{
   exists = false;
}

Answer 2

You might want to also check that you got an OK status code (ie HTTP 200) and that the mime type from the response object matches what you're expecting. You could extend that along the lines of,

public bool doesImageExistRemotely(string uriToImage, string mimeType)
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uriToImage);
    request.Method = "HEAD";

    try
    {
        HttpWebResponse response = (HttpWebResponse)request.GetResponse();

        if (response.StatusCode == HttpStatusCode.OK && response.ContentType == mimeType)
        {
            return true;
        }
        else
        {
            return false;
        }   
    }
    catch
    {
        return false;
    }
}

Answer 3

You have to dispose of the HTTPWebResponse object, otherwise you will have issues as I have had...

    public bool DoesImageExistRemotely(string uriToImage)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(uriToImage);

            request.Method = "HEAD";

            try
            {
                using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
                {

                    if (response.StatusCode == HttpStatusCode.OK)
                    {
                        return true;
                    }
                    else
                    {
                        return false;
                    }
                }
            }
            catch (WebException) { return false; }
            catch
            {
                return false;
            }
    }

Answer 4

I've used something like this before, but there's probably a better way:

try
{
    HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://somewhere/picture.jpg");
    request.Credentials = System.Net.CredentialCache.DefaultCredentials;
    HttpWebResponse response = (HttpWebResponse)request.GetResponse();
    myImg.ImageUrl = "http://somewhere/picture.jpg";
}
catch (Exception ex)
{
    // image doesn't exist, set to default picture
    myImg.ImageUrl = "http://somewhere/default.jpg";
}

Answer 5

If url exists like http:\server.myImageSite.com the answer is false too only if imageSize > 0 is true.

  public static void GetPictureSize(string url, ref float width, ref float height, ref string err)
  {
    System.Net.HttpWebRequest wreq;
    System.Net.HttpWebResponse wresp;
    System.IO.Stream mystream;
    System.Drawing.Bitmap bmp;

    bmp = null;
    mystream = null;
    wresp = null;
    try
    {
        wreq = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(url);
        wreq.AllowWriteStreamBuffering = true;

        wresp = (HttpWebResponse)wreq.GetResponse();

        if ((mystream = wresp.GetResponseStream()) != null)
            bmp = new System.Drawing.Bitmap(mystream);
    }
    catch (Exception er)
    {
        err = er.Message;
        return;
    }
    finally
    {
        if (mystream != null)
            mystream.Close();

        if (wresp != null)
            wresp.Close();
    }
    width = bmp.Width;
    height = bmp.Height;
}

public static bool ImageUrlExists(string url)
{

    float width = 0;
    float height = 0;
    string err = null;
    GetPictureSize(url, ref width, ref height, ref err);
    return width > 0;
}

Answer 6

If you are getting an exception during the request like "The remote server returned an error: (401) Unauthorized.",

This can be resolved by adding the following line

request.Credentials = new NetworkCredential(username, password);

Question and answer added to this questions from check if image exists on intranet.

Answer 7

I'd look into an HttpWebRequest instead - I think the previous answer will actually download data, whereas you should be able to get the response without data from HttpWebRequest.

http://msdn.microsoft.com/en-us/library/456dfw4f.aspx until step #4 should do the trick. There are other fields on HttpWebResponse for getting the numerical code if needs be...

hth Jack