How to check if System.Net.WebClient.DownloadData

Question

I am trying to use WebClient to download a file from web using a WinForms application. However, I really only want to download HTML file. Any other type I will want to ignore.

I checked the WebResponse.ContentType, but its value is always null.

Anyone have any idea what could be the cause?

Answer 1

I apologize for not been very clear. I wrote a wrapper class that extends WebClient. In this wrapper class, I added cookie container and exposed the timeout property for the WebRequest.

I was using DownloadDataAsync() from this wrapper class and I wasn't able to retrieve content-type from WebResponse of this wrapper class. My main intention is to intercept the response and determine if its of text/html nature. If it isn't, I will abort this request.

I managed to obtain the content-type after overriding WebClient.GetWebResponse(WebRequest, IAsyncResult) method.

The following is a sample of my wrapper class:

public class MyWebClient : WebClient
{
    private CookieContainer _cookieContainer;
    private string _userAgent;
    private int _timeout;
    private WebReponse _response;

    public MyWebClient()
    {
        this._cookieContainer = new CookieContainer();
        this.SetTimeout(60 * 1000);
    }

    public MyWebClient SetTimeout(int timeout)
    {
        this.Timeout = timeout;
        return this;
    }

    public WebResponse Response
    {
        get { return this._response; }
    }

    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest request = base.GetWebRequest(address);

        if (request.GetType() == typeof(HttpWebRequest))
        {
            ((HttpWebRequest)request).CookieContainer = this._cookieContainer;
            ((HttpWebRequest)request).UserAgent = this._userAgent;
            ((HttpWebRequest)request).Timeout = this._timeout;
        }

        this._request = request;
        return request;
    }

    protected override WebResponse GetWebResponse(WebRequest request)
    {
        this._response = base.GetWebResponse(request);
        return this._response;
    }

    protected override WebResponse GetWebResponse(WebRequest request, IAsyncResult result)
    {
        this._response = base.GetWebResponse(request, result);
        return this._response;
    }

    public MyWebClient ServerCertValidation(bool validate)
    {
        if (!validate) ServicePointManager.ServerCertificateValidationCallback += delegate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };
        return this;
    }
}