Using Winnovative PDFConverter to save to file an ASP table in C# populated by session data

Question

I am using PDFConverter to save a "Receipt page" onto the computer. The way it's set up is I am using a link from Page X to Response.Redirect() to Receipt Page, so it transfers the session data.

Then I am using Session["Cart"] Data to populate the table with the data from the receipt. The problem is, when I use Winnovative PDFConverter to save the page to a file, it doesn't save the table. That's because the table doesn't get populated as Session data isn't sent, (or it creates a new Session, not sure) and as such my saved file does not contain the table, which is the whole point of the Receipt page. How do I get around this? I found a "workaround" online but it doesn't seem to work. It won't even save the file, instead returning an error.

protected void Save_BtnClick(object sender, EventArgs e) 
    {
        PdfConverter converter = new PdfConverter();
        string url = HttpContext.Current.Request.Url.AbsoluteUri;

        StringWriter sw = new StringWriter();
        Server.Execute("Receipt.aspx", sw); //this line triggers an HttpException
        string htmlCodeToConvert = sw.GetStringBuilder().ToString();

        converter.SavePdfFromUrlToFile(htmlCodeToConvert, @"C:\Users\myname\Downloads\output.pdf"); // <--not even sure what method i should be running here

        //converter.SavePdfFromUrlToFile(url,@"C:\Users\myname\Downloads\output.pdf"); <-- this saves it without the table
    }

EDIT: One solution I thought of was is it possible to use Winnovative's ability to grab certain elements of the page to pass in the already populated table instead of trying to generate the page automatically using the method? I'm not 100% sure how to work it based on the documentation alone and I do not have access to the sample codes.

Answer 1

I don’t know why the Server.Execute is throwing an exception, but here is an alternative to using that call.

You are using Server.Execute to get the web page to convert to HTML. Instead of that approach have Winnovative make that call. The trick is to allow that page request to access the current user’s session. You specify the URL to call and then supply the user credentials in the cookie collection of the PDFConverter.

See this page and choose the approach based on your authentication technique.

Winnovative Authentication Handling

Edit:

@LordHonydew, We have gone in a big circle in the comments and ended up at the beginning. Let me try this again.

First, in the Server.Execute exception is there an inner exception? There could be more information that helps explain what is going wrong. Even after fixing that issue there are other items that must be fixed.

Second, when using Winnovative to generate a PDF from a web page that is secured you must provide credentials to the PDFConverter so that it can access the page and its resources. There are a couple of ways winnovative can get the HTML: one is by giving the PDFConverter the URL to call and another is to use the Server.Execute to get the HTML directly and then provide the PDFConverter with the HTML, which is how you are doing it. Either way the PDFConverter still needs to talk to the server to get the additional page resources. Things like images and CSS files are not in the HTML, they are referenced by the HTML. The converter will make calls to the server to get these items. Since your application is secured you must provide the converter with credentials to access the server. We will do this by using the same authentication cookie that is used for each page request. There are other ways such as supplying user name and password. That link above explains the various ways.

This code gets the auth cookie from the current request and gives it to the converter:

pdfConverter.HttpRequestCookies.Add(FormsAuthentication.FormsCookieName,
     Request.Cookies[FormsAuthentication.FormsCookieName].Value);

Finally, the converter.SavePdfFromUrlToFile is not the right method to use. That would only save the receipt to the local server’s drive. You need to stream it back to the user.

Try the following. Set a breakpoint in the catch block so you can see if there is an inner exception.

protected void Save_BtnClick(object sender, EventArgs e)
    {

        // Get the web page HTML as a string
        string htmlCodeToConvert = null;
        using (StringWriter sw = new StringWriter())
        {
            try
            {
                System.Web.HttpContext.Current.Server.Execute("Receipt.aspx", sw);
                htmlCodeToConvert = sw.ToString();

            }
            catch (Exception ex)
            {
                // set breakpoint below and on an exception see if there is an inner exception.
                throw;                    
            }
        }

        PdfConverter converter = new PdfConverter();
        // Supply auth cookie to converter
        converter.HttpRequestCookies.Add(System.Web.Security.FormsAuthentication.FormsCookieName,
            Request.Cookies[System.Web.Security.FormsAuthentication.FormsCookieName].Value);

        // baseurl is used by converter when it gets CSS and image files
        string baseUrl = Request.Url.Scheme + "://" + Request.Url.Authority +
            Request.ApplicationPath.TrimEnd('/') + "/";

        // create the PDF and get as bytes
        byte[] pdfBytes = converter.GetPdfBytesFromHtmlString(htmlCodeToConvert, baseUrl);

        // Stream bytes to user
        Response.Clear();
        Response.AppendHeader("Content-Disposition", "attachment;filename=Receipt.pdf");
        Response.ContentType = "application/pdf";
        Response.OutputStream.Write(pdfBytes, 0, pdfBytes.Length);
        HttpContext.Current.ApplicationInstance.CompleteRequest();

    }

Answer 2

Please check the Convert a HTML Page to PDF in Same Session demo. You can find there a description of the method to use to preserve the session data during conversion and the C# sample code. The code below is copied from there :

protected void convertToPdfButton_Click(object sender, EventArgs e)
{
    // Save variables in Session object
    Session["firstName"] = firstNameTextBox.Text;
    Session["lastName"] = lastNameTextBox.Text;
    Session["gender"] = maleRadioButton.Checked ? "Male" : "Female";
    Session["haveCar"] = haveCarCheckBox.Checked;
    Session["carType"] = carTypeDropDownList.SelectedValue;
    Session["comments"] = commentsTextBox.Text;

    // Execute the Display_Session_Variables.aspx page and get the HTML string 
    // rendered by this page
    TextWriter outTextWriter = new StringWriter();
    Server.Execute("Display_Session_Variables.aspx", outTextWriter);

    string htmlStringToConvert = outTextWriter.ToString();

    // Create a HTML to PDF converter object with default settings
    HtmlToPdfConverter htmlToPdfConverter = new HtmlToPdfConverter();

    // Set license key received after purchase to use the converter in licensed mode
    // Leave it not set to use the converter in demo mode
    htmlToPdfConverter.LicenseKey = "fvDh8eDx4fHg4P/h8eLg/+Dj/+jo6Og=";

    // Use the current page URL as base URL
    string baseUrl = HttpContext.Current.Request.Url.AbsoluteUri;

    // Convert the page HTML string to a PDF document in a memory buffer
    byte[] outPdfBuffer = htmlToPdfConverter.ConvertHtml(htmlStringToConvert, baseUrl);

    // Send the PDF as response to browser

    // Set response content type
    Response.AddHeader("Content-Type", "application/pdf");

    // Instruct the browser to open the PDF file as an attachment or inline
    Response.AddHeader("Content-Disposition", String.Format("attachment; filename=Convert_Page_in_Same_Session.pdf; size={0}", outPdfBuffer.Length.ToString()));

    // Write the PDF document buffer to HTTP response
    Response.BinaryWrite(outPdfBuffer);

    // End the HTTP response and stop the current page processing
    Response.End();
}


Display Session Variables in Converted HTML Page

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        firstNameLabel.Text = Session["firstName"] != null ? (String)Session["firstName"] : String.Empty;
        lastNameLabel.Text = Session["lastName"] != null ? (String)Session["lastName"] : String.Empty;
        genderLabel.Text = Session["gender"] != null ? (String)Session["gender"] : String.Empty;

        bool iHaveCar = Session["haveCar"] != null ? (bool)Session["haveCar"] : false;
        haveCarLabel.Text = iHaveCar ? "Yes" : "No";
        carTypePanel.Visible = iHaveCar;
        carTypeLabel.Text = iHaveCar && Session["carType"] != null ? (String)Session["carType"] : String.Empty;

        commentsLabel.Text = Session["comments"] != null ? (String)Session["comments"] : String.Empty;
    }
}