Question

I’m working on a ASP.NET (3.5) website that contains a treeview; the nodes’ values are set to a filepath (on the server) of a PDF file. When the user clicks a treenode, the server-side code gets the node value (file path), creates a FileInfo object, and (after setting all the header Content-type, Cache-Control, etc. correctly) calls Response.TransmitFile(xxxxpath) to send to the user’s browser.

This works fine on the major browsers, on major devices (PCs, Macs, iOS devices). The file downloads correctly and opens on the user’s machine. But on certain devices and certain browsers, the PDF file does not open. On Android devices, it appears that Firefox downloads and opens the PDFs correctly, but the stock Android browser does not. On a Kindle Fire, it appears the Silk browser downloads the file successfully, but when trying to open it, I see an error: “PDF trailer not found”….or it says the PDF is DRM-protected (which it is not). I haven’t tried another browser (if there is one) on the Fire.

I’ve experimented using anchor links in static HTML markup, and the problem browsers appear to download and display the PDFs correctly when accessed this way. There seems to be an issue (inconsistency?) with the way ASP.NET sends the response to the browser when done via code. I’ve used Response.Flush, Response.WriteFile, Response.BinaryWrite, Response.Close, Response.End, etc., and they all produce the same result: MOST browsers handle the file, but SOME cannot handle the PDF.

So, is there some issue with the way ASP.NET constructs the Response object (especially when sending back PDFs) that some browsers don’t like? TIA.

Answer 1

Quite simply, the answer to your question is “No.” You may want to post your code if you have doubts about whether or not you’re doing it correctly; otherwise: ‘no’. 🙂

I would think the browsers you mentioned are much more suspect than something as simple and established as writing to the Response stream.

For reference here is a tried and true way I do it using iHttpHandler:

    public void ProcessRequest(System.Web.HttpContext context)
    {
        string sFilePath = context.Server.MapPath(String.Concat("~/App_LocalResources", context.Request.QueryString["path"]));
        try
        {
            context.Response.Clear();
            context.Response.ContentType = "application/octet-stream";

            int iReadLength = 16384;
            int iLastReadLength = iReadLength;
            byte[] buffer = new byte[iReadLength];
            if (System.IO.File.Exists(sFilePath))
            {
                System.IO.FileInfo fInfo = new System.IO.FileInfo(sFilePath);
                context.Response.AddHeader("Content-Length", fInfo.Length.ToString());
                context.Response.AddHeader("Content-Disposition", String.Format("attachment; filename=\"{0}\"", fInfo.Name));
                using (System.IO.FileStream input = new System.IO.FileStream(sFilePath, System.IO.FileMode.Open, System.IO.FileAccess.Read))
                {
                    try
                    {
                        while (iLastReadLength > 0 && context.Response.IsClientConnected)
                        {
                            iLastReadLength = input.Read(buffer, 0, iLastReadLength);

                            if (iLastReadLength > 0)
                            {
                                context.Response.OutputStream.Write(buffer, 0, iLastReadLength);
                                context.Response.OutputStream.Flush();
                            }
                        }
                        context.Response.Flush();
                    }
                    catch
                    {
                    }
                    finally
                    {
                        input.Close();
                    }
                }
            }
        }
        catch
        {
        }
        finally
        {
        }
    }

Since you’ve indicated you are pulling the file from another place, here is how to write that to a memory stream. Just pull from your Response Stream from the remote server (or File Stream, Sql Binary Reader, w/e really), then reset your MemoryStream position and then use the functionality above to write to your Response stream to the client.

int iReadLength = 16384;
long lLastReadLength = iReadLength;
long lDataIndex = 0;
byte[] buffer = new byte[iReadLength];
using (System.IO.MemoryStream msTemp = new System.IO.MemoryStream())
{
    while (lLastReadLength > 0)
    {
        lLastReadLength = reader.GetBytes(0, lDataIndex, buffer, 0, iReadLength);
        lDataIndex += lLastReadLength;

        if (lLastReadLength > 0)
        {
            msTemp.Write(buffer, 0, Convert.ToInt32(lLastReadLength));
            msTemp.Flush();
        }
    }

    // Reset Memory Position
    msTemp.Position = 0;

    // Now write to the Response Stream here
}