Image.FromStream(PostedFile.InputStream) Fails. (Parameter is not valid.) (AsyncFileUpload))

Question

I'm using an AsyncFileUpload (AJAX Toolkit) to upload images. I have a Button which handle the image resizing. This have worked fine for some time, but not anymore...

protected void BtnUploadImage_Click(object sender, EventArgs e)
{
    var imageFileNameRegEx = new Regex(@"(.*?)\.(jpg|jpeg|png|gif)$", 
        RegexOptions.IgnoreCase);
    if (!AsyncFileUpload1.HasFile || 
        !imageFileNameRegEx.IsMatch(AsyncFileUpload1.FileName))
    {
        AsyncFileUpload1.FailedValidation = true;
        ErrorLabel.Visible = true;
        return;
    }
    ErrorLabel.Visible = false;

    var file = AsyncFileUpload1.PostedFile.InputStream;

    var img = Image.FromStream(file, false, false);

...
}

Another thing which I find weird: If I try a image which is smaller than 80kb it works..!

We have tried to restart the server, but no change. Same code runs fine on my machine. (heard that before ?? :) )

I also tried to save the file on the server, then to get the file trough Image.FromFile(), but then I get "Cannot access a closed file."

How to resolve this ?

Answer 1

I would make sure the stream is positioned at the start:

var file = AsyncFileUpload1.FileContent;
file.Seek(0, SeekOrigin.Begin);

var img = Image.FromFile(file);

Second thing to check: the requestLengthDiskThreshold setting. Unless specified this setting has a default of ... yes, 80 KB.

Note: imo there should be no overall difference whether you use Image to read the file stream directly or if you use an intermediate MemoryStream (other than the fact that in the latter case you actually loads the entire file into memory twice). Either way the original file stream will be read from, thus stream position, CAS rights, file permissions, etc still applies.

Note2: and yes, by all means make sure those resources are disposed properly :)

Answer 2

This is correct, it will not work. The problem is that you are crossing a managed/unmanaged boundary, I recently encountered the same. Other problems are that the stream is not directly there and the Image.FromStream has no idea how to deal with it.

The solution is quite straightforward: read everything from PostedFile into a MemoryStream (just use new MemoryStream()) and use the MemoryStream with the Image.FromStream. This will solve your problem.

Make sure to make proper use of using when you work with Image, Graphics and Streams. All of them implement the IDisposable and in an ASP.NET environment, not using using blocks properly, can and will lead to increased memory usage and other nasty side effect on the long run (and ASP.NET apps do run very long!).

The solution should look something like this:

using(Stream memstr = new MemoryStream())
{
    // copy to a memory stream
    Stream uploadStream = AsyncFileUpload1.PostedFile.InputStream;
    byte[] all = new byte[uploadStream.Length];
    uploadStream.Read(all, 0, uploadStream.Length);
    memstr.Write(all, 0, uploadStream.Length);
    memstr.Seek(0, SeekOrigin.Begin);
    using(Graphics g = Graphics.FromStream(memstr))
    {
         // do your img manipulation, or Save it.
    }
}

Update: the crossing managed boundary issue only occurs in the reverse (using Response stream), it seems, not with Upload streams, but I'm not entirely sure.