How to keep the MemoryStream from being closed automatically

Question

I have a memory stream in a function like so

using var document = new PdfDocument();
var memoryStream = new MemoryStream();
document.Save(memoryStream, new GemBox.Pdf.PdfSaveOptions());
memoryStream.Seek(0, SeekOrigin.Begin);
return memoryStream;

It seems like as soons the function returns, the memoryStream is Disposed, later access will throws

System.ObjectDisposedException: Cannot access a closed Stream.

• I would like to use this MemoryStream by seeking to 0 and read again and again later. How can I achieve that?

• If I am using CopyTo, then the new MemoryStream is kept open but is that hugely inefficient? As I understand, the CopyTo will read the whole backing memory and write to the new Stream, basically double the memory usage? The result I received from CopyTo is what I wanted, I am just not sure if that is the right way or if there are better alternatives

    using var document = new PdfDocument();
    var memoryStream = new MemoryStream();
    document.Save(memoryStream, new GemBox.Pdf.PdfSaveOptions());
    memoryStream.Seek(0, SeekOrigin.Begin);
    var newStream = new MemoryStream();
    memoryStream.CopyTo(newStream);
    newStream.Seek(0, SeekOrigin.Begin);
    return newStream;
  

Sample Repro https://dotnetfiddle.net/mCZhug

Callstack at dispose time

Answer 1

The reason why it's closed is because the stream ends up being disposed with the PdfDocument.Dispose() call, that is the whole point of that method.

There are two ways how you can resolve your issue, first is to not call PdfDocument.Dispose() (in other words, remove the using statement):

var document = new PdfDocument();
var memoryStream = new MemoryStream();
// ...

The second solution is this:

using var document = new PdfDocument();
document.CloseStream = false;
var memoryStream = new MemoryStream();
// ...

Setting the PdfDocument.CloseStream option to false has the same effect as not calling PdfDocument.Dispose().

Answer 2

You could create the MemoryStream in your caller and pass it as an argument to your function. That way the caller has complete control of creation, closing and disposal of the stream.

Answer 3

I often flip these things around and change the signature from MemoryStream Method() to void Method(Action<MemoryStream> action) so that I'm injecting in the code that uses the MemoryStream and then I can let all of the disposes happen.

Something like this:

public void UseMemoryStream(Action<MemoryStream> action)
{
    using var document = new PdfDocument();
    using var memoryStream = new MemoryStream();
    document.Save(memoryStream, new GemBox.Pdf.PdfSaveOptions());
    memoryStream.Seek(0, SeekOrigin.Begin);
    action(memoryStream);
}

Answer 4

PdfDocument has CloseStream property - you set it to false:

document.CloseStream = false;

Though the XML-doc states that:

Setting this option to false has the same effect as not calling Close() nor Dispose().

Based on what I can see it is not all it actually does, though, but it is better to consult with the library authors for actual effect of the setting.