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3
Votes

Support to keep the original stream open in PdfToImageConverter after dispose

When using the PdfToImageConverter, there needs to be the option when loading a Stream called keepOpen. This flag will be used to ensure that when PdfToImageConverter is disposed, if keepOpen is true, that the underlying stream is not disposed. 


This is a standard flag used in other C# classes such as StreamReader, etc. 


Usage example:

        public static async Task<List<MemoryStream>> ConvertToImages(Stream pdf, int w = 0, int h = 0)
        {
            try
            {
                using PdfToImageConverter imageConverter = new PdfToImageConverter();
                imageConverter.Load(pdf, keepOpen: true);



The Dispose method of PdfToImageConverter would then be changed to:


internal void Dispose(bool disposeCompletely)
{
    if (Document != IntPtr.Zero)
    {
        Stream stream = StreamManager.Get(DocumentID);
        if (stream != null && !keepOpen)
        {
            stream.Dispose();
            stream = null;
        }

        StreamManager.Unregister(DocumentID);
        if (!Environment.Is64BitProcess)
        {
            StreamManager.Unregister((int)Document);
        }

        PdfiumViewer.FPDF_CloseDocument(Document);
        Document = IntPtr.Zero;
        if (disposeCompletely)
        {
            StreamManager.Clear();
        }
    }

    PageCount = 0;

}

The goal of this is you cannot always assume the caller wants you to dispose of their stream. It may be a FileStream that is opened, used by the PdfToImageConverter class, and then the user may want to do other things with that stream. But now they get hit with a stream disposed exception and there is nothing they can do. The only way to fix this is by VERY inefficiently copying the original stream to a MemoryStream and then using the MemoryStream in the PdfToImageConverter so the MemoryStream is disposed but not the original stream. Again this is very inefficient. 

A keepOpen flag would resolve this and be consistent with other stream manipulation libraries in the .NET world. 


Tested with version: 28.2.7