Small pdf file turns into huge byte array

Question

I'm currently working on a small app that turns text files into PDF files or the reverse. However, I want to be able to keep converted files in memory until the user presses a button to save the file (or a group of files into a .zip), all the converted files are kept in a dictionary with their old path as key and the byte array as value.

Everything was working fine except when for test purposes I took a large text files that has 12000+ lines and tried to go back and forth between text and PDF and now I'm facing a weird problem.

When going from text to PDF with this large file, everything is fine.

However, going from the PDF format of that file to text takes a huge amount of memory in the heap. Eventually going past 2 GB causing an out of memory exception.

I should note that I'm using Itext 7.

Here is the code I'm using:

Text to PDF

        public override byte[] ConvertFile(Stream stream, string path)
        {
            OnFileStartConverting(path);
            string ext = Path.GetExtension(path);
            TextFileType current = TextFileType.Parse(ext);
            MemoryStream resultStream = new MemoryStream();

            if (current.Extension.Equals(TextFileType.Txt.Extension))
            {
                resultStream = TextToPdf(stream, path);
            }
            else if (current.Extension.Equals(TextFileType.Word.Extension))
            {
                throw new NotImplementedException();
            }

            OnFileConverted(path);
            return resultStream.ToArray();
        }

        private MemoryStream TextToPdf(Stream stream, string path)
        {
            MemoryStream resultStream = new MemoryStream();
            StreamReader streamReader = new StreamReader(stream);
            int lineCount = GetNumberOfLines(streamReader);
            PdfWriter writer = new PdfWriter(resultStream);
            PdfDocument pdf = new PdfDocument(writer);
            Document document = new Document(pdf);

            int lineNumber = 1;
            while (!streamReader.EndOfStream)
            {
                string line = streamReader.ReadLine();
                Paragraph paragraph = new Paragraph(line);
                document.Add(paragraph);
                int percent = lineNumber * 100 / lineCount;
                OnFileConverting(path, percent, lineNumber);
                lineNumber++;
            }

            document.Close();
            return resultStream;
        }

PDF to Text

        public override byte[] ConvertFile(Stream stream, string path)
        {
            OnFileStartConverting(path);

            string ext = Path.GetExtension(path);
            TextFileType current = TextFileType.Parse(ext);
            MemoryStream resultStream = new MemoryStream();

            if (current.Extension.Equals(TextFileType.Pdf.Extension))
            {
                resultStream = PdfToText(stream, path);
            }
            else if (current.Extension.Equals(TextFileType.Word.Extension))
            {
                throw new NotImplementedException();
            }

            resultStream.Seek(0, SeekOrigin.Begin);
            OnFileConverted(path);

            return resultStream.ToArray();
        }

        private MemoryStream PdfToText(Stream stream, string path)
        {
            MemoryStream resultStream = new MemoryStream();
            StreamWriter writer = new StreamWriter(resultStream);

            PdfReader reader = new PdfReader(stream);
            PdfDocument pdf = new PdfDocument(reader);
            FilteredEventListener listener = new FilteredEventListener();
            LocationTextExtractionStrategy extractionStrategy =
                listener.AttachEventListener(new LocationTextExtractionStrategy());
            PdfCanvasProcessor parser = new PdfCanvasProcessor(listener);
            int numberOfPages = pdf.GetNumberOfPages();

            for (int i = 1; i <= numberOfPages; i++)
            {
                parser.ProcessPageContent(pdf.GetPage(i));
                writer.WriteLine(extractionStrategy.GetResultantText());
                int percent = i * 100 / numberOfPages;
                OnFileConverting(path, percent, i);
            }

            pdf.Close();
            writer.Flush();

            return resultStream;
        }

Memory usage when going from PDF to text

The PDF file itself isn't even 1000 KB (Its 882 KB) though which is very weird to me. Am I missing something? It's even more weird considering when I try to use the converted file itself it doesn't cause any problem with memory.

user_1729265 · Answer

The cause of the issue is in PdfToText which for documents with multiple pages extracts more text than is there.

The LocationTextExtractionStrategy does not forget its content when you start feeding a new page to it. It is not designed to be re-used across pages, you are expected to create a new instance for each page.

Re-usage in the loop in your code causes

for i=1 the contents of page 1 to be written to writer;
for i=2 the contents of pages 1 and 2 to be written to writer;
for i=3 the contents of pages 1, 2, and 3 to be written to writer;
...

Thus, don't re-use the text extraction strategy across pages. Instead instead move the instantiation of your FilteredEventListener, LocationTextExtractionStrategy, and PdfCanvasProcessor into the loop to create them anew for each page.

Small pdf file turns into huge byte array

1 Answers