StrangeServices/ImageConvertService/Biz/PdfImageReader.cs

using System.IO.Compression;
using UglyToad.PdfPig;

namespace ImageConvertService.Biz;
using Models;

public class PdfImageReader
{
    private static class Signatures
    {
        public static readonly byte[] Zlib = { 0x78, 0x9C };
        public static readonly byte[] Jpg = { 0xFF, 0xD8, 0xFF };
    }

    public ArchiveEntry[] ReadImages(byte[] inputPdfBytes, string? password = null, ArchiveEntryFileTimeTuple? fileTime = null)
    {
        var parsingOptions = new ParsingOptions();

        if (password != null) parsingOptions.Password = password;

        using var document = PdfDocument.Open(inputPdfBytes, parsingOptions);
        var pages = document.GetPages().ToArray();
        var lstResult = new List<ArchiveEntry>(pages.Length);
        Parallel.ForEach(pages, (item, _, pageIndex) =>
        {
            var images = item.GetImages().ToArray();
            for (var imageIndex = 0; imageIndex < images.Length; imageIndex++)
            {
                var pdfImage = images[imageIndex];
                var outputFileName = $"P{pageIndex + 1:0000}_{imageIndex + 1:000}";

                if (pdfImage.TryGetPng(out var pngBytes))
                {
                    lock (lstResult)
                    {
                        lstResult.Add(new ArchiveEntry
                        {
                            PathAndName = outputFileName + ".png",
                            FileTimeTuple = fileTime,
                            Content = pngBytes
                        });
                    }
                }
                else if (pdfImage.TryGetBytesAsMemory(out var rms))
                {
                    int bp = 0;

                    var rawBytes = rms.ToArray();

                    lock (lstResult)
                    {
                        lstResult.Add(new ArchiveEntry
                        {
                            PathAndName = outputFileName + ".bin",
                            FileTimeTuple = fileTime,
                            Content = rawBytes
                        });
                    }
                }
                else
                {
                    var extractedBytes = pdfImage.RawBytes.ToArray();
                    var span = (ReadOnlySpan<byte>)extractedBytes;
                    var extName = ".bin";

                    //de zlib
                    if (span.Length > Signatures.Zlib.Length && span.StartsWith(Signatures.Zlib))
                    {
                        using var inMs = new MemoryStream(extractedBytes);
                        using var decStream = new ZLibStream(inMs, CompressionMode.Decompress);
                        using var outMs = new MemoryStream();
                        decStream.CopyTo(outMs);
                        extractedBytes = outMs.ToArray();
                        span = (ReadOnlySpan<byte>)extractedBytes;
                    }

                    if (span.Length > Signatures.Jpg.Length && span.StartsWith(Signatures.Jpg))
                    {
                        extName = ".jpg";
                    }
                    else
                    {
                        int bp = 0;
                    }

                    lock (lstResult)
                    {
                        lstResult.Add(new ArchiveEntry
                        {
                            PathAndName = outputFileName + extName,
                            FileTimeTuple = fileTime,
                            Content = extractedBytes
                        });
                    }
                }
            }
        });

        return lstResult.ToArray();
    }
}