System.IO.Compression.ZipStorer.ReadFileInfo C# (CSharp) Méthode

        private bool ReadFileInfo()
        {
            if (this.ZipFileStream.Length < 22)
                return false;

            try
            {
                this.ZipFileStream.Seek(-17, SeekOrigin.End);
                BinaryReader br = new BinaryReader(this.ZipFileStream);
                do
                {
                    this.ZipFileStream.Seek(-5, SeekOrigin.Current);
                    UInt32 sig = br.ReadUInt32();
                    if (sig == 0x06054b50)
                    {
                        this.ZipFileStream.Seek(6, SeekOrigin.Current);

                        UInt16 entries = br.ReadUInt16();
                        Int32 centralSize = br.ReadInt32();
                        UInt32 centralDirOffset = br.ReadUInt32();
                        UInt16 commentSize = br.ReadUInt16();

                        // check if comment field is the very last data in file
                        if (this.ZipFileStream.Position + commentSize != this.ZipFileStream.Length)
                            return false;

                        // Copy entire central directory to a memory buffer
                        this.ExistingFiles = entries;
                        this.CentralDirImage = new byte[centralSize];
                        this.ZipFileStream.Seek(centralDirOffset, SeekOrigin.Begin);
                        this.ZipFileStream.Read(this.CentralDirImage, 0, centralSize);

                        // Leave the pointer at the begining of central dir, to append new files
                        this.ZipFileStream.Seek(centralDirOffset, SeekOrigin.Begin);
                        return true;
                    }
                } while (this.ZipFileStream.Position > 0);
            }
            catch { }

            return false;
        }

        /// <summary>
        /// Method to open an existing storage from stream
        /// </summary>
        /// <param name="_stream">Already opened stream with zip contents</param>
        /// <param name="_access">File access mode for stream operations</param>
        /// <returns>A valid ZipStorer object</returns>
        public static ZipStorer Open(Stream _stream, FileAccess _access)
        {
            if (!_stream.CanSeek && _access != FileAccess.Read)
            {
                throw new InvalidOperationException("Stream cannot seek");
            }

            ZipStorer zip = new ZipStorer();

            //zip.FileName = _filename;
            zip.ZipFileStream = _stream;
            zip.Access        = _access;

            if (zip.ReadFileInfo())
            {
                return(zip);
            }

            throw new System.IO.InvalidDataException();
        }