jchandra74/FileUtil.cs

## FileUtil.cs
  //mimetypes: http://www.sitepoint.com/web-foundations/mime-types-complete-list/
  //https://technet.microsoft.com/en-us/library/ee309278(office.12).aspx
 public static class FileUtil
    {
        public static string DetectFileType(string filename, Stream fileStream)
        {
            var ext = Path.GetExtension(filename);

            if (string.IsNullOrEmpty(ext))
            {
                return "application/octet-stream";
            }

            switch (ext.ToUpperInvariant())
            {
                case ".TXT":
                    //check if file contains <html>
                    if (IsHtml(fileStream))
                    {
                        return "text/html";
                    }

                    return "text/plain";
                case ".BINARY":
                    if (IsJpeg(fileStream))
                    {
                        return "image/jpeg";
                    }

                    if (IsOldOfficeDoc(fileStream))
                    {
                        //Assume it is Word
                        return "application/msword";
                    }

                    if (IsZip(fileStream))
                    {
                        var openXmlType = GetOpenXmlType(fileStream);
                        return string.IsNullOrWhiteSpace(openXmlType) ? "application/zip" : openXmlType;
                    }

                    //Don't know what this is, so just return default.
                    return "application/octet-stream";

                default:
                    return MimeMapping.GetMimeMapping(filename);
            }
        }

        public static string DetectExtension(string fileName, Stream s)
        {
            var newExt = "";

            using (var m = new MemoryStream())
            {
                s.Seek(0, SeekOrigin.Begin);
                s.CopyTo(m);
                s.Seek(0, SeekOrigin.Begin);

                var fileType = DetectFileType(fileName, m);

                switch (fileType)
                {
                    case "application/pdf":
                        newExt = ".pdf";
                        break;
                    case "application/zip":
                        newExt = ".zip";
                        break;
                    case "text/html":
                        newExt = ".html";
                        break;
                    case "image/jpeg":
                        newExt = ".jpg";
                        break;
                    case "application/msword":
                        newExt = ".doc";
                        break;
                    case "application/vnd.openxmlformats-officedocument.wordprocessingml.document":
                        newExt = ".docx";
                        break;
                    case "application/vnd.ms-word.document.macroEnabled.12":
                        newExt = ".docm";
                        break;
                    case "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet":
                        newExt = ".xlsx";
                        break;
                    case "application/vnd.ms-excel.sheet.macroEnabled.12":
                        newExt = ".xlsm";
                        break;
                    default:
                        newExt = Path.GetExtension(fileName) ?? "";
                        break;
                }
            }
            return newExt;
        }

        //see: https://en.wikipedia.org/wiki/List_of_file_signatures
        private static readonly byte[] oldOfficeSignature = { 0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1 };
        private static readonly byte[] jpegSignature = { 0xff, 0xd8, 0xff, 0xe0 };
        private static readonly byte[] zipSignature = { 0x50, 0x4b, 0x03, 0x04 };
        private static readonly byte[] pdfSignature = { 0x25, 0x50, 0x44, 0x46 };

        private static string GetOpenXmlType(Stream fileStream)
        {
            fileStream.Seek(0, SeekOrigin.Begin);
            var archive = new ZipArchive(fileStream, ZipArchiveMode.Read);
            var entries = archive.Entries;
            var entry = entries.FirstOrDefault(e => e.Name == "[Content_Types].xml");

            if (entry == null)
            {
                return "";
            }

            using (var reader = new StreamReader(entry.Open()))
            {
                var content = reader.ReadToEnd();

                var result = "";
                if (content.Contains("application/vnd.openxmlformats-officedocument.wordprocessingml"))
                {
                    result = ".doc";
                }

                if (content.Contains("application/vnd.openxmlformats-officedocument.spreadsheetml"))
                {
                    result = ".xls";
                }

                if (string.IsNullOrWhiteSpace(result))
                {
                    return "application/zip";   //Don't know what type of openxml doc this is (only detecting doc and xls)
                }

                result = content.Contains("macroEnabled") ? result + "m" : result + "x";

                switch (result)
                {
                    case ".docx":
                        return "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
                    case ".docm":
                        return "application/vnd.ms-word.document.macroEnabled.12";
                    case ".xlsx":
                        return "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
                    case ".xlsm":
                        return "application/vnd.ms-excel.sheet.macroEnabled.12";
                    default:
                        return "";
                }
            }
        }

        private static bool CompareSignature(Stream stream, byte[] signature)
        {
            var bytes = new byte[signature.Length];
            stream.Seek(0, SeekOrigin.Begin);
            var read = stream.Read(bytes, 0, bytes.Length);
            if (read != signature.Length)
            {
                return false;
            }

            return bytes.SequenceEqual(signature);
        }

        private static bool IsPdf(Stream fileStream)
        {
            return CompareSignature(fileStream, pdfSignature);
        }
        private static bool IsZip(Stream fileStream)
        {
            return CompareSignature(fileStream, zipSignature);
        }

        private static bool IsOldOfficeDoc(Stream fileStream)
        {
            return CompareSignature(fileStream, oldOfficeSignature);
        }

        private static bool IsJpeg(Stream fileStream)
        {
            return CompareSignature(fileStream, jpegSignature);
        }

        private static bool IsHtml(Stream fileStream)
        {
            var text = GetTextFileContent(fileStream);
            return !string.IsNullOrWhiteSpace(text) && text.ToUpperInvariant().Contains("<HTML");
        }

        private static string GetTextFileContent(Stream fileStream)
        {
            fileStream.Seek(0, SeekOrigin.Begin);
            using (var reader = new StreamReader(fileStream))
            {
                return reader.ReadToEnd();
            }
        }
    }
	//mimetypes: http://www.sitepoint.com/web-foundations/mime-types-complete-list/
	//https://technet.microsoft.com/en-us/library/ee309278(office.12).aspx
	public static class FileUtil
	{
	public static string DetectFileType(string filename, Stream fileStream)
	{
	var ext = Path.GetExtension(filename);

	if (string.IsNullOrEmpty(ext))
	{
	return "application/octet-stream";
	}

	switch (ext.ToUpperInvariant())
	{
	case ".TXT":
	//check if file contains <html>
	if (IsHtml(fileStream))
	{
	return "text/html";
	}

	return "text/plain";
	case ".BINARY":
	if (IsJpeg(fileStream))
	{
	return "image/jpeg";
	}

	if (IsOldOfficeDoc(fileStream))
	{
	//Assume it is Word
	return "application/msword";
	}

	if (IsZip(fileStream))
	{
	var openXmlType = GetOpenXmlType(fileStream);
	return string.IsNullOrWhiteSpace(openXmlType) ? "application/zip" : openXmlType;
	}

	//Don't know what this is, so just return default.
	return "application/octet-stream";

	default:
	return MimeMapping.GetMimeMapping(filename);
	}
	}

	public static string DetectExtension(string fileName, Stream s)
	{
	var newExt = "";

	using (var m = new MemoryStream())
	{
	s.Seek(0, SeekOrigin.Begin);
	s.CopyTo(m);
	s.Seek(0, SeekOrigin.Begin);

	var fileType = DetectFileType(fileName, m);

	switch (fileType)
	{
	case "application/pdf":
	newExt = ".pdf";
	break;
	case "application/zip":
	newExt = ".zip";
	break;
	case "text/html":
	newExt = ".html";
	break;
	case "image/jpeg":
	newExt = ".jpg";
	break;
	case "application/msword":
	newExt = ".doc";
	break;
	case "application/vnd.openxmlformats-officedocument.wordprocessingml.document":
	newExt = ".docx";
	break;
	case "application/vnd.ms-word.document.macroEnabled.12":
	newExt = ".docm";
	break;
	case "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet":
	newExt = ".xlsx";
	break;
	case "application/vnd.ms-excel.sheet.macroEnabled.12":
	newExt = ".xlsm";
	break;
	default:
	newExt = Path.GetExtension(fileName) ?? "";
	break;
	}
	}
	return newExt;
	}

	//see: https://en.wikipedia.org/wiki/List_of_file_signatures
	private static readonly byte[] oldOfficeSignature = { 0xd0, 0xcf, 0x11, 0xe0, 0xa1, 0xb1, 0x1a, 0xe1 };
	private static readonly byte[] jpegSignature = { 0xff, 0xd8, 0xff, 0xe0 };
	private static readonly byte[] zipSignature = { 0x50, 0x4b, 0x03, 0x04 };
	private static readonly byte[] pdfSignature = { 0x25, 0x50, 0x44, 0x46 };

	private static string GetOpenXmlType(Stream fileStream)
	{
	fileStream.Seek(0, SeekOrigin.Begin);
	var archive = new ZipArchive(fileStream, ZipArchiveMode.Read);
	var entries = archive.Entries;
	var entry = entries.FirstOrDefault(e => e.Name == "[Content_Types].xml");

	if (entry == null)
	{
	return "";
	}

	using (var reader = new StreamReader(entry.Open()))
	{
	var content = reader.ReadToEnd();

	var result = "";
	if (content.Contains("application/vnd.openxmlformats-officedocument.wordprocessingml"))
	{
	result = ".doc";
	}

	if (content.Contains("application/vnd.openxmlformats-officedocument.spreadsheetml"))
	{
	result = ".xls";
	}

	if (string.IsNullOrWhiteSpace(result))
	{
	return "application/zip"; //Don't know what type of openxml doc this is (only detecting doc and xls)
	}

	result = content.Contains("macroEnabled") ? result + "m" : result + "x";

	switch (result)
	{
	case ".docx":
	return "application/vnd.openxmlformats-officedocument.wordprocessingml.document";
	case ".docm":
	return "application/vnd.ms-word.document.macroEnabled.12";
	case ".xlsx":
	return "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
	case ".xlsm":
	return "application/vnd.ms-excel.sheet.macroEnabled.12";
	default:
	return "";
	}
	}
	}

	private static bool CompareSignature(Stream stream, byte[] signature)
	{
	var bytes = new byte[signature.Length];
	stream.Seek(0, SeekOrigin.Begin);
	var read = stream.Read(bytes, 0, bytes.Length);
	if (read != signature.Length)
	{
	return false;
	}

	return bytes.SequenceEqual(signature);
	}

	private static bool IsPdf(Stream fileStream)
	{
	return CompareSignature(fileStream, pdfSignature);
	}
	private static bool IsZip(Stream fileStream)
	{
	return CompareSignature(fileStream, zipSignature);
	}

	private static bool IsOldOfficeDoc(Stream fileStream)
	{
	return CompareSignature(fileStream, oldOfficeSignature);
	}

	private static bool IsJpeg(Stream fileStream)
	{
	return CompareSignature(fileStream, jpegSignature);
	}

	private static bool IsHtml(Stream fileStream)
	{
	var text = GetTextFileContent(fileStream);
	return !string.IsNullOrWhiteSpace(text) && text.ToUpperInvariant().Contains("<HTML");
	}

	private static string GetTextFileContent(Stream fileStream)
	{
	fileStream.Seek(0, SeekOrigin.Begin);
	using (var reader = new StreamReader(fileStream))
	{
	return reader.ReadToEnd();
	}
	}
	}