Question

如何根据C＃中的文件头识别doc，docx，pdf，xls和xlsx？我不想依赖文件扩展名MimeMapping.GetMimeMapping，因为这两者中的任何一个都可以被操纵。

我知道如何阅读标题，但不知道如果文件是doc，docx，pdf，xls或xlsx，哪些字节组合可以说。有什么想法吗？

Answer 1

此问题包含使用文件的第一个字节来确定文件类型的示例：Using .NET, how can you find the mime type of a file based on the file signature not the extension

这是一篇很长的帖子，所以我在下面发布相关答案：

public class MimeType
{
    private static readonly byte[] BMP = { 66, 77 };
    private static readonly byte[] DOC = { 208, 207, 17, 224, 161, 177, 26, 225 };
    private static readonly byte[] EXE_DLL = { 77, 90 };
    private static readonly byte[] GIF = { 71, 73, 70, 56 };
    private static readonly byte[] ICO = { 0, 0, 1, 0 };
    private static readonly byte[] JPG = { 255, 216, 255 };
    private static readonly byte[] MP3 = { 255, 251, 48 };
    private static readonly byte[] OGG = { 79, 103, 103, 83, 0, 2, 0, 0, 0, 0, 0, 0, 0, 0 };
    private static readonly byte[] PDF = { 37, 80, 68, 70, 45, 49, 46 };
    private static readonly byte[] PNG = { 137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82 };
    private static readonly byte[] RAR = { 82, 97, 114, 33, 26, 7, 0 };
    private static readonly byte[] SWF = { 70, 87, 83 };
    private static readonly byte[] TIFF = { 73, 73, 42, 0 };
    private static readonly byte[] TORRENT = { 100, 56, 58, 97, 110, 110, 111, 117, 110, 99, 101 };
    private static readonly byte[] TTF = { 0, 1, 0, 0, 0 };
    private static readonly byte[] WAV_AVI = { 82, 73, 70, 70 };
    private static readonly byte[] WMV_WMA = { 48, 38, 178, 117, 142, 102, 207, 17, 166, 217, 0, 170, 0, 98, 206, 108 };
    private static readonly byte[] ZIP_DOCX = { 80, 75, 3, 4 };

    public static string GetMimeType(byte[] file, string fileName)
    {

        string mime = "application/octet-stream"; //DEFAULT UNKNOWN MIME TYPE

        //Ensure that the filename isn't empty or null
        if (string.IsNullOrWhiteSpace(fileName))
        {
            return mime;
        }

        //Get the file extension
        string extension = Path.GetExtension(fileName) == null
                               ? string.Empty
                               : Path.GetExtension(fileName).ToUpper();

        //Get the MIME Type
        if (file.Take(2).SequenceEqual(BMP))
        {
            mime = "image/bmp";
        }
        else if (file.Take(8).SequenceEqual(DOC))
        {
            mime = "application/msword";
        }
        else if (file.Take(2).SequenceEqual(EXE_DLL))
        {
            mime = "application/x-msdownload"; //both use same mime type
        }
        else if (file.Take(4).SequenceEqual(GIF))
        {
            mime = "image/gif";
        }
        else if (file.Take(4).SequenceEqual(ICO))
        {
            mime = "image/x-icon";
        }
        else if (file.Take(3).SequenceEqual(JPG))
        {
            mime = "image/jpeg";
        }
        else if (file.Take(3).SequenceEqual(MP3))
        {
            mime = "audio/mpeg";
        }
        else if (file.Take(14).SequenceEqual(OGG))
        {
            if (extension == ".OGX")
            {
                mime = "application/ogg";
            }
            else if (extension == ".OGA")
            {
                mime = "audio/ogg";
            }
            else
            {
                mime = "video/ogg";
            }
        }
        else if (file.Take(7).SequenceEqual(PDF))
        {
            mime = "application/pdf";
        }
        else if (file.Take(16).SequenceEqual(PNG))
        {
            mime = "image/png";
        }
        else if (file.Take(7).SequenceEqual(RAR))
        {
            mime = "application/x-rar-compressed";
        }
        else if (file.Take(3).SequenceEqual(SWF))
        {
            mime = "application/x-shockwave-flash";
        }
        else if (file.Take(4).SequenceEqual(TIFF))
        {
            mime = "image/tiff";
        }
        else if (file.Take(11).SequenceEqual(TORRENT))
        {
            mime = "application/x-bittorrent";
        }
        else if (file.Take(5).SequenceEqual(TTF))
        {
            mime = "application/x-font-ttf";
        }
        else if (file.Take(4).SequenceEqual(WAV_AVI))
        {
            mime = extension == ".AVI" ? "video/x-msvideo" : "audio/x-wav";
        }
        else if (file.Take(16).SequenceEqual(WMV_WMA))
        {
            mime = extension == ".WMA" ? "audio/x-ms-wma" : "video/x-ms-wmv";
        }
        else if (file.Take(4).SequenceEqual(ZIP_DOCX))
        {
            mime = extension == ".DOCX" ? "application/vnd.openxmlformats-officedocument.wordprocessingml.document" : "application/x-zip-compressed";
        }

        return mime;
    }

Answer 2

使用文件签名并不是那么可行（因为新的办公室格式是ZIP文件而旧的Office文件是OLE CF / OLE SS容器），但是您可以使用C＃代码来读取它们并找出它们是什么。

对于最新的Office格式，您可以使用System.IO.Packaging阅读（DOCX / PPTX / XLSX / ...）ZIP文件：https://msdn.microsoft.com/en-us/library/ms568187(v=vs.110).aspx 这样做，您可以找到第一个文档部分的ContentType并推断使用它。

对于较旧的Office文件（Office 2003），您可以使用此库根据其内容区分它们（请注意，MSI和MSG文件也使用此文件格式）： http://sourceforge.net/projects/openmcdf/

，例如，以下是XLS文件的内容：

我希望这有帮助！：）

如果我早些时候找到这个答案的话，那肯定对我有帮助。 ;）

Answer 3

来自user2173353的答案是最正确的答案，因为OP特别提到了Office文件格式。但是，我不想添加整个库（OpenMCDF）来识别传统的Office格式，所以我编写了自己的例程来做这件事。

    public static CfbFileFormat GetCfbFileFormat(Stream fileData)
    {
        if (!fileData.CanSeek)
            throw new ArgumentException("Data stream must be seekable.", nameof(fileData));

        try
        {
            // Notice that values in a CFB files are always little-endian. Fortunately BinaryReader.ReadUInt16/ReadUInt32 reads with little-endian.
            // If using .net < 4.5 this BinaryReader constructor is not available. Use a simpler one but remember to also remove the 'using' statement.
            using (BinaryReader reader = new BinaryReader(fileData, Encoding.Unicode, true))
            {
                // Check that data has the CFB file header
                var header = reader.ReadBytes(8);
                if (!header.SequenceEqual(new byte[] {0xD0, 0xCF, 0x11, 0xE0, 0xA1, 0xB1, 0x1A, 0xE1}))
                    return CfbFileFormat.Unknown;

                // Get sector size (2 byte uint) at offset 30 in the header
                // Value at 1C specifies this as the power of two. The only valid values are 9 or 12, which gives 512 or 4096 byte sector size.
                fileData.Position = 30;
                ushort readUInt16 = reader.ReadUInt16();
                int sectorSize = 1 << readUInt16;

                // Get first directory sector index at offset 48 in the header
                fileData.Position = 48;
                var rootDirectoryIndex = reader.ReadUInt32();

                // File header is one sector wide. After that we can address the sector directly using the sector index
                var rootDirectoryAddress = sectorSize + (rootDirectoryIndex * sectorSize);

                // Object type field is offset 80 bytes into the directory sector. It is a 128 bit GUID, encoded as "DWORD, WORD, WORD, BYTE[8]".
                fileData.Position = rootDirectoryAddress + 80;
                var bits127_96 = reader.ReadInt32();
                var bits95_80 = reader.ReadInt16();
                var bits79_64 = reader.ReadInt16();
                var bits63_0 = reader.ReadBytes(8);

                var guid = new Guid(bits127_96, bits95_80, bits79_64, bits63_0);

                // Compare to known file format GUIDs

                CfbFileFormat result;
                return Formats.TryGetValue(guid, out result) ? result : CfbFileFormat.Unknown;
            }
        }
        catch (IOException)
        {
            return CfbFileFormat.Unknown;
        }
        catch (OverflowException)
        {
            return CfbFileFormat.Unknown;
        }
    }

    public enum CfbFileFormat
    {
        Doc,
        Xls,
        Msi,
        Ppt,
        Unknown
    }

    private static readonly Dictionary<Guid, CfbFileFormat> Formats = new Dictionary<Guid, CfbFileFormat>
    {
        {Guid.Parse("{00020810-0000-0000-c000-000000000046}"), CfbFileFormat.Xls},
        {Guid.Parse("{00020820-0000-0000-c000-000000000046}"), CfbFileFormat.Xls},
        {Guid.Parse("{00020906-0000-0000-c000-000000000046}"), CfbFileFormat.Doc},
        {Guid.Parse("{000c1084-0000-0000-c000-000000000046}"), CfbFileFormat.Msi},
        {Guid.Parse("{64818d10-4f9b-11cf-86ea-00aa00b929e8}"), CfbFileFormat.Ppt}
    };

可以根据需要添加其他格式标识符。

我已经在.doc和.xls上尝试了这个，并且它运行良好。我使用4096字节的扇区大小对CFB文件进行了避免测试，因为我甚至不知道在哪里可以找到它们。

该代码基于以下文件中的信息：

Answer 4

user2173353似乎是用于检测新的Office .docx / .xlsx格式的正确解决方案。要向此添加一些详细信息，下面的检查似乎可以正确识别这些：

    /// <summary>
    /// MS .docx, .xslx and other extensions are (correctly) identified as zip files using signature lookup.
    /// This tests if System.IO.Packaging is able to open, and if package has parts, this is not a zip file.
    /// </summary>
    /// <param name="stream"></param>
    /// <returns></returns>
    private static bool IsPackage(this Stream stream)
    {
        Package package = Package.Open(stream, FileMode.Open, FileAccess.Read);
        return package.GetParts().Any();
    }

如何根据文件头识别doc，docx，pdf，xls和xlsx

4 个答案: