不要使用文件扩展名来计算 MIME 类型,而是使用“Winista”进行二进制分析。
假设有人重命名exe
with a jpg
扩大。您仍然可以确定真实的文件格式。它不检测 swf 或 flv,但几乎可以检测所有其他众所周知的格式,您可以使用十六进制编辑器来添加它可以检测到的更多文件。
下载Winista:here http://www.netomatix.com/Products/DocumentManagement/MimeDetector.aspx or 我的镜子 http://jeremythompson.net/rocks/mimedetect.zip或者我的 GitHubhttps://github.com/MeaningOfLights/MimeDetect https://github.com/MeaningOfLights/MimeDetect.
当 Winista 无法检测到真正的文件格式时,我又求助于 URLMon 方法:
public class urlmonMimeDetect
{
[DllImport(@"urlmon.dll", CharSet = CharSet.Auto)]
private extern static System.UInt32 FindMimeFromData(
System.UInt32 pBC,
[MarshalAs(UnmanagedType.LPStr)] System.String pwzUrl,
[MarshalAs(UnmanagedType.LPArray)] byte[] pBuffer,
System.UInt32 cbSize,
[MarshalAs(UnmanagedType.LPStr)] System.String pwzMimeProposed,
System.UInt32 dwMimeFlags,
out System.UInt32 ppwzMimeOut,
System.UInt32 dwReserverd
);
public string GetMimeFromFile(string filename)
{
if (!File.Exists(filename))
throw new FileNotFoundException(filename + " not found");
byte[] buffer = new byte[256];
using (FileStream fs = new FileStream(filename, FileMode.Open, FileAccess.Read))
{
if (fs.Length >= 256)
fs.Read(buffer, 0, 256);
else
fs.Read(buffer, 0, (int)fs.Length);
}
try
{
System.UInt32 mimetype;
FindMimeFromData(0, null, buffer, 256, null, 0, out mimetype, 0);
System.IntPtr mimeTypePtr = new IntPtr(mimetype);
string mime = Marshal.PtrToStringUni(mimeTypePtr);
Marshal.FreeCoTaskMem(mimeTypePtr);
return mime;
}
catch (Exception e)
{
return "unknown/unknown";
}
}
}
从 Winista 方法内部,我在这里求助于 URLMon:
public MimeType GetMimeTypeFromFile(string filePath)
{
sbyte[] fileData = null;
using (FileStream srcFile = new FileStream(filePath, FileMode.Open, FileAccess.Read))
{
byte[] data = new byte[srcFile.Length];
srcFile.Read(data, 0, (Int32)srcFile.Length);
fileData = Winista.Mime.SupportUtil.ToSByteArray(data);
}
MimeType oMimeType = GetMimeType(fileData);
if (oMimeType != null) return oMimeType;
//We haven't found the file using Magic (eg a text/plain file)
//so instead use URLMon to try and get the files format
Winista.MimeDetect.URLMONMimeDetect.urlmonMimeDetect urlmonMimeDetect = new Winista.MimeDetect.URLMONMimeDetect.urlmonMimeDetect();
string urlmonMimeType = urlmonMimeDetect.GetMimeFromFile(filePath);
if (!string.IsNullOrEmpty(urlmonMimeType))
{
foreach (MimeType mimeType in types)
{
if (mimeType.Name == urlmonMimeType)
{
return mimeType;
}
}
}
return oMimeType;
}
Update:
要使用魔法来计算更多文件,这里是文件签名表 http://www.garykessler.net/library/file_sigs.html