我该如何检测ASP.NET中上传文件的MIME类型？

Question

人们通常如何使用ASP.NET检测上传文件的MIME类型？

Answer 1

在aspx页面中:

<asp:FileUpload ID="FileUpload1" runat="server" />

在codebehind(c#)中:

string contentType = FileUpload1.PostedFile.ContentType

Answer 2

如果重命名和上传文件,上面的代码将不会提供正确的内容类型.

请使用此代码

using System.Runtime.InteropServices;

[DllImport("urlmon.dll", CharSet = CharSet.Unicode, ExactSpelling = true, SetLastError = false)]
static extern int FindMimeFromData(IntPtr pBC,
    [MarshalAs(UnmanagedType.LPWStr)] string pwzUrl,
    [MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.I1, SizeParamIndex = 3)] byte[] pBuffer,
    int cbSize,
    [MarshalAs(UnmanagedType.LPWStr)] string pwzMimeProposed,
    int dwMimeFlags, out IntPtr ppwzMimeOut, int dwReserved);

public static string getMimeFromFile(HttpPostedFile file)
{
    IntPtr mimeout;

    int MaxContent = (int)file.ContentLength;
    if (MaxContent > 4096) MaxContent = 4096;

    byte[] buf = new byte[MaxContent];
    file.InputStream.Read(buf, 0, MaxContent);
    int result = FindMimeFromData(IntPtr.Zero, file.FileName, buf, MaxContent, null, 0, out mimeout, 0);

    if (result != 0)
    {
        Marshal.FreeCoTaskMem(mimeout);
        return "";
    }

    string mime = Marshal.PtrToStringUni(mimeout);
    Marshal.FreeCoTaskMem(mimeout);

    return mime.ToLower();
}

Answer 3

虽然在描述HTTP请求的内容类型可能不正确的情况下,他的说法是正确的,但我不认为非托管调用的编组是值得的.如果你需要回退到扩展到mimetype映射,只需从System.Web.MimeMapping.cctor"借用"代码(使用Reflector).这种字典方法绰绰有余,不需要本机调用.