验证 .vhd 文件实际上是一个 vhd

Question

用户可以上传vhd文件到我的服务器。我想验证他们上传的文件并确保它们实际上是有效的 vhd 文件，而不是用 .vhd 文件扩展名等重新命名的 jpeg。有办法做到这一点吗？

Answer 1

https://www.garykessler.net/library/file_sigs.html（Ctrl + F，然后输入 VHD）

看起来VHD文件的前8个字节如下：63 6F 6E 65 63 74 69 78（conectix in ASCII.）

~~如评论区@jdweng 所建议，你可以使用BinaryReader读取前8个字节，并与上面的值进行比较，以确定文件是否是VHD文件。~~

编辑：不起作用，正在寻找其他解决方案。

编辑 2：文件中确实存在 conectix 文本，但它不在文件开头；文本位于第 [the end of the file] - 0x200 个字节。现在要测试它。仅供参考，该文件是在 Windows 10.

上使用磁盘管理工具生成的

编辑 3：

private static bool IsVhd(string path)
{
    byte[] vhdHeader = { 0x63, 0x6F, 0x6E, 0x65, 0x63, 0x74, 0x69, 0x78 };
    byte[] header;

    FileInfo file = new FileInfo(path);
    long length = file.Length;

    using (BinaryReader br = new BinaryReader(file.OpenRead()))
    {
        br.BaseStream.Position = length - 0x200; //Where the "conectix" is located at
        header = br.ReadBytes(8);
    }

    return vhdHeader.SequenceEqual(header);
}

我相信这样就可以了。

编辑 4：

private static bool IsVhd(string path)
{
    Span<byte> vhdHeader = stackalloc byte[] { 0x63, 0x6F, 0x6E, 0x65, 0x63, 0x74, 0x69, 0x78 };
    Span<byte> header = stackalloc byte[8];

    FileInfo file = new FileInfo(path);
    long length = file.Length;

    using (BinaryReader br = new BinaryReader(file.OpenRead()))
    {
        br.BaseStream.Position = length - 0x200; //Where the "conectix" is located at
        br.Read(header);
    }

    return vhdHeader.SequenceEqual(header);
}

非分配较少的版本，以防您使用 .NET Core。（需要 C# 7.3）

编辑 5：

private static bool IsVhd(string path)
{
    Span<byte> vhdHeader = stackalloc byte[] { 0x63, 0x6F, 0x6E, 0x65, 0x63, 0x74, 0x69, 0x78 };
    Span<byte> header = stackalloc byte[8];

    FileInfo file = new FileInfo(path);
    long length = file.Length;

    using (BinaryReader br = new BinaryReader(file.OpenRead()))
    {
        br.BaseStream.Position = length - 0x200; //Where the "conectix" is located at
        for (int i = 0; i < 8; i++)
            header[i] = br.ReadByte();
    }

    return vhdHeader.SequenceEqual(header);
}

相同，但对于 .NET Frameworks（由于优化，理想版本为 4.7.1；还需要 System.Memory NuGet 包。C# 7.3）

编辑 6： According to the specs，似乎 "hard disk footer" 位于最后 512（如果在 MS Virtual PC 2004 之前创建，则为 511）字节。

Note: Versions previous to Microsoft Virtual PC 2004 create disk images that have a 511-byte disk footer. So the hard disk footer can exist in the last 511 or 512 bytes of the file that holds the hard disk image.

Hard Disk Footer Field Descriptions
The following provides detailed definitions of the hard disk footer fields.
Cookie
Cookies are used to uniquely identify the original creator of the hard disk image. The values are case-sensitive.
Microsoft uses the “conectix” string to identify this file as a hard disk image created by Microsoft Virtual Server, Virtual PC, and predecessor products. The cookie is stored as an eight-character ASCII string with the “c” in the first byte, the “o” in the second byte, and so on.

如果文件大小小于 512 字节，我之前编写的代码将无法运行。我修复了它，所以它现在也可以处理带有 511 字节页脚的文件。此外，我添加了一些注释以帮助维护。

/// <summary>
/// Determines whether the file indicated by the given path is a valid Virtual Hard Disk (.vhd) file.
/// </summary>
/// <param name="path">The path to the .vhd file to check.</param>
/// <returns>Whether the file is a valid vhd file or not.</returns>
//https://www.microsoft.com/en-us/download/details.aspx?id=23850
//See 'Hard Disk Footer Format'
//ASCII string "conectix" (63 6F 6E 65 63 74 69 78) is stored at the last 512 (511 if created on legacy platforms) bytes of the file
private static bool IsVhd(string path)
{
    if (path is null) throw new ArgumentNullException(nameof(path));

    Span<byte> vhdFooterCookie = stackalloc byte[] { 0x63, 0x6F, 0x6E, 0x65, 0x63, 0x74, 0x69, 0x78 };
    Span<byte> cookie = stackalloc byte[9];

    FileInfo file = new FileInfo(path);
    long length = file.Length;
    if (length < 511) return false; //Cannot be smaller than 512 bytes

    using (BinaryReader br = new BinaryReader(file.OpenRead()))
    {
        br.BaseStream.Position = length - 0x200; //Where the footer starts from
#if NETCOREAPP
        br.Read(cookie);
#else
        for (int i = 0; i < 9; i++)
            cookie[i] = br.ReadByte();
#endif
    }

    //SequenceEqual returns false if length is not equal, therefore we slice it to match
    return vhdFooterCookie.SequenceEqual(cookie.Slice(0, 8)) 
           || vhdFooterCookie.SequenceEqual(cookie.Slice(1)); //If created on legacy platform
}

有一些条件编译位，但我相信您可以删除不需要的位来满足您的需要。

验证 .vhd 文件实际上是一个 vhd

Validate that a .vhd file is actually a vhd

c#

asp.net

validation

vhd