如何在Linux操作系统下使用Mono查询子网掩码

我查看了一些Mono源代码并提取了一些代码片段来构建一个返回给定网络接口的IPv4子网掩码的助手。代码不是绝对的美，但它是有效的。

[StructLayout(LayoutKind.Explicit)]
struct ifa_ifu
{
    [FieldOffset(0)]
    public IntPtr ifu_broadaddr;
    [FieldOffset(0)]
    public IntPtr ifu_dstaddr;
}
[StructLayout(LayoutKind.Sequential)]
struct ifaddrs
{
    public IntPtr ifa_next;
    public string ifa_name;
    public uint ifa_flags;
    public IntPtr ifa_addr;
    public IntPtr ifa_netmask;
    public ifa_ifu ifa_ifu;
    public IntPtr ifa_data;
}
[StructLayout(LayoutKind.Sequential)]
struct sockaddr_in
{
    public ushort sin_family;
    public ushort sin_port;
    public uint sin_addr;
}
[StructLayout(LayoutKind.Sequential)]
struct sockaddr_in6
{
    public ushort sin6_family;   /* AF_INET6 */
    public ushort sin6_port;     /* Transport layer port # */
    public uint sin6_flowinfo; /* IPv6 flow information */
    public in6_addr sin6_addr;     /* IPv6 address */
    public uint sin6_scope_id; /* scope id (new in RFC2553) */
}
[StructLayout(LayoutKind.Sequential)]
struct in6_addr
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    public byte[] u6_addr8;
}
[StructLayout(LayoutKind.Sequential)]
struct sockaddr_ll
{
    public ushort sll_family;
    public ushort sll_protocol;
    public int sll_ifindex;
    public ushort sll_hatype;
    public byte sll_pkttype;
    public byte sll_halen;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)]
    public byte[] sll_addr;
}
internal class IPInfoTools
{
    const int AF_INET = 2;
    const int AF_INET6 = 10;
    const int AF_PACKET = 17;
    [DllImport("libc")]
    static extern int getifaddrs (out IntPtr ifap);
    [DllImport ("libc")]
    static extern void freeifaddrs (IntPtr ifap);
    internal static string GetIPv4Mask(string networkInterfaceName)
    {
        IntPtr ifap;
        if (getifaddrs(out ifap) != 0)
        {
            throw new SystemException("getifaddrs() failed");
        }
        try
        {
            var next = ifap;
            while (next != IntPtr.Zero)
            {
                var addr = (ifaddrs)Marshal.PtrToStructure(next, typeof(ifaddrs));
                var name = addr.ifa_name;
                if (addr.ifa_addr != IntPtr.Zero)
                {
                    var sockaddr = (sockaddr_in)Marshal.PtrToStructure(addr.ifa_addr, typeof(sockaddr_in));
                    switch (sockaddr.sin_family)
                    {
                        case AF_INET6:
                            //sockaddr_in6 sockaddr6 = (sockaddr_in6)Marshal.PtrToStructure(addr.ifa_addr, typeof(sockaddr_in6));
                            break;
                        case AF_INET:
                            if (name == networkInterfaceName)
                            {
                                var netmask = (sockaddr_in)Marshal.PtrToStructure(addr.ifa_netmask, typeof(sockaddr_in));
                                var ipAddr = new IPAddress(netmask.sin_addr);  // IPAddress to format into default string notation
                                return ipAddr.ToString();
                            }
                            break;
                        case AF_PACKET:
                            {
                                var sockaddrll = (sockaddr_ll)Marshal.PtrToStructure(addr.ifa_addr, typeof(sockaddr_ll));
                                if (sockaddrll.sll_halen > sockaddrll.sll_addr.Length)
                                {
                                    Console.Error.WriteLine("Got a bad hardware address length for an AF_PACKET {0} {1}",
                                                            sockaddrll.sll_halen, sockaddrll.sll_addr.Length);
                                    next = addr.ifa_next;
                                    continue;
                                }
                            }
                            break;
                    }
                }
                next = addr.ifa_next;
            }
        }
        finally
        {
            freeifaddrs(ifap);
        }
        return null;
    }
}

上述帮助器的用法如下:

String subnetMask = IPInfoTools.GetIPv4Mask("etc0");

我还没有设法在Mono源代码中修复这个问题，因为需要在Mono中更改相当多的文件才能从查询的地方(LinuxNetworkInterface)到使用的地方(LinuxUnicastIPAddressInfo)获得上述信息。但是我会把我的代码发布到Mono bug报告中，这样Mono的开发人员就可以看看了。

Marc，只是想说非常感谢提供的代码。我可以很容易地让它在我的应用程序中工作，它在Ubuntu 10.10和Mono 2.10.6上工作得很好。我希望我能不止一次地给这个投票。

我为Mono构建了一个特殊版本的应用程序，因为Win32版本使用System.Deployment，这在Mono上不可用;所以作为参考，这里是我使用的代码:

UnicastIPAddressInformation addr = GetUnicastAddrFromNic(nic.GetIPProperties().UnicastAddresses);
#if BUILD4MONO
string mask = null;
try {
    mask = IPInfoTools.GetIPv4Mask(nic.Name);  // Marc's function - nic.Name is eth0 or wlan1 etc.
} catch (Exception ex) { // getifaddrs failed
   Console.WriteLine("GetIPRangeInfoFromNetworkInterface failed: {0}", ex.Message);
}
if (mask == null || IPAddress.TryParse(mask, out rangeInfo.SubnetMask) == false) {
    rangeInfo.SubnetMask = IPAddress.Parse("255.255.255.0"); // default to this
}
#else
rangeInfo.SubnetMask = addr.IPv4Mask;  // Win32
#endif

注意:nic只是一个NetworkInterface对象，GetUnicastAddrFromNic()是我做的一个函数，它只是查看网卡的所有UnicastAddresses，并返回AddressFamily为InterNetwork的第一个。

希望有人从Mono团队将应用您的解决方案在一个即将到来的版本。