C# - Converting IntPtr pointing to sockaddr structure to IPAddress

Question

From a P/Invoked native function, I get an IntPtr which points to a sockaddr structure. How can I convert it to an IPAddress?

Thanks!

Answer 1

Since you can't directly Marshal a sockaddr type into an IPAddress type, you'd have to make a managed struct out of it first to marshal it into:

[StructLayout(LayoutKind.Sequential)]
internal struct sockaddr_in
{
    internal EnumLib.ADDRESS_FAMILIES sin_family;
    internal ushort sin_port;
    internal in_addr sin_addr;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 8)] internal byte[] sin_zero;

    internal static sockaddr_in FromString(string host, int port)
    {
    var sockaddr = new sockaddr_in();
    var lpAddressLength = Marshal.SizeOf(sockaddr);
    WSAStringToAddress(host + ":" + port, EnumLib.ADDRESS_FAMILIES.AF_INET, IntPtr.Zero,
                      ref sockaddr, ref lpAddressLength);
    return sockaddr;
    }
}

You could then use Marshal.PtrToStructure to obtain a sockaddr_in type from your IntPtr like so:

(sockaddr_in) Marshal.PtrToStructure(address, typeof(sockaddr_in));

After that it should be fairly simple to create a new IPAddress object from the data you've just retrieved.

You can find the ADDRESS_FAMILIES enum that is contained in EnumLib in the above example here: http://pastie.org/8103489

There are originally more members of the struct over at pinvoke.net, just take a look here if you are interested in them but I reckon you won't need them at all in this specific situation.