MapToIPv4 fails for some IP Addresses

[robsomerville]

My IP of my host is: 10.0.2.181

This function is throwing an exception: (UDPChannel.cs)

    static IPAddress MapToIPv4(IPAddress address)
    {
        if (address.AddressFamily == AddressFamily.InterNetwork)
            return address;
        Byte[] bytes = address.GetAddressBytes();
        Int64 newAddress = (bytes[12] & 0xff) | (bytes[13] & 0xff) << 8 | (bytes[14] & 0xff) << 16 | (bytes[15] & 0xff) << 24;
        return new IPAddress(newAddress);
    }

The value for newAddress is being set to a negative number (I think because the last part of my IP is > 127. My fix was to change to:

    static IPAddress MapToIPv4(IPAddress address)
    {
        if (address.AddressFamily == AddressFamily.InterNetwork)
            return address;
        Byte[] bytes = address.GetAddressBytes();
        Byte[] array = new Byte[4];
        array[0] = bytes[12]; array[1] = bytes[13]; array[2] = bytes[14]; array[3] = bytes[15];
        return new IPAddress(array);
    }

[longshine]

Thank you! It seems the last shifting (bytes[15] & 0xff) << 24 will cause a negative value if the byte is gt 127. You are welcome to fork this repo and make a pull request of fix, if you wish to.

This method is borrowed from IPAddress class in .NET 4.5, which has the same issue :(
See also:

• http://stackoverflow.com/questions/23608829/why-does-ipaddress-maptoipv4-throw-argumentoutofrangeexception
• https://connect.microsoft.com/VisualStudio/feedback/details/871964