public static long DirSize(DirectoryInfo d)
        {
            long Size = 0;

            FileInfo[] fis = d.GetFiles();
            foreach (FileInfo fi in fis)
            {
                Size += fi.Length;
            }

            DirectoryInfo[] dis = d.GetDirectories();
            foreach (DirectoryInfo di in dis)
            {
                Size += DirSize(di);
            }

            return (Size);
        }

CREATE FUNCTION FileSize (@dir VARCHAR(max))
RETURNS BIGINT
EXTERNAL NAME MyAssembly.MyClass.DirSize
GO

Msg 6552, Level 16, State 3, Procedure FileSize, Line 1
CREATE FUNCTION for "FileSize" failed because T-SQL and CLR types for parameter "@dir" do not match.

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

public static long DirSize(SQLString dir)
        {
            DirectoryInfo d = new DirectoryInfo((String) dir);
            long Size = 0;

We walk in the dark places no others will enter
We stand on the bridge and no one may pass

            DirectoryInfo d = new DirectoryInfo(dir.Value);

public static long DirSize(string dir)
        {