FileExtensions.cs

using System;
using System.IO;

namespace RestFiles.ServiceInterface.Support
{
    public static class FileExtensions
    {
        public static string GetSafePath(this string filePath)
        {
            if (string.IsNullOrEmpty(filePath)) return string.Empty;

            //Strip invalid chars
            foreach (var invalidChar in Path.GetInvalidPathChars())
            {
                filePath = filePath.Replace(invalidChar.ToString(), String.Empty);
            }

            return filePath
            .TrimStart('.', '/', '\\')					//Remove illegal chars at the start
            .Replace('\\', '/')							//Switch all to use the same seperator
            .Replace("../", String.Empty)				//Remove access to top-level directories anywhere else 
            .Replace('/', Path.DirectorySeparatorChar); //Switch all to use the OS seperator
        }
    }
}