UriExtensions.cs

    public static class UriExtensions
    {
        public static void AppendPath(this UriBuilder b, string addPath)
        {
            var path = b.Path;
            if (path.EndsWith("/"))
            {
                path = path.TrimEnd('/');
            }

            if (addPath.StartsWith("/"))
            {
                path += addPath;
            }
            else
            {
                path += '/' + addPath;
            }

            b.Path = path;
        }

        public static void AppendQuery(this UriBuilder b, string name, string value)
        {

            // check for '?...' 
            if (b.Query.Length <= 1)
            {
                b.Query = name + "=" + value;
            }
            else
            {
                // b.Query.get always returns '?'
                // b.Query.set always *adds* '?' so doesn't expect it in value
                b.Query = b.Query.Substring(1) + '&' + name + '=' + value;
            }
        }
    }