function URLEncode(s: string): string;

var

  i: integer;

  source: PAnsiChar;

begin

  result := '';

  source := pansichar(s);

  for i := 1 to length(source) do

    if not (source[i - 1] in ['A'..'Z', 'a'..'z', '0'..'9', '-', '_', '~', '.', ':', '/']) then

      result := result + '%' + inttohex(ord(source[i - 1]), 2)

    else

      result := result + source[i - 1];

end;