From: William James <w_a_x_man@...>
Date: 2006-12-29T05:15:11+09:00
Subject: Re: unsafe readline(), anything better?

Rob Muhlestein wrote:
> Looking for a combination of readpartial() and readline() in order to
> safely read a line of maxlen. IO.readline() appears to suffer from lacking
> this maximum allowing DOS against servers reading HTTP headers, for
> example, just by using sock.readline() alone, which is what
> Net::HTTPResponse and others do:
>
>    1974     class << HTTPResponse
>    1975       def read_new(sock)   #:nodoc: internal use only 1976 httpv,
>    code, msg = read_status_line(sock) 1977         res =
>    response_class(code).new(httpv, code, msg) 1978
>    each_response_header(sock) do |k,v| 1979           res.add_field k, v
>    1980         end
>    1981         res
>    1982       end
>    1983
>    1984       private
>    1985
>    1986       def read_status_line(sock) 1987         str = sock.readline
>    1988         m =
>    /\AHTTP(?:\/(\d+\.\d+))?\s+(\d\d\d)\s*(.*)\z/in.match(str) o        r
>    1989           raise HTTPBadResponse, "wrong status line: #{str.dump}"
>    1990         m.captures
>    1991       end
>
> I know this is fundamentally a problem with the popular readline C libs
> out there. Wish they had an nreadline like the sprintf and snprintf
> additional function. Sure I could readchar() or readbytes() watching each
> read for a newline, but that is just unfun. Have I overlooked something
> obvious in my search? Hoping to not have to write my own safe/buffered IO
> layer like I've had to do with other langs.
>
> If there is enough interest, maybe I'll hack a readmaxline() method into
> an IO patch to submit. Actually, on second thought, how about adding a
> second parameter:
>
>     ios.readline(sep_string=$/,maxlen=nil)
>
> The tough question would then be whether to raise an LineTooLong exception
> or just return what could be read of the line up to that point.
>
> Thanks,
>
> Rob

class File
  def safe_readline(sep_string=$/,maxlen=nil)
    buf_size = 1024
    line = ""
    while !self.eof?
      s = read( [ buf_size, maxlen - line.size ].min )
      line << s
      if i = line.index( sep_string )
        line = line[0,i+sep_string.size]
        return [ line, true ]
      end
      return [ line[0,maxlen], false ]  if maxlen &&
        line.size >= maxlen
    end
    [ line, true ]
  end
end

open('junk'){|h| p h.safe_readline("\n",9) }