From: see@... (Douglas Wells)
Date: 2007-08-13T23:34:57+09:00
Subject: Re: TCPSocket Flushing

In article <18e16d93f4d0a9e65517e49c497bcfcd@ruby-forum.com>,
  David -- <neko18@gmail.com> writes:
> I have two programs, a server and a client. I want to send two messages
> to the client when the client connects to the server, with a delay in
> between. However, both messages seem to arrive at the client at the same
> time. Here are the programs:
> 
> ## simpleserver.rb
> ## run this first
> require "socket"
> server = TCPServer.new(2000)
> while connection = server.accept
>   connection.write "one\n"
>   connection.flush
>   sleep 1
>   connection.write "two\n"
>   connection.close
> end
> 
> ## client.rb
> ## run this second
> require "socket"
> sock = TCPSocket.open("localhost", 2000)
> while not sock.eof?
>   print sock.read
> end

If the format of your server "messages" is *always* lines, i.e.,
strings terminated by new-lines and/or carriage-return/line-feeds,
then you should be able to just replace the read with a gets,
e.g.:

    require "socket"
    sock = TCPSocket.open("localhost", 2000)
    while not sock.eof?
      print sock.gets
    end

If that is not the case, you will need to use something like the
following technique:

    require "socket"
    sock = TCPSocket.open("localhost", 2000)
    loop do
      str = sock.recv(100)
      break if str.length == 0
      print str
    end

I have encountered the same problem in the past and I have looked
in vain for any documentation on the subject.  So, the following
is pure supposition on my part, but it reflects my experience in
using sockets in Ruby:

I think that this is due to the magic of sockets in Ruby:  you can
use a socket as either a socket object or as an IO object.  Once
you use it as an IO object, however, it effectively becomes an IO
object and certain socket operations can no longer be used.  So,
once you use either the eof? or read operations, the socket switches
to IO object mode, (i.e., buffered data) and the read call will block
until either the entire read is complete or an EOF occurs.  Since
you didn't specify any size of the read operation, it blocks until
it has read the entire "file."  Even if you had specified a size
to the read operation, it would have blocked until an entire buffer
of that size was filled (or EOF).  Limiting the operations to those
available for sockets (e.g., recv) avoids this problem.

 - dmw

-- 
.   Douglas Wells             .  Connection Technologies      .
.   Internet:  -sp9804- -at - contek.com-                     .