From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2002-04-29T03:44:50+09:00
Subject: Re: Inconsistent network behaviour

Hello,

What you are experiencing is not an inconsistency, it is normal. The reason 
is that TCP is a stream oriented protocol, not a block oriented protocol. 
As a result there is no guarantee that multiple send() will result in 
multiple recv(), it pretty much depends on the buffering of the TCP stack 
and timing.

As a consequence: Never rely on .recv() matching .sent() to break stream 
into pieces, it often works, but sometimes does not. In your case .gets() 
will do a better job.

BTW: I am implementing some SIP in Ruby. Early stage so far.

Yours,

Jean-Hugues

At 01:36 29/04/2002 +0900, you wrote:
>Hi all,
>
>I'm a Ruby newbie when it comes to network programming so while writing
>a little example to teach myself it I came across this rather
>inconsistent behaviour. Firstly here are my two scripts. One is a server
>which listens on a port and the other a client which sends it simple
>messages.
>
>#client.rb
>require "socket"
>session = TCPSocket.new("localhost",5179)
>session.send("INVITE sip:you@bar.com SIP/2.0\n",0)
>session.send("From: me@foo.com\n",0)
>session.send("To: you@bar.com\n",0)
>session.send("\r\n",0)
>session.close
>
>#server.rb
>require "socket"
>def parse_header(socket)
>         data = ""
>         connec = Hash.new
>         while (data != "\r\n")
>                 data = socket.recv(1000)
>                 print "Data read: ",data
>                 property,value = data.split(/: /)
>                 connec[property]=value
>         end
>         connec
>end
>server = TCPServer.new("localhost",5179)
>while (session=server.accept)
>         connection = Hash.new
>         data = session.recv(100)
>         if (data.split)[0] == "INVITE"
>                 connection = parse_header(session)
>         end
>end
>
>When I run the server on my Linux box (Mandrake 8.1, Kernel 2.4.8, Ruby
>1.6.4) I get the desired output:
>
>Data read: me@foo.com
>Data read: you@bar.com
>
>When I run it on a FreeBSD box (FreeBSD 4.4,Ruby 1.6.3) the output is:
>
>Data read: me@foo.com
>To: you@bar.com
>
>The program reads the two lines (sent using two seperate send method
>calls) in with one recv, as well as the final "\r\n" which causes it to
>then go into an infinite loop (printing out Data read: Data read: Data
>read: ...) as it keeps on reading in from the socket even though it is
>closed on the client side.
>
>This is a simple exercise so I'm sure there's a solution, just that I
>can't find anything in the pickaxe book or online docs. Any ideas what
>the problem is and why the behaviour is different on Linux and FreeBSD?
>
>Thanks in advance,
>Farrel Lifson
>--
>|DNA Research Group             mailto:flifson@cs.uct.ac.za
>|Dept. of Computer Science      http://www.cs.uct.ac.za/~flifson
>|University of Cape Town        +27-21-650-3127

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