From: Ben Armstrong <ben@...>
Date: 2004-11-09T05:23:34+09:00
Subject: Re: Socket problem

On Sat, 06 Nov 2004 21:32:19 +0900, ts wrote:

>>>>>> "B" == Ben Armstrong <ben@bgpc.dymaxion.ca> writes:
> 
> B> We're having problems with the standard Socket module with Ruby.
> 
>  Try to use IO#sync=

That didn't help.  Besides, sync is set to true by default.

However, I did pull out a packet sniffer and found out something very
interesting.  It appears that for each operation, the old contents of the
buffer is not being overwritten!  Instead, it just keeps getting appended
to.

Thus, when I send the first line, I am sending "test\r\n".  The server
receives this, and writes back "test\r\n\TEST\r\n".  Since my client only
does a gets on the one line expected, it displays "test\r\n".  

My "fixed" versions (not really fixed, but demonstrate the problem
clearly) are as follows:

-- client.rb --
        require 'socket'
        s=TCPSocket.new("localhost", ARGV[0])
        s.puts("test\r\n")
        printf("garbage: %s",s.gets)
        puts s.gets
        s.puts("Blah, blah\r\n")
        printf("garbage: %s",s.gets)
        printf("garbage: %s",s.gets)
        printf("garbage: %s",s.gets)
        puts s.gets
        s.close
-- end client.rb --

-- server.rb --
        require 'socket'   
        gs = TCPServer.open(0) 
        printf("server is on port %d\n", gs.addr[1]) 
        s=gs.accept
        line = s.gets
        s.flush
        puts("Got line: #{line}")
        s.puts(line.upcase)
        bl = s.gets
        puts ("Got str2 (garbage): #{bl}")    
        bl = s.gets
        puts ("Got str3 (garbage): #{bl}")    
        bl = s.gets
        puts ("Got str4: #{bl}")    
        s.puts(bl.upcase)  
        s.close
-- end server.rb --

The output on the server side is:

server is on port 50507
Got line: test
Got str2 (garbage): test
Got str3 (garbage): TEST
Got str4: Blah, blah

The output on the client side is:

garbage: test
TEST
garbage: test
garbage: TEST
garbage: Blah, blah
BLAH, BLAH

Ignoring the lines marked "garbage" we can now see the intended output:

TEST
BLAH, BLAH

How strange, eh?  OK, how do I discard the buffer between operations?  Or
do I need the developer of the port to help me with this?

Ben
-- 
      Ben Armstrong                -.       Medianet Development Group,
      BArmstrong@dymaxion.ca         `-.    Dymaxion Research Limited
      <URL: http://www.dymaxion.ca/>    `-  Halifax, Nova Scotia, Canada