From: Aredridel <aredridel@...>
Date: 2003-05-17T00:29:08+09:00
Subject: Re: TCP Sockets

On Fri, 2003-05-16 at 08:11, Dominik Werder wrote:
> > Sure, using the method that Nobu proposes you might be able to tell that
> > there are exactly 99 bytes sitting in the socket buffer right now.
> >
> > But how do you know that 99 bytes is a whole request? Maybe the whole
> > request is 138 bytes, but because the message is sent in TCP chunks, the
> > first read() returned 99 bytes, and the next read later returns 39 bytes. 
> > Or
> > maybe it's two requests of 69 bytes each; the first read() returns the 
> > whole
> > first request plus 30 bytes of the second request, and the the second 
> > read()
> > returns the remaining 39 bytes.
> This is not the problem: If the request is not complete in one packet, the 
> rest comes with the following packet.
> But if the request does not come at all cause 99 bytes are not enough, then 
> I got a problem.
> Think about my software as an TCP/IP router. The TCP/IP router doesn't need 
> to have knowledge of the protocol either.

It doesn't need knowledge of the application protocol, but it needs to
know -all- about TCP/IP -- it needs the headers for every packet --
source, destination, flags, window, mss, length.

Once you're at the application (socket) level, you have buffers to deal
with -- you don't know whether the 99 bytes was 1, 2 or 3 packets at
all, unless you know how big the chunks the sender sends are.