Re: Reading binary socket data and copying to another socket ?

From:

Owen Jacobson <angrybaldguy@gmail.com>

Newsgroups:

comp.lang.java.programmer

Date:

Tue, 13 Nov 2007 10:30:07 -0800

Message-ID:

<1194978607.555312.289900@s15g2000prm.googlegroups.com>

On Nov 13, 9:12 am, "sweb...@gmail.com" <sweb...@gmail.com> wrote:

Hi,

I need to write a java process that listens on a socket for a client
sending binary data (actually compressed messages). This socket will
always be open.

This data will then be written to another socket the other end of
which understands the content of the data. The problem I have is that
the data can be sent at any time and there is nothing in the data (no
characters) I can use to indicate the end of a raw message. So how can
I read the original data and decide that it should now be copied to
the out bound socket ?

If I call read(buff[]) then that blocks until the required number of
bytes is received which doesn't help me as I don't know how many bytes
there are, it could be 1 it could be 1000+. I noticed the socket class
has a setSOTimeout() method which might be useful but could I rely on
a timeout for detecting the end of the binary data associated with a
message !

Any idea's how I can cope with this ?

It sounds like you have an app that proxies communication between two
endpoints but does nothing with the communication directly. If that's
the case, then the intermediate app doesn't need to care about message
boundaries: it just needs to copy every byte from the input stream to
the output stream. This will not fragment or damage messages any more
than TCP itself does, and will be transparent to correctly-written
endpoints (that make no assumptions about message boundaries with
respect to read calls).

At a high level, then, all you need is this:

  prepare a buffer
  while there is data:
    read input into the buffer
    write buffer to output

Hope that helps,
Owen