Execute quick hack shell scripts connected to a socket.
# $Header: /CVSROOT/socklinger/DESCRIPTION,v 1.7 2007-04-04 03:44:44 tino Exp $
# 
# $Log: DESCRIPTION,v $
# Revision 1.7  2007-04-04 03:44:44  tino
# Preparing next dist
#
# Revision 1.6  2007/03/27 01:13:12  tino
# Prepared for new dist
#
# Revision 1.5  2006/12/12 11:52:17  tino
# New version with editing in the old edits to do prefork and connect
#
# Revision 1.4  2006/01/25 03:31:13  tino
# dist 1.3.1
#
# Revision 1.3  2005/03/15 18:28:05  tino
# only text reformatted with emacs
#
# Revision 1.2  2004/09/20 01:20:05  tino
# published
#
# Revision 1.1  2004/08/16 01:29:57  Administrator
# initial add

If you look for something of more wide use perhaps have a look
at <a href='http://freshmeat.net/projects/socat'>socat</a> (this
is from somebody else, don't ask me about socat, however I highly
recommend socat if you are not satisfied with socklinger!).

Socklinger is thought for admins in a networked environment, who want
to write some quick hack bash scripts to rapidly implement a socket
based thingie just to get something done and reuse this solution for
themself later on, too.  Socklinger definitively is not designed to
offer a production service to customers.  But it's just what *you*
need to get *your* weird network script running for *your* needs,
saving *your* time.

When you want to write a quick hack, shell is convenient.  However
when you want to do this with networking scripts you often will
observe stange effects if you call scripts from inetd.  This is,
because the "lingering" on sockets is extremely short (or missing)
nowadays to protect against DoS-attacks.  The effect is, that you will
observe that the end of the output of the script just is not
transmitted to the other side.  Socklinger fixes this and restores,
what you know from your good old and reliable SunOS from 1988.

Note that you might be tempted to use the exec-option of netcat, too.
However netcat cannot reuse sockets on stdin like in inetd usage or
when something is running under tcpd-control.  And you don't have
control over the number of scripts running in parallel.

Note that you can run scripts under tcpserver, too.  However you will
observe the linger-problem there.  Often you can fix the problem by
adding a "sleep 10" at the end of the script.  However the hope that
10 seconds are long enough is no solution in my eyes.  And often the
sleep period slows down the other side, because the othere side waits
until the socket is closed. (Any software which relies on the kernel
linger implementation may fall into the same trap as tcpserver.)

Socklinger is designed as a solution for quick hacks, so it's enough
to only run one script in parallel.  This way you don't have to bother
about race conditions in the script.  Socklinger also allows you to
reuse the socket which comes from stdin or run it in a simple
accept-loop.

The source code of socklinger is so easy and lightweight that it can
be adapted to other environments easily.  It has been tested under
several Linux distributions and Cygwin. (Well, not each version!)

There is an example Debian installation proxy which caches all files
downloaded in example/ .  All you need is some machine with an
Internet connection (probably a windows with Cygwin installed) and you
can use the network install ISO image for your Debian.  Please note
that this is another step to reach my real goal: HilbiX, a 1.44 MB
floppy sized console-less networked Linux install.

<b>New features:</b>

Options, like delay (-d).

`killall -1 socklinger` shuts down socklingers gracefully.

With -n0 (or -s) only a single accept() can be done (no looping).
Options disable the old commandline behavior (prefixes n@ and src>dest).

<b>Old features (deprecated, use commandline options):</b>

If given socket is of form "src>dest" it is connected to.  src is the
address to bind to (can be empty).  If @ is missing, only one single
connect is done, else the connect is done in a loop (beware!).

Alternat fork method (postfork) with negative count.  Default for
CygWin, as accept() does not work with postfork under windows.

<b>Future note:</b>

It is likely that Socklinger will be merged into some other of my
tools.  You will read, where you then can find it.  This is
because I need support for non-TCP sockets, too.

<b>CygWin note:</b>

If socklinger does not compile under CygWin try following (do not
overwrite tino/getopt.h!):
<pre>echo >getopt.h; make</pre>

This is a problem with the include chain of system headers I was
unable to fix, but I don't want to "clutter" the release with a file
which usually is not needed.