The netpipes package makes TCP/IP streams usable in shell scripts.
It can also simplify client/server code by allowing the programmer to
skip all the tedious programming bits related to sockets and
concentrate on writing a filter/service.
``Why would anyone want to do that?''-- Richard Stallman faucet is the server end of a TCP/IP stream. It listens on a
port of the local machine waiting for connections. Every time it gets
a connection it forks a process to perform a service for the
connecting client.
hose is the client end of a TCP/IP stream. It actively
connects to a remote port and execs a process to request a service.
encapsulate is an implementation of the Session Control
Protocol. It allows you to multiplex several streams across a single
TCP session and also transmits remote exit status.
ssl-auth is an encryption filter that encapsulates
stdin/stdout from a subprocess (or its own stdin/stdout) in the Secure
Socket Layer protocol as implemented by the SSLeay library. It
can be used to communicate with encrypted daemons (HTTPS daemons, or
SSL IMAP daemons) and can sometimes be used to jury-rig secure
versions of such services.
sockdown is a simple program designed to shut down part or all
of the socket connection. It is primarily useful when the processes
connected to the socket perform both input and output.
getpeername and getsockname are two names for a program
designed to print out the addresses of the ends of a socket.
getpeername prints the address of the remote end and
getsockname prints the address of the local end.
timelimit limits the amount of foreground wallclock time a
process can consume. After the time limit runs out it either kills
the process or exits and leaves it in the background.
EXAMPLES
Here is a simple command I often perform to transfer directory trees
between machines. (rsh does not work because one machine is connected
using SLIP and .rhosts are out of the question).
server$ faucet 3000 --out tar cf - .
client$ hose server 3000 --in tar xvf -
Here is a minimal HTTP client. It is so minimal it speaks old HTTP.
Allow me to apologize ahead of time for the convolutedness of the
following example. It requires an understanding of Bourne shell file
descriptor redirection syntax (and illustrates why csh and tcsh suck
eggs). Do not try to type this from your tcsh command line. Get a
bash (GNU's Bourne Again SHell).
Suppose you want to distinguish between stdout and stderr of a remote process
Close all unneeded file descriptors when you spawn a background task.
That's why the backgrounded cats have 3>&-.
server$ faucet 3000 --in --out --verbose enscript -2rGhp -
client$ ps aux | hose server 3000 --in --out \
sh -c " (cat <&3; sockdown ) & cat >&4 " 3<&0 4>&1 | \
lpr -Pps422
#or perhaps this, but I haven't tested it
client$ ps aux | hose server 3000 --fd 3 \
sh -c " (cat >&3; sockdown 3 ) & cat <&3 " | \
lpr -Pps422
This proves that hose can be used as part of a pipeline to
perform a sort of remote procedure call (RPC). After you have figured
out that example, you will know how to use Bourne shell to shuffle
file descriptors around. It is a handy skill.
Now we go to the extreme, but simplify things by using the
--slave option of hose. The following is a socket relay
gateway$ faucet 3000 -io hose server 4000 --slave
It's a handy little bugger when you want to tunnel through a firewall
on an occasional basis. If you experience ``hanging'' of the
connection, try using the --netslave option instead of
--slave. (telnet proxies would benefit from this)
For those of you who use ssh, here's how to tunnel some information
through an encrypted SSH port forward.
The trick with ssh's port forwarding, is that the shutdown(2) system
call causes ssh to close both halves of the full-duplex connection
instead of only one half. That's why you have to use --fd 1 and --fd
0. If you need to be able to close half of the connection while still
using the other, use the encapsulate wrapper.
Report any bugs or feature requests to thoth@purplefrog.com
CREDITS
Thanks to Harbor Development
Inc. for funding some of the netpipes development.
Thanks to Michal Jaegermann <michal@ellpspace.math.ualberta.ca>
for some bug fixes and glibc portability suggestions against 4.1.1 .
Big thanks to Joe Traister <traister@gate.net> for his
signal handling patches, strerror surrogate, and other assorted hacks.
COPYRIGHT
Copyright (C) 1995-98 Robert Forsman
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
DOWNLOAD
Export Version: ftp://ftp.purplefrog.com/pub/netpipes/
U.S./Canada version with ssl-auth: http://www.cryptography.org/ , then find it in the network/ subdirectory.
AUTHOR
Robert Forsman
thoth@purplefrog.com
Purple Frog Software
http://web.purplefrog.com/~thoth/
