netpipes - Online in the Cloud

PROGRAM:

NAME

netpipes - a package to manipulate BSD TCP/IP stream sockets

version 4.2

SYNOPSIS

faucet port (--in|--out|--err|--fd n)+ [--once] [--verbose] [--quiet] [--unix]
[--foreignhost addr] [--foreignport port] [--localhost addr] [--serial] [--daemon]
[--shutdown (r|w) ] [--pidfile filename] [--noreuseaddr] [--backlog n]
[-[i][o][e][#3[,4[,5...]]][v][1][q][u][d][s]] [-p foreign-port] [-h foreign-host] [-H
local-host] command args

hose hostname port (--in|--out|--err|--fd n|--slave) [--verbose] [--unix] [--localport
port] [--localhost addr] [--retry n] [--delay n] [--shutdown [r|w][a] ] [--noreuseaddr]
[-[i][o][e][#3[,4[,5...]]][s][v][u]] [-p local-port] [-h local-host] command args

encapsulate --fd n [ --verbose ] [ --subproc [ --infd n[=sid] ] [ --outfd n[=sid] ] [
--duplex n[=sid] ] [ --Duplex n[=sid] ] [ --DUPLEX n[=sid] ] [ --prefer-local ] [
--prefer-remote ] [ --local-only ] [ --remote-only ] ] [ --client ] [ --server ]
-[#n][v][s[in][on][dn][ion][oin][l][r][L][R]] command args ...

sockdown [fd [how] ]

getpeername [ -verbose ] [ -sock ] [ fd ]

getsockname [ -verbose ] [ -peer ] [ fd ]

timelimit.netpipes [ -v ] [ -nokill ] time command args

DESCRIPTION

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.

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.netpipes limits the amount of foreground wallclock time a process may 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.

cairo$ hose www.cis.ufl.edu 80 --in --out \
sh -c "(echo 'GET /'; sockdown) & cat > result"

And of course, there is Nick Trown's metaserver for Netrek

cairo$ hose metaserver.ecst.csuchico.edu 3521 --in cat

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

remote$ faucet 3000 --fd 3 \
encapsulate --fd 3 --infd 0 --outfd 1 --outfd 2 --subproc \
remote-app
local$ hose remote 3000 --fd 3 \
encapsulate --fd 3 --outfd 3 --infd 4 --infd 5 --subproc \
sh -c "cat 0<&4 3>&- & cat 0<&5 1>&2 3>&- & \
cat 1>&3 ; exec 3>&-"

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.

server$ faucet 3000 -1v --fd 1 --foreignhost server echo blah
client$ ssh -n -x -L 3000:server:3000 server sleep 60 &
client$ hose localhost 3000 --fd 0 -retry 10 cat

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.

server$ faucet 3000 -1v --fd 3 --foreignhost server \
encapsulate --fd 3 --server -si0o1 tr a-z A-Z
client$ ssh -n -x -L 3000:server:3000 server sleep 60 &
client$ echo blah | hose localhost 3000 --fd 3 -retry 10 \
encapsulate --fd 3 --client

REMARK

The Debian package maintainer has renamed timelimit to the more expressive
timelimit.netpipes, as there exists a better alternative using the same short name, but
which is actively maintained as an independent software.

Use netpipes online using onworks.net services