NAME
faucet - a fixture for a BSD network pipe
netpipes 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
DESCRIPTION
faucet attempts to provide the functionality of pipes over the network.
It behaves as the server end of a server-client connection. When used
with hose(1) it can function as a replacement for
tar -cf - . | rsh other "cd destdir; tar -xf -"
faucet and hose are especially useful when you don’t have easy
non-interactive access to the destination account (such as a root
account where .rhosts are a bad idea).
faucet creates a BSD socket, binds it to the port specified on the
command line, and listens for connections.
Every time faucet gets a connection it exec(2)s command and its args
with stdin, stdout, stderr, and/or arbitrary file descriptors
redirected according to the --in --out --err --fd n flags. faucet also
automagically shuts down the unused half of the connection if only --in
is specified or if only --out and/or --err are specified. See the
--shutdown option for more information.
OPTIONS
If the --once flag is specified, faucet will exec(2) the command
instead of fork(2)ing and exec(2)ing. --once means that the network
pipe is only good for one shot.
The --verbose flag specifies that faucet should print information about
connecting hosts. This information includes the numeric host address,
host names, and foreign port numbers. The --quiet flag specifies that
faucet should NOT print such info. --quiet is the default.
The --unix flag specifies that the port is not an internet port number
or service name, but instead it is a file name for a UNIX domain
socket.
The --foreignhost option specifies that faucet should reject all
connections that do not come from the host machine. Similarly
--foreignport specifies that faucet should reject all connections that
are not bound on their local machine to the port argument. The above
two options allow a crude form of authentication. Note that on UNIX
systems only root can bind a socket to a port number below 1024.
Please do not be fooled into thinking this makes faucet secure. There
are ways to spoof IP numbers that have been known for years (but only
publicized recently). I do think that this method is safe from DNS
spoofs, but you probably should have nospoof on in /etc/host.conf
anyway.
--localhost specifies that the listening socket should be bound to a
specific internet address on this host. This is only useful on hosts
with several internet numbers.
--daemon specifies that the faucet should disassociate from the
controlling terminal once it has started listening on the socket. This
is done using the setsid() system call. If you don’t have setsid on
your system, it uses the standard ‘‘close all file descriptors, ioctl
TIOCNOTTY, fork() and parent exit’’ sequence.
--shutdown is used to turn the (normally) bi-directional socket into a
uni-directional one If the ‘r’ is present, then faucet will close half
the connection to make it a read-only socket. If we try to write, it
will fail. If the remote connection tries to read, it will percieve
the socket as closed. If instead the ‘w’ is present, then faucet will
close the other half of the connection to make it a write-only socket.
If we try to read, we will percieve the socket as closed. If the
remote connection tries to write, it will fail. The default behavior
is to leave both halves open, however the shutdown of half of the
connection is automagically done by certain combinations of the --in,
--out, and --err flags. To suppress their automagic behavior you can
use (respectively) --fd 0, --fd 1, and --fd 2.
--shutdown may not be used with some internet servers (such as certain
httpds) because they interpret the closing of one half of the
connection as a close on the entire connection. This warning applies
to --in, --out, and --err.
--serial causes faucet to wait for one child to finish before accepting
any more connections. Serialization is a very crude form of
critical-section management.
--pidfile filename commands faucet to write its process id into
filename. This is useful when faucet is part of a larger system and a
controlling process might want to kill the faucet. --pidfile functions
properly when using the --daemon option.
By default, faucet performs a
setsockopt(fd, SOL_SOCKET, SO_REUSEADDR...)
which prevents the ‘‘Address in use’’ problem that ‘‘plagued’’ netpipes
versions 4.0 and earlier. --noreuseaddr tells faucet to skip that
system call, and revert to pre-4.1 behavior. Without this call, the
socket is not always available for immediate reuse after the faucet
exits.
--backlog n allows you to specify the second parameter to the listen(2)
system call. The default is 5.
SHORT FLAGS
To reduce the typing requirements for arguments (and to pay homage to
the age-old tradition of UNIX cryptotaxonomy) I have added some short
forms of the flags. Here is a correspondence chart:
+------+--------------+
|Short | Long |
| i | in |
| o | out |
| e | err |
| #n | fdn |
| v | verbose |
| 1 | once |
| q | quiet |
| u | unix |
| d | daemon |
| s | serial |
| p | foreignport |
| h | foreignhost |
| H | localhost |
+------+--------------+
For example, the following command
example$ faucet 3000 --out --verbose --once --foreignhost client echo blah
could be written
example$ faucet 3000 -ov1h client echo blah
The -p, -h, and -H flags take an argument, but the flags may be grouped
into one argument. They then grab the arguments they need from the
command line in the order the flags appear.
example$ faucet 3000 -hpHov1 client 2999 example-le2 echo blah
Whereas each --fd word flag required an individual descriptor, the -#
character flag can take multiple descriptors. The following are
equivalent:
example$ faucet 3000 --fd 0 --fd 1 --verbose --once echo blah
example$ faucet 3000 -#0,1v --once echo blah
example$ faucet 3000 -v1#0,1 echo blah
example$ faucet 3000 -#0,1v1 echo blah
Note that you have to pay attention when using the -# character flag
and the -1 character flag in the same argument. Also, remember the
special shutdown(2) semantics of -in and -out.
EXAMPLES
This creates a TCP-IP socket on the local machine bound to port 3000.
example$ faucet 3000 --out --verbose tar -cf - .
Every time some process (from any machine) attempts to connect to port
3000 on this machine the faucet program will fork(2) a process and the
child will exec(2) a
tar -cf - .
The --out option means that the output of the child process will have
been redirected into the new socket retrieved by the accept(2) call.
--verbose means that faucet will print information about each new
connection.
This creates a UNIX domain socket in the current directory
example$ faucet u-socket --out --err --once --unix csh -c \
"dd if=angio.pgm | funky.perl.script"
The --out --err option means that stdout and stderr will be redirected
in the child process. The --once option means that the faucet will not
fork(2), but exec(2) the process so that only the first process can
connect to the u-socket before the faucet becomes unavailable.
This example listens on a socket until the first connection comes
through. It then spawns a bidirectional copy that is similar to hose
-slave.
faucet 3000 -1v --fd 3 sh -c ’cat <&3 & cat >&3 ; sockdown 3’
SEE ALSO
netpipes (1), hose (1), sockdown (1), getpeername (1), socket (2), bind
(2), listen (2), accept (2), shutdown (2), services (5), gethostbyaddr
(3)
BUGS
There is a problem with almost every OS I have used faucet on. Ports
are sometimes not recycled swiftly enough. If you kill one faucet and
try to start another that wants to listen on the same port you will
often see pre-4.1 faucets print the following warning over and over
again:
faucet: Address 3000 in use, sleeping 10.
faucet: Trying again . . .
but you won’t actually be able to connect(2) to that port (with
hose(1), for example) because you’ll get a ‘‘connection refused’’.
There was also an experimental Linux kernel that NEVER recycled ports
(I quickly switched back to my old kernel).
I have been informed that this is a side-effect of the TCP
specification and that I should use the SO_REUSEADDR option to work
around it, so I do.
NOTES
Doubtless there are bugs in this program, especially in the unix domain
socket portions. I welcome problem reports and would like to make
these programs as "clean" (no leftover files, sockets) as possible.
4.1 added --backlog and --noreuseaddr. --noreuseaddr reflects the fact
that 4.1 also added the SO_REUSEADDR socket option as the default.
4.0 made the full-word arguments use -- like many GNU programs. They
are still available with a single - for backward-compatibility.
3.1 added the single-character flags and the -pidfile option. It also
switched to the setsid(2) system call to detach itself from the process
group for the -daemon flag. I’ve been hacking at UNIX for years, but
there are still some things that I never really learned, and others
that have been changing. I need to buy a book.
Release 2.3 added support for multi-homed hosts: hosts with multiple
internet numbers (such as gateways). Before this faucet assumed that
the first internet number that gethostbyname returned was the only one.
--foreignhost authentication was weakened by this inadequacy so I
beefed up the algorithms. --foreignhost will accept a connection from
any of the internet numbers associated with the host name.
CREDITS
Thanks to Steve Clift <clift@ml.csiro.au> for SGI (SysV) patches.
Many people complained about the old way of specifying the command.
Thanks to whoever gave me the alternative which is now implemented. It
is much better.
Randy Fischer <fischer@ucet.ufl.edu> finally prodded me into fixing the
old lame non-handling of multi-homed host.
Thanks to all who suggested I use setsid() for -daemon mode.
Thanks to the Spring 1996 UF CIS consulting staff <consult@cis.ufl.edu>
for pointing out the sys_errlist[] declaration conflict on FreeBSD.
Sometimes I hate Sun Microsystems.
Thanks to Daniel O’Connor <doconnor@adam.ist.flinders.edu.au> for
suggesting the -pidfile flag.
Big thanks to Joe Traister <traister@gate.net> for his signal handling
patches, strerror surrogate, and other assorted hacks.
Thanks to Thomas A. Endo <tendo@netcom.com> for dropping an
SO_REUSEADDR patch in my lap. Otherwise I wouldn’t have gotten to it
till 2001.
COPYRIGHT
Copyright (C) 1992-98 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.
AUTHOR
Robert Forsman
thoth@purplefrog.com
Purple Frog Software
http://web.purplefrog.com/~thoth/
October 28, 1998