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This commit is contained in:
Ned T. Crigler 2001-09-28 00:50:56 +00:00
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GNU GENERAL PUBLIC LICENSE
Version 2, June 1991
Copyright (C) 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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The hypothetical commands `show w' and `show c' should show the appropriate
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You should also get your employer (if you work as a programmer) or your
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Yoyodyne, Inc., hereby disclaims all copyright interest in the program
`Gnomovision' (which makes passes at compilers) written by James Hacker.
<signature of Ty Coon>, 1 April 1989
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This General Public License does not permit incorporating your program into
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srcdir = @srcdir@
CC = @CC@
CFLAGS = -W -Wall -I. @CFLAGS@
LDFLAGS = @LDFLAGS@
LIBS = @LIBS@
VERSION = 0.3
VPATH = $(srcdir)
OBJ = attach.o master.o main.o
SRC = $(srcdir)/attach.c $(srcdir)/master.c $(srcdir)/main.c
TARFILES = $(srcdir)/README $(srcdir)/COPYING $(srcdir)/*.in $(srcdir)/*.c \
$(srcdir)/*.h $(srcdir)/dtach.spec $(srcdir)/configure \
$(srcdir)/dtach.1
dtach: $(OBJ)
$(CC) -o $@ $(LDFLAGS) $^ $(LIBS)
clean:
rm -f .depend dtach $(OBJ) dtach-$(VERSION).tar.gz
distclean: clean
rm -f config.h Makefile config.log config.status config.cache
tar:
mkdir dtach-$(VERSION)
cp $(TARFILES) dtach-$(VERSION)
tar -cf dtach-$(VERSION).tar dtach-$(VERSION)/
gzip -9f dtach-$(VERSION).tar
rm -rf dtach-$(VERSION)
.depend:
@$(CC) $(CFLAGS) -MM $(SRC) > $@
-include .depend

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dtach is a program written in C that emulates the detach feature of
screen, which allows a program to be executed in an environment that is
protected from the controlling terminal. For instance, the program under
the control of dtach would not be affected by the terminal being
disconnected for some reason.
dtach was written because screen did not adequately meet my needs; I did
not need the other features of screen, such as its support of multiple
terminals or its terminal emulation support. screen was also too big,
bulky, and the source code was also difficult to understand.
screen also interfered with my use of full-screen applications such as
emacs and ircII, since screen excessively interprets the stream between
the program and the attached terminals. dtach does not have a terminal
emulation layer, and passes the raw output stream of the program to the
attached terminals. The input processing that dtach performs is
scanning for the detach character (which signals dtach to detach from
the program) and processing the suspend key (which tells dtach to
temporarily suspend itself without affecting the running program), which
can both be disabled if desired.
Contrary to screen, dtach has minimal features, and is extremely tiny.
The small size allows it to be more easily audited for bugs and security
holes, and also allows it to fit in environments where space is limited,
such as on rescue disks.
dtach has only been tested on the Linux/x86 platform, however it should
be easily portable to other variants of Unix. It currently assumes that
the host system uses POSIX termios, and has a working forkpty function
available.

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/*
dtach - A simple program that emulates the detach feature of screen.
Copyright (C) 2001 Ned T. Crigler
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "detach.h"
#ifndef VDISABLE
#ifdef _POSIX_VDISABLE
#define VDISABLE _POSIX_VDISABLE
#else
#define VDISABLE 0377
#endif
#endif
// The current terminal settings. After coming back from a suspend, we
// restore this.
static struct termios cur_term;
// 1 if the window size changed
static int win_changed;
// 1 if we want a redraw
static int want_redraw;
// This hopefully moves to the bottom of the screen
#define EOS "\033[999H"
// Restores the original terminal settings.
static void
restore_term(void)
{
tcsetattr(0, TCSADRAIN, &orig_term);
// Make cursor visible. Assumes VT100.
printf("\033[?25h\033[?0c");
fflush(stdout);
}
// Connects to a unix domain socket
static int
connect_socket(char *name)
{
int s;
struct sockaddr_un sun;
s = socket(PF_UNIX, SOCK_STREAM, 0);
if (s < 0)
return -1;
sun.sun_family = AF_UNIX;
strcpy(sun.sun_path, name);
if (connect(s, (struct sockaddr*)&sun, sizeof(sun)) < 0)
return -1;
return s;
}
// Signal
static RETSIGTYPE
die(int sig)
{
// Print a nice pretty message for some things.
if (sig == SIGHUP || sig == SIGINT)
printf(EOS "\r\n[detached]\r\n");
else
printf(EOS "\r\n[got signal %d - dying]\r\n", sig);
exit(1);
}
// Window size change.
static RETSIGTYPE
win_change()
{
win_changed = 1;
}
// Handles input from the keyboard.
static void
process_kbd(int s, struct packet *pkt)
{
// Suspend?
if (!no_suspend && (pkt->u.buf[0] == cur_term.c_cc[VSUSP]))
{
// Tell the master that we are suspending.
pkt->type = MSG_DETACH;
write(s, pkt, sizeof(*pkt));
// And suspend...
tcsetattr(0, TCSADRAIN, &orig_term);
kill(getpid(), SIGTSTP);
tcsetattr(0, TCSADRAIN, &cur_term);
// Tell the master that we are returning.
pkt->type = MSG_ATTACH;
write(s, pkt, sizeof(*pkt));
// The window size might have changed, and we definately want
// a redraw. We don't want to pass the suspend, though.
win_changed = 1;
want_redraw = 1;
return;
}
// Detach char?
else if (pkt->u.buf[0] == detach_char)
{
printf(EOS "\r\n[detached]\r\n");
exit(1);
}
// Just in case something pukes out.
else if (pkt->u.buf[0] == '\f')
win_changed = 1;
// Push it out
write(s, pkt, sizeof(*pkt));
}
int
attach_main(int noerror)
{
int s;
struct pollfd polls[2];
struct packet pkt;
unsigned char buf[BUFSIZE];
// The current terminal settings are equal to the original terminal
// settings at this point.
cur_term = orig_term;
// Set a trap to restore the terminal when we die.
atexit(restore_term);
// Set some signals.
signal(SIGPIPE, SIG_IGN);
signal(SIGXFSZ, SIG_IGN);
signal(SIGHUP, die);
signal(SIGTERM, die);
signal(SIGINT, die);
signal(SIGQUIT, die);
signal(SIGWINCH, win_change);
// Attempt to open the socket. Don't display an error if noerror is
// set.
s = connect_socket(sockname);
if (s < 0)
{
if (!noerror)
printf("%s: %s: %s\n", progname, sockname,
strerror(errno));
return 1;
}
// Set raw mode, almost. We allow flow control to work, for instance.
cur_term.c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP|INLCR|IGNCR|ICRNL);
cur_term.c_oflag &= ~(OPOST);
cur_term.c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
cur_term.c_cflag &= ~(CSIZE|PARENB);
cur_term.c_cflag |= CS8;
cur_term.c_cc[VLNEXT] = VDISABLE;
tcsetattr(0, TCSADRAIN, &cur_term);
// Clear the screen. This assumes VT100.
write(1, "\33[H\33[J", 6);
// Set up the poll structures
polls[0].fd = 0;
polls[0].events = POLLIN;
polls[0].revents = 0;
polls[1].fd = s;
polls[1].events = POLLIN;
polls[1].revents = 0;
// Send our window size.
pkt.type = MSG_WINCH;
ioctl(0, TIOCGWINSZ, &pkt.u.ws);
write(s, &pkt, sizeof(pkt));
// We would like a redraw, too.
pkt.type = MSG_REDRAW;
write(s, &pkt, sizeof(pkt));
// Wait for things to happen
while (1)
{
if (poll(polls, 2, -1) < 0)
{
if (errno != EINTR && errno != EAGAIN)
{
printf(EOS "\r\n[poll failed]\r\n");
exit(1);
}
}
// Pty activity
if (polls[1].revents != 0)
{
int len = read(s, buf, sizeof(buf));
if (len == 0)
{
printf(EOS "\r\n[EOF - dtach terminating]"
"\r\n");
exit(1);
}
else if (len < 0)
{
printf(EOS "\r\n[read returned an error]\r\n");
exit(1);
}
// Send the data to the terminal.
write(1, buf, len);
}
// stdin activity
if (polls[0].revents != 0)
{
pkt.type = MSG_PUSH;
memset(pkt.u.buf, 0, sizeof(pkt.u.buf));
pkt.len = read(0, pkt.u.buf, sizeof(pkt.u.buf));
if (pkt.len <= 0)
exit(1);
process_kbd(s, &pkt);
}
// Window size changed?
if (win_changed)
{
win_changed = 0;
pkt.type = MSG_WINCH;
ioctl(0, TIOCGWINSZ, &pkt.u.ws);
write(s, &pkt, sizeof(pkt));
}
// Want a redraw?
if (want_redraw)
{
want_redraw = 0;
pkt.type = MSG_REDRAW;
write(s, &pkt, sizeof(pkt));
}
}
return 0;
}

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/* config.h.in. Generated automatically from configure.in by autoheader. */
/* Define if you have the `forkpty' function. */
#undef HAVE_FORKPTY
/* Define if you have the `getrlimit' function. */
#undef HAVE_GETRLIMIT
/* Define if you have the `util' library (-lutil). */
#undef HAVE_LIBUTIL
/* Define if you have the <pty.h> header file. */
#undef HAVE_PTY_H
/* Define if you have the `socket' function. */
#undef HAVE_SOCKET
/* Define if you have the `strerror' function. */
#undef HAVE_STRERROR
/* Define if you have the <sys/ioctl.h> header file. */
#undef HAVE_SYS_IOCTL_H
/* Define if you have the <sys/resource.h> header file. */
#undef HAVE_SYS_RESOURCE_H
/* Define if you have the <termios.h> header file. */
#undef HAVE_TERMIOS_H
/* Define if you have the <unistd.h> header file. */
#undef HAVE_UNISTD_H
/* Define if you have the <util.h> header file. */
#undef HAVE_UTIL_H
/* Define as the return type of signal handlers (`int' or `void'). */
#undef RETSIGTYPE
/* Define if you have the ANSI C header files. */
#undef STDC_HEADERS
/* Define to `int' if <sys/types.h> does not define. */
#undef pid_t

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dnl Process this file with autoconf to produce a configure script.
AC_INIT(main.c)
dnl Checks for programs.
AC_PROG_CC
dnl Checks for libraries.
AC_CHECK_LIB(util, forkpty)
dnl Checks for header files.
AC_HEADER_STDC
AC_CHECK_HEADERS(sys/ioctl.h sys/resource.h pty.h termios.h util.h unistd.h)
dnl Checks for typedefs, structures, and compiler characteristics.
AC_TYPE_PID_T
dnl Checks for library functions.
AC_PROG_GCC_TRADITIONAL
AC_TYPE_SIGNAL
AC_CHECK_FUNCS(socket strerror forkpty getrlimit)
AC_CONFIG_HEADER(config.h)
AC_OUTPUT(Makefile)

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/*
dtach - A simple program that emulates the detach feature of screen.
Copyright (C) 2001 Ned T. Crigler
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#ifndef detach_h
#define detach_h
#include "config.h"
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef HAVE_PTY_H
#include <pty.h>
#endif
#ifdef HAVE_UTIL_H
#include <util.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_IOCTL_H
#include <sys/ioctl.h>
#endif
#ifdef HAVE_SYS_RESOURCE_H
#include <sys/resource.h>
#endif
#include <poll.h>
#include <termios.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
extern char *progname, *sockname;
extern int detach_char, no_suspend;
extern struct termios orig_term;
enum
{
MSG_PUSH,
MSG_WINCH,
MSG_REDRAW,
MSG_ATTACH,
MSG_DETACH
};
// The client to master protocol.
struct packet
{
unsigned char type;
unsigned char len;
union
{
unsigned char buf[sizeof(struct winsize)];
struct winsize ws;
} u;
};
// The master sends a simple stream of text to the attaching clients, without
// any protocol. This might change back to the packet based protocol in the
// future. In the meantime, however, we minimize the amount of data sent back
// and forth between the client and the master. BUFSIZE is the size of the
// buffer used for the text stream.
#define BUFSIZE 4096
int attach_main(int noerror);
int master_main(char **argv);
#endif

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.TH dtach 1 "September 2001" "dtach 0.3"
.SH NAME
dtach \- simple program that emulates the detach feature of screen.
.SH SYNOPSIS
.B dtach -a
.I <socket> <options>
.br
.B dtach -A
.I <socket> <options> <command...>
.br
.B dtach -c
.I <socket> <options> <command...>
.br
.B dtach -n
.I <socket> <options> <command...>
.SH DESCRIPTION
.B dtach
is a program that emulates the detach feature of screen. It is designed
to be transparent and un-intrusive; it avoids interpreting the input and output
between attached terminals and the program under its control. Consequently, it
works best with full-screen applications such as emacs.
.B dtach
is intended for users who want the detach feature of screen without the other
overhead that screen has. It is tiny, does not use many libraries, and stays
out of the way as much as possible.
.SS SESSIONS
A session in
.B dtach
is a single instance in which a program is running under the control of
.BR dtach .
The program is dissasociated from the original terminal, and is thus protected
from your original terminal being disconnected for some reason.
.PP
Other instances of
.B dtach
can attach themselves to a particular session. Input and output is copied
between the program running in the
.B dtach
session, and the attached terminals.
.PP
.B dtach
avoids interpreting the communication stream between the program and the
attached terminals; it instead relies on the ability of the attached terminals
to manage the screen.
.PP
Sessions are represented by Unix-domain sockets in the filesystem. No other
permission checking other than the filesystem access checks is performed.
.B dtach
creates a master process that monitors the session socket, the program, and any
attached terminals.
.PP
.SS MODES
.B dtach
has several modes of operation. It can create a new session in which a
program is executed, or it can attach to an already existing session. The first
argument specifies which mode
.B dtach
should operate in.
.TP
.B \-a
Attach to an already existing session.
.B dtach
attaches itself to the session specified by
.IR <socket> .
After the attach is completed, the window size of the current terminal is sent
to the master process, and a redraw is also requested.
.TP
.B \-A
Attach to an already existing session, or create a new one.
.B dtach
first tries to attach to the session specified by
.I <socket>
if possible. If the attempt to open the socket fails,
.B dtach
tries to create a new session before attaching to it.
.TP
.B \-c
Creates a new session. A new session is created in which the specified program
is executed.
.B dtach
then tries to attach itself to the newly created session.
.TP
.B \-n
Creates a new session, without attaching to it. A new session is created in
which the specified program is executed.
.B dtach
does not try to attach to the newly created session, however, and exits
instead.
.PP
.SS OPTIONS
.B dtach
has a few options that allow you to modify its behavior. Each attaching
process can have separate settings for these options, which allows for
some flexibility.
.TP
.BI "\-e " "<char>"
Sets the detach character to
.IR <char> .
When the detach character is pressed,
.B dtach
detaches itself from the current session and exits. The process running in
the session is unaffected by the detach. By default, the detach character is
set to ^\\ (Ctrl-\\).
.TP
.B \-E
Disables the detach character.
.B dtach
does not try to scan input from the terminal for a detach character. The only
way to detach from the session is then by sending the attaching process an
appropriate signal.
.TP
.B \-z
Inhibits processing of the suspend key.
Normally,
.B dtach
will suspend itself when the suspend key is pressed. With this option, the
suspend character is sent to the session instead of being handled by
.BR dtach .
.PP
.SH EXAMPLES
The following example creates a new session that has the detach character
and suspend processing disabled. A socket is created in the /tmp directory
for the session.
.nf
$ dtach -c /tmp/foozle -Ez bash
.fi
The following example attaches to the /tmp/foozle session if it exists, and if
not, creates a new session using /tmp/foozle as the socket for the session.
Processing of the suspend character is also disabled for the attach instance.
.nf
$ dtach -A /tmp/foozle -z bash
.fi
.PP
.SH AUTHORS
Ned T. Crigler <crigler@hell-city.org>.
.SH "SEE ALSO"
.BR screen "(1)"

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Summary: A simple program that emulates the detach feature of screen.
Name: dtach
Version: 0.3
Release: 1
Copyright: GPL
URL: http://people.redhat.com/iweiner/dtach
Group: Applications/System
Source: dtach-%{version}.tar.gz
Prefix: /usr
Buildroot: %{_tmppath}/%{name}-%{version}-buildroot
Obsoletes: detach
%description
dtach is a program that emulates the detach feature of screen, without the
other overhead that screen has. It is designed to be transparent and
un-intrusive; it avoids interpreting the input and output between attached
terminals and the program under its control. Consequently, it works best with
full-screen applications such as emacs.
%prep
%setup
%build
%configure
make
%install
rm -rf $RPM_BUILD_ROOT/*
mkdir -p $RPM_BUILD_ROOT/%{_bindir}
mkdir -p $RPM_BUILD_ROOT/usr/share/doc/dtach-%{version}
mkdir -p $RPM_BUILD_ROOT/%{_mandir}/man1
install -m 755 dtach $RPM_BUILD_ROOT/%{_bindir}/dtach
install -m 644 COPYING $RPM_BUILD_ROOT/usr/share/doc/dtach-%{version}
install -m 644 dtach.1 $RPM_BUILD_ROOT/%{_mandir}/man1/dtach.1
%clean
make clean
rm -rf $RPM_BUILD_ROOT
rm -rf $RPM_BUILD_DIR/%{name}-%{version}
%files
%defattr(-,root,root,-)
%doc /usr/share/doc/dtach-%{version}/COPYING
%{_bindir}/dtach
%{_mandir}/man1/*
%changelog
* Wed Sep 26 2001 Ned T. Crigler <crigler@hell-city.org> 0.3
- Use getrlimit and dynamically allocate the data structures, if possible.
- Added some more autoconf checks.
- Initial sourceforge release.
* Thu Sep 20 2001 Ned T. Crigler <crigler@hell-city.org>
- Changed the master to send a stream of text to attaching clients instead
of sending a huge packet all the time.
- Decreased the client <-> master packet size.
- Changed the attach code so that it tells the master when a suspend occurs.
* Tue Sep 18 2001 Ned T. Crigler <crigler@hell-city.org>
- Fixed a typo in dtach.1
* Tue Sep 18 2001 Ned T. Crigler <crigler@hell-city.org> 0.2
- Removed silly thinko regarding terminal settings in attach, we
always set the terminal to raw mode now.
- Moved redraw code into the master, which tries to be smarter when
using ^L.
- Moved the code that obtains the current terminal settings into main,
preventing a race condition between the master and attach processes.
- Rewrote argument parsing code.
- Changed name to dtach.
- Added a man page.
* Mon Sep 17 2001 Ned T. Crigler <crigler@hell-city.org>
- Changed fchmod to chmod in create_socket.
* Mon Sep 17 2001 Isaiah Weiner <iweiner@redhat.com>
- Modified spec file to correct detach binary permissions
- Modified spec file to correct detach documentation path
- Modified spec file URL: to point to http://people.redhat.com/iweiner/detach
- Modified spec file %clean to remove buildroot and builddir.
* Mon Sep 17 2001 Ned T. Crigler <crigler@hell-city.org> 0.1
- Initial rpm release.

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/*
dtach - A simple program that emulates the detach feature of screen.
Copyright (C) 2001 Ned T. Crigler
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "detach.h"
/*
** detach is a quick hack, since I wanted the detach feature of screen without
** all the other crud. It'll work best with full-screen applications, as it
** does not keep track of the screen or anything like that.
*/
// The program version
#define VERSION "0.3"
// Make sure the binary has a copyright.
const char copyright[] = "dtach - version " VERSION " (C)Copyright 2001 Ned T. Crigler";
// argv[0] from the program
char *progname;
// The name of the passed in socket.
char *sockname;
// The character used for detaching. Defaults to '^\'
int detach_char = '\\' - 64;
// 1 if we should not interpret the suspend character.
int no_suspend;
// The original terminal settings. Shared between the master and attach
// processes. The master uses it to initialize the pty, and the attacher uses
// it to restore the original settings.
struct termios orig_term;
static void
usage()
{
printf(
"dtach - version %s, compiled on %s at %s.\n"
"Usage: dtach -a <socket> <options>\n"
" dtach -A <socket> <options> <command...>\n"
" dtach -c <socket> <options> <command...>\n"
" dtach -n <socket> <options> <command...>\n"
"Modes:\n"
" -a\t\tAttach to the specified socket.\n"
" -A\t\tAttach to the specified socket, or create it if it\n"
"\t\t does not exist, running the specified command.\n"
" -c\t\tCreate a new socket and run the specified command.\n"
" -n\t\tCreate a new socket and run the specified command "
"detached.\n"
"Options:\n"
" -e <char>\tSet the detach character to <char>, defaults "
"to ^\\.\n"
" -E\t\tDisable the detach character.\n"
" -z\t\tInhibit processing of the suspend key.\n"
"\nReport any bugs to <crigler@hell-city.org>.\n",
VERSION, __DATE__, __TIME__);
exit(0);
}
int
main(int argc, char **argv)
{
int mode = 0;
// Save the program name
progname = argv[0];
++argv; --argc;
// Parse the arguments
if (argc >= 1 && **argv == '-')
{
if (strncmp(*argv, "--help", strlen(*argv)) == 0)
usage();
else if (strncmp(*argv, "--version", strlen(*argv)) == 0)
{
printf("dtach - version %s, compiled on %s at %s.\n",
VERSION, __DATE__, __TIME__);
return 0;
}
mode = argv[0][1];
if (mode == '?')
usage();
else if (mode != 'a' && mode != 'c' && mode != 'n' &&
mode != 'A')
{
printf("%s: Invalid mode '-%c'\n", progname, mode);
printf("Try '%s -?' for more information.\n",
progname);
return 1;
}
}
if (!mode)
{
printf("%s: No mode was specified.\n", progname);
printf("Try '%s -?' for more information.\n",
progname);
return 1;
}
++argv; --argc;
if (argc < 1)
{
printf("%s: No socket was specified.\n", progname);
printf("Try '%s -?' for more information.\n",
progname);
return 1;
}
sockname = *argv;
++argv; --argc;
while (argc >= 1 && **argv == '-')
{
char *p;
for (p = argv[0] + 1; *p; ++p)
{
if (*p == 'E')
detach_char = -1;
else if (*p == 'z')
no_suspend = 1;
else if (*p == 'e')
{
++argv; --argc;
if (argc < 1)
{
printf("%s: No escape character "
"specified.\n", progname);
printf("Try '%s -?' for more "
"information.\n", progname);
return 1;
}
if (argv[0][0] == '^' && argv[0][1])
{
if (argv[0][1] == '?')
detach_char = '\177';
else
detach_char = argv[0][1] - 64;
}
else
detach_char = argv[0][0];
break;
}
else
{
printf("%s: Invalid option '-%c'\n",
progname, *p);
printf("Try '%s -?' for more information.\n",
progname);
return 1;
}
}
++argv; --argc;
}
if (mode != 'a' && argc < 1)
{
printf("%s: No command was specified.\n", progname);
printf("Try '%s -?' for more information.\n",
progname);
return 1;
}
// Save the original terminal settings.
if (tcgetattr(0, &orig_term) < 0)
{
printf("%s: tcgetattr: %s\n", progname, strerror(errno));
return 1;
}
if (mode == 'a')
{
if (argc > 0)
{
printf("%s: Invalid number of arguments.\n",
progname);
printf("Try '%s -?' for more information.\n",
progname);
return 1;
}
return attach_main(0);
}
else if (mode == 'n')
return master_main(argv);
else if (mode == 'c')
{
if (master_main(argv) != 0)
return 1;
return attach_main(0);
}
else if (mode == 'A')
{
// Try to attach first. If that doesn't work, create a new
// socket.
if (attach_main(1) != 0)
{
if (master_main(argv) != 0)
return 1;
return attach_main(0);
}
}
return 0;
}

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/*
dtach - A simple program that emulates the detach feature of screen.
Copyright (C) 2001 Ned T. Crigler
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
#include "detach.h"
// The pty struct - The pty information is stored here.
struct pty
{
// File descriptor of the pty
int fd;
// The terminal parameters of the pty. Old and new for comparision
// purposes.
struct termios term;
// The current window size of the pty.
struct winsize ws;
};
// The poll structures
static struct pollfd *polls;
// The number of active poll slots
static int num_polls;
// Boolean array for whether a particular connection is attached.
static int *attached;
// The highest file descriptor possible, as returned by getrlimit.
static int highest_fd;
// The number of fixed slots in the poll structures
#define FIXED_SLOTS 2
// Unlink the socket
static void
unlink_socket(void)
{
unlink(sockname);
}
// Signal
static RETSIGTYPE
die(int sig)
{
// Well, the child died.
if (sig == SIGCHLD)
return;
exit(1);
}
// Initialize the pty structure.
static int
init_pty(struct pty *pty, char **argv)
{
pid_t pid;
// Use the original terminal's settings. We don't have to set the
// window size here, because the attacher will send it in a packet.
pty->term = orig_term;
// Create the pty process
pid = forkpty(&pty->fd, NULL, &pty->term, NULL);
if (pid < 0)
return -1;
else if (pid == 0)
{
int i;
// Child.. Close some file descriptors and execute the program.
for (i = highest_fd; i > 2; --i)
close(i);
execvp(*argv, argv);
exit(127);
}
// Parent.. Finish up and return
return 0;
}
// Creates a new unix domain socket.
static int
create_socket(char *name)
{
int s;
struct sockaddr_un sun;
s = socket(PF_UNIX, SOCK_STREAM, 0);
if (s < 0)
return -1;
sun.sun_family = AF_UNIX;
strcpy(sun.sun_path, name);
if (bind(s, (struct sockaddr*)&sun, sizeof(sun)) < 0)
return -1;
if (listen(s, 128) < 0)
return -1;
// chmod it to prevent any suprises
if (chmod(name, 0600) < 0)
return -1;
return s;
}
// Process activity on a pty - Input and terminal changes are sent out to
// the attached clients. If the pty goes away, we die.
static void
pty_activity(struct pty *pty)
{
int i, len;
unsigned char buf[BUFSIZE];
// Read the pty activity
len = read(pty->fd, buf, sizeof(buf));
// Error -> die
if (len <= 0)
exit(1);
// Get the current terminal settings.
if (tcgetattr(pty->fd, &pty->term) < 0)
exit(1);
// Send it out to the clients.
for (i = FIXED_SLOTS; i < num_polls; ++i)
{
if (attached[polls[i].fd])
write(polls[i].fd, buf, len);
}
}
// Process activity on the control socket
static void
control_activity(int s)
{
int fd;
// Accept the new client and link it in.
fd = accept(s, 0, 0);
if (fd < 0)
return;
// Link it in.
polls[num_polls].fd = fd;
polls[num_polls].events = POLLIN;
polls[num_polls].revents = 0;
attached[fd] = 1;
++num_polls;
}
// Process activity from a client.
static void
client_activity(int i, struct pty *pty)
{
int len;
struct packet pkt;
// Read the activity.
len = read(polls[i].fd, &pkt, sizeof(pkt));
if (len <= 0)
{
// Close the socket and go bye bye
attached[polls[i].fd]=0;
close(polls[i].fd);
memcpy(polls + i, polls + i + 1, num_polls - i);
--num_polls;
return;
}
// Okay, check the command byte. Push out data if we need to.
if (pkt.type == MSG_PUSH)
write(pty->fd, pkt.u.buf, pkt.len);
// Window size change.
else if (pkt.type == MSG_WINCH)
{
pty->ws = pkt.u.ws;
ioctl(pty->fd, TIOCSWINSZ, &pty->ws);
}
// Redraw request?
else if (pkt.type == MSG_REDRAW)
{
char c = '\f';
// Guess that ^L might work under certain conditions.
if (((pty->term.c_lflag & (ECHO|ICANON)) == 0) &&
(pty->term.c_cc[VMIN] == 1))
{
write(pty->fd, &c, sizeof(c));
}
}
// Attach request?
else if (pkt.type == MSG_ATTACH)
attached[polls[i].fd] = 1;
else if (pkt.type == MSG_DETACH)
attached[polls[i].fd] = 0;
}
// The master process - It watches over the pty process and the attached
// clients.
static void
master_process(int s, char **argv)
{
struct pty pty;
int i;
#ifdef HAVE_GETRLIMIT
struct rlimit rlim;
// Dynamically allocate structures based on the number of file
// descriptors.
if (getrlimit(RLIMIT_NOFILE, &rlim) < 0)
{
printf("%s: getrlimit: %s\n", progname, strerror(errno));
exit(1);
}
highest_fd = rlim.rlim_cur;
#else
// We can't query the OS for the number of file descriptors, so
// we pull a number out of the air.
highest_fd = 1024;
#endif
polls = (struct pollfd*)malloc(highest_fd * sizeof(struct pollfd));
attached = (int*)malloc(highest_fd * sizeof(int));
// Okay, disassociate ourselves from the original terminal, as we
// don't care what happens to it.
setsid();
// Create a pty in which the process is running.
if (init_pty(&pty, argv) < 0)
{
printf("%s: init_pty: %s\n", progname, strerror(errno));
exit(1);
}
// Set up some signals.
signal(SIGPIPE, SIG_IGN);
signal(SIGXFSZ, SIG_IGN);
signal(SIGHUP, SIG_IGN);
signal(SIGTTIN, SIG_IGN);
signal(SIGTTOU, SIG_IGN);
signal(SIGINT, die);
signal(SIGTERM, die);
signal(SIGCHLD, die);
// Close the original terminal. We are now a daemon.
fclose(stdin);
fclose(stdout);
fclose(stderr);
// Set a trap to unlink the socket when we die
atexit(unlink_socket);
// Set up the poll structures. Slot 0 is the control socket, slot 1
// is the pty, and slot 2 .. n is the connected clients.
polls[0].fd = s;
polls[0].events = POLLIN;
polls[0].revents = 0;
polls[1].fd = pty.fd;
polls[1].events = POLLIN;
polls[1].revents = 0;
num_polls = FIXED_SLOTS;
// Loop forever.
while (1)
{
// Wait for something to happen.
if (poll(polls, num_polls, -1) < 0)
{
if (errno == EINTR || errno == EAGAIN)
continue;
exit(1);
}
// pty activity?
if (polls[1].revents != 0)
pty_activity(&pty);
// New client?
if (polls[0].revents != 0)
control_activity(s);
// Activity on a client?
for (i = 2; i < num_polls; ++i)
{
if (polls[i].revents != 0)
client_activity(i, &pty);
}
}
}
int
master_main(char **argv)
{
int s;
pid_t pid;
// Create the unix domain socket.
s = create_socket(sockname);
if (s < 0)
{
printf("%s: %s: %s\n", progname, sockname, strerror(errno));
return 1;
}
// Fork off so we can daemonize and such
pid = fork();
if (pid < 0)
{
printf("%s: fork: %s\n", progname, strerror(errno));
return 1;
}
else if (pid == 0)
{
// Child - this becomes the master
master_process(s, argv);
return 0;
}
// Parent - just return.
return 0;
}