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Do not load the config file if the server is exiting because it failed
to start, otherwise commands like lsk which start the server again can
end up looping infinitely. Also make the first client exit
correctly. Problem reported by Wael M Nasreddine.

/* $OpenBSD: server.c,v 1.186 2019/06/07 20:09:17 nicm Exp $ */

/*
 * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/un.h>
#include <sys/wait.h>

#include <errno.h>
#include <event.h>
#include <fcntl.h>
#include <paths.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <termios.h>
#include <time.h>
#include <unistd.h>

#include "tmux.h"

/*
 * Main server functions.
 */

struct clients		 clients;

struct tmuxproc		*server_proc;
static int		 server_fd = -1;
static int		 server_exit;
static struct event	 server_ev_accept;

struct cmd_find_state	 marked_pane;

static int	server_loop(void);
static void	server_send_exit(void);
static void	server_accept(int, short, void *);
static void	server_signal(int);
static void	server_child_signal(void);
static void	server_child_exited(pid_t, int);
static void	server_child_stopped(pid_t, int);

/* Set marked pane. */
void
server_set_marked(struct session *s, struct winlink *wl, struct window_pane *wp)
{
	cmd_find_clear_state(&marked_pane, 0);
	marked_pane.s = s;
	marked_pane.wl = wl;
	marked_pane.w = wl->window;
	marked_pane.wp = wp;
}

/* Clear marked pane. */
void
server_clear_marked(void)
{
	cmd_find_clear_state(&marked_pane, 0);
}

/* Is this the marked pane? */
int
server_is_marked(struct session *s, struct winlink *wl, struct window_pane *wp)
{
	if (s == NULL || wl == NULL || wp == NULL)
		return (0);
	if (marked_pane.s != s || marked_pane.wl != wl)
		return (0);
	if (marked_pane.wp != wp)
		return (0);
	return (server_check_marked());
}

/* Check if the marked pane is still valid. */
int
server_check_marked(void)
{
	return (cmd_find_valid_state(&marked_pane));
}

/* Create server socket. */
static int
server_create_socket(char **cause)
{
	struct sockaddr_un	sa;
	size_t			size;
	mode_t			mask;
	int			fd, saved_errno;

	memset(&sa, 0, sizeof sa);
	sa.sun_family = AF_UNIX;
	size = strlcpy(sa.sun_path, socket_path, sizeof sa.sun_path);
	if (size >= sizeof sa.sun_path) {
		errno = ENAMETOOLONG;
		goto fail;
	}
	unlink(sa.sun_path);

	if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
		goto fail;

	mask = umask(S_IXUSR|S_IXGRP|S_IRWXO);
	if (bind(fd, (struct sockaddr *)&sa, sizeof sa) == -1) {
		saved_errno = errno;
		close(fd);
		errno = saved_errno;
		goto fail;
	}
	umask(mask);

	if (listen(fd, 128) == -1) {
		saved_errno = errno;
		close(fd);
		errno = saved_errno;
		goto fail;
	}
	setblocking(fd, 0);

	return (fd);

fail:
	if (cause != NULL) {
		xasprintf(cause, "error creating %s (%s)", socket_path,
		    strerror(errno));
	}
	return (-1);
}

/* Fork new server. */
int
server_start(struct tmuxproc *client, struct event_base *base, int lockfd,
    char *lockfile)
{
	int		 pair[2];
	sigset_t	 set, oldset;
	struct client	*c;
	char		*cause = NULL;

	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
		fatal("socketpair failed");

	sigfillset(&set);
	sigprocmask(SIG_BLOCK, &set, &oldset);
	switch (fork()) {
	case -1:
		fatal("fork failed");
	case 0:
		break;
	default:
		sigprocmask(SIG_SETMASK, &oldset, NULL);
		close(pair[1]);
		return (pair[0]);
	}
	close(pair[0]);
	if (daemon(1, 0) != 0)
		fatal("daemon failed");
	proc_clear_signals(client, 0);
	if (event_reinit(base) != 0)
		fatalx("event_reinit failed");
	server_proc = proc_start("server");
	proc_set_signals(server_proc, server_signal);
	sigprocmask(SIG_SETMASK, &oldset, NULL);

	if (log_get_level() > 1)
		tty_create_log();
	if (pledge("stdio rpath wpath cpath fattr unix getpw recvfd proc exec "
	    "tty ps", NULL) != 0)
		fatal("pledge failed");

	RB_INIT(&windows);
	RB_INIT(&all_window_panes);
	TAILQ_INIT(&clients);
	RB_INIT(&sessions);
	key_bindings_init();

	gettimeofday(&start_time, NULL);

	server_fd = server_create_socket(&cause);
	if (server_fd != -1)
		server_update_socket();
	c = server_client_create(pair[1]);

	if (lockfd >= 0) {
		unlink(lockfile);
		free(lockfile);
		close(lockfd);
	}

	if (cause != NULL) {
		cmdq_append(c, cmdq_get_error(cause));
		free(cause);
		c->flags |= CLIENT_EXIT;
	} else
		start_cfg();

	server_add_accept(0);
	proc_loop(server_proc, server_loop);

	job_kill_all();
	status_prompt_save_history();

	exit(0);
}

/* Server loop callback. */
static int
server_loop(void)
{
	struct client	*c;
	u_int		 items;

	do {
		items = cmdq_next(NULL);
		TAILQ_FOREACH(c, &clients, entry) {
			if (c->flags & CLIENT_IDENTIFIED)
				items += cmdq_next(c);
		}
	} while (items != 0);

	server_client_loop();

	if (!options_get_number(global_options, "exit-empty") && !server_exit)
		return (0);

	if (!options_get_number(global_options, "exit-unattached")) {
		if (!RB_EMPTY(&sessions))
			return (0);
	}

	TAILQ_FOREACH(c, &clients, entry) {
		if (c->session != NULL)
			return (0);
	}

	/*
	 * No attached clients therefore want to exit - flush any waiting
	 * clients but don't actually exit until they've gone.
	 */
	cmd_wait_for_flush();
	if (!TAILQ_EMPTY(&clients))
		return (0);

	if (job_still_running())
		return (0);

	return (1);
}

/* Exit the server by killing all clients and windows. */
static void
server_send_exit(void)
{
	struct client	*c, *c1;
	struct session	*s, *s1;

	cmd_wait_for_flush();

	TAILQ_FOREACH_SAFE(c, &clients, entry, c1) {
		if (c->flags & CLIENT_SUSPENDED)
			server_client_lost(c);
		else {
			if (c->flags & CLIENT_ATTACHED)
				notify_client("client-detached", c);
			proc_send(c->peer, MSG_SHUTDOWN, -1, NULL, 0);
		}
		c->session = NULL;
	}

	RB_FOREACH_SAFE(s, sessions, &sessions, s1)
		session_destroy(s, 1, __func__);
}

/* Update socket execute permissions based on whether sessions are attached. */
void
server_update_socket(void)
{
	struct session	*s;
	static int	 last = -1;
	int		 n, mode;
	struct stat      sb;

	n = 0;
	RB_FOREACH(s, sessions, &sessions) {
		if (s->attached != 0) {
			n++;
			break;
		}
	}

	if (n != last) {
		last = n;

		if (stat(socket_path, &sb) != 0)
			return;
		mode = sb.st_mode & ACCESSPERMS;
		if (n != 0) {
			if (mode & S_IRUSR)
				mode |= S_IXUSR;
			if (mode & S_IRGRP)
				mode |= S_IXGRP;
			if (mode & S_IROTH)
				mode |= S_IXOTH;
		} else
			mode &= ~(S_IXUSR|S_IXGRP|S_IXOTH);
		chmod(socket_path, mode);
	}
}

/* Callback for server socket. */
static void
server_accept(int fd, short events, __unused void *data)
{
	struct sockaddr_storage	sa;
	socklen_t		slen = sizeof sa;
	int			newfd;

	server_add_accept(0);
	if (!(events & EV_READ))
		return;

	newfd = accept(fd, (struct sockaddr *) &sa, &slen);
	if (newfd == -1) {
		if (errno == EAGAIN || errno == EINTR || errno == ECONNABORTED)
			return;
		if (errno == ENFILE || errno == EMFILE) {
			/* Delete and don't try again for 1 second. */
			server_add_accept(1);
			return;
		}
		fatal("accept failed");
	}
	if (server_exit) {
		close(newfd);
		return;
	}
	server_client_create(newfd);
}

/*
 * Add accept event. If timeout is nonzero, add as a timeout instead of a read
 * event - used to backoff when running out of file descriptors.
 */
void
server_add_accept(int timeout)
{
	struct timeval tv = { timeout, 0 };

	if (server_fd == -1)
		return;

	if (event_initialized(&server_ev_accept))
		event_del(&server_ev_accept);

	if (timeout == 0) {
		event_set(&server_ev_accept, server_fd, EV_READ, server_accept,
		    NULL);
		event_add(&server_ev_accept, NULL);
	} else {
		event_set(&server_ev_accept, server_fd, EV_TIMEOUT,
		    server_accept, NULL);
		event_add(&server_ev_accept, &tv);
	}
}

/* Signal handler. */
static void
server_signal(int sig)
{
	int	fd;

	log_debug("%s: %s", __func__, strsignal(sig));
	switch (sig) {
	case SIGTERM:
		server_exit = 1;
		server_send_exit();
		break;
	case SIGCHLD:
		server_child_signal();
		break;
	case SIGUSR1:
		event_del(&server_ev_accept);
		fd = server_create_socket(NULL);
		if (fd != -1) {
			close(server_fd);
			server_fd = fd;
			server_update_socket();
		}
		server_add_accept(0);
		break;
	case SIGUSR2:
		proc_toggle_log(server_proc);
		break;
	}
}

/* Handle SIGCHLD. */
static void
server_child_signal(void)
{
	int	 status;
	pid_t	 pid;

	for (;;) {
		switch (pid = waitpid(WAIT_ANY, &status, WNOHANG|WUNTRACED)) {
		case -1:
			if (errno == ECHILD)
				return;
			fatal("waitpid failed");
		case 0:
			return;
		}
		if (WIFSTOPPED(status))
			server_child_stopped(pid, status);
		else if (WIFEXITED(status) || WIFSIGNALED(status))
			server_child_exited(pid, status);
	}
}

/* Handle exited children. */
static void
server_child_exited(pid_t pid, int status)
{
	struct window		*w, *w1;
	struct window_pane	*wp;

	RB_FOREACH_SAFE(w, windows, &windows, w1) {
		TAILQ_FOREACH(wp, &w->panes, entry) {
			if (wp->pid == pid) {
				wp->status = status;
				wp->flags |= PANE_STATUSREADY;

				log_debug("%%%u exited", wp->id);
				wp->flags |= PANE_EXITED;

				if (window_pane_destroy_ready(wp))
					server_destroy_pane(wp, 1);
				break;
			}
		}
	}
	job_check_died(pid, status);
}

/* Handle stopped children. */
static void
server_child_stopped(pid_t pid, int status)
{
	struct window		*w;
	struct window_pane	*wp;

	if (WSTOPSIG(status) == SIGTTIN || WSTOPSIG(status) == SIGTTOU)
		return;

	RB_FOREACH(w, windows, &windows) {
		TAILQ_FOREACH(wp, &w->panes, entry) {
			if (wp->pid == pid) {
				if (killpg(pid, SIGCONT) != 0)
					kill(pid, SIGCONT);
			}
		}
	}
}