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Change UTF-8 combining to inspect the previous character at the cursor
position rather than keeping the last character from the input stream,
this is how most terminals work and fixes problems with displaying these
characters in vim. GitHub issue 3600.

/* $OpenBSD: server.c,v 1.205 2023/09/15 15:49:05 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 uint64_t		 server_client_flags;
static int		 server_exit;
static struct event	 server_ev_accept;
static struct event	 server_ev_tidy;

struct cmd_find_state	 marked_pane;

static u_int		 message_next;
struct message_list	 message_log;

time_t			 current_time;

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(int flags, 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;

	if (flags & CLIENT_DEFAULTSOCKET)
		mask = umask(S_IXUSR|S_IXGRP|S_IRWXO);
	else
		mask = umask(S_IXUSR|S_IRWXG|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);
}

/* Tidy up every hour. */
static void
server_tidy_event(__unused int fd, __unused short events, __unused void *data)
{
    struct timeval	tv = { .tv_sec = 3600 };
    uint64_t		t = get_timer();

    format_tidy_jobs();

    log_debug("%s: took %llu milliseconds", __func__,
        (unsigned long long)(get_timer() - t));
    evtimer_add(&server_ev_tidy, &tv);
}

/* Fork new server. */
int
server_start(struct tmuxproc *client, int flags, struct event_base *base,
    int lockfd, char *lockfile)
{
	int		 fd;
	sigset_t	 set, oldset;
	struct client	*c = NULL;
	char		*cause = NULL;
	struct timeval	 tv = { .tv_sec = 3600 };

	sigfillset(&set);
	sigprocmask(SIG_BLOCK, &set, &oldset);

	if (~flags & CLIENT_NOFORK) {
		if (proc_fork_and_daemon(&fd) != 0) {
			sigprocmask(SIG_SETMASK, &oldset, NULL);
			return (fd);
		}
	}
	proc_clear_signals(client, 0);
	server_client_flags = flags;

	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");

	input_key_build();
	RB_INIT(&windows);
	RB_INIT(&all_window_panes);
	TAILQ_INIT(&clients);
	RB_INIT(&sessions);
	key_bindings_init();
	TAILQ_INIT(&message_log);
	gettimeofday(&start_time, NULL);

	server_fd = server_create_socket(flags, &cause);
	if (server_fd != -1)
		server_update_socket();
	if (~flags & CLIENT_NOFORK)
		c = server_client_create(fd);
	else
		options_set_number(global_options, "exit-empty", 0);

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

	if (cause != NULL) {
		if (c != NULL) {
			c->exit_message = cause;
			c->flags |= CLIENT_EXIT;
		} else {
			fprintf(stderr, "%s\n", cause);
			exit(1);
		}
	}

	evtimer_set(&server_ev_tidy, server_tidy_event, NULL);
	evtimer_add(&server_ev_tidy, &tv);

	server_acl_init();

	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;

	current_time = time (NULL);

	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 {
			c->flags |= CLIENT_EXIT;
			c->exit_type = CLIENT_EXIT_SHUTDOWN;
		}
		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;
	struct client		*c;

	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;
	}
	c = server_client_create(newfd);
	if (!server_acl_join(c)) {
		c->exit_message = xstrdup("access not allowed");
		c->flags |= CLIENT_EXIT;
	}
}

/*
 * 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 SIGINT:
	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(server_client_flags, 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);
			}
		}
	}
	job_check_died(pid, status);
}

/* Add to message log. */
void
server_add_message(const char *fmt, ...)
{
	struct message_entry	*msg, *msg1;
	char			*s;
	va_list			 ap;
	u_int			 limit;

	va_start(ap, fmt);
	xvasprintf(&s, fmt, ap);
	va_end(ap);

	log_debug("message: %s", s);

	msg = xcalloc(1, sizeof *msg);
	gettimeofday(&msg->msg_time, NULL);
	msg->msg_num = message_next++;
	msg->msg = s;
	TAILQ_INSERT_TAIL(&message_log, msg, entry);

	limit = options_get_number(global_options, "message-limit");
	TAILQ_FOREACH_SAFE(msg, &message_log, entry, msg1) {
		if (msg->msg_num + limit >= message_next)
			break;
		free(msg->msg);
		TAILQ_REMOVE(&message_log, msg, entry);
		free(msg);
	}
}