client.c

/* $OpenBSD$ */

/*
 * 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/socket.h>
#include <sys/un.h>
#include <sys/wait.h>

#include <errno.h>
#include <event.h>
#include <fcntl.h>
#include <imsg.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "tmux.h"

static struct tmuxproc	*client_proc;
static struct tmuxpeer	*client_peer;
static int		 client_flags;
static enum {
	CLIENT_EXIT_NONE,
	CLIENT_EXIT_DETACHED,
	CLIENT_EXIT_DETACHED_HUP,
	CLIENT_EXIT_LOST_TTY,
	CLIENT_EXIT_TERMINATED,
	CLIENT_EXIT_LOST_SERVER,
	CLIENT_EXIT_EXITED,
	CLIENT_EXIT_SERVER_EXITED,
} client_exitreason = CLIENT_EXIT_NONE;
static int		 client_exitflag;
static int		 client_exitval;
static enum msgtype	 client_exittype;
static const char	*client_exitsession;
static const char	*client_execshell;
static const char	*client_execcmd;
static int		 client_attached;
static struct client_files client_files = RB_INITIALIZER(&client_files);

static __dead void	 client_exec(const char *,const char *);
static int		 client_get_lock(char *);
static int		 client_connect(struct event_base *, const char *, int);
static void		 client_send_identify(const char *, const char *);
static void		 client_signal(int);
static void		 client_dispatch(struct imsg *, void *);
static void		 client_dispatch_attached(struct imsg *);
static void		 client_dispatch_wait(struct imsg *);
static const char	*client_exit_message(void);

/*
 * Get server create lock. If already held then server start is happening in
 * another client, so block until the lock is released and return -2 to
 * retry. Return -1 on failure to continue and start the server anyway.
 */
static int
client_get_lock(char *lockfile)
{
	int lockfd;

	log_debug("lock file is %s", lockfile);

	if ((lockfd = open(lockfile, O_WRONLY|O_CREAT, 0600)) == -1) {
		log_debug("open failed: %s", strerror(errno));
		return (-1);
	}

	if (flock(lockfd, LOCK_EX|LOCK_NB) == -1) {
		log_debug("flock failed: %s", strerror(errno));
		if (errno != EAGAIN)
			return (lockfd);
		while (flock(lockfd, LOCK_EX) == -1 && errno == EINTR)
			/* nothing */;
		close(lockfd);
		return (-2);
	}
	log_debug("flock succeeded");

	return (lockfd);
}

/* Connect client to server. */
static int
client_connect(struct event_base *base, const char *path, int flags)
{
	struct sockaddr_un	sa;
	size_t			size;
	int			fd, lockfd = -1, locked = 0;
	char		       *lockfile = NULL;

	memset(&sa, 0, sizeof sa);
	sa.sun_family = AF_UNIX;
	size = strlcpy(sa.sun_path, path, sizeof sa.sun_path);
	if (size >= sizeof sa.sun_path) {
		errno = ENAMETOOLONG;
		return (-1);
	}
	log_debug("socket is %s", path);

retry:
	if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
		return (-1);

	log_debug("trying connect");
	if (connect(fd, (struct sockaddr *)&sa, sizeof sa) == -1) {
		log_debug("connect failed: %s", strerror(errno));
		if (errno != ECONNREFUSED && errno != ENOENT)
			goto failed;
		if (~flags & CLIENT_STARTSERVER)
			goto failed;
		close(fd);

		if (!locked) {
			xasprintf(&lockfile, "%s.lock", path);
			if ((lockfd = client_get_lock(lockfile)) < 0) {
				log_debug("didn't get lock (%d)", lockfd);

				free(lockfile);
				lockfile = NULL;

				if (lockfd == -2)
					goto retry;
			}
			log_debug("got lock (%d)", lockfd);

			/*
			 * Always retry at least once, even if we got the lock,
			 * because another client could have taken the lock,
			 * started the server and released the lock between our
			 * connect() and flock().
			 */
			locked = 1;
			goto retry;
		}

		if (lockfd >= 0 && unlink(path) != 0 && errno != ENOENT) {
			free(lockfile);
			close(lockfd);
			return (-1);
		}
		fd = server_start(client_proc, flags, base, lockfd, lockfile);
	}

	if (locked && lockfd >= 0) {
		free(lockfile);
		close(lockfd);
	}
	setblocking(fd, 0);
	return (fd);

failed:
	if (locked) {
		free(lockfile);
		close(lockfd);
	}
	close(fd);
	return (-1);
}

/* Get exit string from reason number. */
const char *
client_exit_message(void)
{
	static char msg[256];

	switch (client_exitreason) {
	case CLIENT_EXIT_NONE:
		break;
	case CLIENT_EXIT_DETACHED:
		if (client_exitsession != NULL) {
			xsnprintf(msg, sizeof msg, "detached "
			    "(from session %s)", client_exitsession);
			return (msg);
		}
		return ("detached");
	case CLIENT_EXIT_DETACHED_HUP:
		if (client_exitsession != NULL) {
			xsnprintf(msg, sizeof msg, "detached and SIGHUP "
			    "(from session %s)", client_exitsession);
			return (msg);
		}
		return ("detached and SIGHUP");
	case CLIENT_EXIT_LOST_TTY:
		return ("lost tty");
	case CLIENT_EXIT_TERMINATED:
		return ("terminated");
	case CLIENT_EXIT_LOST_SERVER:
		return ("server exited unexpectedly");
	case CLIENT_EXIT_EXITED:
		return ("exited");
	case CLIENT_EXIT_SERVER_EXITED:
		return ("server exited");
	}
	return ("unknown reason");
}

/* Exit if all streams flushed. */
static void
client_exit(void)
{
	struct client_file	*cf;
	size_t 			 left;
	int			 waiting = 0;

	RB_FOREACH (cf, client_files, &client_files) {
		if (cf->event == NULL)
			continue;
		left = EVBUFFER_LENGTH(cf->event->output);
		if (left != 0) {
			waiting++;
			log_debug("file %u %zu bytes left", cf->stream, left);
		}
	}
	if (waiting == 0)
		proc_exit(client_proc);
}

/* Client main loop. */
int
client_main(struct event_base *base, int argc, char **argv, int flags)
{
	struct cmd_parse_result	*pr;
	struct cmd		*cmd;
	struct msg_command	*data;
	int			 fd, i;
	const char		*ttynam, *cwd;
	pid_t			 ppid;
	enum msgtype		 msg;
	struct termios		 tio, saved_tio;
	size_t			 size;

	/* Ignore SIGCHLD now or daemon() in the server will leave a zombie. */
	signal(SIGCHLD, SIG_IGN);

	/* Set up the initial command. */
	if (shell_command != NULL) {
		msg = MSG_SHELL;
		flags |= CLIENT_STARTSERVER;
	} else if (argc == 0) {
		msg = MSG_COMMAND;
		flags |= CLIENT_STARTSERVER;
	} else {
		msg = MSG_COMMAND;

		/*
		 * It sucks parsing the command string twice (in client and
		 * later in server) but it is necessary to get the start server
		 * flag.
		 */
		pr = cmd_parse_from_arguments(argc, argv, NULL);
		if (pr->status == CMD_PARSE_SUCCESS) {
			TAILQ_FOREACH(cmd, &pr->cmdlist->list, qentry) {
				if (cmd->entry->flags & CMD_STARTSERVER)
					flags |= CLIENT_STARTSERVER;
			}
			cmd_list_free(pr->cmdlist);
		} else
			free(pr->error);
	}

	/* Save the flags. */
	client_flags = flags;

	/* Create client process structure (starts logging). */
	client_proc = proc_start("client");
	proc_set_signals(client_proc, client_signal);

	/* Initialize the client socket and start the server. */
	fd = client_connect(base, socket_path, client_flags);
	if (fd == -1) {
		if (errno == ECONNREFUSED) {
			fprintf(stderr, "no server running on %s\n",
			    socket_path);
		} else {
			fprintf(stderr, "error connecting to %s (%s)\n",
			    socket_path, strerror(errno));
		}
		return (1);
	}
	client_peer = proc_add_peer(client_proc, fd, client_dispatch, NULL);

	/* Save these before pledge(). */
	if ((cwd = find_cwd()) == NULL && (cwd = find_home()) == NULL)
		cwd = "/";
	if ((ttynam = ttyname(STDIN_FILENO)) == NULL)
		ttynam = "";

	/*
	 * Drop privileges for client. "proc exec" is needed for -c and for
	 * locking (which uses system(3)).
	 *
	 * "tty" is needed to restore termios(4) and also for some reason -CC
	 * does not work properly without it (input is not recognised).
	 *
	 * "sendfd" is dropped later in client_dispatch_wait().
	 */
	if (pledge(
	    "stdio rpath wpath cpath unix sendfd proc exec tty",
	    NULL) != 0)
		fatal("pledge failed");

	/* Free stuff that is not used in the client. */
	if (ptm_fd != -1)
		close(ptm_fd);
	options_free(global_options);
	options_free(global_s_options);
	options_free(global_w_options);
	environ_free(global_environ);

	/* Set up control mode. */
	if (client_flags & CLIENT_CONTROLCONTROL) {
		if (tcgetattr(STDIN_FILENO, &saved_tio) != 0) {
			fprintf(stderr, "tcgetattr failed: %s\n",
			    strerror(errno));
			return (1);
		}
		cfmakeraw(&tio);
		tio.c_iflag = ICRNL|IXANY;
		tio.c_oflag = OPOST|ONLCR;
		tio.c_lflag = NOKERNINFO;
		tio.c_cflag = CREAD|CS8|HUPCL;
		tio.c_cc[VMIN] = 1;
		tio.c_cc[VTIME] = 0;
		cfsetispeed(&tio, cfgetispeed(&saved_tio));
		cfsetospeed(&tio, cfgetospeed(&saved_tio));
		tcsetattr(STDIN_FILENO, TCSANOW, &tio);
	}

	/* Send identify messages. */
	client_send_identify(ttynam, cwd);

	/* Send first command. */
	if (msg == MSG_COMMAND) {
		/* How big is the command? */
		size = 0;
		for (i = 0; i < argc; i++)
			size += strlen(argv[i]) + 1;
		if (size > MAX_IMSGSIZE - (sizeof *data)) {
			fprintf(stderr, "command too long\n");
			return (1);
		}
		data = xmalloc((sizeof *data) + size);

		/* Prepare command for server. */
		data->argc = argc;
		if (cmd_pack_argv(argc, argv, (char *)(data + 1), size) != 0) {
			fprintf(stderr, "command too long\n");
			free(data);
			return (1);
		}
		size += sizeof *data;

		/* Send the command. */
		if (proc_send(client_peer, msg, -1, data, size) != 0) {
			fprintf(stderr, "failed to send command\n");
			free(data);
			return (1);
		}
		free(data);
	} else if (msg == MSG_SHELL)
		proc_send(client_peer, msg, -1, NULL, 0);

	/* Start main loop. */
	proc_loop(client_proc, NULL);

	/* Run command if user requested exec, instead of exiting. */
	if (client_exittype == MSG_EXEC) {
		if (client_flags & CLIENT_CONTROLCONTROL)
			tcsetattr(STDOUT_FILENO, TCSAFLUSH, &saved_tio);
		client_exec(client_execshell, client_execcmd);
	}

	/* Print the exit message, if any, and exit. */
	if (client_attached) {
		if (client_exitreason != CLIENT_EXIT_NONE)
			printf("[%s]\n", client_exit_message());

		ppid = getppid();
		if (client_exittype == MSG_DETACHKILL && ppid > 1)
			kill(ppid, SIGHUP);
	} else if (client_flags & CLIENT_CONTROLCONTROL) {
		if (client_exitreason != CLIENT_EXIT_NONE)
			printf("%%exit %s\n", client_exit_message());
		else
			printf("%%exit\n");
		printf("\033\\");
		tcsetattr(STDOUT_FILENO, TCSAFLUSH, &saved_tio);
	} else if (client_exitreason != CLIENT_EXIT_NONE)
		fprintf(stderr, "%s\n", client_exit_message());
	setblocking(STDIN_FILENO, 1);
	return (client_exitval);
}

/* Send identify messages to server. */
static void
client_send_identify(const char *ttynam, const char *cwd)
{
	const char	 *s;
	char		**ss;
	size_t		  sslen;
	int		  fd, flags = client_flags;
	pid_t		  pid;

	proc_send(client_peer, MSG_IDENTIFY_FLAGS, -1, &flags, sizeof flags);

	if ((s = getenv("TERM")) == NULL)
		s = "";
	proc_send(client_peer, MSG_IDENTIFY_TERM, -1, s, strlen(s) + 1);

	proc_send(client_peer, MSG_IDENTIFY_TTYNAME, -1, ttynam,
	    strlen(ttynam) + 1);
	proc_send(client_peer, MSG_IDENTIFY_CWD, -1, cwd, strlen(cwd) + 1);

	if ((fd = dup(STDIN_FILENO)) == -1)
		fatal("dup failed");
	proc_send(client_peer, MSG_IDENTIFY_STDIN, fd, NULL, 0);

	pid = getpid();
	proc_send(client_peer, MSG_IDENTIFY_CLIENTPID, -1, &pid, sizeof pid);

	for (ss = environ; *ss != NULL; ss++) {
		sslen = strlen(*ss) + 1;
		if (sslen > MAX_IMSGSIZE - IMSG_HEADER_SIZE)
			continue;
		proc_send(client_peer, MSG_IDENTIFY_ENVIRON, -1, *ss, sslen);
	}

	proc_send(client_peer, MSG_IDENTIFY_DONE, -1, NULL, 0);
}

/* File write error callback. */
static void
client_write_error_callback(__unused struct bufferevent *bev,
    __unused short what, void *arg)
{
	struct client_file	*cf = arg;

	log_debug("write error file %d", cf->stream);

	bufferevent_free(cf->event);
	cf->event = NULL;

	close(cf->fd);
	cf->fd = -1;

	if (client_exitflag)
		client_exit();
}

/* File write callback. */
static void
client_write_callback(__unused struct bufferevent *bev, void *arg)
{
	struct client_file	*cf = arg;

	if (cf->closed && EVBUFFER_LENGTH(cf->event->output) == 0) {
		bufferevent_free(cf->event);
		close(cf->fd);
		RB_REMOVE(client_files, &client_files, cf);
		file_free(cf);
	}

	if (client_exitflag)
		client_exit();
}

/* Open write file. */
static void
client_write_open(void *data, size_t datalen)
{
	struct msg_write_open	*msg = data;
	const char		*path;
	struct msg_write_ready	 reply;
	struct client_file	 find, *cf;
	const int		 flags = O_NONBLOCK|O_WRONLY|O_CREAT;
	int			 error = 0;

	if (datalen < sizeof *msg)
		fatalx("bad MSG_WRITE_OPEN size");
	if (datalen == sizeof *msg)
		path = "-";
	else
		path = (const char *)(msg + 1);
	log_debug("open write file %d %s", msg->stream, path);

	find.stream = msg->stream;
	if ((cf = RB_FIND(client_files, &client_files, &find)) == NULL) {
		cf = file_create(NULL, msg->stream, NULL, NULL);
		RB_INSERT(client_files, &client_files, cf);
	} else {
		error = EBADF;
		goto reply;
	}
	if (cf->closed) {
		error = EBADF;
		goto reply;
	}

	cf->fd = -1;
	if (msg->fd == -1)
		cf->fd = open(path, msg->flags|flags, 0644);
	else {
		if (msg->fd != STDOUT_FILENO && msg->fd != STDERR_FILENO)
			errno = EBADF;
		else {
			cf->fd = dup(msg->fd);
			if (client_flags & CLIENT_CONTROL)
				close(msg->fd); /* can only be used once */
		}
	}
	if (cf->fd == -1) {
		error = errno;
		goto reply;
	}

	cf->event = bufferevent_new(cf->fd, NULL, client_write_callback,
	    client_write_error_callback, cf);
	bufferevent_enable(cf->event, EV_WRITE);
	goto reply;

reply:
	reply.stream = msg->stream;
	reply.error = error;
	proc_send(client_peer, MSG_WRITE_READY, -1, &reply, sizeof reply);
}

/* Write to client file. */
static void
client_write_data(void *data, size_t datalen)
{
	struct msg_write_data	*msg = data;
	struct client_file	 find, *cf;
	size_t			 size = datalen - sizeof *msg;

	if (datalen < sizeof *msg)
		fatalx("bad MSG_WRITE size");
	find.stream = msg->stream;
	if ((cf = RB_FIND(client_files, &client_files, &find)) == NULL)
		fatalx("unknown stream number");
	log_debug("write %zu to file %d", size, cf->stream);

	if (cf->event != NULL)
		bufferevent_write(cf->event, msg + 1, size);
}

/* Close client file. */
static void
client_write_close(void *data, size_t datalen)
{
	struct msg_write_close	*msg = data;
	struct client_file	 find, *cf;

	if (datalen != sizeof *msg)
		fatalx("bad MSG_WRITE_CLOSE size");
	find.stream = msg->stream;
	if ((cf = RB_FIND(client_files, &client_files, &find)) == NULL)
		fatalx("unknown stream number");
	log_debug("close file %d", cf->stream);

	if (cf->event == NULL || EVBUFFER_LENGTH(cf->event->output) == 0) {
		if (cf->event != NULL)
			bufferevent_free(cf->event);
		if (cf->fd != -1)
			close(cf->fd);
		RB_REMOVE(client_files, &client_files, cf);
		file_free(cf);
	}
}

/* File read callback. */
static void
client_read_callback(__unused struct bufferevent *bev, void *arg)
{
	struct client_file	*cf = arg;
	void			*bdata;
	size_t			 bsize;
	struct msg_read_data	*msg;
	size_t			 msglen;

	msg = xmalloc(sizeof *msg);
	for (;;) {
		bdata = EVBUFFER_DATA(cf->event->input);
		bsize = EVBUFFER_LENGTH(cf->event->input);

		if (bsize == 0)
			break;
		if (bsize > MAX_IMSGSIZE - IMSG_HEADER_SIZE - sizeof *msg)
			bsize = MAX_IMSGSIZE - IMSG_HEADER_SIZE - sizeof *msg;
		log_debug("read %zu from file %d", bsize, cf->stream);

		msglen = (sizeof *msg) + bsize;
		msg = xrealloc(msg, msglen);
		msg->stream = cf->stream;
		memcpy(msg + 1, bdata, bsize);
		proc_send(client_peer, MSG_READ, -1, msg, msglen);

		evbuffer_drain(cf->event->input, bsize);
	}
	free(msg);
}

/* File read error callback. */
static void
client_read_error_callback(__unused struct bufferevent *bev,
    __unused short what, void *arg)
{
	struct client_file	*cf = arg;
	struct msg_read_done	 msg;

	log_debug("read error file %d", cf->stream);

	msg.stream = cf->stream;
	msg.error = 0;
	proc_send(client_peer, MSG_READ_DONE, -1, &msg, sizeof msg);

	bufferevent_free(cf->event);
	close(cf->fd);
	RB_REMOVE(client_files, &client_files, cf);
	file_free(cf);
}

/* Open read file. */
static void
client_read_open(void *data, size_t datalen)
{
	struct msg_read_open	*msg = data;
	const char		*path;
	struct msg_read_done	 reply;
	struct client_file	 find, *cf;
	const int		 flags = O_NONBLOCK|O_RDONLY;
	int			 error;

	if (datalen < sizeof *msg)
		fatalx("bad MSG_READ_OPEN size");
	if (datalen == sizeof *msg)
		path = "-";
	else
		path = (const char *)(msg + 1);
	log_debug("open read file %d %s", msg->stream, path);

	find.stream = msg->stream;
	if ((cf = RB_FIND(client_files, &client_files, &find)) == NULL) {
		cf = file_create(NULL, msg->stream, NULL, NULL);
		RB_INSERT(client_files, &client_files, cf);
	} else {
		error = EBADF;
		goto reply;
	}
	if (cf->closed) {
		error = EBADF;
		goto reply;
	}

	cf->fd = -1;
	if (msg->fd == -1)
		cf->fd = open(path, flags);
	else {
		if (msg->fd != STDIN_FILENO)
			errno = EBADF;
		else {
			cf->fd = dup(msg->fd);
			close(msg->fd); /* can only be used once */
		}
	}
	if (cf->fd == -1) {
		error = errno;
		goto reply;
	}

	cf->event = bufferevent_new(cf->fd, client_read_callback, NULL,
	    client_read_error_callback, cf);
	bufferevent_enable(cf->event, EV_READ);
	return;

reply:
	reply.stream = msg->stream;
	reply.error = error;
	proc_send(client_peer, MSG_READ_DONE, -1, &reply, sizeof reply);
}

/* Run command in shell; used for -c. */
static __dead void
client_exec(const char *shell, const char *shellcmd)
{
	const char	*name, *ptr;
	char		*argv0;

	log_debug("shell %s, command %s", shell, shellcmd);

	ptr = strrchr(shell, '/');
	if (ptr != NULL && *(ptr + 1) != '\0')
		name = ptr + 1;
	else
		name = shell;
	if (client_flags & CLIENT_LOGIN)
		xasprintf(&argv0, "-%s", name);
	else
		xasprintf(&argv0, "%s", name);
	setenv("SHELL", shell, 1);

	proc_clear_signals(client_proc, 1);

	setblocking(STDIN_FILENO, 1);
	setblocking(STDOUT_FILENO, 1);
	setblocking(STDERR_FILENO, 1);
	closefrom(STDERR_FILENO + 1);

	execl(shell, argv0, "-c", shellcmd, (char *) NULL);
	fatal("execl failed");
}

/* Callback to handle signals in the client. */
static void
client_signal(int sig)
{
	struct sigaction sigact;
	int		 status;

	if (sig == SIGCHLD)
		waitpid(WAIT_ANY, &status, WNOHANG);
	else if (!client_attached) {
		if (sig == SIGTERM)
			proc_exit(client_proc);
	} else {
		switch (sig) {
		case SIGHUP:
			client_exitreason = CLIENT_EXIT_LOST_TTY;
			client_exitval = 1;
			proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
			break;
		case SIGTERM:
			client_exitreason = CLIENT_EXIT_TERMINATED;
			client_exitval = 1;
			proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
			break;
		case SIGWINCH:
			proc_send(client_peer, MSG_RESIZE, -1, NULL, 0);
			break;
		case SIGCONT:
			memset(&sigact, 0, sizeof sigact);
			sigemptyset(&sigact.sa_mask);
			sigact.sa_flags = SA_RESTART;
			sigact.sa_handler = SIG_IGN;
			if (sigaction(SIGTSTP, &sigact, NULL) != 0)
				fatal("sigaction failed");
			proc_send(client_peer, MSG_WAKEUP, -1, NULL, 0);
			break;
		}
	}
}

/* Callback for client read events. */
static void
client_dispatch(struct imsg *imsg, __unused void *arg)
{
	if (imsg == NULL) {
		client_exitreason = CLIENT_EXIT_LOST_SERVER;
		client_exitval = 1;
		proc_exit(client_proc);
		return;
	}

	if (client_attached)
		client_dispatch_attached(imsg);
	else
		client_dispatch_wait(imsg);
}

/* Dispatch imsgs when in wait state (before MSG_READY). */
static void
client_dispatch_wait(struct imsg *imsg)
{
	char		*data;
	ssize_t		 datalen;
	int		 retval;
	static int	 pledge_applied;

	/*
	 * "sendfd" is no longer required once all of the identify messages
	 * have been sent. We know the server won't send us anything until that
	 * point (because we don't ask it to), so we can drop "sendfd" once we
	 * get the first message from the server.
	 */
	if (!pledge_applied) {
		if (pledge(
		    "stdio rpath wpath cpath unix proc exec tty",
		    NULL) != 0)
			fatal("pledge failed");
		pledge_applied = 1;
	}

	data = imsg->data;
	datalen = imsg->hdr.len - IMSG_HEADER_SIZE;

	switch (imsg->hdr.type) {
	case MSG_EXIT:
	case MSG_SHUTDOWN:
		if (datalen != sizeof retval && datalen != 0)
			fatalx("bad MSG_EXIT size");
		if (datalen == sizeof retval) {
			memcpy(&retval, data, sizeof retval);
			client_exitval = retval;
		}
		client_exitflag = 1;
		client_exit();
		break;
	case MSG_READY:
		if (datalen != 0)
			fatalx("bad MSG_READY size");

		client_attached = 1;
		proc_send(client_peer, MSG_RESIZE, -1, NULL, 0);
		break;
	case MSG_VERSION:
		if (datalen != 0)
			fatalx("bad MSG_VERSION size");

		fprintf(stderr, "protocol version mismatch "
		    "(client %d, server %u)\n", PROTOCOL_VERSION,
		    imsg->hdr.peerid & 0xff);
		client_exitval = 1;
		proc_exit(client_proc);
		break;
	case MSG_SHELL:
		if (datalen == 0 || data[datalen - 1] != '\0')
			fatalx("bad MSG_SHELL string");

		client_exec(data, shell_command);
		/* NOTREACHED */
	case MSG_DETACH:
	case MSG_DETACHKILL:
		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
		break;
	case MSG_EXITED:
		proc_exit(client_proc);
		break;
	case MSG_READ_OPEN:
		client_read_open(data, datalen);
		break;
	case MSG_WRITE_OPEN:
		client_write_open(data, datalen);
		break;
	case MSG_WRITE:
		client_write_data(data, datalen);
		break;
	case MSG_WRITE_CLOSE:
		client_write_close(data, datalen);
		break;
	case MSG_OLDSTDERR:
	case MSG_OLDSTDIN:
	case MSG_OLDSTDOUT:
		fprintf(stderr, "server version is too old for client\n");
		proc_exit(client_proc);
		break;
	}
}

/* Dispatch imsgs in attached state (after MSG_READY). */
static void
client_dispatch_attached(struct imsg *imsg)
{
	struct sigaction	 sigact;
	char			*data;
	ssize_t			 datalen;

	data = imsg->data;
	datalen = imsg->hdr.len - IMSG_HEADER_SIZE;

	switch (imsg->hdr.type) {
	case MSG_DETACH:
	case MSG_DETACHKILL:
		if (datalen == 0 || data[datalen - 1] != '\0')
			fatalx("bad MSG_DETACH string");

		client_exitsession = xstrdup(data);
		client_exittype = imsg->hdr.type;
		if (imsg->hdr.type == MSG_DETACHKILL)
			client_exitreason = CLIENT_EXIT_DETACHED_HUP;
		else
			client_exitreason = CLIENT_EXIT_DETACHED;
		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
		break;
	case MSG_EXEC:
		if (datalen == 0 || data[datalen - 1] != '\0' ||
		    strlen(data) + 1 == (size_t)datalen)
			fatalx("bad MSG_EXEC string");
		client_execcmd = xstrdup(data);
		client_execshell = xstrdup(data + strlen(data) + 1);

		client_exittype = imsg->hdr.type;
		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
		break;
	case MSG_EXIT:
		if (datalen != 0 && datalen != sizeof (int))
			fatalx("bad MSG_EXIT size");

		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
		client_exitreason = CLIENT_EXIT_EXITED;
		break;
	case MSG_EXITED:
		if (datalen != 0)
			fatalx("bad MSG_EXITED size");

		proc_exit(client_proc);
		break;
	case MSG_SHUTDOWN:
		if (datalen != 0)
			fatalx("bad MSG_SHUTDOWN size");

		proc_send(client_peer, MSG_EXITING, -1, NULL, 0);
		client_exitreason = CLIENT_EXIT_SERVER_EXITED;
		client_exitval = 1;
		break;
	case MSG_SUSPEND:
		if (datalen != 0)
			fatalx("bad MSG_SUSPEND size");

		memset(&sigact, 0, sizeof sigact);
		sigemptyset(&sigact.sa_mask);
		sigact.sa_flags = SA_RESTART;
		sigact.sa_handler = SIG_DFL;
		if (sigaction(SIGTSTP, &sigact, NULL) != 0)
			fatal("sigaction failed");
		kill(getpid(), SIGTSTP);
		break;
	case MSG_LOCK:
		if (datalen == 0 || data[datalen - 1] != '\0')
			fatalx("bad MSG_LOCK string");

		system(data);
		proc_send(client_peer, MSG_UNLOCK, -1, NULL, 0);
		break;
	}
}