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If stdin in the client is enable immediately, tmux will eat anything
sent to stdin before it is needed, which can be inconvenient (eg pasting
commands). Instead, start with stdin disabled and reuse MSG_STDIN from
server->client to mean that stdin should be enabled. Based on a diff
from Chris Johnsen.

/* $OpenBSD: client.c,v 1.60 2012/09/03 08:48:57 nicm Exp $ */

/*
 * Copyright (c) 2007 Nicholas Marriott <nicm@users.sourceforge.net>
 *
 * 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/file.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 <pwd.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "tmux.h"

struct imsgbuf	client_ibuf;
struct event	client_event;
struct event	client_stdin;
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;
int		client_exitval;
enum msgtype	client_exittype;
int		client_attached;

int		client_get_lock(char *);
int		client_connect(char *, int);
void		client_send_identify(int);
void		client_send_environ(void);
void		client_write_server(enum msgtype, void *, size_t);
void		client_update_event(void);
void		client_signal(int, short, void *);
void		client_stdin_callback(int, short, void *);
void		client_write(int, const char *, size_t);
void		client_callback(int, short, void *);
int		client_dispatch_attached(void);
int		client_dispatch_wait(void *);
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 -1 to
 * retry. Ignore other errors - just continue and start the server without the
 * lock.
 */
int
client_get_lock(char *lockfile)
{
	int lockfd;

	if ((lockfd = open(lockfile, O_WRONLY|O_CREAT, 0600)) == -1)
		fatal("open failed");

	if (flock(lockfd, LOCK_EX|LOCK_NB) == -1 && errno == EWOULDBLOCK) {
		while (flock(lockfd, LOCK_EX) == -1 && errno == EINTR)
			/* nothing */;
		close(lockfd);
		return (-1);
	}

	return (lockfd);
}

/* Connect client to server. */
int
client_connect(char *path, int start_server)
{
	struct sockaddr_un	sa;
	size_t			size;
	int			fd, lockfd;
	char		       *lockfile;

	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);
	}

retry:
	if ((fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1)
		fatal("socket failed");

	if (connect(fd, (struct sockaddr *) &sa, SUN_LEN(&sa)) == -1) {
		if (errno != ECONNREFUSED && errno != ENOENT)
			goto failed;
		if (!start_server)
			goto failed;
		close(fd);

		xasprintf(&lockfile, "%s.lock", path);
		if ((lockfd = client_get_lock(lockfile)) == -1)
			goto retry;
		if (unlink(path) != 0 && errno != ENOENT)
			return (-1);
		fd = server_start(lockfd, lockfile);
		free(lockfile);
		close(lockfd);
	}

	setblocking(fd, 0);
	return (fd);

failed:
	close(fd);
	return (-1);
}

/* Get exit string from reason number. */
const char *
client_exit_message(void)
{
	switch (client_exitreason) {
	case CLIENT_EXIT_NONE:
		break;
	case CLIENT_EXIT_DETACHED:
		return ("detached");
	case CLIENT_EXIT_DETACHED_HUP:
		return ("detached and SIGHUP");
	case CLIENT_EXIT_LOST_TTY:
		return ("lost tty");
	case CLIENT_EXIT_TERMINATED:
		return ("terminated");
	case CLIENT_EXIT_LOST_SERVER:
		return ("lost server");
	case CLIENT_EXIT_EXITED:
		return ("exited");
	case CLIENT_EXIT_SERVER_EXITED:
		return ("server exited");
	}
	return ("unknown reason");
}

/* Client main loop. */
int
client_main(int argc, char **argv, int flags)
{
	struct cmd		*cmd;
	struct cmd_list		*cmdlist;
	struct msg_command_data	 cmddata;
	int			 cmdflags, fd;
	pid_t			 ppid;
	enum msgtype		 msg;
	char			*cause;
	struct termios		 tio, saved_tio;

	/* Set up the initial command. */
	cmdflags = 0;
	if (shell_cmd != NULL) {
		msg = MSG_SHELL;
		cmdflags = CMD_STARTSERVER;
	} else if (argc == 0) {
		msg = MSG_COMMAND;
		cmdflags = CMD_STARTSERVER|CMD_SENDENVIRON|CMD_CANTNEST;
	} 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.
		 */
		if ((cmdlist = cmd_list_parse(argc, argv, &cause)) == NULL) {
			fprintf(stderr, "%s\n", cause);
			return (1);
		}
		cmdflags &= ~CMD_STARTSERVER;
		TAILQ_FOREACH(cmd, &cmdlist->list, qentry) {
			if (cmd->entry->flags & CMD_STARTSERVER)
				cmdflags |= CMD_STARTSERVER;
			if (cmd->entry->flags & CMD_SENDENVIRON)
				cmdflags |= CMD_SENDENVIRON;
			if (cmd->entry->flags & CMD_CANTNEST)
				cmdflags |= CMD_CANTNEST;
		}
		cmd_list_free(cmdlist);
	}

	/*
	 * Check if this could be a nested session, if the command can't nest:
	 * if the socket path matches $TMUX, this is probably the same server.
	 */
	if (shell_cmd == NULL && environ_path != NULL &&
	    (cmdflags & CMD_CANTNEST) &&
	    strcmp(socket_path, environ_path) == 0) {
		fprintf(stderr, "sessions should be nested with care, "
		    "unset $TMUX to force\n");
		return (1);
	}

	/* Initialise the client socket and start the server. */
	fd = client_connect(socket_path, cmdflags & CMD_STARTSERVER);
	if (fd == -1) {
		fprintf(stderr, "failed to connect to server\n");
		return (1);
	}

	/* Set process title, log and signals now this is the client. */
	setproctitle("client (%s)", socket_path);
	logfile("client");

	/* Create imsg. */
	imsg_init(&client_ibuf, fd);
	event_set(&client_event, fd, EV_READ, client_callback, shell_cmd);

	/* Create stdin handler. */
	setblocking(STDIN_FILENO, 0);
	event_set(&client_stdin, STDIN_FILENO, EV_READ|EV_PERSIST,
	    client_stdin_callback, NULL);
	if (flags & IDENTIFY_TERMIOS) {
		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);
	}

	/* Establish signal handlers. */
	set_signals(client_signal);

	/* Send initial environment. */
	if (cmdflags & CMD_SENDENVIRON)
		client_send_environ();
	client_send_identify(flags);

	/* Send first command. */
	if (msg == MSG_COMMAND) {
		/* Fill in command line arguments. */
		cmddata.pid = environ_pid;
		cmddata.idx = environ_idx;

		/* Prepare command for server. */
		cmddata.argc = argc;
		if (cmd_pack_argv(
		    argc, argv, cmddata.argv, sizeof cmddata.argv) != 0) {
			fprintf(stderr, "command too long\n");
			return (1);
		}

		client_write_server(msg, &cmddata, sizeof cmddata);
	} else if (msg == MSG_SHELL)
		client_write_server(msg, NULL, 0);

	/* Set the event and dispatch. */
	client_update_event();
	event_dispatch();

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

		ppid = getppid();
		if (client_exittype == MSG_DETACHKILL && ppid > 1)
			kill(ppid, SIGHUP);
	} else if (flags & IDENTIFY_TERMIOS)
		tcsetattr(STDOUT_FILENO, TCSAFLUSH, &saved_tio);
	setblocking(STDIN_FILENO, 1);
	return (client_exitval);
}

/* Send identify message to server with the file descriptors. */
void
client_send_identify(int flags)
{
	struct msg_identify_data	data;
	char			       *term;
	int				fd;

	data.flags = flags;

	if (getcwd(data.cwd, sizeof data.cwd) == NULL)
		*data.cwd = '\0';

	term = getenv("TERM");
	if (term == NULL ||
	    strlcpy(data.term, term, sizeof data.term) >= sizeof data.term)
		*data.term = '\0';

	if ((fd = dup(STDIN_FILENO)) == -1)
		fatal("dup failed");
	imsg_compose(&client_ibuf,
	    MSG_IDENTIFY, PROTOCOL_VERSION, -1, fd, &data, sizeof data);
	client_update_event();
}

/* Forward entire environment to server. */
void
client_send_environ(void)
{
	struct msg_environ_data	data;
	char		      **var;

	for (var = environ; *var != NULL; var++) {
		if (strlcpy(data.var, *var, sizeof data.var) >= sizeof data.var)
			continue;
		client_write_server(MSG_ENVIRON, &data, sizeof data);
	}
}

/* Write a message to the server without a file descriptor. */
void
client_write_server(enum msgtype type, void *buf, size_t len)
{
	imsg_compose(&client_ibuf, type, PROTOCOL_VERSION, -1, -1, buf, len);
	client_update_event();
}

/* Update client event based on whether it needs to read or read and write. */
void
client_update_event(void)
{
	short	events;

	event_del(&client_event);
	events = EV_READ;
	if (client_ibuf.w.queued > 0)
		events |= EV_WRITE;
	event_set(
	    &client_event, client_ibuf.fd, events, client_callback, shell_cmd);
	event_add(&client_event, NULL);
}

/* Callback to handle signals in the client. */
/* ARGSUSED */
void
client_signal(int sig, unused short events, unused void *data)
{
	struct sigaction sigact;
	int		 status;

	if (!client_attached) {
		switch (sig) {
		case SIGCHLD:
			waitpid(WAIT_ANY, &status, WNOHANG);
			break;
		case SIGTERM:
			event_loopexit(NULL);
			break;
		}
	} else {
		switch (sig) {
		case SIGHUP:
			client_exitreason = CLIENT_EXIT_LOST_TTY;
			client_exitval = 1;
			client_write_server(MSG_EXITING, NULL, 0);
			break;
		case SIGTERM:
			client_exitreason = CLIENT_EXIT_TERMINATED;
			client_exitval = 1;
			client_write_server(MSG_EXITING, NULL, 0);
			break;
		case SIGWINCH:
			client_write_server(MSG_RESIZE, 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");
			client_write_server(MSG_WAKEUP, NULL, 0);
			break;
		}
	}

	client_update_event();
}

/* Callback for client imsg read events. */
/* ARGSUSED */
void
client_callback(unused int fd, short events, void *data)
{
	ssize_t	n;
	int	retval;

	if (events & EV_READ) {
		if ((n = imsg_read(&client_ibuf)) == -1 || n == 0)
			goto lost_server;
		if (client_attached)
			retval = client_dispatch_attached();
		else
			retval = client_dispatch_wait(data);
		if (retval != 0) {
			event_loopexit(NULL);
			return;
		}
	}

	if (events & EV_WRITE) {
		if (msgbuf_write(&client_ibuf.w) < 0)
			goto lost_server;
	}

	client_update_event();
	return;

lost_server:
	client_exitreason = CLIENT_EXIT_LOST_SERVER;
	client_exitval = 1;
	event_loopexit(NULL);
}

/* Callback for client stdin read events. */
/* ARGSUSED */
void
client_stdin_callback(unused int fd, unused short events, unused void *data1)
{
	struct msg_stdin_data	data;

	data.size = read(STDIN_FILENO, data.data, sizeof data.data);
	if (data.size < 0 && (errno == EINTR || errno == EAGAIN))
		return;

	client_write_server(MSG_STDIN, &data, sizeof data);
	if (data.size <= 0)
		event_del(&client_stdin);
	client_update_event();
}

/* Force write to file descriptor. */
void
client_write(int fd, const char *data, size_t size)
{
	ssize_t	used;

	while (size != 0) {
		used = write(fd, data, size);
		if (used == -1) {
			if (errno == EINTR || errno == EAGAIN)
				continue;
			break;
		}
		data += used;
		size -= used;
	}
}

/* Dispatch imsgs when in wait state (before MSG_READY). */
int
client_dispatch_wait(void *data)
{
	struct imsg		imsg;
	ssize_t			n, datalen;
	struct msg_shell_data	shelldata;
	struct msg_exit_data	exitdata;
	struct msg_stdout_data	stdoutdata;
	struct msg_stderr_data	stderrdata;
	const char             *shellcmd = data;

	for (;;) {
		if ((n = imsg_get(&client_ibuf, &imsg)) == -1)
			fatalx("imsg_get failed");
		if (n == 0)
			return (0);
		datalen = imsg.hdr.len - IMSG_HEADER_SIZE;

		log_debug("got %d from server", imsg.hdr.type);
		switch (imsg.hdr.type) {
		case MSG_EXIT:
		case MSG_SHUTDOWN:
			if (datalen != sizeof exitdata) {
				if (datalen != 0)
					fatalx("bad MSG_EXIT size");
			} else {
				memcpy(&exitdata, imsg.data, sizeof exitdata);
				client_exitval = exitdata.retcode;
			}
			imsg_free(&imsg);
			return (-1);
		case MSG_READY:
			if (datalen != 0)
				fatalx("bad MSG_READY size");

			event_del(&client_stdin);
			client_attached = 1;
			break;
		case MSG_STDIN:
			if (datalen != 0)
				fatalx("bad MSG_STDIN size");

			event_add(&client_stdin, NULL);
			break;
		case MSG_STDOUT:
			if (datalen != sizeof stdoutdata)
				fatalx("bad MSG_STDOUT");
			memcpy(&stdoutdata, imsg.data, sizeof stdoutdata);

			client_write(STDOUT_FILENO, stdoutdata.data, stdoutdata.size);
			break;
		case MSG_STDERR:
			if (datalen != sizeof stderrdata)
				fatalx("bad MSG_STDERR");
			memcpy(&stderrdata, imsg.data, sizeof stderrdata);

			client_write(STDERR_FILENO, stderrdata.data, stderrdata.size);
			break;
		case MSG_VERSION:
			if (datalen != 0)
				fatalx("bad MSG_VERSION size");

			fprintf(stderr, "protocol version mismatch "
			    "(client %u, server %u)\n", PROTOCOL_VERSION,
			    imsg.hdr.peerid);
			client_exitval = 1;

			imsg_free(&imsg);
			return (-1);
		case MSG_SHELL:
			if (datalen != sizeof shelldata)
				fatalx("bad MSG_SHELL size");
			memcpy(&shelldata, imsg.data, sizeof shelldata);
			shelldata.shell[(sizeof shelldata.shell) - 1] = '\0';

			clear_signals(0);

			shell_exec(shelldata.shell, shellcmd);
			/* NOTREACHED */
		case MSG_DETACH:
			client_write_server(MSG_EXITING, NULL, 0);
			break;
		case MSG_EXITED:
			imsg_free(&imsg);
			return (-1);
		default:
			fatalx("unexpected message");
		}

		imsg_free(&imsg);
	}
}

/* Dispatch imsgs in attached state (after MSG_READY). */
/* ARGSUSED */
int
client_dispatch_attached(void)
{
	struct imsg		imsg;
	struct msg_lock_data	lockdata;
	struct sigaction	sigact;
	ssize_t			n, datalen;

	for (;;) {
		if ((n = imsg_get(&client_ibuf, &imsg)) == -1)
			fatalx("imsg_get failed");
		if (n == 0)
			return (0);
		datalen = imsg.hdr.len - IMSG_HEADER_SIZE;

		log_debug("got %d from server", imsg.hdr.type);
		switch (imsg.hdr.type) {
		case MSG_DETACHKILL:
		case MSG_DETACH:
			if (datalen != 0)
				fatalx("bad MSG_DETACH size");

			client_exittype = imsg.hdr.type;
			if (imsg.hdr.type == MSG_DETACHKILL)
				client_exitreason = CLIENT_EXIT_DETACHED_HUP;
			else
				client_exitreason = CLIENT_EXIT_DETACHED;
			client_write_server(MSG_EXITING, NULL, 0);
			break;
		case MSG_EXIT:
			if (datalen != 0 &&
			    datalen != sizeof (struct msg_exit_data))
				fatalx("bad MSG_EXIT size");

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

			imsg_free(&imsg);
			return (-1);
		case MSG_SHUTDOWN:
			if (datalen != 0)
				fatalx("bad MSG_SHUTDOWN size");

			client_write_server(MSG_EXITING, 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 != sizeof lockdata)
				fatalx("bad MSG_LOCK size");
			memcpy(&lockdata, imsg.data, sizeof lockdata);

			lockdata.cmd[(sizeof lockdata.cmd) - 1] = '\0';
			system(lockdata.cmd);
			client_write_server(MSG_UNLOCK, NULL, 0);
			break;
		default:
			fatalx("unexpected message");
		}

		imsg_free(&imsg);
	}
}