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We accidentally haven't been using $TMUX to work out the session for a
while and in fact it is less useful that using the client ttyname. So
don't bother and don't pass it from the client. If we need it in future
it is in c->environ.

/* $OpenBSD: client.c,v 1.74 2013/10/10 12:29:35 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;
const char     *client_exitsession;
int		client_attached;

int		client_get_lock(char *);
int		client_connect(char *, int);
void		client_send_identify(int);
int		client_write_one(enum msgtype, int, const void *, size_t);
int		client_write_server(enum msgtype, const 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 (lockf(lockfd, F_TLOCK, 0) == -1 && errno == EAGAIN) {
		while (lockf(lockfd, F_LOCK, 0) == -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)
{
	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 ("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	*data;
	int			 cmdflags, fd, i;
	pid_t			 ppid;
	enum msgtype		 msg;
	char			*cause;
	struct termios		 tio, saved_tio;
	size_t			 size;

	/* 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_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.
		 */
		cmdlist = cmd_list_parse(argc, argv, NULL, 0, &cause);
		if (cmdlist == 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_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 & 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);
	}

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

	/* Send identify messages. */
	client_send_identify(flags);

	/* 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;
		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 (client_write_server(msg, data, size) != 0) {
			fprintf(stderr, "failed to send command\n");
			free(data);
			return (1);
		}
		free(data);
	} 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 & 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);
	}
	setblocking(STDIN_FILENO, 1);
	return (client_exitval);
}

/* Send identify messages to server. */
void
client_send_identify(int flags)
{
	const char	*s;
	char		**ss;
	int		 fd;

	client_write_one(MSG_IDENTIFY_FLAGS, -1, &flags, sizeof flags);

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

	if ((s = ttyname(STDIN_FILENO)) == NULL)
		s = "";
	client_write_one(MSG_IDENTIFY_TTYNAME, -1, s, strlen(s) + 1);

	if ((fd = open(".", O_RDONLY)) == -1)
		fd = open("/", O_RDONLY);
	client_write_one(MSG_IDENTIFY_CWD, fd, NULL, 0);

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

	for (ss = environ; *ss != NULL; ss++)
		client_write_one(MSG_IDENTIFY_ENVIRON, -1, *ss, strlen(*ss) + 1);
	client_write_one(MSG_IDENTIFY_DONE, -1, NULL, 0);

	client_update_event();
}

/* Helper to send one message. */
int
client_write_one(enum msgtype type, int fd, const void *buf, size_t len)
{
	int	retval;

	retval = imsg_compose(&client_ibuf, type, PROTOCOL_VERSION, -1, fd,
	    (void*)buf, len);
	if (retval != 1)
		return (-1);
	return (0);
}

/* Write a message to the server without a file descriptor. */
int
client_write_server(enum msgtype type, const void *buf, size_t len)
{
	int	retval;

	retval = client_write_one(type, -1, buf, len);
	if (retval == 0)
		client_update_event();
	return (retval);
}

/* 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. */
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. */
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. */
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 *data0)
{
	struct imsg		 imsg;
	char			*data;
	ssize_t			 n, datalen;
	struct msg_stdout_data	 stdoutdata;
	struct msg_stderr_data	 stderrdata;
	int			 retval;

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

		data = imsg.data;
		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 retval && datalen != 0)
				fatalx("bad MSG_EXIT size");
			if (datalen == sizeof retval) {
				memcpy(&retval, data, sizeof retval);
				client_exitval = retval;
			}
			imsg_free(&imsg);
			return (-1);
		case MSG_READY:
			if (datalen != 0)
				fatalx("bad MSG_READY size");

			event_del(&client_stdin);
			client_attached = 1;
			client_write_server(MSG_RESIZE, NULL, 0);
			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 size");
			memcpy(&stdoutdata, data, sizeof stdoutdata);

			client_write(STDOUT_FILENO, stdoutdata.data,
			    stdoutdata.size);
			break;
		case MSG_STDERR:
			if (datalen != sizeof stderrdata)
				fatalx("bad MSG_STDERR size");
			memcpy(&stderrdata, 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 == 0 || data[datalen - 1] != '\0')
				fatalx("bad MSG_SHELL string");

			clear_signals(0);
			shell_exec(data, data0);
			/* NOTREACHED */
		case MSG_DETACH:
		case MSG_DETACHKILL:
			client_write_server(MSG_EXITING, NULL, 0);
			break;
		case MSG_EXITED:
			imsg_free(&imsg);
			return (-1);
		}

		imsg_free(&imsg);
	}
}

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

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

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

		log_debug("got %d from server", imsg.hdr.type);
		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;
			client_write_server(MSG_EXITING, NULL, 0);
			break;
		case MSG_EXIT:
			if (datalen != 0 && datalen != sizeof (int))
				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 == 0 || data[datalen - 1] != '\0')
				fatalx("bad MSG_LOCK string");

			system(data);
			client_write_server(MSG_UNLOCK, NULL, 0);
			break;
		}

		imsg_free(&imsg);
	}
}