clientloop.c

/*
 * 
 * clientloop.c
 * 
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * 
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * 
 * 
 * Created: Sat Sep 23 12:23:57 1995 ylo
 * 
 * The main loop for the interactive session (client side).
 * 
 */

#include "includes.h"
RCSID("$Id: clientloop.c,v 1.5 1999/11/24 13:26:22 damien Exp $");

#include "xmalloc.h"
#include "ssh.h"
#include "packet.h"
#include "buffer.h"
#include "authfd.h"
#include "readconf.h"

/* Flag indicating that stdin should be redirected from /dev/null. */
extern int stdin_null_flag;

/* Name of the host we are connecting to.  This is the name given on the
   command line, or the HostName specified for the user-supplied name
   in a configuration file. */
extern char *host;

/* Flag to indicate that we have received a window change signal which has
   not yet been processed.  This will cause a message indicating the new
   window size to be sent to the server a little later.  This is volatile
   because this is updated in a signal handler. */
static volatile int received_window_change_signal = 0;

/* Terminal modes, as saved by enter_raw_mode. */
static struct termios saved_tio;

/* Flag indicating whether we are in raw mode.  This is used by enter_raw_mode
   and leave_raw_mode. */
static int in_raw_mode = 0;

/* Flag indicating whether the user\'s terminal is in non-blocking mode. */
static int in_non_blocking_mode = 0;

/* Common data for the client loop code. */
static int escape_pending;	/* Last character was the escape character */
static int last_was_cr;		/* Last character was a newline. */
static int exit_status;		/* Used to store the exit status of the command. */
static int stdin_eof;		/* EOF has been encountered on standard error. */
static Buffer stdin_buffer;	/* Buffer for stdin data. */
static Buffer stdout_buffer;	/* Buffer for stdout data. */
static Buffer stderr_buffer;	/* Buffer for stderr data. */
static unsigned int buffer_high;/* Soft max buffer size. */
static int max_fd;		/* Maximum file descriptor number in select(). */
static int connection_in;	/* Connection to server (input). */
static int connection_out;	/* Connection to server (output). */
static unsigned long stdin_bytes, stdout_bytes, stderr_bytes;
static int quit_pending;	/* Set to non-zero to quit the client loop. */
static int escape_char;		/* Escape character. */

/* Returns the user\'s terminal to normal mode if it had been put in raw
   mode. */

void 
leave_raw_mode()
{
	if (!in_raw_mode)
		return;
	in_raw_mode = 0;
	if (tcsetattr(fileno(stdin), TCSADRAIN, &saved_tio) < 0)
		perror("tcsetattr");

	fatal_remove_cleanup((void (*) (void *)) leave_raw_mode, NULL);
}

/* Puts the user\'s terminal in raw mode. */

void 
enter_raw_mode()
{
	struct termios tio;

	if (tcgetattr(fileno(stdin), &tio) < 0)
		perror("tcgetattr");
	saved_tio = tio;
	tio.c_iflag |= IGNPAR;
	tio.c_iflag &= ~(ISTRIP | INLCR | IGNCR | ICRNL | IXON | IXANY | IXOFF);
	tio.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL);
#ifdef IEXTEN
	tio.c_lflag &= ~IEXTEN;
#endif				/* IEXTEN */
	tio.c_oflag &= ~OPOST;
	tio.c_cc[VMIN] = 1;
	tio.c_cc[VTIME] = 0;
	if (tcsetattr(fileno(stdin), TCSADRAIN, &tio) < 0)
		perror("tcsetattr");
	in_raw_mode = 1;

	fatal_add_cleanup((void (*) (void *)) leave_raw_mode, NULL);
}

/* Restores stdin to blocking mode. */

void 
leave_non_blocking()
{
	if (in_non_blocking_mode) {
		(void) fcntl(fileno(stdin), F_SETFL, 0);
		in_non_blocking_mode = 0;
		fatal_remove_cleanup((void (*) (void *)) leave_non_blocking, NULL);
	}
}

/* Puts stdin terminal in non-blocking mode. */

void 
enter_non_blocking()
{
	in_non_blocking_mode = 1;
	(void) fcntl(fileno(stdin), F_SETFL, O_NONBLOCK);
	fatal_add_cleanup((void (*) (void *)) leave_non_blocking, NULL);
}

/* Signal handler for the window change signal (SIGWINCH).  This just
   sets a flag indicating that the window has changed. */

void 
window_change_handler(int sig)
{
	received_window_change_signal = 1;
	signal(SIGWINCH, window_change_handler);
}

/* Signal handler for signals that cause the program to terminate.  These
   signals must be trapped to restore terminal modes. */

void 
signal_handler(int sig)
{
	if (in_raw_mode)
		leave_raw_mode();
	if (in_non_blocking_mode)
		leave_non_blocking();
	channel_stop_listening();
	packet_close();
	fatal("Killed by signal %d.", sig);
}

/* Returns current time in seconds from Jan 1, 1970 with the maximum available
   resolution. */

double 
get_current_time()
{
	struct timeval tv;
	gettimeofday(&tv, NULL);
	return (double) tv.tv_sec + (double) tv.tv_usec / 1000000.0;
}

/* This is called when the interactive is entered.  This checks if there
   is an EOF coming on stdin.  We must check this explicitly, as select()
   does not appear to wake up when redirecting from /dev/null. */

void 
client_check_initial_eof_on_stdin()
{
	int len;
	char buf[1];

	/* If standard input is to be "redirected from /dev/null", we
	   simply mark that we have seen an EOF and send an EOF message to
	   the server. Otherwise, we try to read a single character; it
	   appears that for some files, such /dev/null, select() never
	   wakes up for read for this descriptor, which means that we
	   never get EOF.  This way we will get the EOF if stdin comes
	   from /dev/null or similar. */
	if (stdin_null_flag) {
		/* Fake EOF on stdin. */
		debug("Sending eof.");
		stdin_eof = 1;
		packet_start(SSH_CMSG_EOF);
		packet_send();
	} else {
		/* Enter non-blocking mode for stdin. */
		enter_non_blocking();

		/* Check for immediate EOF on stdin. */
		len = read(fileno(stdin), buf, 1);
		if (len == 0) {
			/* EOF.  Record that we have seen it and send EOF
			   to server. */
			debug("Sending eof.");
			stdin_eof = 1;
			packet_start(SSH_CMSG_EOF);
			packet_send();
		} else if (len > 0) {
			/* Got data.  We must store the data in the
			   buffer, and also process it as an escape
			   character if appropriate. */
			if ((unsigned char) buf[0] == escape_char)
				escape_pending = 1;
			else {
				buffer_append(&stdin_buffer, buf, 1);
				stdin_bytes += 1;
			}
		}
		/* Leave non-blocking mode. */
		leave_non_blocking();
	}
}

/* Get packets from the connection input buffer, and process them as long
   as there are packets available. */

void 
client_process_buffered_input_packets()
{
	int type;
	char *data;
	unsigned int data_len;
	int payload_len;

	/* Process any buffered packets from the server. */
	while (!quit_pending &&
	       (type = packet_read_poll(&payload_len)) != SSH_MSG_NONE) {
		switch (type) {

		case SSH_SMSG_STDOUT_DATA:
			data = packet_get_string(&data_len);
			packet_integrity_check(payload_len, 4 + data_len, type);
			buffer_append(&stdout_buffer, data, data_len);
			stdout_bytes += data_len;
			memset(data, 0, data_len);
			xfree(data);
			break;

		case SSH_SMSG_STDERR_DATA:
			data = packet_get_string(&data_len);
			packet_integrity_check(payload_len, 4 + data_len, type);
			buffer_append(&stderr_buffer, data, data_len);
			stdout_bytes += data_len;
			memset(data, 0, data_len);
			xfree(data);
			break;

		case SSH_SMSG_EXITSTATUS:
			packet_integrity_check(payload_len, 4, type);
			exit_status = packet_get_int();
			/* Acknowledge the exit. */
			packet_start(SSH_CMSG_EXIT_CONFIRMATION);
			packet_send();
			/* Must wait for packet to be sent since we are
			   exiting the loop. */
			packet_write_wait();
			/* Flag that we want to exit. */
			quit_pending = 1;
			break;

		case SSH_SMSG_X11_OPEN:
			x11_input_open(payload_len);
			break;

		case SSH_MSG_PORT_OPEN:
			channel_input_port_open(payload_len);
			break;

		case SSH_SMSG_AGENT_OPEN:
			packet_integrity_check(payload_len, 4, type);
			auth_input_open_request();
			break;

		case SSH_MSG_CHANNEL_OPEN_CONFIRMATION:
			packet_integrity_check(payload_len, 4 + 4, type);
			channel_input_open_confirmation();
			break;

		case SSH_MSG_CHANNEL_OPEN_FAILURE:
			packet_integrity_check(payload_len, 4, type);
			channel_input_open_failure();
			break;

		case SSH_MSG_CHANNEL_DATA:
			channel_input_data(payload_len);
			break;

		case SSH_MSG_CHANNEL_CLOSE:
			packet_integrity_check(payload_len, 4, type);
			channel_input_close();
			break;

		case SSH_MSG_CHANNEL_CLOSE_CONFIRMATION:
			packet_integrity_check(payload_len, 4, type);
			channel_input_close_confirmation();
			break;

		default:
			/* Any unknown packets received during the actual
			   session cause the session to terminate.  This
			   is intended to make debugging easier since no
			   confirmations are sent.  Any compatible
			   protocol extensions must be negotiated during
			   the preparatory phase. */
			packet_disconnect("Protocol error during session: type %d",
					  type);
		}
	}
}

/* Make packets from buffered stdin data, and buffer them for sending to
   the connection. */

void 
client_make_packets_from_stdin_data()
{
	unsigned int len;

	/* Send buffered stdin data to the server. */
	while (buffer_len(&stdin_buffer) > 0 &&
	       packet_not_very_much_data_to_write()) {
		len = buffer_len(&stdin_buffer);
		/* Keep the packets at reasonable size. */
		if (len > packet_get_maxsize())
			len = packet_get_maxsize();
		packet_start(SSH_CMSG_STDIN_DATA);
		packet_put_string(buffer_ptr(&stdin_buffer), len);
		packet_send();
		buffer_consume(&stdin_buffer, len);
		/* If we have a pending EOF, send it now. */
		if (stdin_eof && buffer_len(&stdin_buffer) == 0) {
			packet_start(SSH_CMSG_EOF);
			packet_send();
		}
	}
}

/* Checks if the client window has changed, and sends a packet about it to
   the server if so.  The actual change is detected elsewhere (by a software
   interrupt on Unix); this just checks the flag and sends a message if
   appropriate. */

void 
client_check_window_change()
{
	/* Send possible window change message to the server. */
	if (received_window_change_signal) {
		struct winsize ws;

		/* Clear the window change indicator. */
		received_window_change_signal = 0;

		/* Read new window size. */
		if (ioctl(fileno(stdin), TIOCGWINSZ, &ws) >= 0) {
			/* Successful, send the packet now. */
			packet_start(SSH_CMSG_WINDOW_SIZE);
			packet_put_int(ws.ws_row);
			packet_put_int(ws.ws_col);
			packet_put_int(ws.ws_xpixel);
			packet_put_int(ws.ws_ypixel);
			packet_send();
		}
	}
}

/* Waits until the client can do something (some data becomes available on
   one of the file descriptors). */

void 
client_wait_until_can_do_something(fd_set * readset, fd_set * writeset)
{
	/* Initialize select masks. */
	FD_ZERO(readset);

	/* Read from the connection, unless our buffers are full. */
	if (buffer_len(&stdout_buffer) < buffer_high &&
	    buffer_len(&stderr_buffer) < buffer_high &&
	    channel_not_very_much_buffered_data())
		FD_SET(connection_in, readset);

	/* Read from stdin, unless we have seen EOF or have very much
	   buffered data to send to the server. */
	if (!stdin_eof && packet_not_very_much_data_to_write())
		FD_SET(fileno(stdin), readset);

	FD_ZERO(writeset);

	/* Add any selections by the channel mechanism. */
	channel_prepare_select(readset, writeset);

	/* Select server connection if have data to write to the server. */
	if (packet_have_data_to_write())
		FD_SET(connection_out, writeset);

	/* Select stdout if have data in buffer. */
	if (buffer_len(&stdout_buffer) > 0)
		FD_SET(fileno(stdout), writeset);

	/* Select stderr if have data in buffer. */
	if (buffer_len(&stderr_buffer) > 0)
		FD_SET(fileno(stderr), writeset);

	/* Update maximum file descriptor number, if appropriate. */
	if (channel_max_fd() > max_fd)
		max_fd = channel_max_fd();

	/* Wait for something to happen.  This will suspend the process
	   until some selected descriptor can be read, written, or has
	   some other event pending. 
	   Note: if you want to implement SSH_MSG_IGNORE messages to fool
	   traffic analysis, this might be the place to do it:
	   just have a random timeout for the select, and send a random
	   SSH_MSG_IGNORE packet when the timeout expires. */

	if (select(max_fd + 1, readset, writeset, NULL, NULL) < 0) {
		char buf[100];
		/* Some systems fail to clear these automatically. */
		FD_ZERO(readset);
		FD_ZERO(writeset);
		if (errno == EINTR)
			return;
		/* Note: we might still have data in the buffers. */
		snprintf(buf, sizeof buf, "select: %s\r\n", strerror(errno));
		buffer_append(&stderr_buffer, buf, strlen(buf));
		stderr_bytes += strlen(buf);
		quit_pending = 1;
	}
}

void 
client_suspend_self()
{
	struct winsize oldws, newws;

	/* Flush stdout and stderr buffers. */
	if (buffer_len(&stdout_buffer) > 0)
		write(fileno(stdout),
		      buffer_ptr(&stdout_buffer),
		      buffer_len(&stdout_buffer));
	if (buffer_len(&stderr_buffer) > 0)
		write(fileno(stderr),
		      buffer_ptr(&stderr_buffer),
		      buffer_len(&stderr_buffer));

	/* Leave raw mode. */
	leave_raw_mode();

	/* Free (and clear) the buffer to reduce the amount of data that
	   gets written to swap. */
	buffer_free(&stdin_buffer);
	buffer_free(&stdout_buffer);
	buffer_free(&stderr_buffer);

	/* Save old window size. */
	ioctl(fileno(stdin), TIOCGWINSZ, &oldws);

	/* Send the suspend signal to the program itself. */
	kill(getpid(), SIGTSTP);

	/* Check if the window size has changed. */
	if (ioctl(fileno(stdin), TIOCGWINSZ, &newws) >= 0 &&
	    (oldws.ws_row != newws.ws_row ||
	     oldws.ws_col != newws.ws_col ||
	     oldws.ws_xpixel != newws.ws_xpixel ||
	     oldws.ws_ypixel != newws.ws_ypixel))
		received_window_change_signal = 1;

	/* OK, we have been continued by the user. Reinitialize buffers. */
	buffer_init(&stdin_buffer);
	buffer_init(&stdout_buffer);
	buffer_init(&stderr_buffer);

	/* Re-enter raw mode. */
	enter_raw_mode();
}

void 
client_process_input(fd_set * readset)
{
	int len, pid;
	char buf[8192], *s;

	/* Read input from the server, and add any such data to the buffer
	   of the packet subsystem. */
	if (FD_ISSET(connection_in, readset)) {
		/* Read as much as possible. */
		len = read(connection_in, buf, sizeof(buf));
		if (len == 0) {
			/* Received EOF.  The remote host has closed the connection. */
			snprintf(buf, sizeof buf, "Connection to %.300s closed by remote host.\r\n",
				 host);
			buffer_append(&stderr_buffer, buf, strlen(buf));
			stderr_bytes += strlen(buf);
			quit_pending = 1;
			return;
		}
		/* There is a kernel bug on Solaris that causes select to
		   sometimes wake up even though there is no data
		   available. */
		if (len < 0 && errno == EAGAIN)
			len = 0;

		if (len < 0) {
			/* An error has encountered.  Perhaps there is a network problem. */
			snprintf(buf, sizeof buf, "Read from remote host %.300s: %.100s\r\n",
				 host, strerror(errno));
			buffer_append(&stderr_buffer, buf, strlen(buf));
			stderr_bytes += strlen(buf);
			quit_pending = 1;
			return;
		}
		packet_process_incoming(buf, len);
	}
	/* Read input from stdin. */
	if (FD_ISSET(fileno(stdin), readset)) {
		/* Read as much as possible. */
		len = read(fileno(stdin), buf, sizeof(buf));
		if (len <= 0) {
			/* Received EOF or error.  They are treated
			   similarly, except that an error message is
			   printed if it was an error condition. */
			if (len < 0) {
				snprintf(buf, sizeof buf, "read: %.100s\r\n", strerror(errno));
				buffer_append(&stderr_buffer, buf, strlen(buf));
				stderr_bytes += strlen(buf);
			}
			/* Mark that we have seen EOF. */
			stdin_eof = 1;
			/* Send an EOF message to the server unless there
			   is data in the buffer.  If there is data in the
			   buffer, no message will be sent now.  Code
			   elsewhere will send the EOF when the buffer
			   becomes empty if stdin_eof is set. */
			if (buffer_len(&stdin_buffer) == 0) {
				packet_start(SSH_CMSG_EOF);
				packet_send();
			}
		} else if (escape_char == -1) {
			/* Normal successful read, and no escape
			   character.  Just append the data to buffer. */
			buffer_append(&stdin_buffer, buf, len);
			stdin_bytes += len;
		} else {
			/* Normal, successful read.  But we have an escape
			   character and have to process the characters
			   one by one. */
			unsigned int i;
			for (i = 0; i < len; i++) {
				unsigned char ch;
				/* Get one character at a time. */
				ch = buf[i];

				/* Check if we have a pending escape
				   character. */
				if (escape_pending) {
					/* We have previously seen an escape character. */
					/* Clear the flag now. */
					escape_pending = 0;
					/* Process the escaped character. */
					switch (ch) {
					case '.':
						/* Terminate the connection. */
						snprintf(buf, sizeof buf, "%c.\r\n", escape_char);
						buffer_append(&stderr_buffer, buf, strlen(buf));
						stderr_bytes += strlen(buf);
						quit_pending = 1;
						return;

					case 'Z' - 64:
						/* Suspend the program. */
						/* Print a message to that effect to the user. */
						snprintf(buf, sizeof buf, "%c^Z\r\n", escape_char);
						buffer_append(&stderr_buffer, buf, strlen(buf));
						stderr_bytes += strlen(buf);

						/* Restore terminal modes and suspend. */
						client_suspend_self();

						/* We have been continued. */
						continue;

					case '&':
						/* Detach the program (continue to serve connections,
						   but put in background and no more new connections). */
						if (!stdin_eof) {
							/* Sending SSH_CMSG_EOF alone does not always appear
							   to be enough.  So we try to send an EOF character
							   first. */
							packet_start(SSH_CMSG_STDIN_DATA);
							packet_put_string("\004", 1);
							packet_send();
							/* Close stdin. */
							stdin_eof = 1;
							if (buffer_len(&stdin_buffer) == 0) {
								packet_start(SSH_CMSG_EOF);
								packet_send();
							}
						}
						/* Restore tty modes. */
						leave_raw_mode();

						/* Stop listening for new connections. */
						channel_stop_listening();

						printf("%c& [backgrounded]\n", escape_char);

						/* Fork into background. */
						pid = fork();
						if (pid < 0) {
							error("fork: %.100s", strerror(errno));
							continue;
						}
						if (pid != 0) {	/* This is the parent. */
							/* The parent just exits. */
							exit(0);
						}
						/* The child continues serving connections. */
						continue;

					case '?':
						snprintf(buf, sizeof buf,
"%c?\r\n\
Supported escape sequences:\r\n\
~.  - terminate connection\r\n\
~^Z - suspend ssh\r\n\
~#  - list forwarded connections\r\n\
~&  - background ssh (when waiting for connections to terminate)\r\n\
~?  - this message\r\n\
~~  - send the escape character by typing it twice\r\n\
(Note that escapes are only recognized immediately after newline.)\r\n",
							 escape_char);
						buffer_append(&stderr_buffer, buf, strlen(buf));
						continue;

					case '#':
						snprintf(buf, sizeof buf, "%c#\r\n", escape_char);
						buffer_append(&stderr_buffer, buf, strlen(buf));
						s = channel_open_message();
						buffer_append(&stderr_buffer, s, strlen(s));
						xfree(s);
						continue;

					default:
						if (ch != escape_char) {
							/* Escape character followed by non-special character.
							   Append both to the input buffer. */
							buf[0] = escape_char;
							buf[1] = ch;
							buffer_append(&stdin_buffer, buf, 2);
							stdin_bytes += 2;
							continue;
						}
						/* Note that escape character typed twice
						   falls through here; the latter gets processed
						   as a normal character below. */
						break;
					}
				} else {
					/* The previous character was not an escape char. Check if this
					   is an escape. */
					if (last_was_cr && ch == escape_char) {
						/* It is. Set the flag and continue to next character. */
						escape_pending = 1;
						continue;
					}
				}

				/* Normal character.  Record whether it was a newline, and append it to the
				   buffer. */
				last_was_cr = (ch == '\r' || ch == '\n');
				buf[0] = ch;
				buffer_append(&stdin_buffer, buf, 1);
				stdin_bytes += 1;
				continue;
			}
		}
	}
}

void 
client_process_output(fd_set * writeset)
{
	int len;
	char buf[100];

	/* Write buffered output to stdout. */
	if (FD_ISSET(fileno(stdout), writeset)) {
		/* Write as much data as possible. */
		len = write(fileno(stdout), buffer_ptr(&stdout_buffer),
			    buffer_len(&stdout_buffer));
		if (len <= 0) {
			if (errno == EAGAIN)
				len = 0;
			else {
				/* An error or EOF was encountered.  Put
				   an error message to stderr buffer. */
				snprintf(buf, sizeof buf, "write stdout: %.50s\r\n", strerror(errno));
				buffer_append(&stderr_buffer, buf, strlen(buf));
				stderr_bytes += strlen(buf);
				quit_pending = 1;
				return;
			}
		}
		/* Consume printed data from the buffer. */
		buffer_consume(&stdout_buffer, len);
	}
	/* Write buffered output to stderr. */
	if (FD_ISSET(fileno(stderr), writeset)) {
		/* Write as much data as possible. */
		len = write(fileno(stderr), buffer_ptr(&stderr_buffer),
			    buffer_len(&stderr_buffer));
		if (len <= 0) {
			if (errno == EAGAIN)
				len = 0;
			else {
				/* EOF or error, but can't even print
				   error message. */
				quit_pending = 1;
				return;
			}
		}
		/* Consume printed characters from the buffer. */
		buffer_consume(&stderr_buffer, len);
	}
}

/* Implements the interactive session with the server.  This is called
   after the user has been authenticated, and a command has been
   started on the remote host.  If escape_char != -1, it is the character
   used as an escape character for terminating or suspending the
   session. */

int 
client_loop(int have_pty, int escape_char_arg)
{
	extern Options options;
	double start_time, total_time;
	int len;
	char buf[100];

	debug("Entering interactive session.");

	start_time = get_current_time();

	/* Initialize variables. */
	escape_pending = 0;
	last_was_cr = 1;
	exit_status = -1;
	stdin_eof = 0;
	buffer_high = 64 * 1024;
	connection_in = packet_get_connection_in();
	connection_out = packet_get_connection_out();
	max_fd = connection_in;
	if (connection_out > max_fd)
		max_fd = connection_out;
	stdin_bytes = 0;
	stdout_bytes = 0;
	stderr_bytes = 0;
	quit_pending = 0;
	escape_char = escape_char_arg;

	/* Initialize buffers. */
	buffer_init(&stdin_buffer);
	buffer_init(&stdout_buffer);
	buffer_init(&stderr_buffer);

	/* Set signal handlers to restore non-blocking mode.  */
	signal(SIGINT, signal_handler);
	signal(SIGQUIT, signal_handler);
	signal(SIGTERM, signal_handler);
	signal(SIGPIPE, SIG_IGN);
	if (have_pty)
		signal(SIGWINCH, window_change_handler);

	/* Enter raw mode if have a pseudo terminal. */
	if (have_pty)
		enter_raw_mode();

	/* Check if we should immediately send of on stdin. */
	client_check_initial_eof_on_stdin();

	/* Main loop of the client for the interactive session mode. */
	while (!quit_pending) {
		fd_set readset, writeset;

		/* Precess buffered packets sent by the server. */
		client_process_buffered_input_packets();

		/* Make packets of buffered stdin data, and buffer them
		   for sending to the server. */
		client_make_packets_from_stdin_data();

		/* Make packets from buffered channel data, and buffer
		   them for sending to the server. */
		if (packet_not_very_much_data_to_write())
			channel_output_poll();

		/* Check if the window size has changed, and buffer a
		   message about it to the server if so. */
		client_check_window_change();

		if (quit_pending)
			break;

		/* Wait until we have something to do (something becomes
		   available on one of the descriptors). */
		client_wait_until_can_do_something(&readset, &writeset);

		if (quit_pending)
			break;

		/* Do channel operations. */
		channel_after_select(&readset, &writeset);

		/* Process input from the connection and from stdin.
		   Buffer any data that is available. */
		client_process_input(&readset);

		/* Process output to stdout and stderr.   Output to the
		   connection is processed elsewhere (above). */
		client_process_output(&writeset);

		/* Send as much buffered packet data as possible to the
		   sender. */
		if (FD_ISSET(connection_out, &writeset))
			packet_write_poll();
	}

	/* Terminate the session. */

	/* Stop watching for window change. */
	if (have_pty)
		signal(SIGWINCH, SIG_DFL);

	/* Stop listening for connections. */
	channel_stop_listening();

	/* In interactive mode (with pseudo tty) display a message
	   indicating that the connection has been closed. */
	if (have_pty && options.log_level != SYSLOG_LEVEL_QUIET) {
		snprintf(buf, sizeof buf, "Connection to %.64s closed.\r\n", host);
		buffer_append(&stderr_buffer, buf, strlen(buf));
		stderr_bytes += strlen(buf);
	}
	/* Output any buffered data for stdout. */
	while (buffer_len(&stdout_buffer) > 0) {
		len = write(fileno(stdout), buffer_ptr(&stdout_buffer),
			    buffer_len(&stdout_buffer));
		if (len <= 0) {
			error("Write failed flushing stdout buffer.");
			break;
		}
		buffer_consume(&stdout_buffer, len);
	}

	/* Output any buffered data for stderr. */
	while (buffer_len(&stderr_buffer) > 0) {
		len = write(fileno(stderr), buffer_ptr(&stderr_buffer),
			    buffer_len(&stderr_buffer));
		if (len <= 0) {
			error("Write failed flushing stderr buffer.");
			break;
		}
		buffer_consume(&stderr_buffer, len);
	}

	/* Leave raw mode. */
	if (have_pty)
		leave_raw_mode();

	/* Clear and free any buffers. */
	memset(buf, 0, sizeof(buf));
	buffer_free(&stdin_buffer);
	buffer_free(&stdout_buffer);
	buffer_free(&stderr_buffer);

	/* Report bytes transferred, and transfer rates. */
	total_time = get_current_time() - start_time;
	debug("Transferred: stdin %lu, stdout %lu, stderr %lu bytes in %.1f seconds",
	      stdin_bytes, stdout_bytes, stderr_bytes, total_time);
	if (total_time > 0)
		debug("Bytes per second: stdin %.1f, stdout %.1f, stderr %.1f",
		      stdin_bytes / total_time, stdout_bytes / total_time,
		      stderr_bytes / total_time);

	/* Return the exit status of the program. */
	debug("Exit status %d", exit_status);
	return exit_status;
}