clientloop.c

OpenSSH 是 SSH （Secure SHell） 协议的免费开源实现。它用安全、加密的网络连接工具代替了 telnet、ftp、 rlogin、rsh 和 rcp 工具。OpenSSH 支持

				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. */
				if (compat20) {
					buffer_append(bin, "\004", 1);
					/* fake EOF on stdin */
					return -1;
				} else 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(bin) == 0) {
						packet_start(SSH_CMSG_EOF);
						packet_send();
					}
				}
				continue;

			case '?':
				snprintf(string, sizeof string,
"%c?\r\n\
Supported escape sequences:\r\n\
%c.  - terminate connection\r\n\
%cB  - send a BREAK to the remote system\r\n\
%cC  - open a command line\r\n\
%cR  - Request rekey (SSH protocol 2 only)\r\n\
%c^Z - suspend ssh\r\n\
%c#  - list forwarded connections\r\n\
%c&  - background ssh (when waiting for connections to terminate)\r\n\
%c?  - this message\r\n\
%c%c  - send the escape character by typing it twice\r\n\
(Note that escapes are only recognized immediately after newline.)\r\n",
				    escape_char, escape_char, escape_char, escape_char,
				    escape_char, escape_char, escape_char, escape_char,
				    escape_char, escape_char, escape_char);
				buffer_append(berr, string, strlen(string));
				continue;

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

			case 'C':
				process_cmdline();
				continue;

			default:
				if (ch != escape_char) {
					buffer_put_char(bin, escape_char);
					bytes++;
				}
				/* Escaped characters fall through here */
				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');
		buffer_put_char(bin, ch);
		bytes++;
	}
	return bytes;
}

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

	/* 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 && (errno == EAGAIN || errno == EINTR))
			return;		/* we'll try again later */
		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));
			}
			/* 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 == SSH_ESCAPECHAR_NONE) {
			/*
			 * Normal successful read, and no escape character.
			 * Just append the data to buffer.
			 */
			buffer_append(&stdin_buffer, buf, len);
		} else {
			/*
			 * Normal, successful read.  But we have an escape character
			 * and have to process the characters one by one.
			 */
			if (process_escapes(&stdin_buffer, &stdout_buffer,
			    &stderr_buffer, buf, len) == -1)
				return;
		}
	}
}

static 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 == EINTR || 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));
				quit_pending = 1;
				return;
			}
		}
		/* Consume printed data from the buffer. */
		buffer_consume(&stdout_buffer, len);
		stdout_bytes += 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 == EINTR || 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);
		stderr_bytes += len;
	}
}

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

static void
client_process_buffered_input_packets(void)
{
	dispatch_run(DISPATCH_NONBLOCK, &quit_pending, compat20 ? xxx_kex : NULL);
}

/* scan buf[] for '~' before sending data to the peer */

static int
simple_escape_filter(Channel *c, char *buf, int len)
{
	/* XXX we assume c->extended is writeable */
	return process_escapes(&c->input, &c->output, &c->extended, buf, len);
}

static void
client_channel_closed(int id, void *arg)
{
	channel_cancel_cleanup(id);
	session_closed = 1;
	leave_raw_mode();
}

/*
 * 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 != SSH_ESCAPECHAR_NONE, 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, int ssh2_chan_id)
{
	fd_set *readset = NULL, *writeset = NULL;
	double start_time, total_time;
	int max_fd = 0, max_fd2 = 0, len, rekeying = 0;
	u_int nalloc = 0;
	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 = MAX(connection_in, connection_out);
	if (control_fd != -1)
		max_fd = MAX(max_fd, control_fd);

	if (!compat20) {
		/* enable nonblocking unless tty */
		if (!isatty(fileno(stdin)))
			set_nonblock(fileno(stdin));
		if (!isatty(fileno(stdout)))
			set_nonblock(fileno(stdout));
		if (!isatty(fileno(stderr)))
			set_nonblock(fileno(stderr));
		max_fd = MAX(max_fd, fileno(stdin));
		max_fd = MAX(max_fd, fileno(stdout));
		max_fd = MAX(max_fd, fileno(stderr));
	}
	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);

	client_init_dispatch();

	/*
	 * Set signal handlers, (e.g. to restore non-blocking mode)
	 * but don't overwrite SIG_IGN, matches behaviour from rsh(1)
	 */
	if (signal(SIGHUP, SIG_IGN) != SIG_IGN)
		signal(SIGHUP, signal_handler);
	if (signal(SIGINT, SIG_IGN) != SIG_IGN)
		signal(SIGINT, signal_handler);
	if (signal(SIGQUIT, SIG_IGN) != SIG_IGN)
		signal(SIGQUIT, signal_handler);
	if (signal(SIGTERM, SIG_IGN) != SIG_IGN)
		signal(SIGTERM, signal_handler);
	signal(SIGWINCH, window_change_handler);

	if (have_pty)
		enter_raw_mode();

	if (compat20) {
		session_ident = ssh2_chan_id;
		if (escape_char != SSH_ESCAPECHAR_NONE)
			channel_register_filter(session_ident,
			    simple_escape_filter);
		if (session_ident != -1)
			channel_register_cleanup(session_ident,
			    client_channel_closed);
	} else {
		/* Check if we should immediately send eof on stdin. */
		client_check_initial_eof_on_stdin();
	}

	/* Main loop of the client for the interactive session mode. */
	while (!quit_pending) {

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

		if (compat20 && session_closed && !channel_still_open())
			break;

		rekeying = (xxx_kex != NULL && !xxx_kex->done);

		if (rekeying) {
			debug("rekeying in progress");
		} else {
			/*
			 * Make packets of buffered stdin data, and buffer
			 * them for sending to the server.
			 */
			if (!compat20)
				client_make_packets_from_stdin_data();

			/*
			 * Make packets from buffered channel data, and
			 * enqueue 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).
		 */
		max_fd2 = max_fd;
		client_wait_until_can_do_something(&readset, &writeset,
		    &max_fd2, &nalloc, rekeying);

		if (quit_pending)
			break;

		/* Do channel operations unless rekeying in progress. */
		if (!rekeying) {
			channel_after_select(readset, writeset);
			if (need_rekeying || packet_need_rekeying()) {
				debug("need rekeying");
				xxx_kex->done = 0;
				kex_send_kexinit(xxx_kex);
				need_rekeying = 0;
			}
		}

		/* Buffer input from the connection.  */
		client_process_net_input(readset);

		/* Accept control connections.  */
		client_process_control(readset);

		if (quit_pending)
			break;

		if (!compat20) {
			/* Buffer data from stdin */
			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();
	}
	if (readset)
		xfree(readset);
	if (writeset)
		xfree(writeset);

	/* Terminate the session. */

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

	channel_free_all();

	if (have_pty)
		leave_raw_mode();

	/* restore blocking io */
	if (!isatty(fileno(stdin)))
		unset_nonblock(fileno(stdin));
	if (!isatty(fileno(stdout)))
		unset_nonblock(fileno(stdout));
	if (!isatty(fileno(stderr)))
		unset_nonblock(fileno(stderr));

	/*
	 * If there was no shell or command requested, there will be no remote
	 * exit status to be returned.  In that case, clear error code if the
	 * connection was deliberately terminated at this end.
	 */
	if (no_shell_flag && received_signal == SIGTERM) {
		received_signal = 0;
		exit_status = 0;
	}

	if (received_signal)
		fatal("Killed by signal %d.", (int) received_signal);

	/*
	 * 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));
	}

	/* 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);
		stdout_bytes += 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);
		stderr_bytes += len;
	}