mosh-server: Support timeouts on lost connectivity to network client.

Closes #690.

man/mosh-server.1

@@ -82,6 +82,43 @@ Locale-related environment variable to try as part of a fallback
 environment, if the startup environment does not specify a character
 set of UTF-8.
 
+.SH ENVIRONMENT VARIABLES
+These variables allow server-side configuration of Mosh's behavior.
+They may be set by administrators in system login/rc files,
+/etc/login.conf, or similar mechanisms, or users in their shell's
+login/rc files.  \fBmosh-server\fP passes these variables to the login
+session and shell that it starts, but changing them there will have no
+effect.
+
+.TP
+.B MOSH_SERVER_NETWORK_TMOUT
+If this variable is set to a positive integer number, it specifies how
+long (in seconds) \fBmosh-server\fP will wait to receive an update from the
+client before exiting.  Since \fPmosh\fP is very useful for mobile
+clients with intermittent operation and connectivity, we suggest
+setting this variable to a high value, such as 604800 (one week) or
+2592000 (30 days).  Otherwise, \fBmosh-server\fP will wait
+indefinitely for a client to reappear.  This variable is somewhat
+similar to the \fBTMOUT\fP variable found in many Bourne shells.
+However, it is not a login-session inactivity timeout; it only applies
+to network connectivity.
+
+.TP
+.B MOSH_SERVER_SIGNAL_TMOUT
+If this variable is set to a positive integer number, it specifies how
+long (in seconds) \fBmosh-server\fP will ignore SIGUSR1 while waiting
+to receive an update from the client.  Otherwise, \fBSIGUSR1\fP will
+always terminate \fBmosh-server\fP.  Users and administrators may
+implement scripts to clean up disconnected Mosh sessions.  With this
+variable set, a user or administrator can issue
+
+.nf
+$ pkill -SIGUSR1 mosh-server
+.fi
+
+to kill disconnected sessions without killing connected login
+sessions.
+
 .SH EXAMPLE
 
 .nf

man/mosh.1

@@ -92,6 +92,13 @@ command to run server helper on remote machine (default: "mosh-server")
 The server helper is unprivileged and can be installed in the user's
 home directory.
 
+This option can be used to set environment variables for the server by
+using the
+.BR env (1)
+command to wrap the actual server command.  See
+.BR mosh-server (1)
+for available environment variables.
+
 .TP
 .B \-\-ssh=\fICOMMAND\fP
 OpenSSH command to remotely execute mosh-server on remote machine (default: "ssh")

scripts/mosh.pl

@@ -266,6 +266,8 @@ sub predict_check {
   $colors = 0;
 }
 
+$ENV{ 'MOSH_CLIENT_PID' } = $$; # We don't support this, but it's useful for test and debug.
+
 my $pid = open(my $pipe, "-|");
 die "$0: fork: $!\n" unless ( defined $pid );
 if ( $pid == 0 ) { # child

src/frontend/mosh-server.cc

@@ -54,6 +54,7 @@
 #include <netdb.h>
 #include <time.h>
 #include <sys/stat.h>
+#include <inttypes.h>
 
 #ifdef HAVE_UTMPX_H
 #include <utmpx.h>
@@ -93,7 +94,9 @@ typedef Network::Transport< Terminal::Complete, Network::UserStream > ServerConn
 
 static void serve( int host_fd,
 		   Terminal::Complete &terminal,
-		   ServerConnection &network );
+		   ServerConnection &network,
+		   long network_timeout,
+		   long network_signaled_timeout );
 
 static int run_server( const char *desired_ip, const char *desired_port,
 		       const string &command_path, char *command_argv[],
@@ -340,6 +343,34 @@ int main( int argc, char *argv[] )
 static int run_server( const char *desired_ip, const char *desired_port,
 		       const string &command_path, char *command_argv[],
 		       const int colors, bool verbose, bool with_motd ) {
+  /* get network idle timeout */
+  long network_timeout = 0;
+  char *timeout_envar = getenv( "MOSH_SERVER_NETWORK_TMOUT" );
+  if ( timeout_envar && *timeout_envar ) {
+    errno = 0;
+    char *endptr;
+    network_timeout = strtol( timeout_envar, &endptr, 10 );
+    if ( *endptr != '\0' || ( network_timeout == 0 && errno == EINVAL ) ) {
+      fprintf( stderr, "MOSH_SERVER_NETWORK_TMOUT not a valid integer, ignoring\n" );
+    } else if ( network_timeout < 0 ) {
+      fprintf( stderr, "MOSH_SERVER_NETWORK_TMOUT is negative, ignoring\n" );
+      network_timeout = 0;
+    }
+  }
+  /* get network signaled idle timeout */
+  long network_signaled_timeout = 0;
+  char *signal_envar = getenv( "MOSH_SERVER_SIGNAL_TMOUT" );
+  if ( signal_envar && *signal_envar ) {
+    errno = 0;
+    char *endptr;
+    network_signaled_timeout = strtol( signal_envar, &endptr, 10 );
+    if ( *endptr != '\0' || ( network_signaled_timeout == 0 && errno == EINVAL ) ) {
+      fprintf( stderr, "MOSH_SERVER_SIGNAL_TMOUT not a valid integer, ignoring\n" );
+    } else if ( network_signaled_timeout < 0 ) {
+      fprintf( stderr, "MOSH_SERVER_SIGNAL_TMOUT is negative, ignoring\n" );
+      network_signaled_timeout = 0;
+    }
+  }
   /* get initial window size */
   struct winsize window_size;
   if ( ioctl( STDIN_FILENO, TIOCGWINSZ, &window_size ) < 0 ||
@@ -505,7 +536,7 @@ static int run_server( const char *desired_ip, const char *desired_port,
 #endif
 
     try {
-      serve( master, terminal, *network );
+      serve( master, terminal, *network, network_timeout, network_signaled_timeout );
     } catch ( const Network::NetworkException &e ) {
       fprintf( stderr, "Network exception: %s\n",
 	       e.what() );
@@ -531,12 +562,16 @@ static int run_server( const char *desired_ip, const char *desired_port,
   return 0;
 }
 
-static void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &network )
+static void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &network, long network_timeout, long network_signaled_timeout )
 {
+  /* scale timeouts */
+  const uint64_t network_timeout_ms = static_cast<uint64_t>( network_timeout ) * 1000;
+  const uint64_t network_signaled_timeout_ms = static_cast<uint64_t>( network_signaled_timeout ) * 1000;
   /* prepare to poll for events */
   Select &sel = Select::get_instance();
   sel.add_signal( SIGTERM );
   sel.add_signal( SIGINT );
+  sel.add_signal( SIGUSR1 );
 
   uint64_t last_remote_num = network.get_remote_state_num();
 
@@ -549,14 +584,31 @@ static void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &
 
   while ( 1 ) {
     try {
+      static const uint64_t timeout_if_no_client = 60000;
+      int timeout = INT_MAX;
       uint64_t now = Network::timestamp();
 
-      const int timeout_if_no_client = 60000;
-      int timeout = min( network.wait_time(), terminal.wait_time( now ) );
+      timeout = min( timeout, network.wait_time() );
+      timeout = min( timeout, terminal.wait_time( now ) );
       if ( (!network.get_remote_state_num())
 	   || network.shutdown_in_progress() ) {
         timeout = min( timeout, 5000 );
       }
+      /*
+       * The server goes completely asleep if it has no remote peer.
+       * We may want to wake up sooner.
+       */
+      if ( network_timeout_ms ) {
+	int64_t network_sleep = network_timeout_ms -
+	  ( now - network.get_latest_remote_state().timestamp );
+	if ( network_sleep < 0 ) {
+	  network_sleep = 0;
+	} else if ( network_sleep > INT_MAX ) {
+	  /* 24 days might be too soon.  That's OK. */
+	  network_sleep = INT_MAX;
+	}
+	timeout = min( timeout, static_cast<int>(network_sleep) );
+      }
 
       /* poll for events */
       sel.clear_fds();
@@ -679,7 +731,20 @@ static void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &
 	}
       }
 
-      if ( sel.any_signal() ) {
+      bool idle_shutdown = false;
+      if ( network_timeout_ms &&
+	   network_timeout_ms <= time_since_remote_state ) {
+	idle_shutdown = true;
+	fprintf( stderr, "Network idle for %" PRIu64 " seconds.\n", time_since_remote_state / 1000 );
+      }
+      if ( sel.signal( SIGUSR1 ) ) {
+	if ( !network_signaled_timeout_ms || network_signaled_timeout_ms <= time_since_remote_state ) {
+	  idle_shutdown = true;
+	  fprintf( stderr, "Network idle for %"PRIu64" seconds when SIGUSR1 received\n", time_since_remote_state / 1000 );
+	}
+      }
+
+      if ( sel.any_signal() || idle_shutdown ) {
 	/* shutdown signal */
 	if ( network.has_remote_addr() && (!network.shutdown_in_progress()) ) {
 	  network.start_shutdown();
@@ -736,8 +801,8 @@ static void serve( int host_fd, Terminal::Complete &terminal, ServerConnection &
       }
 
       if ( !network.get_remote_state_num()
-           && time_since_remote_state >= uint64_t( timeout_if_no_client ) ) {
-        fprintf( stderr, "No connection within %d seconds.\n",
+           && time_since_remote_state >= timeout_if_no_client ) {
+        fprintf( stderr, "No connection within %" PRIu64 " seconds.\n",
                  timeout_if_no_client / 1000 );
         break;
       }

src/tests/Makefile.am

@@ -12,9 +12,11 @@ displaytests = \
 	emulation-80th-column.test \
 	emulation-back-tab.test \
 	emulation-multiline-scroll.test \
-	window-resize.test \
+	server-network-timeout.test \
+	server-signal-timeout.test \
 	unicode-combine-fallback-assert.test \
-	unicode-later-combining.test
+	unicode-later-combining.test \
+	window-resize.test
 
 check_PROGRAMS = ocb-aes encrypt-decrypt base64
 TESTS = ocb-aes encrypt-decrypt base64 $(displaytests)

src/tests/e2e-test-server

@@ -5,13 +5,16 @@
 # then captures screen with `tmux capture-pane`.  Captures exitstatus
 # of both and returns appropriate errors.
 #
+export MOSH_SERVER_PID=$PPID
+
 if [ $# -lt 2 ]; then
     printf "not enough args\n" >&2
     exit 99
 fi
 testname=$1
 shift
 rm -f $testname.capture $testname.exitstatus
+trap ":" TERM HUP QUIT # If the session closes on us, let the test we're running drive.
 trap 'rv=$?; echo $rv > $testname.exitstatus; exit $rv' EXIT
 # check for tmux
 if [ -z "$TMUX_PANE" ]; then

src/tests/server-network-timeout.test

@@ -0,0 +1,114 @@
+#!/bin/sh
+
+#
+# This test checks for operation of the MOSH_SERVER_NETWORK_TIMEOUT variable.
+# It does this by
+# * setting the variable
+# * killing the client (and its network traffic)
+# * waiting server-side, for the server to die
+# If it is killed, the test is successful.
+# If it survives that long and the server is still around, the test fails.
+# The client waits a bit longer than the server so that status can be collected
+# properly.
+#
+
+TIMEOUT=10
+
+fail()
+{
+    printf "$@" 2>&1
+    exit 99
+}
+
+
+
+PATH=$PATH:.:$srcdir
+# Top-level wrapper.
+if [ $# -eq 0 ]; then
+    e2e-test $0 client baseline
+    exit
+fi
+
+# OK, we have arguments, we're one of the test hooks.
+
+client()
+{
+    case "$myname" in
+	server-network-timeout)
+	    export MOSH_SERVER_NETWORK_TMOUT=$TIMEOUT;;
+	server-signal-timeout)
+	    export MOSH_SERVER_SIGNAL_TMOUT=$TIMEOUT;;
+	*)
+	    fail "unexpected test name %s\n" "$myname"
+    esac
+    shift
+    eval "$@"
+    # The client may be murdered.  We need to expect that...
+    retval=$?
+    case $retval in
+	0|1)
+	    fail "mosh-client had a normal exit\n";; # test condition failed
+	137)
+	    # Aha, signal 9.  Wait.
+	    sleep $(( $TIMEOUT + 12 ))
+	    exit 0
+	    ;;
+	*)
+	    fail "unknown client wrapper failure, retval=%d\n" $retval
+	    ;;
+    esac
+    fail "client wrapper shouldnt get here\n"
+}
+baseline()
+{
+    # check for our wonderful variable
+    if [ -z "$MOSH_SERVER_NETWORK_TMOUT" -a -z "$MOSH_SERVER_SIGNAL_TMOUT" ]; then
+	env
+	fail "Variable unset\n"
+    fi
+    # check for our client
+    if [ -z "$MOSH_CLIENT_PID" ]; then
+	env
+	fail "Client pid unavailable\n"
+    fi
+    if ! kill -0 $MOSH_CLIENT_PID; then
+	fail "mosh client is unexpectedly missing\n"
+    fi
+    # Set up for good return and cleanup on being killed
+    trap "echo got killed >&2; sleep 1; exit 0" SIGHUP SIGTERM
+    sleep 1
+
+    # Kill the client, to stop network traffic.
+    kill -KILL $MOSH_CLIENT_PID
+    case "$myname" in
+	server-network-timeout)
+	    # Just wait.  This is the hardest part.
+	    sleep $(( $TIMEOUT + 7 ))
+	    ;;
+	server-signal-timeout)
+	    # Wait for the timeout to expire.
+	    sleep $(( $TIMEOUT + 2 ))
+	    # Tell the server to go away.
+	    kill -USR1 $MOSH_SERVER_PID
+	    sleep 5
+	    ;;
+	*)
+	    fail "unexpected test name %s\n" "$myname"
+    esac
+    # If we're still alive and the server is too, the test failed.
+    # XXX the server is getting killed and we're getting here anyway.
+    # Exit with error only if server is still around.
+    ! kill -0 $MOSH_SERVER_PID
+    exit
+}
+
+myname="$(basename $0 .test)"
+
+case $1 in
+    baseline|variant)
+	baseline;;
+    client)
+	client "$@";;
+    *)
+	fail "unknown test argument %s\n" $1;;
+esac

src/tests/server-signal-timeout.test

@@ -0,0 +1 @@
+server-network-timeout.test

src/util/select.cc

@@ -43,5 +43,4 @@ void Select::handle_signal( int signum )
 
   Select &sel = get_instance();
   sel.got_signal[ signum ] = 1;
-  sel.got_any_signal = 1;
 }