Report errors from mosh-server startup to the user

scripts/mosh.pl

@@ -350,121 +350,135 @@ sub predict_check {
   $userhost = "$user$ip";
 }
 
-my $pid = open(my $pipe, "-|");
-die "$0: fork: $!\n" unless ( defined $pid );
-if ( $pid == 0 ) { # child
-  open(STDERR, ">&STDOUT") or die;
+# Construct server exec arguments.
+my @sshopts = ( '-n' );
+if ($ssh_pty) {
+  push @sshopts, '-tt';
+}
 
-  my @sshopts = ( '-n' );
-  if ($ssh_pty) {
-      push @sshopts, '-tt';
+my $ssh_connection = "";
+if ( $use_remote_ip eq 'remote' ) {
+  # Ask the server for its IP.  The user's shell may not be
+  # Posix-compatible so invoke sh explicitly.
+  $ssh_connection = "sh -c " .
+    shell_quote ( '[ -n "$SSH_CONNECTION" ] && printf "\nMOSH SSH_CONNECTION %s\n" "$SSH_CONNECTION"' ) .
+    " ; ";
+  # Only with 'remote', we may need to tell SSH which protocol to use.
+  if ( $family eq 'inet' ) {
+    push @sshopts, '-4';
+  } elsif ( $family eq 'inet6' ) {
+    push @sshopts, '-6';
   }
+}
+my @server = ( 'new' );
 
-  my $ssh_connection = "";
-  if ( $use_remote_ip eq 'remote' ) {
-    # Ask the server for its IP.  The user's shell may not be
-    # Posix-compatible so invoke sh explicitly.
-    $ssh_connection = "sh -c " .
-      shell_quote ( '[ -n "$SSH_CONNECTION" ] && printf "\nMOSH SSH_CONNECTION %s\n" "$SSH_CONNECTION"' ) .
-      " ; ";
-    # Only with 'remote', we may need to tell SSH which protocol to use.
-    if ( $family eq 'inet' ) {
-      push @sshopts, '-4';
-    } elsif ( $family eq 'inet6' ) {
-      push @sshopts, '-6';
-    }
-  }
-  my @server = ( 'new' );
+push @server, ( '-c', $colors );
 
-  push @server, ( '-c', $colors );
+push @server, @bind_arguments;
 
-  push @server, @bind_arguments;
+if ( defined $port_request ) {
+  push @server, ( '-p', $port_request );
+}
 
-  if ( defined $port_request ) {
-    push @server, ( '-p', $port_request );
-  }
+for ( &locale_vars ) {
+  push @server, ( '-l', $_ );
+}
 
-  for ( &locale_vars ) {
-    push @server, ( '-l', $_ );
-  }
+if ( scalar @command > 0 ) {
+  push @server, '--', @command;
+}
+
+if ( $use_remote_ip eq 'proxy' ) {
+  my $quoted_proxy_command = shell_quote( $0, "--family=$family" );
+  push @sshopts, ( '-S', 'none', '-o', "ProxyCommand=$quoted_proxy_command --fake-proxy -- %h %p" );
+}
+my @exec_argv = ( @ssh, @sshopts, $userhost, '--', $ssh_connection . "$server " . shell_quote( @server ) );
+
+# Override command line for local execution.
+if ( defined( $localhost )) {
+  @exec_argv = ( "$server " . shell_quote( @server ) );
+}
+
+my $pid = open(my $pipe, "-|");
+die "$0: fork: $!\n" unless ( defined $pid );
+if ( $pid == 0 ) { # child
+  open(STDERR, ">&STDOUT") or die;
 
-  if ( scalar @command > 0 ) {
-    push @server, '--', @command;
+  if ( !defined( $localhost) && $use_remote_ip eq 'proxy' ) {
+    # Non-standard shells and broken shrc files cause the ssh
+    # proxy to break mysteriously.
+    $ENV{ 'SHELL' } = '/bin/sh';
   }
 
   if ( defined( $localhost )) {
     delete $ENV{ 'SSH_CONNECTION' };
     chdir; # $HOME
     print "MOSH IP ${userhost}\n";
-    exec( "$server " . shell_quote( @server ) );
-    die "Cannot exec $server: $!\n";
-  }
-  if ( $use_remote_ip eq 'proxy' ) {
-    # Non-standard shells and broken shrc files cause the ssh
-    # proxy to break mysteriously.
-    $ENV{ 'SHELL' } = '/bin/sh';
-    my $quoted_proxy_command = shell_quote( $0, "--family=$family" );
-    push @sshopts, ( '-S', 'none', '-o', "ProxyCommand=$quoted_proxy_command --fake-proxy -- %h %p" );
   }
-  my @exec_argv = ( @ssh, @sshopts, $userhost, '--', $ssh_connection . "$server " . shell_quote( @server ) );
+
   exec @exec_argv;
-  die "Cannot exec ssh: $!\n";
-} else { # parent
-  my ( $sship, $port, $key );
-  my $bad_udp_port_warning = 0;
-  LINE: while ( <$pipe> ) {
-    chomp;
-    if ( m{^MOSH IP } ) {
-      if ( defined $ip ) {
-	die "$0 error: detected attempt to redefine MOSH IP.\n";
-      }
-      ( $ip ) = m{^MOSH IP (\S+)\s*$} or die "Bad MOSH IP string: $_\n";
-    } elsif ( m{^MOSH SSH_CONNECTION } ) {
-      my @words = split;
-      if ( scalar @words == 6 ) {
-	$sship = $words[4];
-      } else {
-	die "Bad MOSH SSH_CONNECTION string: $_\n";
-      }
-    } elsif ( m{^MOSH CONNECT } ) {
-      if ( ( $port, $key ) = m{^MOSH CONNECT (\d+?) ([A-Za-z0-9/+]{22})\s*$} ) {
-	last LINE;
-      } else {
-	die "Bad MOSH CONNECT string: $_\n";
-      }
+  die "Cannot exec child: $!\n";
+}
+# parent
+my ( $sship, $port, $key );
+my $bad_udp_port_warning = 0;
+LINE: while ( <$pipe> ) {
+  chomp;
+  if ( m{^MOSH IP } ) {
+    if ( defined $ip ) {
+      die "$0 error: detected attempt to redefine MOSH IP.\n";
+    }
+    ( $ip ) = m{^MOSH IP (\S+)\s*$} or die "Bad MOSH IP string: $_\n";
+  } elsif ( m{^MOSH SSH_CONNECTION } ) {
+    my @words = split;
+    if ( scalar @words == 6 ) {
+      $sship = $words[4];
     } else {
-      if ( defined $port_request and $port_request =~ m{:} and m{Bad UDP port} ) {
-	$bad_udp_port_warning = 1;
-      }
-      print "$_\n";
+      die "Bad MOSH SSH_CONNECTION string: $_\n";
     }
-  }
-  close $pipe;
-  waitpid $pid, 0;
-
-  if ( not defined $ip ) {
-    if ( defined $sship ) {
-      warn "$0: Using remote IP address ${sship} from \$SSH_CONNECTION for hostname ${userhost}\n";
-      $ip = $sship;
+  } elsif ( m{^MOSH CONNECT } ) {
+    if ( ( $port, $key ) = m{^MOSH CONNECT (\d+?) ([A-Za-z0-9/+]{22})\s*$} ) {
+      last LINE;
     } else {
-      die "$0: Did not find remote IP address (is SSH ProxyCommand disabled?).\n";
+      die "Bad MOSH CONNECT string: $_\n";
     }
+  } else {
+    if ( defined $port_request and $port_request =~ m{:} and m{Bad UDP port} ) {
+      $bad_udp_port_warning = 1;
+    }
+    print "$_\n";
   }
+}
+if ( not close $pipe ) {
+  if ( $! == 0 ) {
+    die_on_exitstatus($?, "server command", shell_quote(@exec_argv));
+  } else {
+    die("$0: error closing server pipe: $!\n")
+  }
+}
 
-  if ( not defined $key or not defined $port ) {
-    if ( $bad_udp_port_warning ) {
-      die "$0: Server does not support UDP port range option.\n";
-    }
-    die "$0: Did not find mosh server startup message. (Have you installed mosh on your server?)\n";
+if ( not defined $ip ) {
+  if ( defined $sship ) {
+    warn "$0: Using remote IP address ${sship} from \$SSH_CONNECTION for hostname ${userhost}\n";
+    $ip = $sship;
+  } else {
+    die "$0: Did not find remote IP address (is SSH ProxyCommand disabled?).\n";
   }
+}
 
-  # Now start real mosh client
-  $ENV{ 'MOSH_KEY' } = $key;
-  $ENV{ 'MOSH_PREDICTION_DISPLAY' } = $predict;
-  $ENV{ 'MOSH_NO_TERM_INIT' } = '1' if !$term_init;
-  exec {$client} ("$client", "-# @cmdline |", $ip, $port);
+if ( not defined $key or not defined $port ) {
+  if ( $bad_udp_port_warning ) {
+    die "$0: Server does not support UDP port range option.\n";
+  }
+  die "$0: Did not find mosh server startup message. (Have you installed mosh on your server?)\n";
 }
 
+# Now start real mosh client
+$ENV{ 'MOSH_KEY' } = $key;
+$ENV{ 'MOSH_PREDICTION_DISPLAY' } = $predict;
+$ENV{ 'MOSH_NO_TERM_INIT' } = '1' if !$term_init;
+exec {$client} ("$client", "-# @cmdline |", $ip, $port);
+
 sub shell_quote { join ' ', map {(my $a = $_) =~ s/'/'\\''/g; "'$a'"} @_ }
 
 sub locale_vars {
@@ -536,3 +550,20 @@ sub resolvename {
   }
   return @res;
 }
+
+sub die_on_exitstatus {
+  my ($exitstatus, $what_command, $exec_string) = @_;
+
+  if (POSIX::WIFSIGNALED($exitstatus)) {
+    my $termsig = POSIX::WTERMSIG($exitstatus);
+    die("$0: $what_command exited on signal $termsig: $exec_string\n" );
+  }
+  if (!POSIX::WIFEXITED($exitstatus)) {
+    die("$0: $what_command unexpectedly terminated with exit status $exitstatus: $exec_string\n");
+  }
+  my $exitcode = POSIX::WEXITSTATUS($exitstatus);
+  if ($exitcode != 0) {
+    die("$0: $what_command failed with exitstatus $exitcode: $exec_string\n");
+  }
+  return;
+}

src/tests/Makefile.am

@@ -31,6 +31,7 @@ displaytests = \
 	pty-deadlock.test \
 	repeat.test \
 	repeat-with-input.test \
+	server-failure.test \
 	server-network-timeout.test \
 	server-signal-timeout.test \
 	window-resize.test \

src/tests/e2e-test

@@ -237,21 +237,21 @@ for run in $server_tests; do
 	if [ "$server_rv" -ne 0 ]; then
 	    test_error "server harness exited with status %s\n" "$server_rv"
 	fi
-    fi
-    if [ "${run}" != "direct" ]; then
-	# Check for "round-trip" failures
-	if grep -q "round-trip Instruction verification failed" "${test_dir}/${run}.server.stderr"; then
-	    test_error "Round-trip Instruction verification failed on server during %s\n" "$run"
-	fi
-	# Check for 0-timeout select() issue
-	if egrep -q "(polls, rate limiting|consecutive polls)" "${test_dir}/${run}.server.stderr"; then
-	    if [ "osx" != "${TRAVIS_OS_NAME}" ]; then
-		test_error "select() with zero timeout called too often on server during %s\n" "$run"
+	if [ "${run}" != "direct" ]; then
+	    # Check for "round-trip" failures
+	    if grep -q "round-trip Instruction verification failed" "${test_dir}/${run}.server.stderr"; then
+		test_error "Round-trip Instruction verification failed on server during %s\n" "$run"
+	    fi
+	    # Check for 0-timeout select() issue
+	    if egrep -q "(polls, rate limiting|consecutive polls)" "${test_dir}/${run}.server.stderr"; then
+		if [ "osx" != "${TRAVIS_OS_NAME}" ]; then
+		    test_error "select() with zero timeout called too often on server during %s\n" "$run"
+		fi
+	    fi
+	    # Check for assert()
+	    if egrep -q "assertion.*failed" "${test_dir}/${run}.server.stderr"; then
+		test_error "assertion during %s\n" "$run"
 	    fi
-	fi
-	# Check for assert()
-	if egrep -q "assertion.*failed" "${test_dir}/${run}.server.stderr"; then
-	    test_error "assertion during %s\n" "$run"
 	fi
     fi
     # XXX We'd also like to check for "target state Instruction

src/tests/server-failure.test

@@ -0,0 +1,69 @@
+#!/bin/sh
+
+#
+# Run mosh with a bad server command, check that it reports this usefully.
+#
+
+# shellcheck source=e2e-test-subrs
+. "$(dirname "$0")/e2e-test-subrs"
+PATH=$PATH:.:$srcdir
+# Top-level wrapper.
+if [ $# -eq 0 ]; then
+    e2e-test "$0" baseline client server mosh-args post
+    exit
+fi
+
+# OK, we have arguments, we're one of the test hooks.
+if [ $# -lt 1 ]; then
+    fail "bad arguments %s\n" "$@"
+fi
+
+# The mosh session test command is never run.
+baseline()
+{
+    printf "@@@ done\n"
+}
+
+# Return inverted exitstatus from mosh-client.
+client()
+{
+    ! "$@"
+    exit
+}
+
+# Add a do-nothing server command, to disable the standard harness
+# checks in e2e-test.
+server()
+{
+    exit 0
+}
+
+# Make mosh.pl fail with a bad server.
+mosh_args()
+{
+    printf "%s\n" "--server false"
+}
+
+# Check for correct reporting of that failure.
+post()
+{
+    if ! grep 'server command failed with exitstatus' "$(basename "$0").d/baseline.tmux.log"; then
+	exit 1
+    fi
+}
+
+case $1 in
+    baseline)
+	baseline;;
+    client)
+	shift
+	client "$@";;
+    mosh-args)
+	mosh_args;;
+    post)
+	post;;
+    server)
+	server;;
+    *)
+	fail "unknown test argument %s\n" "$1";;
+esac