scripts/mosh: Add -6 option to connect with IPv6

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

man/mosh.1

@@ -120,6 +120,19 @@ Synonym for \-\-predict=always
 .B \-n
 Synonym for \-\-predict=never
 
+.TP
+.B --family=\fIFAMILY\fP
+Force the use of a particular address family, which defaults to `inet'
+(IPv4), and can also be `inet6' (IPv6; requires IO::Socket::IP).
+
+.TP
+.B -4
+Synonym for \-\-family=inet
+
+.TP
+.B -6
+Synonym for \-\-family=inet6
+
 .TP
 .B \-p \fIPORT\fP[:\fIPORT2\fP], \-\-port=\fIPORT\fP[:\fIPORT2\fP]
 Use a particular server-side UDP port or port range,

scripts/mosh

@@ -46,6 +46,7 @@ my $predict = undef;
 
 my $bind_ip = undef;
 
+my $family = 'inet';
 my $port_request = undef;
 
 my $ssh = 'ssh';
@@ -69,6 +70,8 @@ qq{Usage: $0 [options] [--] [user@]host [command...]
 -n      --predict=never         never use local echo
         --predict=experimental  aggressively echo even when incorrect
 
+-4      --family=inet        use IPv4 only [default]
+-6      --family=inet6       use IPv6 only
 -p PORT[:PORT2]
         --port=PORT[:PORT2]  server-side UDP port or range
         --bind-server={ssh|any|IP}  ask the server to reply from an IP address
@@ -110,6 +113,9 @@ GetOptions( 'client=s' => \$client,
 	    'port=s' => \$port_request,
 	    'a' => sub { $predict = 'always' },
 	    'n' => sub { $predict = 'never' },
+	    'family=s' => \$family,
+	    '4' => sub { $family = 'inet' },
+	    '6' => sub { $family = 'inet6' },
 	    'p=s' => \$port_request,
 	    'ssh=s' => \$ssh,
 	    'init!' => \$term_init,
@@ -168,13 +174,16 @@ if ( not defined $bind_ip or $bind_ip =~ m{^ssh$}i ) {
 
 if ( defined $fake_proxy ) {
   use Errno qw(EINTR);
+  BEGIN { eval { require IO::Socket::IP; IO::Socket::IP->import('-register'); }; }
   use POSIX qw(_exit);
 
   my ( $host, $port ) = @ARGV;
 
   # Resolve hostname and connect
-  my $sock = IO::Socket->new( Domain => AF_INET,
-			      Family => AF_INET,
+  my $afstr = 'AF_' . uc( $family );
+  my $af = eval { IO::Socket->$afstr } or die "$0: Invalid family $family\n";
+  my $sock = IO::Socket->new( Domain => $af,
+			      Family => $af,
 			      PeerHost => $host,
 			      PeerPort => $port,
 			      Proto => "tcp" )
@@ -254,7 +263,7 @@ if ( $pid == 0 ) { # child
     push @server, '--', @command;
   }
 
-  my $quoted_self = shell_quote( $0 );
+  my $quoted_self = shell_quote( $0, "--family=$family" );
   exec "$ssh " . shell_quote( '-S', 'none', '-o', "ProxyCommand=$quoted_self --fake-proxy -- %h %p", '-n', '-tt', $userhost, '--', "$server " . shell_quote( @server ) );
   die "Cannot exec ssh: $!\n";
 } else { # parent