Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
vncxfer: A CGI script to set up TCP redirection between a VNC Viewer # and VNC Server using the Web Server as a relay point.
#!/usr/bin/perl
#!/usr/local/bin/perl
#
# vncxfer: A CGI script to set up TCP redirection between a VNC Viewer
# and VNC Server using the Web Server as a relay point.
#
# Copy this to a place on a website where CGI scripts will be run.
# e.g. http://somesite.com/cgi-bin/vncxfer
#
# One user goes to the the above URL and chooses a session name and then
# clicks "Submit". That starts up a helper program on the web server to
# act as a relay.
#
# The other user does the same, using the SAME session name.
#
# The page that is returned to them tells them the port number and VNC
# Host:Display to use in their viewer or VNC server.
#
# The VNC Server makes a reverse VNC connection to the relay point.
# e.g. somesite:com:5950
#
# The VNC Viewer makes a normal VNC connection to the relay point.
# e.g. vncviewer somesite:com:50
#
# Unfortunately most Web servers will not allow this sort of thing:
#
# 1) They forbid running CGI programs that run as daemons that listen
# on TCP ports for incoming connections.
#
# 2) The firewall configuration of the webserver disallows connections
# to the "session" ports, e.g. 5950, etc.
#
# Put here a list of ports to use for transfer sessions. The Web server's
# firewall configuration MUST NOT block this port(s).
#
my @allowed_ports = qw(
5955
5956
5957
5958
5959
5960
);
# Maximum time in seconds to wait for both the VNC Viewer
# and VNC Server to connect:
#
my $max_wait = 300;
# The form action="..." program, it may need to be "/cgi-bin/vncxfer", etc.
#
my $program = "vncxfer";
##########################################################################
# no config needed below here.
use POSIX qw(setsid);
my $oldsockets = 0;
if (! $oldsockets) {
use IO::Socket::INET;
}
my $oldfh = 'LISTEN000';
if (@ARGV && $ARGV[0] =~ /^vncxfer:/) {
# Started in session helper mode:
helper($ARGV[0]);
exit 0;
}
# Parse CGI request:
#
my $request;
if ($ENV{'REQUEST_METHOD'} eq "POST") {
read(STDIN, $request, $ENV{'CONTENT_LENGTH'});
} elsif ($ENV{'REQUEST_METHOD'} eq "GET" ) {
$request = $ENV{'QUERY_STRING'};
} else {
$request = $ARGV[0];
}
my %request = &url_decode(split(/[&=]/, $request));
# html for top and bottom:
#
my $htop = "<html><body BGCOLOR=#FFFFFF>\n";
my $hbot = "</body></html>\n";
select(STDERR); $| = 1;
select(STDOUT); $| = 1;
# content-type:
#
print STDOUT "Content-Type: text/html\r\n";
# see if session is set:
#
my $session = '';
if (exists $request{session}) {
$session = $request{session};
}
$session =~ s/\W//g; # word characters only.
if ($session eq '') {
# No session, show the create-a-session form:
print STDOUT "\r\n";
print_form();
exit 0;
}
# determine hostnames and IP addresses:
#
my $server = $ENV{HTTP_HOST};
$server =~ s/:\d+//g;
my ($nm, $aliases, $type, $len, @addrs) = gethostbyname($server);
my $server_ip = join('.', unpack('C4', $addrs[0]));
my $sport = $ENV{SERVER_PORT};
# find an existing session, or start one up:
#
my $port = find_or_start_session($session);
if ($port ne '') {
# print some http header lines indicating the port:
#
my $disp = $port - 5900;
print STDOUT "VNC-Host-Display: $server:$disp\r\n";
print STDOUT "VNC-IP-Display: $server_ip:$disp\r\n";
print STDOUT "VNC-Host-Port: $server:$port\r\n";
print STDOUT "VNC-IP-Port: $server_ip:$port\r\n";
print STDOUT "\r\n";
# print connection info to the browser:
#
print STDOUT <<END;
$htop
<b>VNC Transfer (vncxfer)</b>
<p>
Your VNC session name is: $session<br>
Your VNC session port is: $port<br>
Both VNC Viewer and Server must connect within $max_wait seconds.<br>
<p>
For the VNC Viewer, use either of these as VNC Host displays:
<p>
&nbsp;&nbsp;&nbsp;$server:$disp
<p>
&nbsp;&nbsp;&nbsp;$server_ip:$disp
<p>
E.g.:
<pre>
vncviewer $server_ip:$disp
</pre>
&nbsp;<br>
<p>
For the VNC Server, it needs to do a reverse connection to either of these:
<p>
&nbsp;&nbsp;&nbsp;$server:$port
<p>
&nbsp;&nbsp;&nbsp;$server_ip:$port
<p>
E.g.:
<pre>
x11vnc -connect $server_ip:$port
</pre>
$hbot
END
} else {
print STDOUT "\r\n";
# whoops:
#
print STDOUT <<END;
$htop
<b>VNC Transfer (vncxfer)</b>
<p>
<font color="red">A Free VNC Port could not be found or the helper could not be started!</font>
$hbot
END
}
exit 0;
#######################################################################
sub url_decode {
foreach (@_) {
tr/+/ /;
s/%(..)/pack("c",hex($1))/ge;
}
@_;
}
# starting form:
#
sub print_form {
print STDOUT <<END;
<html>
<body BGCOLOR=#FFFFFF>
<b>VNC Transfer (vncxfer)</b>
<p>
To start a VNC Transfer agent for you, enter a name for your session:
<p>
<form name="start" action="$program" method="get">
<b>Your Session Name:</b> <input type="text" name="session" value="" size=12>
<b><input type="submit" value="Submit"></b>
<form>
<p>
This name will be used by the other VNC party to identify the session and connect with you.
</body>
</html>
END
}
sub do_listen {
my $port = shift;
if (! $oldsockets) {
my $sock = IO::Socket::INET->new(
Listen => 2,
LocalPort => $port,
Proto => "tcp"
);
return $sock;
} else {
my $AF_INET = 2;
my $SOCK_STREAM = 1;
my $SockAddr = 'S n a4 x8';
my ($n1, $a1, $proto) = getprotobyname('tcp');
my $us = pack($SockAddr, $AF_INET, $port, "\0\0\0\0");
my $listen = ++$oldfh;
my $package = caller;
$listen =~ s/^[^']+$/$package'$&/;
if (! socket($listen, $AF_INET, $SOCK_STREAM, $proto)) {
return '';
}
if (! bind($listen, $us)) {
return '';
}
if (! listen($listen, 2)) {
return '';
}
return $listen;
}
}
sub find_or_start_session {
my $session = shift;
chdir("/tmp");
# we scrape ps(1) output to find an existing session:
#
my $ps = "ps";
if (-f "/usr/ucb/ps") {
$ps = "/usr/ucb/ps";
}
open(PS, "env COLUMNS=256 $ps wwwwwwwwaux |");
while (<PS>) {
if (/\bvncxfer:(\w+):(\d+)/) {
my $s = $1;
my $p = $2;
if ($s eq $session) {
return $p;
}
}
}
close PS;
# no session, so we will start it.
# look for a free port:
#
my $use_port = '';
foreach my $p (@allowed_ports) {
my $sock = do_listen($p);
if ($sock) {
$use_port = $p;
close $sock;
last;
}
}
if ($use_port eq '') {
# all in use.
return '';
}
# start the helper in the background:
#
my $pf = fork();
if (! defined $pf) {
return '';
} elsif ($pf) {
sleep 2;
wait;
} else {
close STDIN;
close STDOUT;
close STDERR;
POSIX::setsid();
sleep 1;
system("$0 'vncxfer:$session:$use_port' &");
exit 0;
}
sleep 2;
return $use_port;
}
# SIGALRM timeout handler:
#
sub timeout {
close LOG;
exit 0;
}
sub helper {
my $tag = shift;
# set this to somefile for logging:
#open(LOG, ">>/tmp/vncxfer.log");
open(LOG, ">/dev/null");
select(LOG); $| = 1;
close(STDERR);
open(STDERR, ">&LOG");
# split the vncxfer:session:port string:
#
my ($name, $session, $port) = split(/:/, $tag, 3);
# check port:
#
if ($port !~ /^\d+$/) {
print LOG "bad port $tag\n";
close LOG;
exit 1;
}
# try to listen on port:
#
my $sock = do_listen($port);
if (! $sock) {
print LOG "bad sock $tag\n";
close LOG;
exit 1;
}
# set timeout handler:
#
$SIG{ARLM} = \&timeout;
alarm($max_wait);
# wait for first connection:
#
my ($client1, $ip1, $client2, $ip2);
if (! $oldsockets) {
($client1, $ip1) = $sock->accept();
} else {
$client1 = ++$oldfh;
my $package = caller;
$client1 =~ s/^[^']+$/$package'$&/;
$ip1 = accept($client1, $sock);
}
print LOG "1st connection $tag $ip1\n";
# wait for second connection:
#
if (! $oldsockets) {
($client2, $ip2) = $sock->accept();
} else {
$client2 = ++$oldfh;
my $package = caller;
$client2 =~ s/^[^']+$/$package'$&/;
$ip2 = accept($client2, $sock);
}
print LOG "2nd connection $tag $ip2\n";
alarm(0);
$SIG{ALRM} = 'DEFAULT';
# no need to listen anymore:
#
close($sock);
# fork a child to handle I/O one direction, and
# we do the other direction:
#
my $parent = $$;
my $child = fork;
if (! defined $child) {
exit 1;
}
if ($child) {
print LOG "pproxy parent\[$$] STDIN -> socket\n";
xfer($client1, $client2);
select(undef, undef, undef, 0.25);
if (kill 0, $child) {
select(undef, undef, undef, 1.5);
kill "TERM", $child;
}
} else {
print LOG "pproxy child \[$$] socket -> STDOUT\n";
xfer($client2, $client1);
select(undef, undef, undef, 0.25);
if (kill 0, $parent) {
select(undef, undef, undef, 1.5);
kill "TERM", $parent;
}
}
exit;
}
# utlity to transfer bytes from one socket to another:
# taken from PPROXY in ss_vncviewer.
#
sub xfer {
my($in, $out) = @_;
$RIN = $WIN = $EIN = "";
$ROUT = "";
vec($RIN, fileno($in), 1) = 1;
vec($WIN, fileno($in), 1) = 1;
$EIN = $RIN | $WIN;
while (1) {
my $nf = 0;
while (! $nf) {
$nf = select($ROUT=$RIN, undef, undef, undef);
}
my $len = sysread($in, $buf, 8192);
if (! defined($len)) {
next if $! =~ /^Interrupted/;
print STDERR "pproxy\[$$]: $!\n";
last;
} elsif ($len == 0) {
print STDERR "pproxy\[$$]: Input is EOF.\n";
last;
}
my $offset = 0;
my $quit = 0;
while ($len) {
my $written = syswrite($out, $buf, $len, $offset);
if (! defined $written) {
print STDERR "pproxy\[$$]: Output is EOF. $!\n";
$quit = 1;
last;
}
$len -= $written;
$offset += $written;
}
last if $quit;
}
close($in);
close($out);
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.