dev_gateway

   1 #!/usr/bin/env perl
   2 use strict;
   3 use warnings;
   4
   5 use Pod::Usage;
   6 use Getopt::Long;
   7
   8 use Memoize;
   9 memoize('list_busy_ports');
  10
  11 use Socket;
  12
  13 #use Smart::Comments;
  14
  15 ### process options
  16 my $gateway_host = 'sgn-devel.sgn.cornell.edu';
  17 my $local_port   = 80;
  18 my $user = '';
  19 my $gateway_port;
  20 my @allowed_gateway_ports = 8080..8090;
  21
  22 GetOptions( 'port|p=i'        => \$local_port,
  23             'user|u=s'        => \$user,
  24             'remote_port|r=i' => \$gateway_port,
  25           )
  26     or pod2usage('invalid options');
  27
  28 $gateway_host = shift @ARGV if @ARGV;
  29 pod2usage() if @ARGV;
  30 $user .= '@' if $user;
  31
  32 ### make sure this is a valid hostname before trying the ssh commands
  33 # (the error checking on the ssh commands leaves a bit to be desired)
  34 validate_hostname( $gateway_host );
  35
  36 ### find an available port
  37 my $host = "$user$gateway_host";
  38 $gateway_port ||= find_available_port( $host, @allowed_gateway_ports );
  39
  40 is_port_available( $host, $gateway_port )
  41     or die "Remote port $gateway_port already in use, cannot set up gateway.\n";
  42
  43 ### open the ssh connection
  44 print "Forwarding local port $local_port to http://$gateway_host:$gateway_port\n";
  45 print "Press Ctrl-c to close the connection.\n";
  46 exec "ssh -N -R $gateway_port:localhost:$local_port '$user$gateway_host'";
  47
  48
  49 ############ subroutines
  50
  51 sub validate_hostname {
  52     my $host = shift;
  53     die "Could not resolve hostname $host\n" unless gethostbyname( $host );
  54 }
  55
  56 sub find_available_port {
  57     my ( $ssh_host, @acceptable_ports ) = @_;
  58
  59     my $busy_ports = list_busy_ports( $ssh_host );
  60
  61     die "Failed to connect to $user$gateway_host\n"
  62         unless %$busy_ports;
  63
  64     for( @acceptable_ports ) {
  65         return $_ unless $busy_ports->{$_};
  66     }
  67
  68     die "All remote ports seem to be busy.\n",
  69         "Tried ports ".join(', ',@acceptable_ports).".\n";
  70 }
  71
  72 sub list_busy_ports {
  73     my ( $ssh_host ) = @_;
  74
  75     ### use netstat on the remote host to find ports that are already in use
  76
  77     my %busy_ports;
  78     open( my $netstat, "ssh '$user$gateway_host' 'netstat -ltunp 2>/dev/null' |" ) or die "$! running ssh\n";
  79     while( <$netstat> ) {
  80         #no warnings 'uninitialized';
  81         my $local = ( split )[3];
  82         my ($busy_port) = $local =~ /:(\d+)/
  83             or next;
  84         $busy_ports{$busy_port} = 1;
  85     }
  86
  87     ### busy_ports: %busy_ports
  88
  89     # hash of {  port_number => 1 }
  90     return \%busy_ports;
  91 }
  92
  93 sub is_port_available {
  94     my ( $ssh_host, $port ) = @_;
  95
  96     my $busy_ports = list_busy_ports( $ssh_host );
  97
  98     return ! $busy_ports->{$port};
  99 }
 100
 101 __END__
 102
 103 =head1 NAME
 104
 105 dev_gateway - use C<ssh> to make a remote machine act as a gateway to a local port
 106
 107 =head1 SYNOPSIS
 108
 109   dev_gateway foo.example.com
 110
 111   dev_gateway -u bob -p 5432 foo.example.com
 112
 113   dev_gateway --user alice --p 3000 foo.example.com
 114
 115 =head1 OPTIONS
 116
 117 =over 8
 118
 119 =item  -p --port  <num>
 120
 121 Port on the local machine to forward.  Default 80.
 122
 123 =item  -u --user  <name>
 124
 125 Username to connect as.  Defaults to current local user.
 126
 127 =item  -r --remote_port <number>
 128
 129 Force the remote port to use.  Should usually be in the range 8080 - 8090.
 130
 131 =back
 132
 133 =cut