ip-discover: Setup a device for discovery on a network using socat

README.md

ip-discover

Setup a device for discovery on a network using socat

On the device to be discovered:

• Copy ip-discovery to /usr/bin and run chmod +x /usr/bin/ip-discovery
• Copy ip-discovery.service to /etc/systemd/system, adjust the code-word, and run sudo systemctl daemon-reload && sudo systemctl start ip-discovery

On the device wanting to discover the device to be discovered:

• Copy ip-discover to your home folder and run . ~/ip-discover
• Discover the device to be discovered by running ip-discover code-word
• Update your SSH config and see the changes by running ssh-ip-discover code-word

gistfile1.txt

# $ sudo tcpdump -v -n -A "(src host 192.168.0.176 and dst port 1900) or (src host 192.168.0.251 and dst port 1900)"
use 5.010;
use IO::Socket::Multicast;
 
my $s = IO::Socket::Multicast->new(LocalPort=>1900, ReuseAddr=>1) or die $!;
$s->mcast_add('239.255.255.250');
$s->mcast_loopback(0);
$_ and say $_ while $_ = search($s);

sub search {
  my $s = shift;
  sleep 1;
  $s->mcast_send(qq(M-SEARCH * HTTP/1.1\r\nMx: 5\r\nSt: ssdp:all\r\nMan: "ssdp:discover"\r\nUser-Agent: UPnP/1.1 mac/1.0 upnpx/1.0\r\nConnection: close\r\nHost: 239.255.255.250:1900\r\n), '239.255.255.250:1900');
  $s->recv(my $data, 1024);
  return $data;
}

how-to-socat

From: https://github.com/dannybackx/arduino-upnp/blob/master/libraries/UPnP/examples/UPnP/scripts/how-to-socat

Monitor messages in the UPnP multicast group :

socat UDP4-RECVFROM:1900,ip-add-membership=239.255.255.250:0.0.0.0,fork -

Send a message to UPnP via multicast :

cat >x <<end
NOTIFY * HTTP/1.1
HOST: 239.255.255.250:1900
NT: upnp:rootdevice
NTS: ssdp:alive
CACHE-CONTROL: max-age=1200
SERVER: Arduino/1.0 UPNP/1.1 UPnP Motion Sensor Kit/32302000102
USN: uuid:38323636-4558-4dda-9188-cda0e606724c
LOCATION: http://192.168.1.99:80/this-is-fake-description.xml

end
cat x | socat - UDP4-DATAGRAM:239.255.255.250:1900,bind=:2900,ip-add-membership=239.255.255.250:eth0

ip-discover

ip-discover () 
{ 
    which socat &>/dev/null || { echo "missing socat"; return 1; }
    while :; do
        ip="$(echo -n ${1:-ip-discovery} | socat STDIO UDP4-DATAGRAM:255.255.255.255:6666,broadcast,range=0.0.0.0/0)";
        test -n "$ip" && { 
            echo $ip;
            break
        } || echo -n . >&2
        sleep 1;
    done
}

ssh-ip-discover ()
{
  [ -z "$1" ] && { echo "Usage: $FUNCNAME host"; return 2; }
  config=${SSH_CONFIG:-~/.ssh/config}
  perl -pi.bak -E 'BEGIN { $/="\n\n"; ($host, $ip) = (shift @ARGV, shift @ARGV); } next unless /^Host $host/i; s/Hostname\s+([\d\.]+)/Hostname $ip/is' $1 $(ip-discover $1) $config
  test -e $config.bak || return 1
  echo "$config backed up to $config.bak"
  diff $config.bak $config
}

ip-discovery

#!/usr/bin/env bash

read key
[ "$key" == "${1:-${0##*/}}" ] && echo $SOCAT_IP_LOCADDR

ip-discovery.service

[Unit]
Description=Allow discovery via broadcast UDP
After=network.target

[Service]
Type=simple
ExecStart=socat UDP4-RECVFROM:6666,fork,so-broadcast,so-timestamp,ip-pktinfo,ip-recverr,ip-recvopts,ip-recvtos SYSTEM:"/usr/bin/ip-discovery code-word"
# Discover IP using:
# $ echo -n code-word | socat STDIO UDP4-DATAGRAM:255.255.255.255:6666,broadcast,range=0.0.0.0/0
KillMode=process

[Install]
WantedBy=multi-user.target