Find online hosts in own subnet, serve results as JSON over HTTP

• Crude demo-hack, written entirely in Shell-script
• Runs without dependencies in Alpine Linux-container
• Does network host discovery using ICMP Echo (ping) and filters responding hosts. (NOTE: ICMP echo-replies must be enabled, net.ipv4.icmp_echo_ignore_all=0)
• Single shell script for ICMP flooding, "web-server" + JSON encoding (host-disco/icmp_discov_httpd.sh)
• Serves output as JSON over HTTP ("web server" runs on port 1500 by default), example-output:

  {
      "hosts": [
          "172.24.0.1",
          "172.24.0.4",
          "172.24.0.3",
          "172.24.0.5",
          "172.24.0.2"
      ]
  }

• MQTT server aka mosquitto
• MQTT clients aka client-1 & client-2
• ICMP host-discovery-service aka host-disco (see host-disco/icmp_discov_httpd.sh)

Ignore the MQTT server and clients, they are only included to have hosts to discover.

The scripts run-test.sh/run-test.cmd demonstrates this, by starting all services and then gradually stopping them again.

Running the script demonstrates the host-discovery service responding to changes approximately within a second.