addrserv.go

// This program is a simple web server that listens for IP address
// updates. There's no authentication or security at all; I use it
// to keep track of beaglebones on a LAN.
package main

import (
        "fmt"
        "log"
        "net/http"
        "os"
        "time"
)

type entry struct {
        IP     string
        Update time.Time
}

var table = map[string]*entry{}

func receiveAddr(w http.ResponseWriter, r *http.Request) {
        log.Printf("%s %s", r.RemoteAddr, r.URL)
        ip := r.FormValue("ip")
        host := r.FormValue("host")

        table[host] = &entry{
                IP:     ip,
                Update: time.Now(),
        }
}

func displayIP(w http.ResponseWriter, r *http.Request) {
        log.Printf("%s %s", r.RemoteAddr, r.URL)
        for host, entry := range table {
                out := fmt.Sprintf("%s\n\tIP: %s\n\tUpdate: %s\n",
                        host, entry.IP, entry.Update)
                w.Write([]byte(out))
        }
}

func dropHost(w http.ResponseWriter, r *http.Request) {
        log.Printf("%s %s", r.RemoteAddr, r.URL)
        host := r.FormValue("host")
        delete(table, host)
}

func main() {
        port := os.Getenv("PORT")
        if port == "" {
                port = "8080"
        }

        http.HandleFunc("/", displayIP)
        http.HandleFunc("/update", receiveAddr)
	http.HandleFunc("/delete", dropHost)
        log.Fatal(http.ListenAndServe(":"+port, nil))
}

update-ip.sh

# Throw this in /etc/network/if-up.d, chmod+x, and when your machine's
# network comes up, it will send it's address to the server. It will
# always exit without error to ensure that it doesn't conflict with
# booting.
#!/bin/sh
SERVER=addr.example.local
PORT=8080

[ -z "$IFACE" ] && exit 0
[ "$IFACE" != "lo" ] || exit 0

IP="$(ifconfig $IFACE | grep inet | grep -v inet6 | awk '{print $2;}' | awk -F: '{print $2;}')"
echo "$IFACE IP: ${IP}"
[ -z "$IP" ] && exit 0

curl "$SERVER:$PORT/update?ip=$IP&host=$(hostname)-$IFACE"