Very basic icanhazip.com-like service

remoteip.go

package main

import (
        "flag"
        "fmt"
        "log"
        "net"
        "net/http"
        "strings"
)

var addr = flag.String("l", ":8080", "listen on port")

func main() {
        flag.Parse()

        http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
                ra := r.RemoteAddr
                if ip := r.Header.Get("X-Forwarded-For"); ip != "" {
                        ra = ip
                } else if ip := r.Header.Get("X-Real-IP"); ip != "" {
                        ra = ip
                } else {
                        ra, _, _ = net.SplitHostPort(ra)
                }

                ra = strings.Split(ra, ",")[0]

                fmt.Fprintf(w, ra)
        })

        log.Printf("Listening for requests on %s", *addr)
        log.Fatal(http.ListenAndServe(*addr, nil))
}