package main

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

var PROXY_HEADER string = os.Getenv("PROXY_HEADER")

func respondWithIp(writer http.ResponseWriter, request *http.Request) {
	remote := request.RemoteAddr
	if PROXY_HEADER != "" {
		ipHeader := request.Header[PROXY_HEADER]
		if len(ipHeader) != 1 {
			fmt.Println("Error: Reading proxy header", PROXY_HEADER, "in request from", request.RemoteAddr, "got", ipHeader)
			writer.WriteHeader(http.StatusInternalServerError)
			fmt.Fprintf(writer, "Internal Server Error")
			return
		}
		remote = ipHeader[0]
	}
	fmt.Fprintf(writer, "%s\n", remote)
}

func main() {
	addr := ":8080"
	http.HandleFunc("/", respondWithIp)
	fmt.Println("Starting server on", addr)
	http.ListenAndServe(addr, nil)
}