ip-checker/main.go

package main

import (
	"fmt"
	"html/template"
	"log"
	"net/http"
	"os"
	"strings"
)

type ServerConfig struct {
	listen string
}

func main() {
	config := ServerConfig{
		listen: getEnvOr("IP_CHECKER_LISTEN", ":8080"),
	}

	tmpl := template.Must(template.ParseFiles("assets/index.html"))

	http.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("./assets/static"))))

	http.HandleFunc("/{$}", func(w http.ResponseWriter, r *http.Request) {
		handleRequest(w, r, tmpl)
	})

	http.HandleFunc("/robots.txt", func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, `User-Agent: *
Disallow: /harming/humans
Disallow: /ignoring/human/orders
Disallow: /harm/to/self
`)
	})

	log.Printf("Starting server on %s", config.listen)
	log.Fatal(http.ListenAndServe(config.listen, nil))
}

func handleRequest(w http.ResponseWriter, r *http.Request, tmpl *template.Template) {
	sourceIP := func() string {
		if r.Header.Get("CF-Connecting-IP") != "" {
			return r.Header.Get("CF-Connecting-IP")
		}
		if r.Header.Get("X-Forwarded-For") != "" {
			return r.Header.Get("X-Forwarded-For")
		}
		return strings.Split(r.RemoteAddr, ":")[0]
	}()

	isHeadless := strings.HasPrefix(r.Header.Get("User-Agent"), "curl/")

	log.Printf("r.URL.Path: %s, sourceIP: %s, isHeadless: %t, User-Agent: %s", r.URL.Path, sourceIP, isHeadless, r.Header.Get("User-Agent"))

	if isHeadless {
		fmt.Fprintf(w, "%s\n", sourceIP)
	} else {
		csp := []string{
			"default-src 'none'",
			"img-src 'self'",
			"script-src-elem 'self'",
			"style-src-elem 'self' fonts.googleapis.com",
			"font-src fonts.gstatic.com",
			"connect-src api.ip.sb api-v3.speedtest.cn api.ipapi.is",
		}
		w.Header().Set("Content-Security-Policy", strings.Join(csp, "; "))

		data := map[string]string{
			"sourceIP": sourceIP,
		}

		err := tmpl.Execute(w, data)
		if err != nil {
			http.Error(w, "Unable to load template", http.StatusInternalServerError)
			log.Printf("Template execution error: %v", err)
			return
		}
	}
}

func getEnvOr(key, defaultValue string) string {
	if value, exists := os.LookupEnv(key); exists {
		return value
	}
	return defaultValue
}