prints when a cert expires

certlife.go

package main

import (
	"crypto/tls"
	"fmt"
	"log"
	"os"
	"time"
)

func main() {
	var host, port string
	if len(os.Args) == 3 {
		host = os.Args[1]
		port = os.Args[2]
	} else {
		fmt.Println("Please specify Host and Port.")
		os.Exit(1)
	}

	conn, err := tls.Dial("tcp", fmt.Sprintf("%s:%s", host, port), &tls.Config{})
	if err != nil {
		log.Fatalln(err)
	}
	defer conn.Close()

	certs := conn.ConnectionState().PeerCertificates
	loc, _ := time.LoadLocation("Europe/Berlin")

	var cert time.Time
	for _, c := range certs {
		fmt.Println(c.NotAfter.In(loc), "\t", c.Subject)
		if !c.IsCA {
			cert = c.NotAfter
		}
	}

	diff := time.Until(cert)

	if diff < 24*time.Hour {
		fmt.Printf("\nExpires in: \033[1;31m%.0f\033[0m hours.\n", diff.Hours())
	} else {
		fmt.Printf("\nExpires in: \033[1;32m%.0f\033[0m days.\n", diff.Hours()/24)
	}
}