Check TLS (https) certificate

tls_check.go

package main

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

var (
	domain *string
	port   *int
)

type target struct {
	domain string
	port   int
}

func init() {

	domain = flag.String("d", "", "Domain to ckeck.")
	port = flag.Int("p", 443, "Http port. Default is 443.")
}

func (t *target) Url() string {
	if t.port == 0 {
		return fmt.Sprintf("%s:443", t.domain)
	}

	return fmt.Sprintf("%s:%d", t.domain, t.port)

}

func (t *target) CheckTLS() {
	conn, err := tls.Dial("tcp", t.Url(), nil)
	if err != nil {
		fmt.Println("[ERROR] Server doesn't support SSL certificate err: " + err.Error())
	} else {
		err = conn.VerifyHostname(t.domain)
		if err != nil {
			fmt.Println("Hostname doesn't match with certificate: " + err.Error())
		}

		expiry := conn.ConnectionState().PeerCertificates[0].NotAfter
		fmt.Printf("Issuer: %s\nExpiry: %v\n", conn.ConnectionState().PeerCertificates[0].Issuer, expiry.Format(time.RFC850))

		currentTime := time.Now()
		diff := currentTime.Sub(expiry)
		if diff > 0 {
			fmt.Println("EXPIRED!!")
		}

	}

}

func main() {

	var t target

	// parse flags from command line
	flag.Parse()

	if *domain == "" {
		log.Println("[ERROR] domain can't be empty.")
		os.Exit(0)
	}

	t = target{domain: *domain, port: *port}

	t.CheckTLS()

}