Prints "NotAfter" field of a certificate for each host in tls.txt

expired.go

package main

import (
	"bufio"
	"crypto/tls"
	"time"
	"net"
	"fmt"
	"os"
)

func main() {
	file, err := os.Open("tls.txt")
	if err != nil {
		panic(err)
	}
	defer file.Close()
	hosts := []string{}
	scanner := bufio.NewScanner(file)
	for scanner.Scan() {
		hosts = append(hosts, scanner.Text())
	}
	if scanner.Err() != nil {
		panic("error")
	}
	for _, h := range hosts {
		tconn, err := net.DialTimeout("tcp", h, 600*time.Millisecond)
		if err != nil {
			continue
		}
		conn := tls.Client(tconn, &tls.Config{InsecureSkipVerify: true})
		defer conn.Close()
		if err := conn.Handshake(); err != nil {
			continue
		}
		state := conn.ConnectionState()
		cert := state.PeerCertificates[0]
		fmt.Println(h, "\nNot valid after:", cert.NotAfter)
	}
}