#!/bin/bash
set -euo pipefail

# ==== Variables ====
# Output warning if fewer than this number of seconds until expiry
WARNSECONDS=1209600 # Two weeks
# File containing a newline separated list of host:port combinations to be checked, e.g.:
# example.org
# example.org:1234
# 1.2.3.4
# 1.2.3.4:1234
# [2001:12:34::]
# [2001:12:34::]:1234
HOSTSANDPORTS="hostsandports.txt"
# Number of seconds before OpenSSL should timeout when connecting to hosts
TIMEOUT=10
# ==== Variables ====

IPV4REGEX="((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(\.|$)){4}"
IPV6REGEX="(([0-9a-fA-F]{1,4}:){7,7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,7}:|([0-9a-fA-F]{1,4}:){1,6}:[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,5}(:[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}:){1,4}(:[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}:){1,3}(:[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}:){1,2}(:[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}:((:[0-9a-fA-F]{1,4}){1,6})|:((:[0-9a-fA-F]{1,4}){1,7}|:)|fe80:(:[0-9a-fA-F]{0,4}){0,4}%[0-9a-zA-Z]{1,}|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])|([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])\.){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]))"

# Loop through all host:port combinations
while read -r HOSTANDPORT ; do

#  echo "DEBUG: HOSTANDPORT: $HOSTANDPORT."

  # Get the host and port
  # Is it an IPv6 address?
  if echo "$HOSTANDPORT" | grep -P "^\[$IPV6REGEX" ; then
    HOST=$(echo "$HOSTANDPORT" | grep -Eo "^\[.*?\]" | sed "s/\[//g ; s/\]//g")
    PORT=$(echo "$HOSTANDPORT" | sed "s/.*\]//" | cut -s -d ":" -f "2")
  # Let's assume it's an IPv4 address or a hostname
  else
    HOST=$(echo "$HOSTANDPORT" | cut -d ":" -f "1")
    # Port after colon, or nothing if no port given (assumes 443 later on)
    PORT=$(echo "$HOSTANDPORT" | cut -s -d ":" -f "2")
  fi

#  echo "DEBUG: HOST: $HOST."

  # Assume no STARTTLS (unless special ports later on)
  STARTTLS=""

  if [ "$PORT" = "" ] ; then
    # Assume 443 if no port specified
    PORT=443
  elif [ "$PORT" -eq 25 ] ; then
    # Assume SMTP STARTTLS if port 25
    STARTTLS="-starttls smtp"
  elif [ "$PORT" -eq 143 ] ; then
    # Assume IMAP STARTTLS if port 143
    STARTTLS="-starttls imap"
  fi

#  echo "DEBUG: PORT: $PORT."
#  echo "DEBUG: STARTTLS: $STARTTLS."

  # Sanity check (IPv4)
  NOIPV4=0
  # Does it have an A record?
  if [ $(dig A "$HOST" +short | wc -l) -eq 0 ] ; then
    NOIPV4=1
  fi
  # Is it in fact an IPv4 address?
  if echo "$HOST" | grep -Pq "^$IPV4REGEX$" ; then
    NOIPV4=0
  fi

  # Try various TLS versions against this host:port to try and get a response (IPv4)
  EXPIRYSTRING4=0
  RETCODE=1
  for PROTOCOL in -tls1_3 -tls1_2 -tls1_1 -tls1 ; do
    if [ "$NOIPV4" -eq 1 ] ; then
      break
    fi
    if [ "$RETCODE" -eq 0 ] ; then
      break
    fi
    set +e
    # Get the "Not After" field for the certificate expiry
    EXPIRYSTRING4=$(echo "Q" | timeout "$TIMEOUT" openssl s_client -4 $STARTTLS -connect "$HOST:$PORT" -servername "$HOST" "$PROTOCOL" 2> /dev/null | openssl x509 -noout -text 2> /dev/null | grep "Not After" | sed -r 's/\s*Not After : //')
    RETCODE="$?"
    set -e
  done

  # Sanity check (IPv6)
  NOIPV6=0
  # Does it have a AAAA record?
  if [ $(dig AAAA "$HOST" +short | wc -l) -eq 0 ] ; then
    NOIPV6=1
  fi
  # Is it in fact an IPv6 address?
  if echo "$HOST" | grep -Pq "^$IPV6REGEX$" ; then
    NOIPV6=0
  fi

  # Try various TLS versions against this host:port to try and get a response (IPv6)
  EXPIRYSTRING6=0
  RETCODE=1
  for PROTOCOL in -tls1_3 -tls1_2 -tls1_1 -tls1 ; do
    if [ "$NOIPV6" -eq 1 ] ; then
      break
    fi
    if [ "$RETCODE" -eq 0 ] ; then
      break
    fi
    set +e
    # Get the "Not After" field for the certificate expiry
    EXPIRYSTRING6=$(echo "Q" | timeout "$TIMEOUT" openssl s_client -6 $STARTTLS -connect "[$HOST]:$PORT" -servername "$HOST" "$PROTOCOL" 2> /dev/null | openssl x509 -noout -text 2> /dev/null | grep "Not After" | sed -r 's/\s*Not After : //')
    RETCODE="$?"
    set -e
  done

#  echo "DEBUG: EXPIRYSTRING4: $EXPIRYSTRING4."
#  echo "DEBUG: EXPIRYSTRING6: $EXPIRYSTRING6."

  NOW=$(date +%s)
#  echo "DEBUG: NOW: $NOW."

  # Convert expiry into unixtime (IPv4)
  EXPIRY4=$(date -d "$EXPIRYSTRING4" +%s)
#  echo "DEBUG: EXPIRY4: $EXPIRY4."

  # Convert expiry into unixtime (IPv6)
  EXPIRY6=$(date -d "$EXPIRYSTRING6" +%s)
#  echo "DEBUG: EXPIRY6: $EXPIRY6."

  # Number of seconds left (IPv4)
  DIFFERENCE4=$((EXPIRY4 - NOW))
#  echo "DEBUG: DIFFERENCE4: $DIFFERENCE4."

  # Number of seconds left (IPv6)
  DIFFERENCE6=$((EXPIRY6 - NOW))
#  echo "DEBUG: DIFFERENCE6: $DIFFERENCE6."

  # Warn if less than WARNSECONDS less (IPv4)
  if [ "$DIFFERENCE4" -lt "$WARNSECONDS" ] && [ "$NOIPV4" -eq 0 ] ; then
    echo "Warning!  The certificate at $HOST:$PORT (IPv4) expires in $DIFFERENCE4 seconds (~$((DIFFERENCE4 / 60 / 60 / 24)) days)."
#  else
#    echo "DEBUG: The certificate at $HOST:$PORT (IPv4) expires in $DIFFERENCE4 seconds (~$((DIFFERENCE4 / 60 / 60 / 24)) days)."
  fi

  # Warn if less than WARNSECONDS less (IPv6)
  if [ "$DIFFERENCE6" -lt "$WARNSECONDS" ] && [ "$NOIPV6" -eq 0 ] ; then
    echo "Warning!  The certificate at $HOST:$PORT (IPv6) expires in $DIFFERENCE6 seconds (~$((DIFFERENCE6 / 60 / 60 / 24)) days)."
#  else
#    echo "DEBUG: The certificate at $HOST:$PORT (IPv6) expires in $DIFFERENCE6 seconds (~$((DIFFERENCE6 / 60 / 60 / 24)) days)."
  fi

done < "$HOSTSANDPORTS"