Fix garbled screen when HTTP Age is not a non-negative int

As suggested in https://github.com/testssl/testssl.sh/pull/2885 parsing
of the server determined HTTP age var wasn't strict enough.

https://www.rfc-editor.org/rfc/rfc7234#section-1.2.1 requires the
variable to be a non-negative integer but testssl.sh assumed it was
like that but did't check whether that really was the case. This was
labled as a (potential) security problem. Potential as it didn't
look exploitable after review -- the header as a whole was already
sanitized.

This PR fixes the typs confusion and the garbled screen by checking
the variable early in run_http_header() and reset it to NaN. That
will be used later in run_http_date() to raise a low severity finding.

Kudos to @Tristanhx for catching this and for the suggested PR.

Also, only when running in debug mode, this PR fixes that during
service_detection() parts of the not-yet-sanitized header ended
up on the screen. The fix just calls sanitze_http_header() for the
temporary variable $TMPFILE.

testssl.sh

@@ -2503,6 +2503,8 @@ service_detection() {
                wait_kill $! $((HEADER_MAXSLEEP * 10))
                was_killed=$?
           fi
+          # make sure that we don't have non-printable chars sneaked in -- relecant only in debug mode level 2
+          sanitze_http_header $TMPFILE
           head $TMPFILE | grep -aq '^HTTP/' && SERVICE=HTTP
           [[ -z "$SERVICE" ]] && head $TMPFILE | grep -Ewaq "SMTP|ESMTP|Exim|IdeaSmtpServer|Kerio Connect|Postfix" && SERVICE=SMTP  # I know some overlap here
           [[ -z "$SERVICE" ]] && head $TMPFILE | grep -Ewaq "POP|POP3|Gpop|OK Dovecot" && SERVICE=POP                               # I know some overlap here
@@ -2577,7 +2579,9 @@ connectivity_problem() {
      fi
 }
 
-
+# arg1: filename (global)
+# return: sanitzes arg1
+#
 sanitze_http_header() {
      # some sed implementations were sometime not fine with HTTP headers containing x0d x0a (CRLF: usual case)
      # Also we use tr here to remove any crtl chars which the server side offers --> possible security problem.
@@ -2636,6 +2640,7 @@ run_http_header() {
                ((NR_HEADER_FAIL++))
           fi
      fi
+
      HTTP_TIME=$(awk -F': ' '/^date:/ { print $2 }  /^Date:/ { print $2 }' $HEADERFILE)
      HTTP_AGE=$(awk -F': ' '/^[aA][gG][eE]: / { print $2 }' $HEADERFILE)
      if [[ ! -s $HEADERFILE ]]; then
@@ -2663,6 +2668,10 @@ run_http_header() {
      # Populate vars for HTTP time
      [[ -n "$HTTP_AGE" ]] && HTTP_AGE="$(strip_lf "$HTTP_AGE")"
      [[ -n "$HTTP_TIME" ]] && HTTP_TIME="$(strip_lf "$HTTP_TIME")"
+     if [[ -n "$HTTP_AGE" ]] && [[ ! "$HTTP_AGE" =~ ^[0-9]+$ ]];  then
+          HTTP_AGE="NaN"
+     fi
+
      debugme echo "NOW_TIME: $NOW_TIME | HTTP_AGE: $HTTP_AGE | HTTP_TIME: $HTTP_TIME"
 
      HTTP_STATUS_CODE=$(awk '/^HTTP\// { print $2 }' $HEADERFILE 2>>$ERRFILE)
@@ -2793,13 +2802,20 @@ run_http_date() {
                outln
                pr_bold " HTTP Age"
                out " (RFC 7234)          $HTTP_AGE"
+               if [[ "$HTTP_AGE" = NaN ]]; then
+                    out ", "
+                    # https://www.rfc-editor.org/rfc/rfc7234#section-1.2.1
+                    pr_svrty_low "RFC 7234, sec 1.2.1. requires numbers"
+                    fileout "HTTP_headerAge" "LOW" "$HTTP_AGE was not a non-negative integer, see RFC 7234, sec 1.2.1."
+               else
                     fileout "HTTP_headerAge" "INFO" "$HTTP_AGE seconds"
                fi
+          fi
      else
           out "Got no HTTP time, maybe try different URL?";
           fileout "$jsonID" "INFO" "Got no HTTP time, maybe try different URL?"
      fi
-     debugme tm_out ", HTTP_TIME + HTTP_AGE in epoch: $HTTP_TIME / $HTTP_AGE"
+     debugme tm_out ", HTTP_TIME | HTTP_AGE: $HTTP_TIME | $HTTP_AGE"
      outln
      match_ipv4_httpheader "$1"
      return 0