Fixes to DNS lookups during status checks when there are timeouts, enforce timeouts better (#2191)

* add dns query handling changes

* replace exception pass with error message

* simplify dns exception catching

* Add not set case to blacklist lookup result handling

management/dns_update.py

@@ -992,6 +992,7 @@ def set_custom_dns_record(qname, rtype, value, action, env):
 def get_secondary_dns(custom_dns, mode=None):
 	resolver = dns.resolver.get_default_resolver()
 	resolver.timeout = 10
+	resolver.lifetime = 10
 
 	values = []
 	for qname, rtype, value in custom_dns:
@@ -1009,10 +1010,17 @@ def get_secondary_dns(custom_dns, mode=None):
 			# doesn't.
 			if not hostname.startswith("xfr:"):
 				if mode == "xfr":
-					response = dns.resolver.resolve(hostname+'.', "A", raise_on_no_answer=False)
-					values.extend(map(str, response))
-					response = dns.resolver.resolve(hostname+'.', "AAAA", raise_on_no_answer=False)
-					values.extend(map(str, response))
+					try:
+						response = resolver.resolve(hostname+'.', "A", raise_on_no_answer=False)
+						values.extend(map(str, response))
+					except dns.exception.DNSException:
+						pass
+						
+					try:
+						response = resolver.resolve(hostname+'.', "AAAA", raise_on_no_answer=False)
+						values.extend(map(str, response))
+					except dns.exception.DNSException:
+						pass
 					continue
 				values.append(hostname)
 
@@ -1030,15 +1038,17 @@ def set_secondary_dns(hostnames, env):
 		# Validate that all hostnames are valid and that all zone-xfer IP addresses are valid.
 		resolver = dns.resolver.get_default_resolver()
 		resolver.timeout = 5
+		resolver.lifetime = 5
+		
 		for item in hostnames:
 			if not item.startswith("xfr:"):
 				# Resolve hostname.
 				try:
 					response = resolver.resolve(item, "A")
-				except (dns.resolver.NoNameservers, dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
+				except (dns.resolver.NoNameservers, dns.resolver.NXDOMAIN, dns.resolver.NoAnswer, dns.resolver.Timeout):
 					try:
 						response = resolver.resolve(item, "AAAA")
-					except (dns.resolver.NoNameservers, dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
+					except (dns.resolver.NoNameservers, dns.resolver.NXDOMAIN, dns.resolver.NoAnswer, dns.resolver.Timeout):
 						raise ValueError("Could not resolve the IP address of %s." % item)
 			else:
 				# Validate IP address.
@@ -1071,7 +1081,7 @@ def get_custom_dns_records(custom_dns, qname, rtype):
 def build_recommended_dns(env):
 	ret = []
 	for (domain, zonefile, records) in build_zones(env):
-		# remove records that we don't dislay
+		# remove records that we don't display
 		records = [r for r in records if r[3] is not False]
 
 		# put Required at the top, then Recommended, then everythiing else

management/status_checks.py

@@ -308,6 +308,8 @@ def run_network_checks(env, output):
 		output.print_ok("IP address is not blacklisted by zen.spamhaus.org.")
 	elif zen == "[timeout]":
 		output.print_warning("Connection to zen.spamhaus.org timed out. We could not determine whether your server's IP address is blacklisted. Please try again later.")
+	elif zen == "[Not Set]":
+		output.print_warning("Could not connect to zen.spamhaus.org. We could not determine whether your server's IP address is blacklisted. Please try again later.")
 	else:
 		output.print_error("""The IP address of this machine %s is listed in the Spamhaus Block List (code %s),
 			which may prevent recipients from receiving your email. See http://www.spamhaus.org/query/ip/%s."""
@@ -541,7 +543,7 @@ def check_dns_zone(domain, env, output, dns_zonefiles):
 		for ns in custom_secondary_ns:
 			# We must first resolve the nameserver to an IP address so we can query it.
 			ns_ips = query_dns(ns, "A")
-			if not ns_ips:
+			if not ns_ips or ns_ips in {'[Not Set]', '[timeout]'}:
 				output.print_error("Secondary nameserver %s is not valid (it doesn't resolve to an IP address)." % ns)
 				continue
 			# Choose the first IP if nameserver returns multiple
@@ -744,6 +746,8 @@ def check_mail_domain(domain, env, output):
 		output.print_ok("Domain is not blacklisted by dbl.spamhaus.org.")
 	elif dbl == "[timeout]":
 		output.print_warning("Connection to dbl.spamhaus.org timed out. We could not determine whether the domain {} is blacklisted. Please try again later.".format(domain))
+	elif dbl == "[Not Set]":
+		output.print_warning("Could not connect to dbl.spamhaus.org. We could not determine whether the domain {} is blacklisted. Please try again later.".format(domain))
 	else:
 		output.print_error("""This domain is listed in the Spamhaus Domain Block List (code %s),
 			which may prevent recipients from receiving your mail.
@@ -788,12 +792,17 @@ def query_dns(qname, rtype, nxdomain='[Not Set]', at=None, as_list=False):
 	# running bind server), or if the 'at' argument is specified, use that host
 	# as the nameserver.
 	resolver = dns.resolver.get_default_resolver()
-	if at:
+	
+	# Make sure at is not a string that cannot be used as a nameserver
+	if at and at not in {'[Not set]', '[timeout]'}:
 		resolver = dns.resolver.Resolver()
 		resolver.nameservers = [at]
 
 	# Set a timeout so that a non-responsive server doesn't hold us back.
 	resolver.timeout = 5
+	# The number of seconds to spend trying to get an answer to the question. If the
+	# lifetime expires a dns.exception.Timeout exception will be raised.
+	resolver.lifetime = 5
 
 	# Do the query.
 	try: