Error-proofed DNS-resolution

filter_subdomains.py

@@ -10,10 +10,12 @@ import re
 import sys
 
 import dns.resolver
+import dns.exception
 import progressbar
 
 import regexes
 
+DNS_TIMEOUT = 5.0
 
 def is_subdomain_matching(subdomain: str) -> bool:
     """
@@ -21,9 +23,20 @@ def is_subdomain_matching(subdomain: str) -> bool:
     """
     # TODO Look at the whole chain rather than the last one
     try:
-        query = dns.resolver.query(subdomain, 'A')
+        query = dns.resolver.query(subdomain, 'A', lifetime=DNS_TIMEOUT)
     except dns.resolver.NXDOMAIN:
         return False
+    except dns.resolver.NoAnswer:
+        return False
+    except dns.resolver.YXDOMAIN:
+        print(f"Query name too long for {subdomain}", file=sys.stderr)
+        return False
+    except dns.resolver.NoNameservers:
+        print(f"All nameservers broken for {subdomain}", file=sys.stderr)
+        return False
+    except dns.exception.Timeout:
+        print(f"Timeout for {subdomain}", file=sys.stderr)
+        return False
     canonical = query.canonical_name.to_text()
     for regex in regexes.REGEXES:
         if re.match(regex, canonical):