rewrite socket error handling, fixes #522

socket.error is deprecated and is the same as OSError since python 3.3.
Of course OSError can mean a lot of stuff, so not sure how that goes...

socket.herror is for gethostbyaddr and has some documented h_error values in netdb.h
(but, AFAIK, these symbols are not available via python).

added a handler for h_error 0 (#522), which crashed since a while.
removed some unclear error values, let's see what happens.

src/nsupdate/main/dnstools.py

@@ -186,7 +186,7 @@ def delete(fqdn, rdtype=None):
         except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
             # no dns entry, it is already deleted
             ok = False
-        except (dns.resolver.Timeout, dns.resolver.NoNameservers) as e:  # socket.error also?
+        except (dns.resolver.Timeout, dns.resolver.NoNameservers) as e:  # OSError (socket.error) also?
             # maybe could be caused by secondary DNS Timeout and master still ok?
             # assume the delete is OK...
             ok = True
@@ -215,7 +215,7 @@ def update(fqdn, ipaddr, ttl=60):
     except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
         # no dns entry yet, ok
         ok = True
-    except (dns.resolver.Timeout, dns.resolver.NoNameservers) as e:  # socket.error also?
+    except (dns.resolver.Timeout, dns.resolver.NoNameservers) as e:  # OSError (socket.error) also?
         # maybe could be caused by secondary DNS Timeout and master still ok?
         # assume the update is OK...
         ok = True
@@ -264,7 +264,7 @@ def query_ns(fqdn, rdtype, prefer_primary=False):
         ip = str(list(answer)[0])
         logger.debug("query: %s answer: %s" % (fqdn, ip))
         return ip
-    except (dns.resolver.Timeout, dns.resolver.NoNameservers, dns.message.UnknownTSIGKey) as e:  # socket.error also?
+    except (dns.resolver.Timeout, dns.resolver.NoNameservers, dns.message.UnknownTSIGKey) as e:  # OSError (socket.error) also?
         logger.warning("error when querying for name '%s' in zone '%s' with rdtype '%s' [%s]." % (
                        fqdn.host, origin, rdtype, str(e)))
         set_ns_availability(origin, False)
@@ -279,6 +279,10 @@ def rev_lookup(ipaddr):
 
     :param ipaddr: ip address (str)
     :return: hostname (or empty string if lookup failed)
+
+# define TRY_AGAIN      2       /* Non-Authoritative Host not found,
+                                   or SERVERFAIL.  */
+
     """
     if ipaddr:
         retries = 4
@@ -287,18 +291,20 @@ def rev_lookup(ipaddr):
             retries -= 1
             try:
                 return socket.gethostbyaddr(ipaddr)[0]
-            except socket.error as err:
-                if err.errno in (-5, 4):
-                    # -5 / 4 == no address associated with hostname (invalid ip?)
-                    logger.warning("errno -5 when trying to reverse lookup %r" % ipaddr)
-                    break
-                if err.errno in (errno.EPERM, ):
-                    # EPERM == 1 == unknown host
-                    break
-                if err.errno not in (errno.ENOENT, errno.EAGAIN):
-                    # ENOENT == 2 == UDP Packet lost?
-                    # EAGAIN == "try again"
-                    raise
+            except socket.herror as err:
+                if err.errno in (0, 1, 3, 4, ):
+                    # numeric values from linux netdb.h:
+                    # 0 == Resolver Error 0 (no error), e.g. Host x.x.x.x.in-addr.arpa not found: 2(SERVFAIL)
+                    # 1 == HOST_NOT_FOUND (Authoritative Answer Host not found)
+                    # 3 == NO_RECOVERY (Non recoverable errors, FORMERR, REFUSED, NOTIMP)
+                    # 4 == NO_DATA (Valid name, no data record of requested type)
+                    break  # give up
+                elif err.errno in (2, ):
+                    # 2 == TRY_AGAIN (Non-Authoritative Host not found, or SERVERFAIL)
+                    pass  # retry
+                else:
+                    # something with no specific handling yet
+                    raise  # crash
             time.sleep(delay)
             delay *= 2
     return ''
@@ -381,10 +387,10 @@ def update_ns(fqdn, rdtype='A', ipaddr=None, action='upd', ttl=60):
             raise DnsUpdateError(rcode_text)
         return response
     # TODO simplify exception handling when https://github.com/rthalley/dnspython/pull/85 is merged/released
-    except socket.error as e:
-        logger.error("socket.error [%s] - zone: %s" % (str(e), origin, ))
+    except OSError as e:  # was: socket.error (deprecated)
+        logger.error("OSError [%s] - zone: %s" % (str(e), origin, ))
         set_ns_availability(domain, False)
-        raise DnsUpdateError("SocketError %d" % e.errno)
+        raise DnsUpdateError("OSError %s - zone: %s" % (str(e), origin, ))
     except EOFError as e:
         logger.error("EOFError [%s] - zone: %s" % (str(e), origin, ))
         set_ns_availability(domain, False)

src/nsupdate/main/views.py

@@ -240,7 +240,7 @@ def form_valid(self, form):
             success, level, msg = False, messages.ERROR, 'Host already exists in DNS.'
         except dnstools.DNSException as e:
             success, level, msg = False, messages.ERROR, 'DNSException [%s]' % str(e)
-        except socket.error as err:
+        except OSError as err:  # was: socket.error (deprecated)
             success, level, msg = False, messages.ERROR, 'Communication to name server failed [%s]' % str(err)
         else:
             self.object.created_by = self.request.user