Add raise_on_no_answer option

diff --git a/ChangeLog b/ChangeLog
index 73452c2a8e6c74db5f645454758cea98b73ea85e..d13e7a0dbb6551d55c035104089ed097cffbe94e 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2011-03-22  Bob Halley  <halley@dnspython.org>
+
+       * dns/resolver.py: a boolean parameter, 'raise_on_no_answer', has
+       been added to the query() methods.  In no-error, no-data
+       situations, this parameter determines whether NoAnswer should be
+       raised or not.  If True, NoAnswer is raised.  If False, then an
+       Answer() object with a None rrset will be returned.
+
 2011-01-11  Bob Halley  <halley@dnspython.org>
 
        * Dnspython was erroneously doing case-insensitive comparisons

diff --git a/dns/resolver.py b/dns/resolver.py
index 30977f3a8bbb98164be057ce1952d426620317ce..ad2223dfcd405109fecd44d68b633b2c851beeaf 100644 (file)
--- a/dns/resolver.py
+++ b/dns/resolver.py
@@ -94,7 +94,8 @@ class Answer(object):
     @ivar expiration: The time when the answer expires
     @type expiration: float (seconds since the epoch)
     """
-    def __init__(self, qname, rdtype, rdclass, response):
+    def __init__(self, qname, rdtype, rdclass, response,
+                 raise_on_no_answer=True):
         self.qname = qname
         self.rdtype = rdtype
         self.rdclass = rdclass
@@ -122,11 +123,30 @@ class Answer(object):
                             break
                         continue
                     except KeyError:
-                        raise NoAnswer
-                raise NoAnswer
-        if rrset is None:
+                        if raise_on_no_answer:
+                            raise NoAnswer
+                if raise_on_no_answer:
+                    raise NoAnswer
+        if rrset is None and raise_on_no_answer:
             raise NoAnswer
         self.rrset = rrset
+        if rrset is None:
+            while 1:
+                # Look for a SOA RR whose owner name is a superdomain
+                # of qname.
+                try:
+                    srrset = response.find_rrset(response.authority, qname,
+                                                rdclass, dns.rdatatype.SOA)
+                    if min_ttl == -1 or srrset.ttl < min_ttl:
+                        min_ttl = srrset.ttl
+                    if srrset[0].minimum < min_ttl:
+                        min_ttl = srrset[0].minimum
+                    break
+                except KeyError:
+                    try:
+                        qname = qname.parent()
+                    except dns.name.NoParent:
+                        break
         self.expiration = time.time() + min_ttl
 
     def __getattr__(self, attr):
@@ -546,7 +566,7 @@ class Resolver(object):
         return min(self.lifetime - duration, self.timeout)
 
     def query(self, qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN,
-              tcp=False, source=None):
+              tcp=False, source=None, raise_on_no_answer=True):
         """Query nameservers to find the answer to the question.
 
         The I{qname}, I{rdtype}, and I{rdclass} parameters may be objects
@@ -564,10 +584,14 @@ class Resolver(object):
         @type tcp: bool
         @param source: bind to this IP address (defaults to machine default IP).
         @type source: IP address in dotted quad notation
+        @param raise_on_no_answer: raise NoAnswer if there's no answer
+        (defaults is True).
+        @type raise_on_no_answer: bool
         @rtype: dns.resolver.Answer instance
         @raises Timeout: no answers could be found in the specified lifetime
         @raises NXDOMAIN: the query name does not exist
-        @raises NoAnswer: the response did not contain an answer
+        @raises NoAnswer: the response did not contain an answer and
+        raise_on_no_answer is True.
         @raises NoNameservers: no non-broken nameservers are available to
         answer the question."""
 
@@ -678,7 +702,8 @@ class Resolver(object):
             break
         if all_nxdomain:
             raise NXDOMAIN
-        answer = Answer(qname, rdtype, rdclass, response)
+        answer = Answer(qname, rdtype, rdclass, response,
+                        raise_on_no_answer)
         if self.cache:
             self.cache.put((qname, rdtype, rdclass), answer)
         return answer
@@ -731,14 +756,15 @@ def get_default_resolver():
     return default_resolver
 
 def query(qname, rdtype=dns.rdatatype.A, rdclass=dns.rdataclass.IN,
-          tcp=False, source=None):
+          tcp=False, source=None, raise_on_no_answer=True):
     """Query nameservers to find the answer to the question.
 
     This is a convenience function that uses the default resolver
     object to make the query.
     @see: L{dns.resolver.Resolver.query} for more information on the
     parameters."""
-    return get_default_resolver().query(qname, rdtype, rdclass, tcp, source)
+    return get_default_resolver().query(qname, rdtype, rdclass, tcp, source,
+                                        raise_on_no_answer)
 
 def zone_for_name(name, rdclass=dns.rdataclass.IN, tcp=False, resolver=None):
     """Find the name of the zone which contains the specified name.