Merge pull request #542 from rthalley/canonical_name

Canonical name

6 files changed, 100 insertions, 0 deletions

diff --git a/dns/asyncresolver.py b/dns/asyncresolver.py
index 3ac334f..0aaeb9c 100644
--- a/dns/asyncresolver.py
+++ b/dns/asyncresolver.py
@@ -165,6 +165,28 @@ class Resolver(dns.resolver.Resolver):
                                   rdclass=dns.rdataclass.IN,
                                   *args, **kwargs)
 
+    async def canonical_name(self, name):
+        """Determine the canonical name of *name*.
+
+        The canonical name is the name the resolver uses for queries
+        after all CNAME and DNAME renamings have been applied.
+
+        *name*, a ``dns.name.Name`` or ``str``, the query name.
+
+        This method can raise any exception that ``resolve()`` can
+        raise, other than ``dns.resolver.NoAnswer`` and
+        ``dns.resolver.NXDOMAIN``.
+
+        Returns a ``dns.name.Name``.
+        """
+        try:
+            answer = await self.resolve(name, raise_on_no_answer=False)
+            canonical_name = answer.canonical_name
+        except dns.resolver.NXDOMAIN as e:
+            canonical_name = e.canonical_name
+        return canonical_name
+
+
 default_resolver = None
 
 
@@ -212,6 +234,14 @@ async def resolve_address(ipaddr, *args, **kwargs):
 
     return await get_default_resolver().resolve_address(ipaddr, *args, **kwargs)
 
+async def canonical_name(name):
+    """Determine the canonical name of *name*.
+
+    See ``dns.resolver.Resolver.canonical_name`` for more information on the
+    parameters and possible exceptions.
+    """
+
+    return await get_default_resolver().canonical_name(name)
 
 async def zone_for_name(name, rdclass=dns.rdataclass.IN, tcp=False,
                         resolver=None, backend=None):
diff --git a/dns/resolver.py b/dns/resolver.py
index ec16376..bad24dc 100644
--- a/dns/resolver.py
+++ b/dns/resolver.py
@@ -81,6 +81,9 @@ class NXDOMAIN(dns.exception.DNSException):
         IN = dns.rdataclass.IN
         CNAME = dns.rdatatype.CNAME
         cname = None
+        # This code assumes the CNAME chain is in proper order, though
+        # the Answer code does not make a similar assumption when
+        # chaining.
         for qname in self.kwargs['qnames']:
             response = self.kwargs['responses'][qname]
             for answer in response.answer:
@@ -1172,6 +1175,27 @@ class Resolver:
                             rdclass=dns.rdataclass.IN,
                             *args, **kwargs)
 
+    def canonical_name(self, name):
+        """Determine the canonical name of *name*.
+
+        The canonical name is the name the resolver uses for queries
+        after all CNAME and DNAME renamings have been applied.
+
+        *name*, a ``dns.name.Name`` or ``str``, the query name.
+
+        This method can raise any exception that ``resolve()`` can
+        raise, other than ``dns.resolver.NoAnswer`` and
+        ``dns.resolver.NXDOMAIN``.
+
+        Returns a ``dns.name.Name``.
+        """
+        try:
+            answer = self.resolve(name, raise_on_no_answer=False)
+            canonical_name = answer.canonical_name
+        except dns.resolver.NXDOMAIN as e:
+            canonical_name = e.canonical_name
+        return canonical_name
+
     def use_tsig(self, keyring, keyname=None,
                  algorithm=dns.tsig.default_algorithm):
         """Add a TSIG signature to each query.
@@ -1296,6 +1320,16 @@ def resolve_address(ipaddr, *args, **kwargs):
     return get_default_resolver().resolve_address(ipaddr, *args, **kwargs)
 
 
+def canonical_name(name):
+    """Determine the canonical name of *name*.
+
+    See ``dns.resolver.Resolver.canonical_name`` for more information on the
+    parameters and possible exceptions.
+    """
+
+    return get_default_resolver().canonical_name(name)
+
+
 def zone_for_name(name, rdclass=dns.rdataclass.IN, tcp=False, resolver=None):
     """Find the name of the zone which contains the specified name.
 
diff --git a/doc/async-resolver-functions.rst b/doc/async-resolver-functions.rst
index fc5798a..b2669f3 100644
--- a/doc/async-resolver-functions.rst
+++ b/doc/async-resolver-functions.rst
@@ -5,4 +5,5 @@ Asynchronous Resolver Functions
 
 .. autofunction:: dns.asyncresolver.resolve
 .. autofunction:: dns.asyncresolver.resolve_address
+.. autofunction:: dns.asyncresolver.canonical_name
 .. autofunction:: dns.asyncresolver.zone_for_name
diff --git a/doc/resolver-functions.rst b/doc/resolver-functions.rst
index 6e57957..179484c 100644
--- a/doc/resolver-functions.rst
+++ b/doc/resolver-functions.rst
@@ -5,6 +5,7 @@ Resolver Functions and The Default Resolver
 
 .. autofunction:: dns.resolver.resolve
 .. autofunction:: dns.resolver.resolve_address
+.. autofunction:: dns.resolver.canonical_name
 .. autofunction:: dns.resolver.zone_for_name
 .. autofunction:: dns.resolver.query
 .. autodata:: dns.resolver.default_resolver
diff --git a/tests/test_async.py b/tests/test_async.py
index db108c8..690a1eb 100644
--- a/tests/test_async.py
+++ b/tests/test_async.py
@@ -182,6 +182,26 @@ class AsyncTests(unittest.TestCase):
         dnsgoogle = dns.name.from_text('dns.google.')
         self.assertEqual(answer[0].target, dnsgoogle)
 
+    def testCanonicalNameNoCNAME(self):
+        cname = dns.name.from_text('www.google.com')
+        async def run():
+            return await dns.asyncresolver.canonical_name('www.google.com')
+        self.assertEqual(self.async_run(run), cname)
+
+    def testCanonicalNameCNAME(self):
+        name = dns.name.from_text('www.dnspython.org')
+        cname = dns.name.from_text('dmfrjf4ips8xa.cloudfront.net')
+        async def run():
+            return await dns.asyncresolver.canonical_name(name)
+        self.assertEqual(self.async_run(run), cname)
+
+    def testCanonicalNameDangling(self):
+        name = dns.name.from_text('dangling-cname.dnspython.org')
+        cname = dns.name.from_text('dangling-target.dnspython.org')
+        async def run():
+            return await dns.asyncresolver.canonical_name(name)
+        self.assertEqual(self.async_run(run), cname)
+
     def testResolverBadScheme(self):
         res = dns.asyncresolver.Resolver(configure=False)
         res.nameservers = ['bogus://dns.google/dns-query']
diff --git a/tests/test_resolver.py b/tests/test_resolver.py
index b63ec19..31e49f8 100644
--- a/tests/test_resolver.py
+++ b/tests/test_resolver.py
@@ -510,6 +510,20 @@ class LiveResolverTests(unittest.TestCase):
         answer2 = res.resolve('dns.google.', 'A')
         self.assertIs(answer2, answer1)
 
+    def testCanonicalNameNoCNAME(self):
+        cname = dns.name.from_text('www.google.com')
+        self.assertEqual(dns.resolver.canonical_name('www.google.com'), cname)
+
+    def testCanonicalNameCNAME(self):
+        name = dns.name.from_text('www.dnspython.org')
+        cname = dns.name.from_text('dmfrjf4ips8xa.cloudfront.net')
+        self.assertEqual(dns.resolver.canonical_name(name), cname)
+
+    def testCanonicalNameDangling(self):
+        name = dns.name.from_text('dangling-cname.dnspython.org')
+        cname = dns.name.from_text('dangling-target.dnspython.org')
+        self.assertEqual(dns.resolver.canonical_name(name), cname)
+
 class PollingMonkeyPatchMixin(object):
     def setUp(self):
         self.__native_selector_class = dns.query._selector_class