[2219] regression fix: support glue_ok option at the zone cut in the main find

in the old implementation we did it for the specialized finder context, but
we are currently using the generic context, so we need to handle the case
in the main method.  (and, technically, this case should be handled in the
main method even if we had a specialized context as it's an API contract.)

src/lib/datasrc/memory/tests/zone_finder_unittest.cc

@@ -180,6 +180,8 @@ public:
             {"example.org. 300 IN NS ns.example.org.", &rr_ns_},
             {"example.org. 300 IN A 192.0.2.1", &rr_a_},
             {"ns.example.org. 300 IN A 192.0.2.2", &rr_ns_a_},
+            // This one will place rr_ns_a_ at a zone cut, making it a glue:
+            {"ns.example.org. 300 IN NS 192.0.2.2", &rr_ns_ns_},
             {"ns.example.org. 300 IN AAAA 2001:db8::2", &rr_ns_aaaa_},
             {"cname.example.org. 300 IN CNAME canonical.example.org",
              &rr_cname_},
@@ -370,6 +372,7 @@ public:
         rr_ns_aaaa_,
         // A of example.org
         rr_a_;
+    RRsetPtr rr_ns_ns_;         // used to make rr_ns_a_ a glue.
     RRsetPtr rr_cname_;         // CNAME in example.org (RDATA will be added)
     RRsetPtr rr_cname_a_; // for mixed CNAME + A case
     RRsetPtr rr_dname_;         // DNAME in example.org (RDATA will be added)
@@ -711,6 +714,9 @@ TEST_F(InMemoryZoneFinderTest, glue) {
     EXPECT_NO_THROW(addZoneData(rr_grandchild_ns_));
     // glue under the deeper zone cut
     EXPECT_NO_THROW(addZoneData(rr_grandchild_glue_));
+    // glue 'at the' zone cut
+    EXPECT_NO_THROW(addZoneData(rr_ns_a_));
+    EXPECT_NO_THROW(addZoneData(rr_ns_ns_));
 
     // by default glue is hidden due to the zone cut
     findTest(rr_child_glue_->getName(), RRType::A(), ZoneFinder::DELEGATION,
@@ -743,6 +749,13 @@ TEST_F(InMemoryZoneFinderTest, glue) {
     findTest(Name("www.grand.child.example.org"), RRType::TXT(),
              ZoneFinder::DELEGATION, true, rr_child_ns_,
              ZoneFinder::RESULT_DEFAULT, NULL, ZoneFinder::FIND_GLUE_OK);
+
+    // Glue at a zone cut
+    findTest(Name("ns.example.org"), RRType::A(),
+             ZoneFinder::DELEGATION, true, rr_ns_ns_);
+    findTest(Name("ns.example.org"), RRType::A(), ZoneFinder::SUCCESS,
+             true, rr_ns_a_, ZoneFinder::RESULT_DEFAULT,
+             NULL, ZoneFinder::FIND_GLUE_OK);
 }
 
 /**

src/lib/datasrc/memory/zone_finder.cc

@@ -582,10 +582,13 @@ InMemoryZoneFinder::find_internal(const isc::dns::Name& name,
 
     // If the node callback is enabled, this may be a zone cut.  If it
     // has a NS RR, we should return a delegation, but not in the apex.
-    // There is one exception: the case for DS query, which should always
-    // be considered in-zone lookup.
+    // There are two exceptions:
+    // - the case for DS query, which should always be considered in-zone
+    //   lookup.
+    // - when we are looking for glue records (FIND_GLUE_OK)
     if (node->getFlag(ZoneNode::FLAG_CALLBACK) &&
-            node != zone_data_.getOriginNode() && type != RRType::DS()) {
+        (options & FIND_GLUE_OK) == 0 &&
+        node != zone_data_.getOriginNode() && type != RRType::DS()) {
         found = RdataSet::find(node->getData(), RRType::NS());
         if (found != NULL) {
             LOG_DEBUG(logger, DBG_TRACE_DATA,