[1177] Function definiton for finding previous name

It will be needed for DNSSEC logic. Not implemented nor tested:
* The InMemory just throws NotImplemented
* The Database one will be done in next commits

src/lib/datasrc/database.cc

@@ -565,6 +565,11 @@ DatabaseClient::Finder::find(const isc::dns::Name& name,
 }
 
 Name
+DatabaseClient::Finder::findPreviousName(const Name&) const {
+    return (Name::ROOT_NAME()); // TODO Implement
+}
+
+Name
 DatabaseClient::Finder::getOrigin() const {
     return (origin_);
 }

src/lib/datasrc/database.h

@@ -590,6 +590,12 @@ public:
                                 const FindOptions options = FIND_DEFAULT);
 
         /**
+         * \brief Implementation of ZoneFinder::findPreviousName method.
+         */
+        virtual isc::dns::Name findPreviousName(const isc::dns::Name& query)
+            const;
+
+        /**
          * \brief The zone ID
          *
          * This function provides the stored zone ID as passed to the

src/lib/datasrc/memory_datasrc.cc

@@ -661,6 +661,12 @@ InMemoryZoneFinder::getFileName() const {
     return (impl_->file_name_);
 }
 
+isc::dns::Name
+InMemoryZoneFinder::findPreviousName(const isc::dns::Name&) const {
+    isc_throw(NotImplemented, "InMemory data source doesn't support DNSSEC "
+              "yet, can't find previous name");
+}
+
 /// Implementation details for \c InMemoryClient hidden from the public
 /// interface.
 ///

src/lib/datasrc/memory_datasrc.h

@@ -75,6 +75,12 @@ public:
                             isc::dns::RRsetList* target = NULL,
                             const FindOptions options = FIND_DEFAULT);
 
+    /// \brief Imelementation of the ZoneFinder::findPreviousName method
+    ///
+    /// This one throws NotImplemented exception, as InMemory doesn't
+    /// support DNSSEC currently.
+    virtual isc::dns::Name findPreviousName(const isc::dns::Name& query) const;
+
     /// \brief Inserts an rrset into the zone.
     ///
     /// It puts another RRset into the zone.

src/lib/datasrc/tests/memory_datasrc_unittest.cc

@@ -395,6 +395,14 @@ public:
 };
 
 /**
+ * \brief Check that findPreviousName throws as it should now.
+ */
+TEST_F(InMemoryZoneFinderTest, findPreviousName) {
+    EXPECT_THROW(zone_finder_.findPreviousName(Name("www.example.org")),
+                 isc::NotImplemented);
+}
+
+/**
  * \brief Test InMemoryZoneFinder::InMemoryZoneFinder constructor.
  *
  * Takes the created zone finder and checks its properties they are the same

src/lib/datasrc/zone.h

@@ -145,7 +145,7 @@ public:
     //@}
 
     ///
-    /// \name Search Method
+    /// \name Search Methods
     ///
     //@{
     /// Search the zone for a given pair of domain name and RR type.
@@ -208,6 +208,28 @@ public:
                             isc::dns::RRsetList* target = NULL,
                             const FindOptions options
                             = FIND_DEFAULT) = 0;
+
+    /// \brief Get previous name in the zone
+    ///
+    /// Gets the previous name in the DNSSEC order. This can be used
+    /// to find the correct NSEC or NSEC3 records for proving nonexistenc
+    /// of domains.
+    ///
+    /// The concrete implementation might throw anything it thinks appropriate,
+    /// however it is recommended to stick to the ones listed here. The user
+    /// of this method should be able to handle any exceptions.
+    ///
+    /// \param query The name for which one we look for a previous one. The
+    ///     queried name doesn't have to exist in the zone.
+    /// \return The preceding name
+    ///
+    /// \throw NotImplemented in case the data source backend doesn't support
+    ///     DNSSEC.
+    /// \throw DataSourceError for low-level or internal datasource errors
+    ///     (like broken connection to database, wrong data living there).
+    /// \throw std::bad_alloc For allocation errors.
+    virtual isc::dns::Name findPreviousName(const isc::dns::Name& query)
+        const = 0;
     //@}
 };