Commit 41362fbd authored by Jerry's avatar Jerry
Browse files

merge trac422 : Implement memory Data Source Class


git-svn-id: svn://bind10.isc.org/svn/bind10/trunk@3866 e5f2f494-b856-4b98-b285-d166d9295462
parent 7e0a51e9
130. [func] jerry
src/lib/datasrc: Introduced a new class MemoryDataSrc to provide
the general interface for memory data source. For the initial
implementation, we don't make it a derived class of AbstractDataSrc
because the interface is so different(we'll eventually consider this
as part of the generalization work).
(Trac #422, svn r3566)
129. [func] jinmei
src/lib/dns: Added new functions masterLoad() for loading master
zone files. The initial implementation can only parse a limited
......
......@@ -26,10 +26,10 @@ namespace isc {
namespace auth {
void
Query::process() const {
const ZoneTable::FindResult result = zone_table_.find(qname_);
const ZoneTable::FindResult result = zone_table_.findZone(qname_);
if (result.code != ZoneTable::SUCCESS &&
result.code != ZoneTable::PARTIALMATCH) {
if (result.code != isc::datasrc::result::SUCCESS &&
result.code != isc::datasrc::result::PARTIALMATCH) {
response_.setRcode(Rcode::SERVFAIL());
return;
}
......
......@@ -55,7 +55,7 @@ TEST_F(QueryTest, noZone) {
TEST_F(QueryTest, matchZone) {
// add a matching zone. since the zone is empty right now, the response
// should have NXDOMAIN.
zone_table.add(ZonePtr(new MemoryZone(qclass, Name("example.com"))));
zone_table.addZone(ZonePtr(new MemoryZone(qclass, Name("example.com"))));
query.process();
EXPECT_EQ(Rcode::NXDOMAIN(), response.getRcode());
}
......@@ -63,7 +63,7 @@ TEST_F(QueryTest, matchZone) {
TEST_F(QueryTest, noMatchZone) {
// there's a zone in the table but it doesn't match the qname. should
// result in SERVFAIL.
zone_table.add(ZonePtr(new MemoryZone(qclass, Name("example.org"))));
zone_table.addZone(ZonePtr(new MemoryZone(qclass, Name("example.org"))));
query.process();
EXPECT_EQ(Rcode::SERVFAIL(), response.getRcode());
}
......
......@@ -16,3 +16,4 @@ libdatasrc_la_SOURCES += sqlite3_datasrc.h sqlite3_datasrc.cc
libdatasrc_la_SOURCES += query.h query.cc
libdatasrc_la_SOURCES += cache.h cache.cc
libdatasrc_la_SOURCES += zonetable.h zonetable.cc
libdatasrc_la_SOURCES += memory_datasrc.h memory_datasrc.cc
// Copyright (C) 2010 Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.
#include <dns/name.h>
#include <datasrc/memory_datasrc.h>
using namespace std;
using namespace isc::dns;
namespace isc {
namespace datasrc {
/// Implementation details for \c MemoryDataSrc hidden from the public
/// interface.
///
/// For now, \c MemoryDataSrc only contains a \c ZoneTable object, which
/// consists of (pointers to) \c MemoryZone objects, we may add more
/// member variables later for new features.
struct MemoryDataSrc::MemoryDataSrcImpl {
ZoneTable zone_table;
};
MemoryDataSrc::MemoryDataSrc() : impl_(new MemoryDataSrcImpl)
{}
MemoryDataSrc::~MemoryDataSrc() {
delete impl_;
}
result::Result
MemoryDataSrc::addZone(ZonePtr zone) {
if (!zone) {
isc_throw(InvalidParameter,
"Null pointer is passed to MemoryDataSrc::addZone()");
}
return (impl_->zone_table.addZone(zone));
}
MemoryDataSrc::FindResult
MemoryDataSrc::findZone(const isc::dns::Name& name) const {
return (FindResult(impl_->zone_table.findZone(name).code,
impl_->zone_table.findZone(name).zone));
}
} // end of namespace datasrc
} // end of namespace dns
// Copyright (C) 2010 Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.
#ifndef __MEMORY_DATA_SOURCE_H
#define __MEMORY_DATA_SOURCE_H 1
#include <datasrc/zonetable.h>
namespace isc {
namespace dns {
class Name;
};
namespace datasrc {
/// \brief A data source that uses in memory dedicated backend.
///
/// The \c MemoryDataSrc class represents a data source and provides a
/// basic interface to help DNS lookup processing. For a given domain
/// name, its \c findZone() method searches the in memory dedicated backend
/// for the zone that gives a longest match against that name.
///
/// The in memory dedicated backend are assumed to be of the same RR class,
/// but the \c MemoryDataSrc class does not enforce the assumption through
/// its interface.
/// For example, the \c addZone() method does not check if the new zone is of
/// the same RR class as that of the others already in the dedicated backend.
/// It is caller's responsibility to ensure this assumption.
///
/// <b>Notes to developer:</b>
///
/// For now, we don't make it a derived class of AbstractDataSrc because the
/// interface is so different (we'll eventually consider this as part of the
/// generalization work).
///
/// The addZone() method takes a (Boost) shared pointer because it would be
/// inconvenient to require the caller to maintain the ownership of zones,
/// while it wouldn't be safe to delete unnecessary zones inside the dedicated
/// backend.
///
/// The findZone() method takes a domain name and returns the best matching \c
/// MemoryZone in the form of (Boost) shared pointer, so that it can provide
/// the general interface for all data sources.
///
/// Currently, \c FindResult::zone is immutable for safety.
/// In future versions we may want to make it changeable. For example,
/// we may want to allow configuration update on an existing zone.
class MemoryDataSrc {
public:
/// \brief A helper structure to represent the search result of
/// <code>MemoryDataSrc::find()</code>.
///
/// This is a straightforward pair of the result code and a share pointer
/// to the found zone to represent the result of \c find().
/// We use this in order to avoid overloading the return value for both
/// the result code ("success" or "not found") and the found object,
/// i.e., avoid using \c NULL to mean "not found", etc.
///
/// This is a simple value class with no internal state, so for
/// convenience we allow the applications to refer to the members
/// directly.
///
/// See the description of \c find() for the semantics of the member
/// variables.
struct FindResult {
FindResult(result::Result param_code, const ConstZonePtr param_zone) :
code(param_code), zone(param_zone)
{}
const result::Result code;
const ConstZonePtr zone;
};
///
/// \name Constructors and Destructor.
///
/// \b Note:
/// The copy constructor and the assignment operator are intentionally
/// defined as private, making this class non copyable.
//@{
private:
MemoryDataSrc(const MemoryDataSrc& source);
MemoryDataSrc& operator=(const MemoryDataSrc& source);
public:
/// Default constructor.
///
/// This constructor internally involves resource allocation, and if
/// it fails, a corresponding standard exception will be thrown.
/// It never throws an exception otherwise.
MemoryDataSrc();
/// The destructor.
~MemoryDataSrc();
//@}
/// Add a \c Zone to the \c MemoryDataSrc.
///
/// \c Zone must not be associated with a NULL pointer; otherwise
/// an exception of class \c InvalidParameter will be thrown.
/// If internal resource allocation fails, a corresponding standard
/// exception will be thrown.
/// This method never throws an exception otherwise.
///
/// \param zone A \c Zone object to be added.
/// \return \c result::SUCCESS If the zone is successfully
/// added to the memory data source.
/// \return \c result::EXIST The memory data source already
/// stores a zone that has the same origin.
result::Result addZone(ZonePtr zone);
/// Find a \c Zone that best matches the given name in the \c MemoryDataSrc.
///
/// It searches the internal storage for a \c Zone that gives the
/// longest match against \c name, and returns the result in the
/// form of a \c FindResult object as follows:
/// - \c code: The result code of the operation.
/// - \c result::SUCCESS: A zone that gives an exact match
// is found
/// - \c result::PARTIALMATCH: A zone whose origin is a
// super domain of \c name is found (but there is no exact match)
/// - \c result::NOTFOUND: For all other cases.
/// - \c zone: A <Boost> shared pointer to the found \c Zone object if one
// is found; otherwise \c NULL.
///
/// This method never throws an exception.
///
/// \param name A domain name for which the search is performed.
/// \return A \c FindResult object enclosing the search result (see above).
FindResult findZone(const isc::dns::Name& name) const;
private:
struct MemoryDataSrcImpl;
MemoryDataSrcImpl* impl_;
};
}
}
#endif // __DATA_SOURCE_MEMORY_H
// Local Variables:
// mode: c++
// End:
......@@ -25,11 +25,12 @@ run_unittests_SOURCES += query_unittest.cc
run_unittests_SOURCES += cache_unittest.cc
run_unittests_SOURCES += test_datasrc.h test_datasrc.cc
run_unittests_SOURCES += zonetable_unittest.cc
run_unittests_SOURCES += memory_datasrc_unittest.cc
run_unittests_CPPFLAGS = $(AM_CPPFLAGS) $(GTEST_INCLUDES)
run_unittests_LDFLAGS = $(AM_LDFLAGS) $(GTEST_LDFLAGS)
run_unittests_LDADD = $(GTEST_LDADD)
run_unittests_LDADD += $(SQLITE_LIBS)
run_unittests_LDADD += $(top_builddir)/src/lib/datasrc/libdatasrc.la
run_unittests_LDADD += $(top_builddir)/src/lib/datasrc/libdatasrc.la
run_unittests_LDADD += $(top_builddir)/src/lib/dns/libdns++.la
run_unittests_LDADD += $(top_builddir)/src/lib/cc/libcc.la
run_unittests_LDADD += $(top_builddir)/src/lib/exceptions/libexceptions.la
......
// Copyright (C) 2010 Internet Systems Consortium, Inc. ("ISC")
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
// PERFORMANCE OF THIS SOFTWARE.
#include <exceptions/exceptions.h>
#include <dns/name.h>
#include <dns/rrclass.h>
#include <datasrc/zonetable.h>
#include <datasrc/memory_datasrc.h>
#include <gtest/gtest.h>
using namespace isc::dns;
using namespace isc::datasrc;
namespace {
class MemoryDataSrcTest : public ::testing::Test {
protected:
MemoryDataSrcTest()
{}
MemoryDataSrc memory_datasrc;
};
TEST_F(MemoryDataSrcTest, add_find_Zone) {
// test add zone
// Bogus zone (NULL)
EXPECT_THROW(memory_datasrc.addZone(ZonePtr()), isc::InvalidParameter);
// add zones with different names one by one
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(), Name("a")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::CH(), Name("b")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(), Name("c")))));
// add zones with the same name suffix
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::CH(),
Name("x.d.e.f")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::CH(),
Name("o.w.y.d.e.f")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::CH(),
Name("p.w.y.d.e.f")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(),
Name("q.w.y.d.e.f")))));
// add super zone and its subzone
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::CH(), Name("g.h")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(), Name("i.g.h")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(),
Name("z.d.e.f")))));
EXPECT_EQ(result::SUCCESS, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(),
Name("j.z.d.e.f")))));
// different zone class isn't allowed.
EXPECT_EQ(result::EXIST, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::CH(),
Name("q.w.y.d.e.f")))));
// names are compared in a case insensitive manner.
EXPECT_EQ(result::EXIST, memory_datasrc.addZone(
ZonePtr(new MemoryZone(RRClass::IN(),
Name("Q.W.Y.d.E.f")))));
// test find zone
EXPECT_EQ(result::SUCCESS, memory_datasrc.findZone(Name("a")).code);
EXPECT_EQ(Name("a"),
memory_datasrc.findZone(Name("a")).zone->getOrigin());
EXPECT_EQ(result::SUCCESS,
memory_datasrc.findZone(Name("j.z.d.e.f")).code);
EXPECT_EQ(Name("j.z.d.e.f"),
memory_datasrc.findZone(Name("j.z.d.e.f")).zone->getOrigin());
// NOTFOUND
EXPECT_EQ(result::NOTFOUND, memory_datasrc.findZone(Name("d.e.f")).code);
EXPECT_EQ(ConstZonePtr(), memory_datasrc.findZone(Name("d.e.f")).zone);
EXPECT_EQ(result::NOTFOUND,
memory_datasrc.findZone(Name("w.y.d.e.f")).code);
EXPECT_EQ(ConstZonePtr(),
memory_datasrc.findZone(Name("w.y.d.e.f")).zone);
// there's no exact match. the result should be the longest match,
// and the code should be PARTIALMATCH.
EXPECT_EQ(result::PARTIALMATCH,
memory_datasrc.findZone(Name("j.g.h")).code);
EXPECT_EQ(Name("g.h"),
memory_datasrc.findZone(Name("g.h")).zone->getOrigin());
EXPECT_EQ(result::PARTIALMATCH,
memory_datasrc.findZone(Name("z.i.g.h")).code);
EXPECT_EQ(Name("i.g.h"),
memory_datasrc.findZone(Name("z.i.g.h")).zone->getOrigin());
}
}
......@@ -53,61 +53,61 @@ protected:
ZonePtr zone1, zone2, zone3;
};
TEST_F(ZoneTableTest, add) {
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone1));
EXPECT_EQ(ZoneTable::EXIST, zone_table.add(zone1));
TEST_F(ZoneTableTest, addZone) {
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone1));
EXPECT_EQ(result::EXIST, zone_table.addZone(zone1));
// names are compared in a case insensitive manner.
EXPECT_EQ(ZoneTable::EXIST, zone_table.add(
EXPECT_EQ(result::EXIST, zone_table.addZone(
ZonePtr(new MemoryZone(RRClass::IN(), Name("EXAMPLE.COM")))));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone2));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone3));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone2));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone3));
// Zone table is indexed only by name. Duplicate origin name with
// different zone class isn't allowed.
EXPECT_EQ(ZoneTable::EXIST, zone_table.add(
EXPECT_EQ(result::EXIST, zone_table.addZone(
ZonePtr(new MemoryZone(RRClass::CH(),
Name("example.com")))));
/// Bogus zone (NULL)
EXPECT_THROW(zone_table.add(ZonePtr()), isc::InvalidParameter);
EXPECT_THROW(zone_table.addZone(ZonePtr()), isc::InvalidParameter);
}
TEST_F(ZoneTableTest, remove) {
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone1));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone2));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone3));
TEST_F(ZoneTableTest, removeZone) {
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone1));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone2));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone3));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.remove(Name("example.net")));
EXPECT_EQ(ZoneTable::NOTFOUND, zone_table.remove(Name("example.net")));
EXPECT_EQ(result::SUCCESS, zone_table.removeZone(Name("example.net")));
EXPECT_EQ(result::NOTFOUND, zone_table.removeZone(Name("example.net")));
}
TEST_F(ZoneTableTest, find) {
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone1));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone2));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone3));
TEST_F(ZoneTableTest, findZone) {
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone1));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone2));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone3));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.find(Name("example.com")).code);
EXPECT_EQ(result::SUCCESS, zone_table.findZone(Name("example.com")).code);
EXPECT_EQ(Name("example.com"),
zone_table.find(Name("example.com")).zone->getOrigin());
zone_table.findZone(Name("example.com")).zone->getOrigin());
EXPECT_EQ(ZoneTable::NOTFOUND,
zone_table.find(Name("example.org")).code);
EXPECT_EQ(static_cast<const Zone*>(NULL),
zone_table.find(Name("example.org")).zone);
EXPECT_EQ(result::NOTFOUND,
zone_table.findZone(Name("example.org")).code);
EXPECT_EQ(ConstZonePtr(),
zone_table.findZone(Name("example.org")).zone);
// there's no exact match. the result should be the longest match,
// and the code should be PARTIALMATCH.
EXPECT_EQ(ZoneTable::PARTIALMATCH,
zone_table.find(Name("www.example.com")).code);
EXPECT_EQ(result::PARTIALMATCH,
zone_table.findZone(Name("www.example.com")).code);
EXPECT_EQ(Name("example.com"),
zone_table.find(Name("www.example.com")).zone->getOrigin());
zone_table.findZone(Name("www.example.com")).zone->getOrigin());
// make sure the partial match is indeed the longest match by adding
// a zone with a shorter origin and query again.
ZonePtr zone_com(new MemoryZone(RRClass::IN(), Name("com")));
EXPECT_EQ(ZoneTable::SUCCESS, zone_table.add(zone_com));
EXPECT_EQ(result::SUCCESS, zone_table.addZone(zone_com));
EXPECT_EQ(Name("example.com"),
zone_table.find(Name("www.example.com")).zone->getOrigin());
zone_table.findZone(Name("www.example.com")).zone->getOrigin());
}
}
......@@ -77,29 +77,30 @@ ZoneTable::~ZoneTable() {
delete impl_;
}
ZoneTable::Result
ZoneTable::add(ZonePtr zone) {
result::Result
ZoneTable::addZone(ZonePtr zone) {
if (!zone) {
isc_throw(InvalidParameter,
"Null pointer is passed to ZoneTable::add()");
"Null pointer is passed to ZoneTable::addZone()");
}
if (impl_->zones.insert(
ZoneTableImpl::NameAndZone(zone->getOrigin(), zone)).second
== true) {
return (SUCCESS);
return (result::SUCCESS);
} else {
return (EXIST);
return (result::EXIST);
}
}
ZoneTable::Result
ZoneTable::remove(const Name& origin) {
return (impl_->zones.erase(origin) == 1 ? SUCCESS : NOTFOUND);
result::Result
ZoneTable::removeZone(const Name& origin) {
return (impl_->zones.erase(origin) == 1 ? result::SUCCESS :
result::NOTFOUND);
}
ZoneTable::FindResult
ZoneTable::find(const Name& name) const {
ZoneTable::findZone(const Name& name) const {
// Inefficient internal loop to find a longest match.
// This will be replaced with a single call to more intelligent backend.
for (int i = 0; i < name.getLabelCount(); ++i) {
......@@ -107,11 +108,11 @@ ZoneTable::find(const Name& name) const {
ZoneTableImpl::ZoneMap::const_iterator found =
impl_->zones.find(matchname);
if (found != impl_->zones.end()) {
return (FindResult(i == 0 ? SUCCESS : PARTIALMATCH,
(*found).second.get()));
return (FindResult(i == 0 ? result::SUCCESS :
result::PARTIALMATCH, (*found).second));
}
}
return (FindResult(NOTFOUND, NULL));
return (FindResult(result::NOTFOUND, ConstZonePtr()));
}
} // end of namespace datasrc
} // end of namespace isc
......@@ -26,6 +26,21 @@ class RRClass;
};
namespace datasrc {
namespace result {
/// Result codes of various public methods of in memory data source
///
/// The detailed semantics may differ in different methods.
/// See the description of specific methods for more details.
///
/// Note: this is intended to be used from other data sources eventually,
/// but for now it's specific to in memory data source and its backend.
enum Result {
SUCCESS, ///< The operation is successful.
EXIST, ///< The search key is already stored.
NOTFOUND, ///< The specified object is not found.
PARTIALMATCH ///< \c Only a partial match is found.
};
}
/// \brief The base class for a single authoritative zone
///
......@@ -223,81 +238,22 @@ private:
/// \brief A set of authoritative zones.
///
/// The \c ZoneTable class represents a set of zones of the same RR class
/// and provides a basic interface to help DNS lookup processing.
/// For a given domain name, its \c find() method searches the set for a zone
/// that gives a longest match against that name.
///
/// The set of zones are assumed to be of the same RR class, but the
/// \c ZoneTable class does not enforce the assumption through its interface.
/// For example, the \c add() method does not check if the new zone
/// is of the same RR class as that of the others already in the table.
/// It is caller's responsibility to ensure this assumption.
///
/// <b>Notes to developer:</b>
///
/// The add() method takes a (Boost) shared pointer because it would be
/// inconvenient to require the caller to maintain the ownership of zones,
/// while it wouldn't be safe to delete unnecessary zones inside the zone
/// table.
///
/// On the other hand, the find() method returns a bare pointer, rather than
/// the shared pointer, in order to minimize the dependency on Boost
/// definitions in our public interfaces. This means the caller can only
/// refer to the returned object (via the pointer) for a short period.
/// It should be okay for simple lookup purposes, but if we see the need
/// for keeping a \c Zone object for a longer period of context, we may
/// have to revisit this decision.
/// \c ZoneTable class is primarily intended to be used as a backend for the
/// \c MemoryDataSrc class, but is exposed as a separate class in case some
/// application wants to use it directly (e.g. for a customized data source
/// implementation).
///
/// Currently, \c FindResult::zone is immutable for safety.
/// In future versions we may want to make it changeable. For example,
/// we may want to allow configuration update on an existing zone.
///
/// In BIND 9's "zt" module, the equivalent of \c find() has an "option"
/// parameter. The only defined option is the one to specify the "no exact"
/// mode, and the only purpose of that mode is to prefer a second longest match
/// even if there is an exact match in order to deal with type DS query.
/// This trick may help enhance performance, but it also seems to make the
/// implementation complicated for a very limited, minor case. So, for now,
/// we don't introduce the special mode, and, since it was the only reason to
/// have search options in BIND 9, our initial implementation doesn't provide