Adding upstream version 2.2.0.upstream/2.2.0upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

37 files changed, 12048 insertions, 0 deletions

diff --git a/src/lib/cc/Makefile.am b/src/lib/cc/Makefile.am
new file mode 100644
index 0000000..2497524
--- /dev/null
+++ b/src/lib/cc/Makefile.am
@@ -0,0 +1,45 @@
+SUBDIRS = . tests
+
+AM_CPPFLAGS = -I$(top_srcdir)/src/lib -I$(top_builddir)/src/lib
+AM_CPPFLAGS += $(BOOST_INCLUDES)
+AM_CXXFLAGS = $(KEA_CXXFLAGS)
+
+lib_LTLIBRARIES = libkea-cc.la
+libkea_cc_la_SOURCES = base_stamped_element.cc base_stamped_element.h
+libkea_cc_la_SOURCES += data.cc data.h
+libkea_cc_la_SOURCES += element_value.h
+libkea_cc_la_SOURCES += cfg_to_element.h dhcp_config_error.h
+libkea_cc_la_SOURCES += command_interpreter.cc command_interpreter.h
+libkea_cc_la_SOURCES += json_feed.cc json_feed.h
+libkea_cc_la_SOURCES += server_tag.cc server_tag.h
+libkea_cc_la_SOURCES += simple_parser.cc simple_parser.h
+libkea_cc_la_SOURCES += stamped_element.cc stamped_element.h
+libkea_cc_la_SOURCES += stamped_value.cc stamped_value.h
+libkea_cc_la_SOURCES += user_context.cc user_context.h
+
+libkea_cc_la_LIBADD  = $(top_builddir)/src/lib/asiolink/libkea-asiolink.la
+libkea_cc_la_LIBADD += $(top_builddir)/src/lib/util/libkea-util.la
+libkea_cc_la_LIBADD += $(top_builddir)/src/lib/exceptions/libkea-exceptions.la
+libkea_cc_la_LIBADD += $(BOOST_LIBS)
+
+libkea_cc_la_LDFLAGS = -no-undefined -version-info 39:0:0
+
+# Specify the headers for copying into the installation directory tree.
+libkea_cc_includedir = $(pkgincludedir)/cc
+libkea_cc_include_HEADERS = \
+	base_stamped_element.h \
+	cfg_to_element.h \
+	command_interpreter.h \
+	data.h \
+	dhcp_config_error.h \
+	element_value.h \
+	json_feed.h \
+	server_tag.h \
+	simple_parser.h \
+	stamped_element.h \
+	stamped_value.h \
+	user_context.h
+
+EXTRA_DIST = cc.dox
+
+CLEANFILES = *.gcno *.gcda
diff --git a/src/lib/cc/Makefile.in b/src/lib/cc/Makefile.in
new file mode 100644
index 0000000..481dfb9
--- /dev/null
+++ b/src/lib/cc/Makefile.in
@@ -0,0 +1,970 @@
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+	-rm -f ./$(DEPDIR)/stamped_element.Plo
+	-rm -f ./$(DEPDIR)/stamped_value.Plo
+	-rm -f ./$(DEPDIR)/user_context.Plo
+	-rm -f Makefile
+maintainer-clean-am: distclean-am maintainer-clean-generic
+
+mostlyclean: mostlyclean-recursive
+
+mostlyclean-am: mostlyclean-compile mostlyclean-generic \
+	mostlyclean-libtool
+
+pdf: pdf-recursive
+
+pdf-am:
+
+ps: ps-recursive
+
+ps-am:
+
+uninstall-am: uninstall-libLTLIBRARIES \
+	uninstall-libkea_cc_includeHEADERS
+
+.MAKE: $(am__recursive_targets) install-am install-strip
+
+.PHONY: $(am__recursive_targets) CTAGS GTAGS TAGS all all-am \
+	am--depfiles check check-am clean clean-generic \
+	clean-libLTLIBRARIES clean-libtool cscopelist-am ctags \
+	ctags-am distclean distclean-compile distclean-generic \
+	distclean-libtool distclean-tags distdir dvi dvi-am html \
+	html-am info info-am install install-am install-data \
+	install-data-am install-dvi install-dvi-am install-exec \
+	install-exec-am install-html install-html-am install-info \
+	install-info-am install-libLTLIBRARIES \
+	install-libkea_cc_includeHEADERS install-man install-pdf \
+	install-pdf-am install-ps install-ps-am install-strip \
+	installcheck installcheck-am installdirs installdirs-am \
+	maintainer-clean maintainer-clean-generic mostlyclean \
+	mostlyclean-compile mostlyclean-generic mostlyclean-libtool \
+	pdf pdf-am ps ps-am tags tags-am uninstall uninstall-am \
+	uninstall-libLTLIBRARIES uninstall-libkea_cc_includeHEADERS
+
+.PRECIOUS: Makefile
+
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/src/lib/cc/base_stamped_element.cc b/src/lib/cc/base_stamped_element.cc
new file mode 100644
index 0000000..c3b6f38
--- /dev/null
+++ b/src/lib/cc/base_stamped_element.cc
@@ -0,0 +1,28 @@
+// Copyright (C) 2019-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/base_stamped_element.h>
+
+namespace isc {
+namespace data {
+
+BaseStampedElement::BaseStampedElement()
+    /// @todo Change it to microsec_clock once we transition to subsecond
+    /// precision.
+    : id_(0), timestamp_(boost::posix_time::second_clock::local_time()) {
+}
+
+void
+BaseStampedElement::updateModificationTime() {
+    /// @todo Change it to microsec_clock once we transition to subsecond
+    /// precision.
+    setModificationTime(boost::posix_time::second_clock::local_time());
+}
+
+} // end of namespace isc::data
+} // end of namespace isc
diff --git a/src/lib/cc/base_stamped_element.h b/src/lib/cc/base_stamped_element.h
new file mode 100644
index 0000000..beb3090
--- /dev/null
+++ b/src/lib/cc/base_stamped_element.h
@@ -0,0 +1,80 @@
+// Copyright (C) 2019,2021 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef BASE_STAMPED_ELEMENT_H
+#define BASE_STAMPED_ELEMENT_H
+
+#include <cc/data.h>
+#include <boost/date_time/posix_time/posix_time.hpp>
+#include <cstdint>
+
+namespace isc {
+namespace data {
+
+/// @brief This class represents configuration element which is
+/// associated with database identifier and the modification
+/// timestamp.
+///
+/// The @c StampedElement class derives from this class to extend
+/// it with the capability to associate the configuration elements
+/// with server tags. The @c db::Server class derives from it to
+/// store a single server tag identifying a server it describes.
+///
+/// @note This class is not derived from @c Element and should not
+/// be confused with the classes being derived from @c Element class.
+/// Those classes are used to represent JSON structures, whereas this
+/// class represents data fetched from the database.
+class BaseStampedElement {
+public:
+
+    /// @brief Constructor.
+    ///
+    /// Sets timestamp to the current time.
+    BaseStampedElement();
+
+    /// @brief Sets element's database identifier.
+    ///
+    /// @param id New id.
+    void setId(const uint64_t id) {
+        id_ = id;
+    }
+
+    /// @brief Returns element's database identifier.
+    uint64_t getId() const {
+        return (id_);
+    }
+
+    /// @brief Sets timestamp to the explicitly provided value.
+    ///
+    /// @param timestamp New timestamp value.
+    void setModificationTime(const boost::posix_time::ptime& timestamp) {
+        timestamp_ = timestamp;
+    }
+
+    /// @brief Sets timestamp to the current time.
+    void updateModificationTime();
+
+    /// @brief Returns timestamp.
+    boost::posix_time::ptime getModificationTime() const {
+        return (timestamp_);
+    }
+
+protected:
+
+    /// @brief Database identifier of the configuration element.
+    ///
+    /// The default value of 0 indicates that the identifier is
+    /// not set.
+    uint64_t id_;
+
+    /// @brief Holds timestamp value.
+    boost::posix_time::ptime timestamp_;
+};
+
+} // end of namespace isc::data
+} // end of namespace isc
+
+#endif
diff --git a/src/lib/cc/cc.dox b/src/lib/cc/cc.dox
new file mode 100644
index 0000000..da8d79b
--- /dev/null
+++ b/src/lib/cc/cc.dox
@@ -0,0 +1,107 @@
+// Copyright (C) 2016-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+/**
+ @page libcc libkea-cc - Kea Configuration Utilities Library
+
+@section ccSimpleParser Simple JSON Parser
+
+Since the early beginnings, our configuration parsing code was a mess. It
+started back in 2011 when Tomek joined ISC recently and was told to implement
+Kea configuration handling in similar way as DNS Auth module. The code grew
+over time (DHCP configuration is significantly more complex than DNS, with
+more interdependent values) and as of Kea 1.1 release it became very difficult
+to manage. The decision has been made to significantly refactor or even
+partially rewrite the parser code. The design for this effort is documented
+here: https://gitlab.isc.org/isc-projects/kea/wikis/designs/simple-parser-design. It discusses the original issues
+and the proposed architecture.
+
+There are several aspects of this new approach. The base class for all
+parsers is @ref isc::data::SimpleParser. It simplifies the parsers
+based on DhcpConfigParser by rejecting the concept of build/commit
+phases.  Instead, there should be a single method called parse that
+takes ConstElementPtr as a single parameter (that's the JSON
+structures to be parsed) and returns the config structure to be used
+in CfgMgr. An example of such a method can be the following:
+
+@code
+std::pair<OptionDescriptor, std::string>
+OptionDataParser::parse(isc::data::ConstElementPtr single_option)
+@endcode
+
+Since each derived class will have the same parameter, but a different return
+type, it's not possible to use virtual methods mechanism. That's perfectly
+ok, though, as there is only a single instance of the class needed to parse
+arbitrary number of parameters of the same type. There is no need to
+keep pointers to the parser object. As such there are fewer incentives to have
+one generic way to handle all parsers.
+
+@subsection ccSimpleParserDefaults Default values in Simple Parser
+
+Another simplification comes from the fact that almost all parameters
+are mandatory in SimpleParser. One source of complexities in the old
+parser was the necessity to deal with optional parameters. Simple
+parser deals with that by explicitly requiring the input structure to
+have all parameters filled. Obviously, it's not feasible to expect
+everyone to always specify all parameters, therefore there's an easy
+way to fill missing parameters with their default values. There are
+several methods to do this, but the most generic one is:
+
+@code
+static size_t
+isc::data::SimpleParser::setDefaults(isc::data::ElementPtr scope,
+                                     const SimpleDefaults& default_values);
+@endcode
+
+It takes a pointer to element to be filled with default values and
+vector of default values. Having those values specified in a single
+place in a way that can easily be read even by non-programmers is a
+big advantage of this approach. Here's an example from simple_parser.cc file:
+
+@code
+/// This table defines default values for option definitions in DHCPv6
+const SimpleDefaults OPTION6_DEF_DEFAULTS = {
+    { "record-types", Element::string,  ""},
+    { "space",        Element::string,  "dhcp6"},
+    { "array",        Element::boolean, "false"},
+    { "encapsulate",  Element::string,  "" }
+};
+@endcode
+
+This array (which technically is implemented as a vector and
+initialized the C++11 way) can be passed to the aforementioned
+setDefaults. That code will iterate over all default values and see if
+there are explicit values provided. If not, the gaps will be filled
+with default values. There are also convenience methods specified for
+filling in option data defaults, option definition defaults and
+setAllDefaults that sets all defaults (starts with global, but then
+walks down the Element tree and fills defaults in subsequent scopes).
+
+@subsection ccSimpleParserInherits Inheriting parameters between scopes
+
+SimpleParser provides a mechanism to inherit parameters between scopes,
+e.g. to inherit global parameters in the subnet scope if more specific
+values are not defined in the subnet scope. This is achieved by calling
+@code
+static size_t SimpleParser::deriveParams(isc::data::ConstElementPtr parent,
+                                         isc::data::ElementPtr child,
+                                         const ParamsList& params);
+
+@endcode
+
+ParamsList is a simple vector<string>. There will be more specific
+methods implemented in the future, but for the time being only
+@ref isc::data::SimpleParser::deriveParams is implemented.
+
+@subsection ccMTConsiderations Multi-Threading Consideration for Configuration Utilities
+
+No configuration utility is thread safe. For instance stamped values are
+not thread safe so any read access must be done in a context where write
+access at the same time is not possible. Note that configuration is
+performed by the main thread with service threads stopped so this constraint
+is fulfilled.
+
+*/
diff --git a/src/lib/cc/cfg_to_element.h b/src/lib/cc/cfg_to_element.h
new file mode 100644
index 0000000..480dd1f
--- /dev/null
+++ b/src/lib/cc/cfg_to_element.h
@@ -0,0 +1,48 @@
+// Copyright (C) 2017 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef CFG_TO_ELEMENT_H
+#define CFG_TO_ELEMENT_H
+
+#include <exceptions/exceptions.h>
+#include <cc/data.h>
+
+namespace isc {
+
+/// @brief Cannot unparse error
+///
+/// This exception is expected to be thrown when toElement fails
+/// and to skip flawed elements is not wanted.
+class ToElementError : public isc::Exception {
+public:
+    ToElementError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+namespace data {
+
+/// @brief Abstract class for configuration Cfg_* classes
+///
+struct CfgToElement {
+    /// Destructor
+    virtual ~CfgToElement() { }
+
+    /// @brief Unparse a configuration object
+    ///
+    /// Returns an element which must parse into the same object, i.e.
+    /// @code
+    /// for all valid config C parse(parse(C)->toElement()) == parse(C)
+    /// @endcode
+    ///
+    /// @return a pointer to a configuration which can be parsed into
+    /// the initial configuration object
+    virtual isc::data::ElementPtr toElement() const = 0;
+};
+
+}; // namespace isc::dhcp
+}; // namespace isc
+
+#endif // CFG_TO_ELEMENT_H
diff --git a/src/lib/cc/command_interpreter.cc b/src/lib/cc/command_interpreter.cc
new file mode 100644
index 0000000..68f880c
--- /dev/null
+++ b/src/lib/cc/command_interpreter.cc
@@ -0,0 +1,284 @@
+// Copyright (C) 2009-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <exceptions/exceptions.h>
+#include <cc/command_interpreter.h>
+#include <cc/data.h>
+#include <string>
+#include <set>
+
+using namespace std;
+
+using isc::data::Element;
+using isc::data::ConstElementPtr;
+using isc::data::ElementPtr;
+using isc::data::JSONError;
+
+namespace isc {
+namespace config {
+
+const char *CONTROL_COMMAND = "command";
+const char *CONTROL_RESULT = "result";
+const char *CONTROL_TEXT = "text";
+const char *CONTROL_ARGUMENTS = "arguments";
+const char *CONTROL_SERVICE = "service";
+const char *CONTROL_REMOTE_ADDRESS = "remote-address";
+
+// Full version, with status, text and arguments
+ConstElementPtr
+createAnswer(const int status_code, const std::string& text,
+             const ConstElementPtr& arg) {
+    if (status_code != 0 && text.empty()) {
+        isc_throw(CtrlChannelError, "Text has to be provided for status_code != 0");
+    }
+
+    ElementPtr answer = Element::createMap();
+    ElementPtr result = Element::create(status_code);
+    answer->set(CONTROL_RESULT, result);
+
+    if (!text.empty()) {
+        answer->set(CONTROL_TEXT, Element::create(text));
+    }
+    if (arg) {
+        answer->set(CONTROL_ARGUMENTS, arg);
+    }
+    return (answer);
+}
+
+ConstElementPtr
+createAnswer() {
+    return (createAnswer(0, string(""), ConstElementPtr()));
+}
+
+ConstElementPtr
+createAnswer(const int status_code, const std::string& text) {
+    return (createAnswer(status_code, text, ElementPtr()));
+}
+
+ConstElementPtr
+createAnswer(const int status_code, const ConstElementPtr& arg) {
+    return (createAnswer(status_code, "", arg));
+}
+
+ConstElementPtr
+parseAnswer(int &rcode, const ConstElementPtr& msg) {
+    if (!msg) {
+        isc_throw(CtrlChannelError, "No answer specified");
+    }
+    if (msg->getType() != Element::map) {
+        isc_throw(CtrlChannelError,
+                  "Invalid answer Element specified, expected map");
+    }
+    if (!msg->contains(CONTROL_RESULT)) {
+        isc_throw(CtrlChannelError,
+                  "Invalid answer specified, does not contain mandatory 'result'");
+    }
+
+    ConstElementPtr result = msg->get(CONTROL_RESULT);
+    if (result->getType() != Element::integer) {
+            isc_throw(CtrlChannelError,
+                      "Result element in answer message is not a string");
+    }
+
+    rcode = result->intValue();
+
+    // If there are arguments, return them.
+    ConstElementPtr args = msg->get(CONTROL_ARGUMENTS);
+    if (args) {
+        return (args);
+    }
+
+    // There are no arguments, let's try to return just the text status
+    return (msg->get(CONTROL_TEXT));
+}
+
+std::string
+answerToText(const ConstElementPtr& msg) {
+    if (!msg) {
+        isc_throw(CtrlChannelError, "No answer specified");
+    }
+    if (msg->getType() != Element::map) {
+        isc_throw(CtrlChannelError,
+                  "Invalid answer Element specified, expected map");
+    }
+    if (!msg->contains(CONTROL_RESULT)) {
+        isc_throw(CtrlChannelError,
+                  "Invalid answer specified, does not contain mandatory 'result'");
+    }
+
+    ConstElementPtr result = msg->get(CONTROL_RESULT);
+    if (result->getType() != Element::integer) {
+            isc_throw(CtrlChannelError,
+                      "Result element in answer message is not a string");
+    }
+
+    stringstream txt;
+    int rcode = result->intValue();
+    if (rcode == 0) {
+        txt << "success(0)";
+    } else {
+        txt << "failure(" << rcode << ")";
+    }
+
+    // Was any text provided? If yes, include it.
+    ConstElementPtr txt_elem = msg->get(CONTROL_TEXT);
+    if (txt_elem) {
+        txt << ", text=" << txt_elem->stringValue();
+    }
+
+    return (txt.str());
+}
+
+ConstElementPtr
+createCommand(const std::string& command) {
+    return (createCommand(command, ElementPtr(), ""));
+}
+
+ConstElementPtr
+createCommand(const std::string& command, ConstElementPtr arg) {
+    return (createCommand(command, arg, ""));
+}
+
+ConstElementPtr
+createCommand(const std::string& command, const std::string& service) {
+    return (createCommand(command, ElementPtr(), service));
+}
+
+ConstElementPtr
+createCommand(const std::string& command,
+              ConstElementPtr arg,
+              const std::string& service) {
+    ElementPtr query = Element::createMap();
+    ElementPtr cmd = Element::create(command);
+    query->set(CONTROL_COMMAND, cmd);
+    if (arg) {
+        query->set(CONTROL_ARGUMENTS, arg);
+    }
+    if (!service.empty()) {
+        ElementPtr services = Element::createList();
+        services->add(Element::create(service));
+        query->set(CONTROL_SERVICE, services);
+    }
+    return (query);
+}
+
+std::string
+parseCommand(ConstElementPtr& arg, ConstElementPtr command) {
+    if (!command) {
+        isc_throw(CtrlChannelError, "No command specified");
+    }
+    if (command->getType() != Element::map) {
+        isc_throw(CtrlChannelError, "Invalid command Element specified, expected map");
+    }
+    if (!command->contains(CONTROL_COMMAND)) {
+        isc_throw(CtrlChannelError,
+                  "Invalid answer specified, does not contain mandatory 'command'");
+    }
+
+    // Make sure that all specified parameters are supported.
+    auto command_params = command->mapValue();
+    for (auto param : command_params) {
+        if ((param.first != CONTROL_COMMAND) &&
+            (param.first != CONTROL_ARGUMENTS) &&
+            (param.first != CONTROL_SERVICE) &&
+            (param.first != CONTROL_REMOTE_ADDRESS)) {
+            isc_throw(CtrlChannelError, "Received command contains unsupported "
+                      "parameter '" << param.first << "'");
+        }
+    }
+
+    ConstElementPtr cmd = command->get(CONTROL_COMMAND);
+    if (cmd->getType() != Element::string) {
+        isc_throw(CtrlChannelError,
+                  "'command' element in command message is not a string");
+    }
+
+    arg = command->get(CONTROL_ARGUMENTS);
+
+    return (cmd->stringValue());
+}
+
+std::string
+parseCommandWithArgs(ConstElementPtr& arg, ConstElementPtr command) {
+    std::string command_name = parseCommand(arg, command);
+
+    // This function requires arguments within the command.
+    if (!arg) {
+        isc_throw(CtrlChannelError,
+                  "no arguments specified for the '" << command_name
+                  << "' command");
+    }
+
+    // Arguments must be a map.
+    if (arg->getType() != Element::map) {
+        isc_throw(CtrlChannelError, "arguments specified for the '" << command_name
+                  << "' command are not a map");
+    }
+
+    // At least one argument is required.
+    if (arg->size() == 0) {
+        isc_throw(CtrlChannelError, "arguments must not be empty for "
+                  "the '" << command_name << "' command");
+    }
+
+    return (command_name);
+}
+
+ConstElementPtr
+combineCommandsLists(const ConstElementPtr& response1,
+                     const ConstElementPtr& response2) {
+    // Usually when this method is called there should be two non-null
+    // responses. If there is just a single response, return this
+    // response.
+    if (!response1 && response2) {
+        return (response2);
+
+    } else if (response1 && !response2) {
+        return (response1);
+
+    } else if (!response1 && !response2) {
+        return (ConstElementPtr());
+
+    } else {
+        // Both responses are non-null so we need to combine the lists
+        // of supported commands if the status codes are 0.
+        int status_code;
+        ConstElementPtr args1 = parseAnswer(status_code, response1);
+        if (status_code != 0) {
+            return (response1);
+        }
+
+        ConstElementPtr args2 = parseAnswer(status_code, response2);
+        if (status_code != 0) {
+            return (response2);
+        }
+
+        const std::vector<ElementPtr> vec1 = args1->listValue();
+        const std::vector<ElementPtr> vec2 = args2->listValue();
+
+        // Storing command names in a set guarantees that the non-unique
+        // command names are aggregated.
+        std::set<std::string> combined_set;
+        for (auto v = vec1.cbegin(); v != vec1.cend(); ++v) {
+            combined_set.insert((*v)->stringValue());
+        }
+        for (auto v = vec2.cbegin(); v != vec2.cend(); ++v) {
+            combined_set.insert((*v)->stringValue());
+        }
+
+        // Create a combined list of commands.
+        ElementPtr combined_list = Element::createList();
+        for (auto s = combined_set.cbegin(); s != combined_set.cend(); ++s) {
+            combined_list->add(Element::create(*s));
+        }
+        return (createAnswer(CONTROL_RESULT_SUCCESS, combined_list));
+    }
+}
+
+}
+}
diff --git a/src/lib/cc/command_interpreter.h b/src/lib/cc/command_interpreter.h
new file mode 100644
index 0000000..2b5b114
--- /dev/null
+++ b/src/lib/cc/command_interpreter.h
@@ -0,0 +1,204 @@
+// Copyright (C) 2009-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef COMMAND_INTERPRETER_H
+#define COMMAND_INTERPRETER_H
+
+#include <cc/data.h>
+#include <string>
+
+/// @file command_interpreter.h
+///
+/// This file contains several functions and constants that are used for
+/// handling commands and responses sent over control channel. The design
+/// is described here: https://gitlab.isc.org/isc-projects/kea/wikis/Stats-design, but also
+/// in @ref ctrlSocket section in the Developer's Guide.
+
+namespace isc {
+namespace config {
+
+/// @brief String used for commands ("command")
+extern const char *CONTROL_COMMAND;
+
+/// @brief String used for result, i.e. integer status ("result")
+extern const char *CONTROL_RESULT;
+
+/// @brief String used for storing textual description ("text")
+extern const char *CONTROL_TEXT;
+
+/// @brief String used for arguments map ("arguments")
+extern const char *CONTROL_ARGUMENTS;
+
+/// @brief String used for service list ("service")
+extern const char *CONTROL_SERVICE;
+
+/// @brief String used for remote address ("remote-address")
+extern const char *CONTROL_REMOTE_ADDRESS;
+
+/// @brief Status code indicating a successful operation
+const int CONTROL_RESULT_SUCCESS = 0;
+
+/// @brief Status code indicating a general failure
+const int CONTROL_RESULT_ERROR = 1;
+
+/// @brief Status code indicating that the specified command is not supported.
+const int CONTROL_RESULT_COMMAND_UNSUPPORTED = 2;
+
+/// @brief Status code indicating that the specified command was completed
+///        correctly, but failed to produce any results. For example, get
+///        completed the search, but couldn't find the object it was looking for.
+const int CONTROL_RESULT_EMPTY = 3;
+
+/// @brief A standard control channel exception that is thrown if a function
+/// is there is a problem with one of the messages
+class CtrlChannelError : public isc::Exception {
+public:
+    CtrlChannelError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) {}
+};
+
+/// @brief Creates a standard config/command level success answer message
+///        (i.e. of the form { "result": 0 }
+/// @return Standard command/config success answer message
+isc::data::ConstElementPtr createAnswer();
+
+/// @brief Creates a standard config/command level answer message
+/// (i.e. of the form { "result": 1, "text": "Invalid command received" }
+///
+/// @param status_code The return code (0 for success)
+/// @param status_text A string to put into the "text" argument
+/// @return Standard command/config answer message
+isc::data::ConstElementPtr createAnswer(const int status_code,
+                                        const std::string& status_text);
+
+/// @brief Creates a standard config/command level answer message
+/// (i.e. of the form { "result": status_code, "arguments": arg }
+///
+/// @param status_code The return code (0 for success)
+/// @param arg The optional argument for the answer. This can be of
+///        any Element type. May be NULL.
+/// @return Standard command/config answer message
+isc::data::ConstElementPtr createAnswer(const int status_code,
+                                        const isc::data::ConstElementPtr& arg);
+
+/// @brief Creates a standard config/command level answer message
+///
+/// @param status_code The return code (0 for success)
+/// @param status textual representation of the status (used mostly for errors)
+/// @param arg The optional argument for the answer. This can be of
+///        any Element type. May be NULL.
+/// @return Standard command/config answer message
+isc::data::ConstElementPtr createAnswer(const int status_code,
+                                        const std::string& status,
+                                        const isc::data::ConstElementPtr& arg);
+
+/// @brief Parses a standard config/command level answer message.
+///
+/// @param status_code This value will be set to the return code contained in
+///              the message
+/// @param msg The message to parse
+/// @return The optional argument in the message.
+isc::data::ConstElementPtr parseAnswer(int &status_code,
+                                       const isc::data::ConstElementPtr& msg);
+
+/// @brief Converts answer to printable text
+///
+/// @param msg answer to be parsed
+/// @return printable string
+std::string answerToText(const isc::data::ConstElementPtr& msg);
+
+/// @brief Creates a standard command message with no
+/// argument (of the form { "command": "my_command" })
+///
+/// @param command The command string
+/// @return The created message
+isc::data::ConstElementPtr createCommand(const std::string& command);
+
+/// @brief Creates a standard command message with the
+/// given argument (of the form { "command": "my_command", "arguments": arg }
+///
+/// @param command The command string
+/// @param arg The optional argument for the command. This can be of
+///        any Element type. May be NULL.
+/// @return The created message
+isc::data::ConstElementPtr createCommand(const std::string& command,
+                                         isc::data::ConstElementPtr arg);
+
+/// @brief Creates a standard config/command command message with no
+/// argument and with the given service (of the form
+/// { "command": "my_command", "service": [ service ] })
+///
+/// @param command The command string
+/// @param service The target service. May be empty.
+/// @return The created message
+ isc::data::ConstElementPtr createCommand(const std::string& command,
+                                          const std::string& service);
+
+/// @brief Creates a standard config/command command message with the
+/// given argument and given service (of the form
+/// { "command": "my_command", "arguments": arg, "service": [ service ] }
+///
+/// @param command The command string
+/// @param arg The optional argument for the command. This can be of
+///        any Element type. May be NULL.
+/// @param service The target service. May be empty.
+/// @return The created message
+isc::data::ConstElementPtr createCommand(const std::string& command,
+                                         isc::data::ConstElementPtr arg,
+                                         const std::string& service);
+
+/// @brief Parses the given command into a string containing the actual
+///        command and an ElementPtr containing the optional argument.
+///
+/// @throw CtrlChannelError if this is not a well-formed command
+///
+/// @param arg This value will be set to the ElementPtr pointing to
+///        the argument, or to an empty Map (ElementPtr) if there was none.
+/// @param command The command message containing the command (as made
+///        by createCommand()
+/// @return The command name.
+std::string parseCommand(isc::data::ConstElementPtr& arg,
+                         isc::data::ConstElementPtr command);
+
+
+/// @brief Parses the given command into a string containing the command
+///        name and an ElementPtr containing the mandatory argument.
+///
+/// This function expects that command arguments are specified and are
+/// a map.
+///
+/// @throw CtrlChannelError if this is not a well-formed command,
+///        arguments are not specified or are not a map.
+///
+/// @param arg Reference to the data element to which command arguments
+///        will be assigned.
+/// @param command The command message containing the command and
+///        the arguments.
+/// @return Command name.
+std::string parseCommandWithArgs(isc::data::ConstElementPtr& arg,
+                                 isc::data::ConstElementPtr command);
+
+/// @brief Combines lists of commands carried in two responses.
+///
+/// This method is used to combine list of commands returned by the
+/// two command managers.
+///
+/// If the same command appears in two responses only a single
+/// instance is returned in the combined response.
+///
+/// @param response1 First command response.
+/// @param response2 Second command response.
+///
+/// @return Pointer to the 'list-commands' response holding combined
+/// list of commands.
+isc::data::ConstElementPtr
+combineCommandsLists(const isc::data::ConstElementPtr& response1,
+                     const isc::data::ConstElementPtr& response2);
+
+}; // end of namespace isc::config
+}; // end of namespace isc
+
+#endif // COMMAND_INTERPRETER_H
diff --git a/src/lib/cc/data.cc b/src/lib/cc/data.cc
new file mode 100644
index 0000000..20c2015
--- /dev/null
+++ b/src/lib/cc/data.cc
@@ -0,0 +1,1598 @@
+// Copyright (C) 2010-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/data.h>
+
+#include <cstring>
+#include <cassert>
+#include <climits>
+#include <list>
+#include <map>
+#include <cstdio>
+#include <iostream>
+#include <iomanip>
+#include <string>
+#include <sstream>
+#include <fstream>
+#include <cerrno>
+
+#include <boost/lexical_cast.hpp>
+
+#include <cmath>
+
+using namespace std;
+
+namespace {
+const char* const WHITESPACE = " \b\f\n\r\t";
+} // end anonymous namespace
+
+namespace isc {
+namespace data {
+
+std::string
+Element::Position::str() const {
+    std::ostringstream ss;
+    ss << file_ << ":" << line_ << ":" << pos_;
+    return (ss.str());
+}
+
+std::ostream&
+operator<<(std::ostream& out, const Element::Position& pos) {
+    out << pos.str();
+    return (out);
+}
+
+std::string
+Element::str() const {
+    std::stringstream ss;
+    toJSON(ss);
+    return (ss.str());
+}
+
+std::string
+Element::toWire() const {
+    std::stringstream ss;
+    toJSON(ss);
+    return (ss.str());
+}
+
+void
+Element::toWire(std::ostream& ss) const {
+    toJSON(ss);
+}
+
+bool
+Element::getValue(int64_t&) const {
+    return (false);
+}
+
+bool
+Element::getValue(double&) const {
+    return (false);
+}
+
+bool
+Element::getValue(bool&) const {
+    return (false);
+}
+
+bool
+Element::getValue(std::string&) const {
+    return (false);
+}
+
+bool
+Element::getValue(std::vector<ElementPtr>&) const {
+    return (false);
+}
+
+bool
+Element::getValue(std::map<std::string, ConstElementPtr>&) const {
+    return (false);
+}
+
+bool
+Element::setValue(const long long int) {
+    return (false);
+}
+
+bool
+Element::setValue(const double) {
+    return (false);
+}
+
+bool
+Element::setValue(const bool) {
+    return (false);
+}
+
+bool
+Element::setValue(const std::string&) {
+    return (false);
+}
+
+bool
+Element::setValue(const std::vector<ElementPtr>&) {
+    return (false);
+}
+
+bool
+Element::setValue(const std::map<std::string, ConstElementPtr>&) {
+    return (false);
+}
+
+ConstElementPtr
+Element::get(const int) const {
+    throwTypeError("get(int) called on a non-container Element");
+}
+
+ElementPtr
+Element::getNonConst(const int) const {
+    throwTypeError("get(int) called on a non-container Element");
+}
+
+void
+Element::set(const size_t, ElementPtr) {
+    throwTypeError("set(int, element) called on a non-list Element");
+}
+
+void
+Element::add(ElementPtr) {
+    throwTypeError("add() called on a non-list Element");
+}
+
+void
+Element::remove(const int) {
+    throwTypeError("remove(int) called on a non-container Element");
+}
+
+size_t
+Element::size() const {
+    throwTypeError("size() called on a non-list Element");
+}
+
+bool
+Element::empty() const {
+    throwTypeError("empty() called on a non-container Element");
+}
+
+ConstElementPtr
+Element::get(const std::string&) const {
+    throwTypeError("get(string) called on a non-map Element");
+}
+
+void
+Element::set(const std::string&, ConstElementPtr) {
+    throwTypeError("set(name, element) called on a non-map Element");
+}
+
+void
+Element::remove(const std::string&) {
+    throwTypeError("remove(string) called on a non-map Element");
+}
+
+bool
+Element::contains(const std::string&) const {
+    throwTypeError("contains(string) called on a non-map Element");
+}
+
+ConstElementPtr
+Element::find(const std::string&) const {
+    throwTypeError("find(string) called on a non-map Element");
+}
+
+bool
+Element::find(const std::string&, ConstElementPtr&) const {
+    return (false);
+}
+
+namespace {
+inline void
+throwJSONError(const std::string& error, const std::string& file, int line,
+               int pos) {
+    std::stringstream ss;
+    ss << error << " in " + file + ":" << line << ":" << pos;
+    isc_throw(JSONError, ss.str());
+}
+} // end anonymous namespace
+
+std::ostream&
+operator<<(std::ostream& out, const Element& e) {
+    return (out << e.str());
+}
+
+bool
+operator==(const Element& a, const Element& b) {
+    return (a.equals(b));
+}
+
+bool operator!=(const Element& a, const Element& b) {
+    return (!a.equals(b));
+}
+
+bool
+operator<(Element const& a, Element const& b) {
+    if (a.getType() != b.getType()) {
+        isc_throw(BadValue, "cannot compare Elements of different types");
+    }
+    switch (a.getType()) {
+    case Element::integer:
+        return a.intValue() < b.intValue();
+    case Element::real:
+        return a.doubleValue() < b.doubleValue();
+    case Element::boolean:
+        return b.boolValue() || !a.boolValue();
+    case Element::string:
+        return std::strcmp(a.stringValue().c_str(), b.stringValue().c_str()) < 0;
+    }
+    isc_throw(BadValue, "cannot compare Elements of type " <<
+                            std::to_string(a.getType()));
+}
+
+//
+// factory functions
+//
+ElementPtr
+Element::create(const Position& pos) {
+    return (ElementPtr(new NullElement(pos)));
+}
+
+ElementPtr
+Element::create(const long long int i, const Position& pos) {
+    return (ElementPtr(new IntElement(static_cast<int64_t>(i), pos)));
+}
+
+ElementPtr
+Element::create(const int i, const Position& pos) {
+    return (create(static_cast<long long int>(i), pos));
+}
+
+ElementPtr
+Element::create(const long int i, const Position& pos) {
+    return (create(static_cast<long long int>(i), pos));
+}
+
+ElementPtr
+Element::create(const uint32_t i, const Position& pos) {
+    return (create(static_cast<long long int>(i), pos));
+}
+
+ElementPtr
+Element::create(const double d, const Position& pos) {
+    return (ElementPtr(new DoubleElement(d, pos)));
+}
+
+ElementPtr
+Element::create(const bool b, const Position& pos) {
+    return (ElementPtr(new BoolElement(b, pos)));
+}
+
+ElementPtr
+Element::create(const std::string& s, const Position& pos) {
+    return (ElementPtr(new StringElement(s, pos)));
+}
+
+ElementPtr
+Element::create(const char *s, const Position& pos) {
+    return (create(std::string(s), pos));
+}
+
+ElementPtr
+Element::createList(const Position& pos) {
+    return (ElementPtr(new ListElement(pos)));
+}
+
+ElementPtr
+Element::createMap(const Position& pos) {
+    return (ElementPtr(new MapElement(pos)));
+}
+
+
+//
+// helper functions for fromJSON factory
+//
+namespace {
+bool
+charIn(const int c, const char* chars) {
+    const size_t chars_len = std::strlen(chars);
+    for (size_t i = 0; i < chars_len; ++i) {
+        if (chars[i] == c) {
+            return (true);
+        }
+    }
+    return (false);
+}
+
+void
+skipChars(std::istream& in, const char* chars, int& line, int& pos) {
+    int c = in.peek();
+    while (charIn(c, chars) && c != EOF) {
+        if (c == '\n') {
+            ++line;
+            pos = 1;
+        } else {
+            ++pos;
+        }
+        in.ignore();
+        c = in.peek();
+    }
+}
+
+// skip on the input stream to one of the characters in chars
+// if another character is found this function throws JSONError
+// unless that character is specified in the optional may_skip
+//
+// It returns the found character (as an int value).
+int
+skipTo(std::istream& in, const std::string& file, int& line, int& pos,
+       const char* chars, const char* may_skip="") {
+    int c = in.get();
+    ++pos;
+    while (c != EOF) {
+        if (c == '\n') {
+            pos = 1;
+            ++line;
+        }
+        if (charIn(c, may_skip)) {
+            c = in.get();
+            ++pos;
+        } else if (charIn(c, chars)) {
+            while (charIn(in.peek(), may_skip)) {
+                if (in.peek() == '\n') {
+                    pos = 1;
+                    ++line;
+                } else {
+                    ++pos;
+                }
+                in.ignore();
+            }
+            return (c);
+        } else {
+            throwJSONError(std::string("'") + std::string(1, c) + "' read, one of \"" + chars + "\" expected", file, line, pos);
+        }
+    }
+    throwJSONError(std::string("EOF read, one of \"") + chars + "\" expected", file, line, pos);
+    return (c); // shouldn't reach here, but some compilers require it
+}
+
+// TODO: Should we check for all other official escapes here (and
+// error on the rest)?
+std::string
+strFromStringstream(std::istream& in, const std::string& file,
+                    const int line, int& pos) {
+    std::stringstream ss;
+    int c = in.get();
+    ++pos;
+    if (c == '"') {
+        c = in.get();
+        ++pos;
+    } else {
+        throwJSONError("String expected", file, line, pos);
+    }
+
+    while (c != EOF && c != '"') {
+        if (c == '\\') {
+            // see the spec for allowed escape characters
+            int d;
+            switch (in.peek()) {
+            case '"':
+                c = '"';
+                break;
+            case '/':
+                c = '/';
+                break;
+            case '\\':
+                c = '\\';
+                break;
+            case 'b':
+                c = '\b';
+                break;
+            case 'f':
+                c = '\f';
+                break;
+            case 'n':
+                c = '\n';
+                break;
+            case 'r':
+                c = '\r';
+                break;
+            case 't':
+                c = '\t';
+                break;
+            case 'u':
+                // skip first 0
+                in.ignore();
+                ++pos;
+                c = in.peek();
+                if (c != '0') {
+                    throwJSONError("Unsupported unicode escape", file, line, pos);
+                }
+                // skip second 0
+                in.ignore();
+                ++pos;
+                c = in.peek();
+                if (c != '0') {
+                    throwJSONError("Unsupported unicode escape", file, line, pos - 2);
+                }
+                // get first digit
+                in.ignore();
+                ++pos;
+                d = in.peek();
+                if ((d >= '0') && (d <= '9')) {
+                    c = (d - '0') << 4;
+                } else if ((d >= 'A') && (d <= 'F')) {
+                    c = (d - 'A' + 10) << 4;
+                } else if ((d >= 'a') && (d <= 'f')) {
+                    c = (d - 'a' + 10) << 4;
+                } else {
+                    throwJSONError("Not hexadecimal in unicode escape", file, line, pos - 3);
+                }
+                // get second digit
+                in.ignore();
+                ++pos;
+                d = in.peek();
+                if ((d >= '0') && (d <= '9')) {
+                    c |= d - '0';
+                } else if ((d >= 'A') && (d <= 'F')) {
+                    c |= d - 'A' + 10;
+                } else if ((d >= 'a') && (d <= 'f')) {
+                    c |= d - 'a' + 10;
+                } else {
+                    throwJSONError("Not hexadecimal in unicode escape", file, line, pos - 4);
+                }
+                break;
+            default:
+                throwJSONError("Bad escape", file, line, pos);
+            }
+            // drop the escaped char
+            in.ignore();
+            ++pos;
+        }
+        ss.put(c);
+        c = in.get();
+        ++pos;
+    }
+    if (c == EOF) {
+        throwJSONError("Unterminated string", file, line, pos);
+    }
+    return (ss.str());
+}
+
+std::string
+wordFromStringstream(std::istream& in, int& pos) {
+    std::stringstream ss;
+    while (isalpha(in.peek())) {
+        ss << (char) in.get();
+    }
+    pos += ss.str().size();
+    return (ss.str());
+}
+
+std::string
+numberFromStringstream(std::istream& in, int& pos) {
+    std::stringstream ss;
+    while (isdigit(in.peek()) || in.peek() == '+' || in.peek() == '-' ||
+           in.peek() == '.' || in.peek() == 'e' || in.peek() == 'E') {
+        ss << (char) in.get();
+    }
+    pos += ss.str().size();
+    return (ss.str());
+}
+
+// Should we change from IntElement and DoubleElement to NumberElement
+// that can also hold an e value? (and have specific getters if the
+// value is larger than an int can handle)
+//
+ElementPtr
+fromStringstreamNumber(std::istream& in, const std::string& file,
+                       const int line, int& pos) {
+    // Remember position where the value starts. It will be set in the
+    // Position structure of the Element to be created.
+    const uint32_t start_pos = pos;
+    // This will move the pos to the end of the value.
+    const std::string number = numberFromStringstream(in, pos);
+
+    if (number.find_first_of(".eE") < number.size()) {
+        try {
+            return (Element::create(boost::lexical_cast<double>(number),
+                                    Element::Position(file, line, start_pos)));
+        } catch (const boost::bad_lexical_cast&) {
+            throwJSONError(std::string("Number overflow: ") + number,
+                           file, line, start_pos);
+        }
+    } else {
+        try {
+            return (Element::create(boost::lexical_cast<int64_t>(number),
+                                    Element::Position(file, line, start_pos)));
+        } catch (const boost::bad_lexical_cast&) {
+            throwJSONError(std::string("Number overflow: ") + number, file,
+                           line, start_pos);
+        }
+    }
+    return (ElementPtr());
+}
+
+ElementPtr
+fromStringstreamBool(std::istream& in, const std::string& file,
+                     const int line, int& pos) {
+    // Remember position where the value starts. It will be set in the
+    // Position structure of the Element to be created.
+    const uint32_t start_pos = pos;
+    // This will move the pos to the end of the value.
+    const std::string word = wordFromStringstream(in, pos);
+
+    if (word == "true") {
+        return (Element::create(true, Element::Position(file, line,
+                                                        start_pos)));
+    } else if (word == "false") {
+        return (Element::create(false, Element::Position(file, line,
+                                                         start_pos)));
+    } else {
+        throwJSONError(std::string("Bad boolean value: ") + word, file,
+                       line, start_pos);
+    }
+    return (ElementPtr());
+}
+
+ElementPtr
+fromStringstreamNull(std::istream& in, const std::string& file,
+                     const int line, int& pos) {
+    // Remember position where the value starts. It will be set in the
+    // Position structure of the Element to be created.
+    const uint32_t start_pos = pos;
+    // This will move the pos to the end of the value.
+    const std::string word = wordFromStringstream(in, pos);
+    if (word == "null") {
+        return (Element::create(Element::Position(file, line, start_pos)));
+    } else {
+        throwJSONError(std::string("Bad null value: ") + word, file,
+                       line, start_pos);
+        return (ElementPtr());
+    }
+}
+
+ElementPtr
+fromStringstreamString(std::istream& in, const std::string& file, int& line,
+                       int& pos) {
+    // Remember position where the value starts. It will be set in the
+    // Position structure of the Element to be created.
+    const uint32_t start_pos = pos;
+    // This will move the pos to the end of the value.
+    const std::string string_value = strFromStringstream(in, file, line, pos);
+    return (Element::create(string_value, Element::Position(file, line,
+                                                            start_pos)));
+}
+
+ElementPtr
+fromStringstreamList(std::istream& in, const std::string& file, int& line,
+                     int& pos) {
+    int c = 0;
+    ElementPtr list = Element::createList(Element::Position(file, line, pos));
+    ElementPtr cur_list_element;
+
+    skipChars(in, WHITESPACE, line, pos);
+    while (c != EOF && c != ']') {
+        if (in.peek() != ']') {
+            cur_list_element = Element::fromJSON(in, file, line, pos);
+            list->add(cur_list_element);
+            c = skipTo(in, file, line, pos, ",]", WHITESPACE);
+        } else {
+            c = in.get();
+            ++pos;
+        }
+    }
+    return (list);
+}
+
+ElementPtr
+fromStringstreamMap(std::istream& in, const std::string& file, int& line,
+                    int& pos) {
+    ElementPtr map = Element::createMap(Element::Position(file, line, pos));
+    skipChars(in, WHITESPACE, line, pos);
+    int c = in.peek();
+    if (c == EOF) {
+        throwJSONError(std::string("Unterminated map, <string> or } expected"), file, line, pos);
+    } else if (c == '}') {
+        // empty map, skip closing curly
+        in.ignore();
+    } else {
+        while (c != EOF && c != '}') {
+            std::string key = strFromStringstream(in, file, line, pos);
+
+            skipTo(in, file, line, pos, ":", WHITESPACE);
+            // skip the :
+
+            ConstElementPtr value = Element::fromJSON(in, file, line, pos);
+            map->set(key, value);
+
+            c = skipTo(in, file, line, pos, ",}", WHITESPACE);
+        }
+    }
+    return (map);
+}
+} // end anonymous namespace
+
+std::string
+Element::typeToName(Element::types type) {
+    switch (type) {
+    case Element::integer:
+        return (std::string("integer"));
+    case Element::real:
+        return (std::string("real"));
+    case Element::boolean:
+        return (std::string("boolean"));
+    case Element::string:
+        return (std::string("string"));
+    case Element::list:
+        return (std::string("list"));
+    case Element::map:
+        return (std::string("map"));
+    case Element::null:
+        return (std::string("null"));
+    case Element::any:
+        return (std::string("any"));
+    default:
+        return (std::string("unknown"));
+    }
+}
+
+Element::types
+Element::nameToType(const std::string& type_name) {
+    if (type_name == "integer") {
+        return (Element::integer);
+    } else if (type_name == "real") {
+        return (Element::real);
+    } else if (type_name == "boolean") {
+        return (Element::boolean);
+    } else if (type_name == "string") {
+        return (Element::string);
+    } else if (type_name == "list") {
+        return (Element::list);
+    } else if (type_name == "map") {
+        return (Element::map);
+    } else if (type_name == "named_set") {
+        return (Element::map);
+    } else if (type_name == "null") {
+        return (Element::null);
+    } else if (type_name == "any") {
+        return (Element::any);
+    } else {
+        isc_throw(TypeError, type_name + " is not a valid type name");
+    }
+}
+
+ElementPtr
+Element::fromJSON(std::istream& in, bool preproc) {
+
+    int line = 1, pos = 1;
+    stringstream filtered;
+    if (preproc) {
+        preprocess(in, filtered);
+    }
+
+    ElementPtr value = fromJSON(preproc ? filtered : in, "<istream>", line, pos);
+
+    return (value);
+}
+
+ElementPtr
+Element::fromJSON(std::istream& in, const std::string& file_name, bool preproc) {
+    int line = 1, pos = 1;
+    stringstream filtered;
+    if (preproc) {
+        preprocess(in, filtered);
+    }
+    return (fromJSON(preproc ? filtered : in, file_name, line, pos));
+}
+
+ElementPtr
+Element::fromJSON(std::istream& in, const std::string& file, int& line,
+                  int& pos) {
+    int c = 0;
+    ElementPtr element;
+    bool el_read = false;
+    skipChars(in, WHITESPACE, line, pos);
+    while (c != EOF && !el_read) {
+        c = in.get();
+        pos++;
+        switch(c) {
+            case '1':
+            case '2':
+            case '3':
+            case '4':
+            case '5':
+            case '6':
+            case '7':
+            case '8':
+            case '9':
+            case '0':
+            case '-':
+            case '+':
+            case '.':
+                in.putback(c);
+                --pos;
+                element = fromStringstreamNumber(in, file, line, pos);
+                el_read = true;
+                break;
+            case 't':
+            case 'f':
+                in.putback(c);
+                --pos;
+                element = fromStringstreamBool(in, file, line, pos);
+                el_read = true;
+                break;
+            case 'n':
+                in.putback(c);
+                --pos;
+                element = fromStringstreamNull(in, file, line, pos);
+                el_read = true;
+                break;
+            case '"':
+                in.putback('"');
+                --pos;
+                element = fromStringstreamString(in, file, line, pos);
+                el_read = true;
+                break;
+            case '[':
+                element = fromStringstreamList(in, file, line, pos);
+                el_read = true;
+                break;
+            case '{':
+                element = fromStringstreamMap(in, file, line, pos);
+                el_read = true;
+                break;
+            case EOF:
+                break;
+            default:
+                throwJSONError(std::string("error: unexpected character ") + std::string(1, c), file, line, pos);
+                break;
+        }
+    }
+    if (el_read) {
+        return (element);
+    } else {
+        isc_throw(JSONError, "nothing read");
+    }
+}
+
+ElementPtr
+Element::fromJSON(const std::string& in, bool preproc) {
+    std::stringstream ss;
+    ss << in;
+
+    int line = 1, pos = 1;
+    stringstream filtered;
+    if (preproc) {
+        preprocess(ss, filtered);
+    }
+    ElementPtr result(fromJSON(preproc ? filtered : ss, "<string>", line, pos));
+    skipChars(ss, WHITESPACE, line, pos);
+    // ss must now be at end
+    if (ss.peek() != EOF) {
+        throwJSONError("Extra data", "<string>", line, pos);
+    }
+    return result;
+}
+
+ElementPtr
+Element::fromJSONFile(const std::string& file_name, bool preproc) {
+    // zero out the errno to be safe
+    errno = 0;
+
+    std::ifstream infile(file_name.c_str(), std::ios::in | std::ios::binary);
+    if (!infile.is_open()) {
+        const char* error = strerror(errno);
+        isc_throw(InvalidOperation, "failed to read file '" << file_name
+                  << "': " << error);
+    }
+
+    return (fromJSON(infile, file_name, preproc));
+}
+
+// to JSON format
+
+void
+IntElement::toJSON(std::ostream& ss) const {
+    ss << intValue();
+}
+
+void
+DoubleElement::toJSON(std::ostream& ss) const {
+    // The default output for doubles nicely drops off trailing
+    // zeros, however this produces strings without decimal points
+    // for whole number values.  When reparsed this will create
+    // IntElements not DoubleElements.  Rather than used a fixed
+    // precision, we'll just tack on an ".0" when the decimal point
+    // is missing.
+    ostringstream val_ss;
+    val_ss << doubleValue();
+    ss << val_ss.str();
+    if (val_ss.str().find_first_of('.') == string::npos) {
+        ss << ".0";
+    }
+}
+
+void
+BoolElement::toJSON(std::ostream& ss) const {
+    if (boolValue()) {
+        ss << "true";
+    } else {
+        ss << "false";
+    }
+}
+
+void
+NullElement::toJSON(std::ostream& ss) const {
+    ss << "null";
+}
+
+void
+StringElement::toJSON(std::ostream& ss) const {
+    ss << "\"";
+    const std::string& str = stringValue();
+    for (size_t i = 0; i < str.size(); ++i) {
+        const char c = str[i];
+        // Escape characters as defined in JSON spec
+        // Note that we do not escape forward slash; this
+        // is allowed, but not mandatory.
+        switch (c) {
+        case '"':
+            ss << '\\' << c;
+            break;
+        case '\\':
+            ss << '\\' << c;
+            break;
+        case '\b':
+            ss << '\\' << 'b';
+            break;
+        case '\f':
+            ss << '\\' << 'f';
+            break;
+        case '\n':
+            ss << '\\' << 'n';
+            break;
+        case '\r':
+            ss << '\\' << 'r';
+            break;
+        case '\t':
+            ss << '\\' << 't';
+            break;
+        default:
+            if (((c >= 0) && (c < 0x20)) || (c < 0) || (c >= 0x7f)) {
+                std::ostringstream esc;
+                esc << "\\u"
+                    << hex
+                    << setw(4)
+                    << setfill('0')
+                    << (static_cast<unsigned>(c) & 0xff);
+                ss << esc.str();
+            } else {
+                ss << c;
+            }
+        }
+    }
+    ss << "\"";
+}
+
+void
+ListElement::toJSON(std::ostream& ss) const {
+    ss << "[ ";
+
+    const std::vector<ElementPtr>& v = listValue();
+    for (auto it = v.begin(); it != v.end(); ++it) {
+        if (it != v.begin()) {
+            ss << ", ";
+        }
+        (*it)->toJSON(ss);
+    }
+    ss << " ]";
+}
+
+void
+MapElement::toJSON(std::ostream& ss) const {
+    ss << "{ ";
+
+    const std::map<std::string, ConstElementPtr>& m = mapValue();
+    for (auto it = m.begin(); it != m.end(); ++it) {
+        if (it != m.begin()) {
+            ss << ", ";
+        }
+        ss << "\"" << (*it).first << "\": ";
+        if ((*it).second) {
+            (*it).second->toJSON(ss);
+        } else {
+            ss << "None";
+        }
+    }
+    ss << " }";
+}
+
+// throws when one of the types in the path (except the one
+// we're looking for) is not a MapElement
+// returns 0 if it could simply not be found
+// should that also be an exception?
+ConstElementPtr
+MapElement::find(const std::string& id) const {
+    const size_t sep = id.find('/');
+    if (sep == std::string::npos) {
+        return (get(id));
+    } else {
+        ConstElementPtr ce = get(id.substr(0, sep));
+        if (ce) {
+            // ignore trailing slash
+            if  (sep + 1 != id.size()) {
+                return (ce->find(id.substr(sep + 1)));
+            } else {
+                return (ce);
+            }
+        } else {
+            return (ElementPtr());
+        }
+    }
+}
+
+ElementPtr
+Element::fromWire(const std::string& s) {
+    std::stringstream ss;
+    ss << s;
+    int line = 0, pos = 0;
+    return (fromJSON(ss, "<wire>", line, pos));
+}
+
+ElementPtr
+Element::fromWire(std::stringstream& in, int) {
+    //
+    // Check protocol version
+    //
+    //for (int i = 0 ; i < 4 ; ++i) {
+    //    const unsigned char version_byte = get_byte(in);
+    //    if (PROTOCOL_VERSION[i] != version_byte) {
+    //        throw DecodeError("Protocol version incorrect");
+    //    }
+    //}
+    //length -= 4;
+    int line = 0, pos = 0;
+    return (fromJSON(in, "<wire>", line, pos));
+}
+
+void
+MapElement::set(const std::string& key, ConstElementPtr value) {
+    m[key] = value;
+}
+
+bool
+MapElement::find(const std::string& id, ConstElementPtr& t) const {
+    try {
+        ConstElementPtr p = find(id);
+        if (p) {
+            t = p;
+            return (true);
+        }
+    } catch (const TypeError&) {
+        // ignore
+    }
+    return (false);
+}
+
+bool
+IntElement::equals(const Element& other) const {
+    return (other.getType() == Element::integer) &&
+           (i == other.intValue());
+}
+
+bool
+DoubleElement::equals(const Element& other) const {
+    return (other.getType() == Element::real) &&
+           (fabs(d - other.doubleValue()) < 1e-14);
+}
+
+bool
+BoolElement::equals(const Element& other) const {
+    return (other.getType() == Element::boolean) &&
+           (b == other.boolValue());
+}
+
+bool
+NullElement::equals(const Element& other) const {
+    return (other.getType() == Element::null);
+}
+
+bool
+StringElement::equals(const Element& other) const {
+    return (other.getType() == Element::string) &&
+           (s == other.stringValue());
+}
+
+bool
+ListElement::equals(const Element& other) const {
+    if (other.getType() == Element::list) {
+        const size_t s = size();
+        if (s != other.size()) {
+            return (false);
+        }
+        for (size_t i = 0; i < s; ++i) {
+            if (!get(i)->equals(*other.get(i))) {
+                return (false);
+            }
+        }
+        return (true);
+    } else {
+        return (false);
+    }
+}
+
+void
+ListElement::sort(std::string const& index /* = std::string() */) {
+    if (l.empty()) {
+        return;
+    }
+
+    int const t(l.at(0)->getType());
+    std::function<bool(ElementPtr, ElementPtr)> comparator;
+    if (t == map) {
+        if (index.empty()) {
+            isc_throw(BadValue, "index required when sorting maps");
+        }
+        comparator = [&](ElementPtr const& a, ElementPtr const& b) {
+            ConstElementPtr const& ai(a->get(index));
+            ConstElementPtr const& bi(b->get(index));
+            if (ai && bi) {
+                return *ai < *bi;
+            }
+            return true;
+        };
+    } else if (t == list) {
+        // Nested lists. Not supported.
+        return;
+    } else {
+        // Assume scalars.
+        if (!index.empty()) {
+            isc_throw(BadValue, "index given when sorting scalars?");
+        }
+        comparator = [&](ElementPtr const& a, ElementPtr const& b) {
+            return *a < *b;
+        };
+    }
+
+    std::sort(l.begin(), l.end(), comparator);
+}
+
+bool
+MapElement::equals(const Element& other) const {
+    if (other.getType() == Element::map) {
+        if (size() != other.size()) {
+            return (false);
+        }
+        for (auto kv : mapValue()) {
+            auto key = kv.first;
+            if (other.contains(key)) {
+                if (!get(key)->equals(*other.get(key))) {
+                    return (false);
+                }
+            } else {
+                return (false);
+            }
+        }
+        return (true);
+    } else {
+        return (false);
+    }
+}
+
+bool
+isNull(ConstElementPtr p) {
+    return (!p);
+}
+
+void
+removeIdentical(ElementPtr a, ConstElementPtr b) {
+    if (!b) {
+        return;
+    }
+    if (a->getType() != Element::map || b->getType() != Element::map) {
+        isc_throw(TypeError, "Non-map Elements passed to removeIdentical");
+    }
+
+    // As maps do not allow entries with multiple keys, we can either iterate
+    // over a checking for identical entries in b or vice-versa.  As elements
+    // are removed from a if a match is found, we choose to iterate over b to
+    // avoid problems with element removal affecting the iterator.
+    for (auto kv : b->mapValue()) {
+        auto key = kv.first;
+        if (a->contains(key)) {
+            if (a->get(key)->equals(*b->get(key))) {
+                a->remove(key);
+            }
+        }
+    }
+}
+
+ConstElementPtr
+removeIdentical(ConstElementPtr a, ConstElementPtr b) {
+    ElementPtr result = Element::createMap();
+
+    if (!b) {
+        return (result);
+    }
+
+    if (a->getType() != Element::map || b->getType() != Element::map) {
+        isc_throw(TypeError, "Non-map Elements passed to removeIdentical");
+    }
+
+    for (auto kv : a->mapValue()) {
+        auto key = kv.first;
+        if (!b->contains(key) ||
+            !a->get(key)->equals(*b->get(key))) {
+            result->set(key, kv.second);
+        }
+    }
+
+    return (result);
+}
+
+void
+merge(ElementPtr element, ConstElementPtr other) {
+    if (element->getType() != Element::map ||
+        other->getType() != Element::map) {
+        isc_throw(TypeError, "merge arguments not MapElements");
+    }
+
+    for (auto kv : other->mapValue()) {
+        auto key = kv.first;
+        auto value = kv.second;
+        if (value && value->getType() != Element::null) {
+            element->set(key, value);
+        } else if (element->contains(key)) {
+            element->remove(key);
+        }
+    }
+}
+
+void
+mergeDiffAdd(ElementPtr& element, ElementPtr& other,
+             HierarchyDescriptor& hierarchy, std::string key, size_t idx) {
+    if (element->getType() != other->getType()) {
+        isc_throw(TypeError, "mergeDiffAdd arguments not same type");
+    }
+
+    if (element->getType() == Element::list) {
+        // Store new elements in a separate container so we don't overwrite
+        // options as we add them (if there are duplicates).
+        ElementPtr new_elements = Element::createList();
+        for (auto& right : other->listValue()) {
+            // Check if we have any description of the key in the configuration
+            // hierarchy.
+            auto f = hierarchy[idx].find(key);
+            if (f != hierarchy[idx].end()) {
+                bool found = false;
+                ElementPtr mutable_right = boost::const_pointer_cast<Element>(right);
+                for (auto& left : element->listValue()) {
+                    ElementPtr mutable_left = boost::const_pointer_cast<Element>(left);
+                    // Check if the elements refer to the same configuration
+                    // entity.
+                    if (f->second.match_(mutable_left, mutable_right)) {
+                        found = true;
+                        mergeDiffAdd(mutable_left, mutable_right, hierarchy, key, idx);
+                    }
+                }
+                if (!found) {
+                    new_elements->add(right);
+                }
+            } else {
+                new_elements->add(right);
+            }
+        }
+        // Finally add the new elements.
+        for (auto& right : new_elements->listValue()) {
+            element->add(right);
+        }
+        return;
+    }
+
+    if (element->getType() == Element::map) {
+        for (auto kv : other->mapValue()) {
+            auto current_key = kv.first;
+            auto value = boost::const_pointer_cast<Element>(kv.second);
+            if (value && value->getType() != Element::null) {
+                if (element->contains(current_key) &&
+                    (value->getType() == Element::map ||
+                     value->getType() == Element::list)) {
+                    ElementPtr mutable_element = boost::const_pointer_cast<Element>(element->get(current_key));
+                    mergeDiffAdd(mutable_element, value, hierarchy, current_key, idx + 1);
+                } else {
+                    element->set(current_key, value);
+                }
+            }
+        }
+        return;
+    }
+    element = other;
+}
+
+void
+mergeDiffDel(ElementPtr& element, ElementPtr& other,
+             HierarchyDescriptor& hierarchy, std::string key, size_t idx) {
+    if (element->getType() != other->getType()) {
+        isc_throw(TypeError, "mergeDiffDel arguments not same type");
+    }
+
+    if (element->getType() == Element::list) {
+        for (auto const& value : other->listValue()) {
+            ElementPtr mutable_right = boost::const_pointer_cast<Element>(value);
+            for (uint32_t iter = 0; iter < element->listValue().size();) {
+                bool removed = false;
+                // Check if we have any description of the key in the
+                // configuration hierarchy.
+                auto f = hierarchy[idx].find(key);
+                if (f != hierarchy[idx].end()) {
+                    ElementPtr mutable_left = boost::const_pointer_cast<Element>(element->listValue().at(iter));
+                    // Check if the elements refer to the same configuration
+                    // entity.
+                    if (f->second.match_(mutable_left, mutable_right)) {
+                        // Check if the user supplied data only contains
+                        // identification information, so the intent is to
+                        // delete the element, not just element data.
+                        if (f->second.no_data_(mutable_right)) {
+                            element->remove(iter);
+                            removed = true;
+                        } else {
+                            mergeDiffDel(mutable_left, mutable_right, hierarchy, key, idx);
+                            if (mutable_left->empty()) {
+                                element->remove(iter);
+                                removed = true;
+                            }
+                        }
+                    }
+                } else if (element->listValue().at(iter)->equals(*value)) {
+                    element->remove(iter);
+                    removed = true;
+                }
+                if (!removed) {
+                    ++iter;
+                }
+            }
+        }
+        return;
+    }
+
+    if (element->getType() == Element::map) {
+        // If the resulting element still contains data, we need to restore the
+        // key parameters, so we store them here.
+        ElementPtr new_elements = Element::createMap();
+        for (auto kv : other->mapValue()) {
+            auto current_key = kv.first;
+            auto value = boost::const_pointer_cast<Element>(kv.second);
+            if (value && value->getType() != Element::null) {
+                if (element->contains(current_key)) {
+                    ElementPtr mutable_element = boost::const_pointer_cast<Element>(element->get(current_key));
+                    if (mutable_element->getType() == Element::map ||
+                        mutable_element->getType() == Element::list) {
+                        mergeDiffDel(mutable_element, value, hierarchy, current_key, idx + 1);
+                        if (mutable_element->empty()) {
+                            element->remove(current_key);
+                        }
+                    } else {
+                        // Check if we have any description of the key in the
+                        // configuration hierarchy.
+                        auto f = hierarchy[idx].find(key);
+                        if (f != hierarchy[idx].end()) {
+                            // Check if the key is used for element
+                            // identification.
+                            if (f->second.is_key_(current_key)) {
+                                // Store the key parameter.
+                                new_elements->set(current_key, mutable_element);
+                            }
+                        }
+                        element->remove(current_key);
+                    }
+                }
+            }
+        }
+        // If the element still contains data, restore the key elements.
+        if (element->size()) {
+            for (auto kv : new_elements->mapValue()) {
+                element->set(kv.first, kv.second);
+            }
+        }
+        return;
+    }
+    element = ElementPtr(new NullElement);
+}
+
+void
+extend(const std::string& container, const std::string& extension,
+       ElementPtr& element, ElementPtr& other, HierarchyDescriptor& hierarchy,
+       std::string key, size_t idx, bool alter) {
+    if (element->getType() != other->getType()) {
+        isc_throw(TypeError, "extend arguments not same type");
+    }
+
+    if (element->getType() == Element::list) {
+        for (auto& right : other->listValue()) {
+            // Check if we have any description of the key in the configuration
+            // hierarchy.
+            auto f = hierarchy[idx].find(key);
+            if (f != hierarchy[idx].end()) {
+                ElementPtr mutable_right = boost::const_pointer_cast<Element>(right);
+                for (auto& left : element->listValue()) {
+                    ElementPtr mutable_left = boost::const_pointer_cast<Element>(left);
+                    if (container == key) {
+                        alter = true;
+                    }
+                    if (f->second.match_(mutable_left, mutable_right)) {
+                        extend(container, extension, mutable_left, mutable_right,
+                               hierarchy, key, idx, alter);
+                    }
+                }
+            }
+        }
+        return;
+    }
+
+    if (element->getType() == Element::map) {
+        for (auto kv : other->mapValue()) {
+            auto current_key = kv.first;
+            auto value = boost::const_pointer_cast<Element>(kv.second);
+            if (value && value->getType() != Element::null) {
+                if (element->contains(current_key) &&
+                    (value->getType() == Element::map ||
+                     value->getType() == Element::list)) {
+                    ElementPtr mutable_element = boost::const_pointer_cast<Element>(element->get(current_key));
+                    if (container == key) {
+                        alter = true;
+                    }
+                    extend(container, extension, mutable_element, value, hierarchy, current_key, idx + 1, alter);
+                } else if (alter && current_key == extension) {
+                    element->set(current_key, value);
+                }
+            }
+        }
+        return;
+    }
+}
+
+ElementPtr
+copy(ConstElementPtr from, int level) {
+    if (!from) {
+        isc_throw(BadValue, "copy got a null pointer");
+    }
+    int from_type = from->getType();
+    if (from_type == Element::integer) {
+        return (ElementPtr(new IntElement(from->intValue())));
+    } else if (from_type == Element::real) {
+        return (ElementPtr(new DoubleElement(from->doubleValue())));
+    } else if (from_type == Element::boolean) {
+        return (ElementPtr(new BoolElement(from->boolValue())));
+    } else if (from_type == Element::null) {
+        return (ElementPtr(new NullElement()));
+    } else if (from_type == Element::string) {
+        return (ElementPtr(new StringElement(from->stringValue())));
+    } else if (from_type == Element::list) {
+        ElementPtr result = ElementPtr(new ListElement());
+        for (auto elem : from->listValue()) {
+            if (level == 0) {
+                result->add(elem);
+            } else {
+                result->add(copy(elem, level - 1));
+            }
+        }
+        return (result);
+    } else if (from_type == Element::map) {
+        ElementPtr result = ElementPtr(new MapElement());
+        for (auto kv : from->mapValue()) {
+            auto key = kv.first;
+            auto value = kv.second;
+            if (level == 0) {
+                result->set(key, value);
+            } else {
+                result->set(key, copy(value, level - 1));
+            }
+        }
+        return (result);
+    } else {
+        isc_throw(BadValue, "copy got an element of type: " << from_type);
+    }
+}
+
+namespace {
+
+// Helper function which blocks infinite recursion
+bool
+isEquivalent0(ConstElementPtr a, ConstElementPtr b, unsigned level) {
+    // check looping forever on cycles
+    if (!level) {
+        isc_throw(BadValue, "isEquivalent got infinite recursion: "
+                  "arguments include cycles");
+    }
+    if (!a || !b) {
+        isc_throw(BadValue, "isEquivalent got a null pointer");
+    }
+    // check types
+    if (a->getType() != b->getType()) {
+        return (false);
+    }
+    if (a->getType() == Element::list) {
+        // check empty
+        if (a->empty()) {
+            return (b->empty());
+        }
+        // check size
+        if (a->size() != b->size()) {
+            return (false);
+        }
+
+        // copy b into a list
+        const size_t s = a->size();
+        std::list<ConstElementPtr> l;
+        for (size_t i = 0; i < s; ++i) {
+            l.push_back(b->get(i));
+        }
+
+        // iterate on a
+        for (size_t i = 0; i < s; ++i) {
+            ConstElementPtr item = a->get(i);
+            // lookup this item in the list
+            bool found = false;
+            for (auto it = l.begin(); it != l.end(); ++it) {
+                // if found in the list remove it
+                if (isEquivalent0(item, *it, level - 1)) {
+                    found = true;
+                    l.erase(it);
+                    break;
+                }
+            }
+            // if not found argument differs
+            if (!found) {
+                return (false);
+            }
+        }
+
+        // sanity check: the list must be empty
+        if (!l.empty()) {
+            isc_throw(Unexpected, "isEquivalent internal error");
+        }
+        return (true);
+    } else if (a->getType() == Element::map) {
+        // check sizes
+        if (a->size() != b->size()) {
+            return (false);
+        }
+        // iterate on the first map
+        for (auto kv : a->mapValue()) {
+            // get the b value for the given keyword and recurse
+            ConstElementPtr item = b->get(kv.first);
+            if (!item || !isEquivalent0(kv.second, item, level - 1)) {
+                return (false);
+            }
+        }
+        return (true);
+    } else {
+        return (a->equals(*b));
+    }
+}
+
+} // end anonymous namespace
+
+bool
+isEquivalent(ConstElementPtr a, ConstElementPtr b) {
+    return (isEquivalent0(a, b, 100));
+}
+
+void
+prettyPrint(ConstElementPtr element, std::ostream& out,
+            unsigned indent, unsigned step) {
+    if (!element) {
+        isc_throw(BadValue, "prettyPrint got a null pointer");
+    }
+    if (element->getType() == Element::list) {
+        // empty list case
+        if (element->empty()) {
+            out << "[ ]";
+            return;
+        }
+
+        // complex ? multiline : oneline
+        if (!element->get(0)) {
+            isc_throw(BadValue, "prettyPrint got a null pointer");
+        }
+        int first_type = element->get(0)->getType();
+        bool complex = false;
+        if ((first_type == Element::list) || (first_type == Element::map)) {
+            complex = true;
+        }
+        std::string separator = complex ? ",\n" : ", ";
+
+        // open the list
+        out << "[" << (complex ? "\n" : " ");
+
+        // iterate on items
+        const auto& l = element->listValue();
+        for (auto it = l.begin(); it != l.end(); ++it) {
+            // add the separator if not the first item
+            if (it != l.begin()) {
+                out << separator;
+            }
+            // add indentation
+            if (complex) {
+                out << std::string(indent + step, ' ');
+            }
+            // recursive call
+            prettyPrint(*it, out, indent + step, step);
+        }
+
+        // close the list
+        if (complex) {
+            out << "\n" << std::string(indent, ' ');
+        } else {
+            out << " ";
+        }
+        out << "]";
+    } else if (element->getType() == Element::map) {
+        // empty map case
+        if (element->size() == 0) {
+            out << "{ }";
+            return;
+        }
+
+        // open the map
+        out << "{\n";
+
+        // iterate on keyword: value
+        const auto& m = element->mapValue();
+        bool first = true;
+        for (auto it = m.begin(); it != m.end(); ++it) {
+            // add the separator if not the first item
+            if (first) {
+                first = false;
+            } else {
+                out << ",\n";
+            }
+            // add indentation
+            out << std::string(indent + step, ' ');
+            // add keyword:
+            out << "\"" << it->first << "\": ";
+            // recursive call
+            prettyPrint(it->second, out, indent + step, step);
+        }
+
+        // close the map
+        out << "\n" << std::string(indent, ' ') << "}";
+    } else {
+        // not a list or a map
+        element->toJSON(out);
+    }
+}
+
+std::string
+prettyPrint(ConstElementPtr element, unsigned indent, unsigned step) {
+    std::stringstream ss;
+    prettyPrint(element, ss, indent, step);
+    return (ss.str());
+}
+
+void Element::preprocess(std::istream& in, std::stringstream& out) {
+
+    std::string line;
+
+    while (std::getline(in, line)) {
+        // If this is a comments line, replace it with empty line
+        // (so the line numbers will still match
+        if (!line.empty() && line[0] == '#') {
+            line = "";
+        }
+
+        // getline() removes end line characters. Unfortunately, we need
+        // it for getting the line numbers right (in case we report an
+        // error.
+        out << line;
+        out << "\n";
+    }
+}
+
+} // end of isc::data namespace
+} // end of isc namespace
diff --git a/src/lib/cc/data.h b/src/lib/cc/data.h
new file mode 100644
index 0000000..7cb2380
--- /dev/null
+++ b/src/lib/cc/data.h
@@ -0,0 +1,1008 @@
+// Copyright (C) 2010-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef ISC_DATA_H
+#define ISC_DATA_H 1
+
+#include <iostream>
+#include <map>
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include <boost/shared_ptr.hpp>
+
+#include <stdint.h>
+
+#include <exceptions/exceptions.h>
+
+namespace isc { namespace data {
+
+class Element;
+// todo: describe the rationale behind ElementPtr?
+typedef boost::shared_ptr<Element> ElementPtr;
+typedef boost::shared_ptr<const Element> ConstElementPtr;
+
+///
+/// @brief A standard Data module exception that is thrown if a function
+/// is called for an Element that has a wrong type (e.g. int_value on a
+/// ListElement)
+///
+class TypeError : public isc::Exception {
+public:
+    TypeError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) {}
+};
+
+///
+/// @brief A standard Data module exception that is thrown if a parse
+/// error is encountered when constructing an Element from a string
+///
+// i'd like to use Exception here but we need one that is derived from
+// runtime_error (as this one is directly based on external data, and
+// i want to add some values to any static data string that is provided)
+class JSONError : public isc::Exception {
+public:
+    JSONError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) {}
+};
+
+///
+/// @brief The @c Element class represents a piece of data, used by
+/// the command channel and configuration parts.
+///
+/// An @c Element can contain simple types (int, real, string, bool and
+/// None), and composite types (list and string->element maps)
+///
+/// Elements should in calling functions usually be referenced through
+/// an @c ElementPtr, which can be created using the factory functions
+/// @c Element::create() and @c Element::fromJSON()
+///
+/// Notes to developers: Element is a base class, implemented by a
+/// specific subclass for each type (IntElement, BoolElement, etc).
+/// Element does define all functions for all types, and defaults to
+/// raising a @c TypeError for functions that are not supported for
+/// the type in question.
+///
+class Element {
+
+public:
+    /// @brief Represents the position of the data element within a
+    /// configuration string.
+    ///
+    /// Position comprises a file name, line number and an offset within this
+    /// line where the element value starts. For example, if the JSON string is
+    ///
+    /// @code
+    /// { "foo": "some string",
+    ///   "bar": 123 }
+    /// \endcode
+    ///
+    /// the position of the element "bar" is: line_ = 2; pos_ = 9, because
+    /// beginning of the value "123" is at offset 9 from the beginning of
+    /// the second line, including whitespaces.
+    ///
+    /// Note that the @c Position structure is used as an argument to @c Element
+    /// constructors and factory functions to avoid ambiguity and so that the
+    /// uint32_t arguments holding line number and position within the line are
+    /// not confused with the @c Element values passed to these functions.
+    struct Position {
+        std::string file_; ///< File name.
+        uint32_t line_;    ///< Line number.
+        uint32_t pos_;     ///< Position within the line.
+
+        /// @brief Default constructor.
+        Position() : file_(""), line_(0), pos_(0) {
+        }
+
+        /// @brief Constructor.
+        ///
+        /// @param file File name.
+        /// @param line Line number.
+        /// @param pos Position within the line.
+        Position(const std::string& file, const uint32_t line,
+                 const uint32_t pos)
+            : file_(file), line_(line), pos_(pos) {
+        }
+
+        /// @brief Returns the position in the textual format.
+        ///
+        /// The returned position has the following format: file:line:pos.
+        std::string str() const;
+    };
+
+    /// @brief Returns @c Position object with line_ and pos_ set to 0, and
+    /// with an empty file name.
+    ///
+    /// The object containing two zeros is a default for most of the
+    /// methods creating @c Element objects. The returned value is static
+    /// so as it is not created everytime the function with the default
+    /// position argument is called.
+    static const Position& ZERO_POSITION() {
+        static Position position("", 0, 0);
+        return (position);
+    }
+
+private:
+    // technically the type could be omitted; is it useful?
+    // should we remove it or replace it with a pure virtual
+    // function getType?
+    int type_;
+
+    /// @brief Position of the element in the configuration string.
+    Position position_;
+
+protected:
+
+    /// @brief Constructor.
+    ///
+    /// @param t Element type.
+    /// @param pos Structure holding position of the value of the data element.
+    /// It comprises the line number and the position within this line. The values
+    /// held in this structure are used for error logging purposes.
+    Element(int t, const Position& pos = ZERO_POSITION())
+        : type_(t), position_(pos) {
+    }
+
+
+public:
+
+    // any is a special type used in list specifications, specifying
+    // that the elements can be of any type
+    enum types { integer, real, boolean, null, string, list, map, any };
+    // base class; make dtor virtual
+    virtual ~Element() {};
+
+    /// @return the type of this element
+    int getType() const { return (type_); }
+
+    /// @brief Returns position where the data element's value starts in a
+    /// configuration string.
+    ///
+    /// @warning The returned reference is valid as long as the object which
+    /// created it lives.
+    const Position& getPosition() const { return (position_); }
+
+    /// Returns a string representing the Element and all its
+    /// child elements; note that this is different from stringValue(),
+    /// which only returns the single value of a StringElement
+    ///
+    /// The resulting string will contain the Element in JSON format.
+    ///
+    /// @return std::string containing the string representation
+    std::string str() const;
+
+    /// Returns the wireformat for the Element and all its child
+    /// elements.
+    ///
+    /// @return std::string containing the element in wire format
+    std::string toWire() const;
+    void toWire(std::ostream& out) const;
+
+    /// @brief Add the position to a TypeError message
+    /// should be used in place of isc_throw(TypeError, error)
+#define throwTypeError(error)                   \
+    {                                           \
+        std::string msg_ = error;               \
+        if ((position_.file_ != "") ||          \
+            (position_.line_ != 0) ||           \
+            (position_.pos_ != 0)) {            \
+            msg_ += " in (" + position_.str() + ")";   \
+        }                                       \
+        isc_throw(TypeError, msg_);             \
+    }
+
+    /// @name pure virtuals, every derived class must implement these
+
+    /// @return true if the other ElementPtr has the same type and value
+    virtual bool equals(const Element& other) const = 0;
+
+    /// Converts the Element to JSON format and appends it to
+    /// the given stringstream.
+    virtual void toJSON(std::ostream& ss) const = 0;
+
+    /// @name Type-specific getters
+    ///
+    /// @brief These functions only
+    /// work on their corresponding Element type. For all other
+    /// types, a TypeError is thrown.
+    /// If you want an exception-safe getter method, use
+    /// getValue() below
+    //@{
+    virtual int64_t intValue() const
+    { throwTypeError("intValue() called on non-integer Element"); };
+    virtual double doubleValue() const
+    { throwTypeError("doubleValue() called on non-double Element"); };
+    virtual bool boolValue() const
+    { throwTypeError("boolValue() called on non-Bool Element"); };
+    virtual std::string stringValue() const
+    { throwTypeError("stringValue() called on non-string Element"); };
+    virtual const std::vector<ElementPtr>& listValue() const {
+        // replace with real exception or empty vector?
+        throwTypeError("listValue() called on non-list Element");
+    };
+    virtual const std::map<std::string, ConstElementPtr>& mapValue() const {
+        // replace with real exception or empty map?
+        throwTypeError("mapValue() called on non-map Element");
+    };
+    //@}
+
+    /// @name Exception-safe getters
+    ///
+    /// @brief The getValue() functions return false if the given reference
+    /// is of another type than the element contains
+    /// By default it always returns false; the derived classes
+    /// override the function for their type, copying their
+    /// data to the given reference and returning true
+    ///
+    //@{
+    virtual bool getValue(int64_t& t) const;
+    virtual bool getValue(double& t) const;
+    virtual bool getValue(bool& t) const;
+    virtual bool getValue(std::string& t) const;
+    virtual bool getValue(std::vector<ElementPtr>& t) const;
+    virtual bool getValue(std::map<std::string, ConstElementPtr>& t) const;
+    //@}
+
+    ///
+    /// @name Exception-safe setters.
+    ///
+    /// @brief Return false if the Element is not
+    /// the right type. Set the value and return true if the Elements
+    /// is of the correct type
+    ///
+    /// Notes: Read notes of IntElement definition about the use of
+    ///        long long int, long int and int.
+    //@{
+    virtual bool setValue(const long long int v);
+    bool setValue(const long int i) { return (setValue(static_cast<long long int>(i))); };
+    bool setValue(const int i) { return (setValue(static_cast<long long int>(i))); };
+    virtual bool setValue(const double v);
+    virtual bool setValue(const bool t);
+    virtual bool setValue(const std::string& v);
+    virtual bool setValue(const std::vector<ElementPtr>& v);
+    virtual bool setValue(const std::map<std::string, ConstElementPtr>& v);
+    //@}
+
+    // Other functions for specific subtypes
+
+    /// @name ListElement functions
+    ///
+    /// @brief If the Element on which these functions are called are not
+    /// an instance of ListElement, a TypeError exception is thrown.
+    //@{
+    /// Returns the ElementPtr at the given index. If the index is out
+    /// of bounds, this function throws an std::out_of_range exception.
+    /// @param i The position of the ElementPtr to return
+    virtual ConstElementPtr get(const int i) const;
+
+    /// @brief returns element as non-const pointer
+    ///
+    /// @param i The position of the ElementPtr to retrieve
+    /// @return specified element pointer
+    virtual ElementPtr getNonConst(const int i) const;
+
+    /// Sets the ElementPtr at the given index. If the index is out
+    /// of bounds, this function throws an std::out_of_range exception.
+    /// @param i The position of the ElementPtr to set
+    /// @param element The ElementPtr to set at the position
+    virtual void set(const size_t i, ElementPtr element);
+
+    /// Adds an ElementPtr to the list
+    /// @param element The ElementPtr to add
+    virtual void add(ElementPtr element);
+
+    /// Removes the element at the given position. If the index is out
+    /// of nothing happens.
+    /// @param i The index of the element to remove.
+    virtual void remove(const int i);
+
+    /// Returns the number of elements in the list.
+    virtual size_t size() const;
+
+    /// Return true if there are no elements in the list.
+    virtual bool empty() const;
+    //@}
+
+
+    /// @name MapElement functions
+    ///
+    /// @brief If the Element on which these functions are called are not
+    /// an instance of MapElement, a TypeError exception is thrown.
+    //@{
+    /// Returns the ElementPtr at the given key
+    /// @param name The key of the Element to return
+    /// @return The ElementPtr at the given key, or null if not present
+    virtual ConstElementPtr get(const std::string& name) const;
+
+    /// Sets the ElementPtr at the given key
+    /// @param name The key of the Element to set
+    /// @param element The ElementPtr to set at the given key.
+    virtual void set(const std::string& name, ConstElementPtr element);
+
+    /// Remove the ElementPtr at the given key
+    /// @param name The key of the Element to remove
+    virtual void remove(const std::string& name);
+
+    /// Checks if there is data at the given key
+    /// @param name The key of the Element checked for existence
+    /// @return true if there is data at the key, false if not.
+    virtual bool contains(const std::string& name) const;
+
+    /// Recursively finds any data at the given identifier. The
+    /// identifier is a /-separated list of names of nested maps, with
+    /// the last name being the leaf that is returned.
+    ///
+    /// For instance, if you have a MapElement that contains another
+    /// MapElement at the key "foo", and that second MapElement contains
+    /// Another Element at key "bar", the identifier for that last
+    /// element from the first is "foo/bar".
+    ///
+    /// @param identifier The identifier of the element to find
+    /// @return The ElementPtr at the given identifier. Returns a
+    /// null ElementPtr if it is not found, which can be checked with
+    /// Element::is_null(ElementPtr e).
+    virtual ConstElementPtr find(const std::string& identifier) const;
+
+    /// See @c Element::find()
+    /// @param identifier The identifier of the element to find
+    /// @param t Reference to store the resulting ElementPtr, if found.
+    /// @return true if the element was found, false if not.
+    virtual bool find(const std::string& identifier, ConstElementPtr& t) const;
+    //@}
+
+    /// @name Factory functions
+
+    // TODO: should we move all factory functions to a different class
+    // so as not to burden the Element base with too many functions?
+    // and/or perhaps even to a separate header?
+
+    /// @name Direct factory functions
+    /// @brief These functions simply wrap the given data directly
+    /// in an Element object, and return a reference to it, in the form
+    /// of an @c ElementPtr.
+    /// These factory functions are exception-free (unless there is
+    /// no memory available, in which case bad_alloc is raised by the
+    /// underlying system).
+    /// (Note that that is different from an NullElement, which
+    /// represents an empty value, and is created with Element::create())
+    ///
+    /// Notes: Read notes of IntElement definition about the use of
+    ///        long long int, long int and int.
+    //@{
+    static ElementPtr create(const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const long long int i,
+                             const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const int i,
+                             const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const long int i,
+                             const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const uint32_t i,
+                             const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const double d,
+                             const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const bool b,
+                             const Position& pos = ZERO_POSITION());
+    static ElementPtr create(const std::string& s,
+                             const Position& pos = ZERO_POSITION());
+    // need both std:string and char *, since c++ will match
+    // bool before std::string when you pass it a char *
+    static ElementPtr create(const char *s,
+                             const Position& pos = ZERO_POSITION());
+
+    /// @brief Creates an empty ListElement type ElementPtr.
+    ///
+    /// @param pos A structure holding position of the data element value
+    /// in the configuration string. It is used for error logging purposes.
+    static ElementPtr createList(const Position& pos = ZERO_POSITION());
+
+    /// @brief Creates an empty MapElement type ElementPtr.
+    ///
+    /// @param pos A structure holding position of the data element value
+    /// in the configuration string. It is used for error logging purposes.
+    static ElementPtr createMap(const Position& pos = ZERO_POSITION());
+    //@}
+
+    /// @name Compound factory functions
+
+    /// @brief These functions will parse the given string (JSON)
+    /// representation  of a compound element. If there is a parse
+    /// error, an exception of the type isc::data::JSONError is thrown.
+
+    //@{
+    /// Creates an Element from the given JSON string
+    /// @param in The string to parse the element from
+    /// @param preproc specified whether preprocessing (e.g. comment removal)
+    ///                should be performed
+    /// @return An ElementPtr that contains the element(s) specified
+    /// in the given string.
+    static ElementPtr fromJSON(const std::string& in, bool preproc = false);
+
+    /// Creates an Element from the given input stream containing JSON
+    /// formatted data.
+    ///
+    /// @param in The string to parse the element from
+    /// @param preproc specified whether preprocessing (e.g. comment removal)
+    ///                should be performed
+    /// @throw JSONError
+    /// @return An ElementPtr that contains the element(s) specified
+    /// in the given input stream.
+    static ElementPtr fromJSON(std::istream& in, bool preproc = false);
+
+    /// Creates an Element from the given input stream containing JSON
+    /// formatted data.
+    ///
+    /// @param in The string to parse the element from
+    /// @param file_name specified input file name (used in error reporting)
+    /// @param preproc specified whether preprocessing (e.g. comment removal)
+    ///                should be performed
+    /// @throw JSONError
+    /// @return An ElementPtr that contains the element(s) specified
+    /// in the given input stream.
+    /// @throw JSONError
+    static ElementPtr fromJSON(std::istream& in, const std::string& file_name,
+                               bool preproc = false);
+
+    /// Creates an Element from the given input stream, where we keep
+    /// track of the location in the stream for error reporting.
+    ///
+    /// @param in The string to parse the element from.
+    /// @param file The input file name.
+    /// @param line A reference to the int where the function keeps
+    /// track of the current line.
+    /// @param pos A reference to the int where the function keeps
+    /// track of the current position within the current line.
+    /// @throw JSONError
+    /// @return An ElementPtr that contains the element(s) specified
+    /// in the given input stream.
+    // make this one private?
+    /// @throw JSONError
+    static ElementPtr fromJSON(std::istream& in, const std::string& file,
+                               int& line, int &pos);
+
+    /// Reads contents of specified file and interprets it as JSON.
+    ///
+    /// @param file_name name of the file to read
+    /// @param preproc specified whether preprocessing (e.g. comment removal)
+    ///                should be performed
+    /// @return An ElementPtr that contains the element(s) specified
+    /// if the given file.
+    static ElementPtr fromJSONFile(const std::string& file_name,
+                                   bool preproc = false);
+    //@}
+
+    /// @name Type name conversion functions
+
+    /// Returns the name of the given type as a string
+    ///
+    /// @param type The type to return the name of
+    /// @return The name of the type, or "unknown" if the type
+    ///         is not known.
+    static std::string typeToName(Element::types type);
+
+    /// Converts the string to the corresponding type
+    /// Throws a TypeError if the name is unknown.
+    ///
+    /// @param type_name The name to get the type of
+    /// @return the corresponding type value
+    static Element::types nameToType(const std::string& type_name);
+
+    /// @brief input text preprocessor
+    ///
+    /// This method performs preprocessing of the input stream (which is
+    /// expected to contain a text version of to be parsed JSON). For now the
+    /// sole supported operation is bash-style (line starting with #) comment
+    /// removal, but it will be extended later to cover more cases (C, C++ style
+    /// comments, file inclusions, maybe macro replacements?).
+    ///
+    /// This method processes the whole input stream. It reads all contents of
+    /// the input stream, filters the content and returns the result in a
+    /// different stream.
+    ///
+    /// @param in input stream to be preprocessed
+    /// @param out output stream (filtered content will be written here)
+    static void preprocess(std::istream& in, std::stringstream& out);
+
+    /// @name Wire format factory functions
+
+    /// These function pparse the wireformat at the given stringstream
+    /// (of the given length). If there is a parse error an exception
+    /// of the type isc::cc::DecodeError is raised.
+
+    //@{
+    /// Creates an Element from the wire format in the given
+    /// stringstream of the given length.
+    /// Since the wire format is JSON, this is the same as
+    /// fromJSON, and could be removed.
+    ///
+    /// @param in The input stringstream.
+    /// @param length The length of the wireformat data in the stream
+    /// @return ElementPtr with the data that is parsed.
+    static ElementPtr fromWire(std::stringstream& in, int length);
+
+    /// Creates an Element from the wire format in the given string
+    /// Since the wire format is JSON, this is the same as
+    /// fromJSON, and could be removed.
+    ///
+    /// @param s The input string
+    /// @return ElementPtr with the data that is parsed.
+    static ElementPtr fromWire(const std::string& s);
+    //@}
+
+    /// @brief Remove all empty maps and lists from this Element and its
+    /// descendants.
+    void removeEmptyContainersRecursively() {
+        if (type_ == list || type_ == map) {
+            size_t s(size());
+            for (size_t i = 0; i < s; ++i) {
+                // Get child.
+                ElementPtr child;
+                if (type_ == list) {
+                    child = getNonConst(i);
+                } else if (type_ == map) {
+                    std::string const key(get(i)->stringValue());
+                    // The ElementPtr - ConstElementPtr disparity between
+                    // ListElement and MapElement is forcing a const cast here.
+                    // It's undefined behavior to modify it after const casting.
+                    // The options are limited. I've tried templating, moving
+                    // this function from a member function to free-standing and
+                    // taking the Element template as argument. I've tried
+                    // making it a virtual function with overridden
+                    // implementations in ListElement and MapElement. Nothing
+                    // works.
+                    child = boost::const_pointer_cast<Element>(get(key));
+                }
+
+                // Makes no sense to continue for non-container children.
+                if (child->getType() != list && child->getType() != map) {
+                    continue;
+                }
+
+                // Recurse if not empty.
+                if (!child->empty()){
+                    child->removeEmptyContainersRecursively();
+                }
+
+                // When returning from recursion, remove if empty.
+                if (child->empty()) {
+                    remove(i);
+                    --i;
+                    --s;
+                }
+            }
+        }
+    }
+};
+
+/// Notes: IntElement type is changed to int64_t.
+///        Due to C++ problems on overloading and automatic type conversion,
+///          (C++ tries to convert integer type values and reference/pointer
+///           if value types do not match exactly)
+///        We decided the storage as int64_t,
+///           three (long long, long, int) override function definitions
+///           and cast int/long/long long to int64_t via long long.
+///        Therefore, call by value methods (create, setValue) have three
+///        (int,long,long long) definitions. Others use int64_t.
+///
+class IntElement : public Element {
+    int64_t i;
+public:
+    IntElement(int64_t v, const Position& pos = ZERO_POSITION())
+        : Element(integer, pos), i(v) { }
+    int64_t intValue() const { return (i); }
+    using Element::getValue;
+    bool getValue(int64_t& t) const { t = i; return (true); }
+    using Element::setValue;
+    bool setValue(long long int v) { i = v; return (true); }
+    void toJSON(std::ostream& ss) const;
+    bool equals(const Element& other) const;
+};
+
+class DoubleElement : public Element {
+    double d;
+
+public:
+    DoubleElement(double v, const Position& pos = ZERO_POSITION())
+        : Element(real, pos), d(v) {};
+    double doubleValue() const { return (d); }
+    using Element::getValue;
+    bool getValue(double& t) const { t = d; return (true); }
+    using Element::setValue;
+    bool setValue(const double v) { d = v; return (true); }
+    void toJSON(std::ostream& ss) const;
+    bool equals(const Element& other) const;
+};
+
+class BoolElement : public Element {
+    bool b;
+
+public:
+    BoolElement(const bool v, const Position& pos = ZERO_POSITION())
+        : Element(boolean, pos), b(v) {};
+    bool boolValue() const { return (b); }
+    using Element::getValue;
+    bool getValue(bool& t) const { t = b; return (true); }
+    using Element::setValue;
+    bool setValue(const bool v) { b = v; return (true); }
+    void toJSON(std::ostream& ss) const;
+    bool equals(const Element& other) const;
+};
+
+class NullElement : public Element {
+public:
+    NullElement(const Position& pos = ZERO_POSITION())
+        : Element(null, pos) {};
+    void toJSON(std::ostream& ss) const;
+    bool equals(const Element& other) const;
+};
+
+class StringElement : public Element {
+    std::string s;
+
+public:
+    StringElement(std::string v, const Position& pos = ZERO_POSITION())
+        : Element(string, pos), s(v) {};
+    std::string stringValue() const { return (s); }
+    using Element::getValue;
+    bool getValue(std::string& t) const { t = s; return (true); }
+    using Element::setValue;
+    bool setValue(const std::string& v) { s = v; return (true); }
+    void toJSON(std::ostream& ss) const;
+    bool equals(const Element& other) const;
+};
+
+class ListElement : public Element {
+    std::vector<ElementPtr> l;
+
+public:
+    ListElement(const Position& pos = ZERO_POSITION())
+        : Element(list, pos) {}
+    const std::vector<ElementPtr>& listValue() const { return (l); }
+    using Element::getValue;
+    bool getValue(std::vector<ElementPtr>& t) const {
+        t = l;
+        return (true);
+    }
+    using Element::setValue;
+    bool setValue(const std::vector<ElementPtr>& v) {
+        l = v;
+        return (true);
+    }
+    using Element::get;
+    ConstElementPtr get(int i) const { return (l.at(i)); }
+    ElementPtr getNonConst(int i) const  { return (l.at(i)); }
+    using Element::set;
+    void set(size_t i, ElementPtr e) {
+        l.at(i) = e;
+    }
+    void add(ElementPtr e) { l.push_back(e); };
+    using Element::remove;
+    void remove(int i) { l.erase(l.begin() + i); };
+    void toJSON(std::ostream& ss) const;
+    size_t size() const { return (l.size()); }
+    bool empty() const { return (l.empty()); }
+    bool equals(const Element& other) const;
+
+    /// @brief Sorts the elements inside the list.
+    ///
+    /// The list must contain elements of the same type.
+    /// Call with the key by which you want to sort when the list contains maps.
+    /// Nested lists are not supported.
+    /// Call without a parameter when sorting any other type.
+    ///
+    /// @param index the key by which you want to sort when the list contains
+    /// maps
+    void sort(std::string const& index = std::string());
+};
+
+class MapElement : public Element {
+    std::map<std::string, ConstElementPtr> m;
+
+public:
+    MapElement(const Position& pos = ZERO_POSITION()) : Element(map, pos) {}
+    // @todo should we have direct iterators instead of exposing the std::map
+    // here?
+    const std::map<std::string, ConstElementPtr>& mapValue() const override {
+        return (m);
+    }
+    using Element::getValue;
+    bool getValue(std::map<std::string, ConstElementPtr>& t) const override {
+        t = m;
+        return (true);
+    }
+    using Element::setValue;
+    bool setValue(const std::map<std::string, ConstElementPtr>& v) override {
+        m = v;
+        return (true);
+    }
+    using Element::get;
+    ConstElementPtr get(const std::string& s) const override {
+        auto found = m.find(s);
+        return (found != m.end() ? found->second : ConstElementPtr());
+    }
+
+    /// @brief Get the i-th element in the map.
+    ///
+    /// Useful when required to iterate with an index.
+    ///
+    /// @param i the position of the element you want to return
+    /// @return the element at position i
+    ConstElementPtr get(int const i) const override {
+        auto it(m.begin());
+        std::advance(it, i);
+        return create(it->first);
+    }
+
+    using Element::set;
+    void set(const std::string& key, ConstElementPtr value) override;
+    using Element::remove;
+    void remove(const std::string& s) override { m.erase(s); }
+
+    /// @brief Remove the i-th element from the map.
+    ///
+    /// @param i the position of the element you want to remove
+    void remove(int const i) override {
+        auto it(m.begin());
+        std::advance(it, i);
+        m.erase(it);
+    }
+
+    bool contains(const std::string& s) const override {
+        return (m.find(s) != m.end());
+    }
+    void toJSON(std::ostream& ss) const override;
+
+    // we should name the two finds better...
+    // find the element at id; raises TypeError if one of the
+    // elements at path except the one we're looking for is not a
+    // mapelement.
+    // returns an empty element if the item could not be found
+    ConstElementPtr find(const std::string& id) const override;
+
+    // find the Element at 'id', and store the element pointer in t
+    // returns true if found, or false if not found (either because
+    // it doesn't exist or one of the elements in the path is not
+    // a MapElement)
+    bool find(const std::string& id, ConstElementPtr& t) const override;
+
+    /// @brief Returns number of stored elements
+    ///
+    /// @return number of elements.
+    size_t size() const override {
+        return (m.size());
+    }
+
+    bool equals(const Element& other) const override;
+
+    bool empty() const override { return (m.empty()); }
+};
+
+/// Checks whether the given ElementPtr is a NULL pointer
+/// @param p The ElementPtr to check
+/// @return true if it is NULL, false if not.
+bool isNull(ConstElementPtr p);
+
+///
+/// @brief Remove all values from the first ElementPtr that are
+/// equal in the second. Both ElementPtrs MUST be MapElements
+/// The use for this function is to end up with a MapElement that
+/// only contains new and changed values (for ModuleCCSession and
+/// configuration update handlers)
+/// Raises a TypeError if a or b are not MapElements
+void removeIdentical(ElementPtr a, ConstElementPtr b);
+
+/// @brief Create a new ElementPtr from the first ElementPtr, removing all
+/// values that are equal in the second. Both ElementPtrs MUST be MapElements.
+/// The returned ElementPtr will be a MapElement that only contains new and
+/// changed values (for ModuleCCSession and configuration update handlers).
+/// Raises a TypeError if a or b are not MapElements
+ConstElementPtr removeIdentical(ConstElementPtr a, ConstElementPtr b);
+
+/// @brief Merges the data from other into element. (on the first level). Both
+/// elements must be MapElements. Every string, value pair in other is copied
+/// into element (the ElementPtr of value is copied, this is not a new object)
+/// Unless the value is a NullElement, in which case the key is removed from
+/// element, rather than setting the value to the given NullElement.
+/// This way, we can remove values from for instance maps with configuration
+/// data (which would then result in reverting back to the default).
+/// Raises a TypeError if either ElementPtr is not a MapElement
+void merge(ElementPtr element, ConstElementPtr other);
+
+/// @brief Function used to check if two MapElements refer to the same
+/// configuration data. It can check if the two MapElements have the same or
+/// have equivalent value for some members.
+/// e.g.
+/// (
+///  left->get("prefix")->stringValue() == right->get("prefix")->stringValue() &&
+///  left->get("prefix-len")->intValue() == right->get("prefix-len")->intValue() &&
+///  left->get("delegated-len")->intValue() == right->get("delegated-len")->intValue()
+/// )
+typedef std::function<bool (ElementPtr&, ElementPtr&)> MatchTestFunc;
+
+/// @brief Function used to check if the data provided for the element contains
+/// only information used for identification, or it contains extra useful data.
+typedef std::function<bool (ElementPtr&)> NoDataTestFunc;
+
+/// @brief Function used to check if the key is used for identification
+typedef std::function<bool (const std::string&)> IsKeyTestFunc;
+
+/// @brief Structure holding the test functions used to traverse the element
+/// hierarchy.
+struct HierarchyTraversalTest {
+    MatchTestFunc match_;
+    NoDataTestFunc no_data_;
+    IsKeyTestFunc is_key_;
+};
+
+/// @brief Mapping between a container name and functions used to match elements
+/// inside the container.
+typedef std::map<std::string, HierarchyTraversalTest> FunctionMap;
+
+/// @brief Hierarchy descriptor of the containers in a specific Element
+/// hierarchy tree. The position inside the vector indicates the level at which
+/// the respective containers are located.
+///
+/// e.g.
+/// {
+///   { { "pools", { ... , ... } }, { "pd-pools", { ... , ... } }, { "option-data", { ... , ... } } },
+///   { { "option-data", { ... , ... } } }
+/// }
+/// At first subnet level the 'pools', 'pd-pools' and 'option-data' containers
+/// can be found.
+/// At second subnet level the 'option-data' container can be found
+/// (obviously only inside 'pools' and 'pd-pools' containers).
+typedef std::vector<FunctionMap> HierarchyDescriptor;
+
+/// @brief Merges the diff data by adding the missing elements from 'other'
+/// to 'element' (recursively). Both elements must be the same Element type.
+/// Raises a TypeError if elements are not the same Element type.
+/// @note
+/// for non map and list elements the values are updated with the new values
+/// for maps:
+///     - non map and list elements are added/updated with the new values
+///     - list and map elements are processed recursively
+/// for lists:
+///     - regardless of the element type, all elements from 'other' are added to
+///       'element'
+///
+/// @param element The element to which new data is added.
+/// @param other The element containing the data which needs to be added.
+/// @param hierarchy The hierarchy describing the elements relations and
+/// identification keys.
+/// @param key The container holding the current element.
+/// @param idx The level inside the hierarchy the current element is located.
+void mergeDiffAdd(ElementPtr& element, ElementPtr& other,
+                  HierarchyDescriptor& hierarchy, std::string key,
+                  size_t idx = 0);
+
+/// @brief Merges the diff data by removing the data present in 'other' from
+/// 'element' (recursively). Both elements must be the same Element type.
+/// Raises a TypeError if elements are not the same Element type.
+/// for non map and list elements the values are set to NullElement
+/// for maps:
+///     - non map and list elements are removed from the map
+///     - list and map elements are processed recursively
+/// for lists:
+///     - regardless of the element type, all elements from 'other' matching
+///       elements in 'element' are removed
+///
+/// @param element The element from which new data is removed.
+/// @param other The element containing the data which needs to be removed.
+/// @param hierarchy The hierarchy describing the elements relations and
+/// identification keys.
+/// @param key The container holding the current element.
+/// @param idx The level inside the hierarchy the current element is located.
+void mergeDiffDel(ElementPtr& element, ElementPtr& other,
+                  HierarchyDescriptor& hierarchy, std::string key,
+                  size_t idx = 0);
+
+/// @brief Extends data by adding the specified 'extension' elements from
+/// 'other' inside the 'container' element (recursively). Both elements must be
+/// the same Element type.
+/// Raises a TypeError if elements are not the same Element type.
+///
+/// @param container The container holding the data that must be extended.
+/// @param extension The name of the element that contains the data that must be
+/// added (if not already present) in order to extend the initial data.
+/// @param element The element from which new data is added.
+/// @param other The element containing the data which needs to be added.
+/// @param hierarchy The hierarchy describing the elements relations and
+/// identification keys.
+/// @param key The container holding the current element.
+/// @param idx The level inside the hierarchy the current element is located.
+/// @param alter The flag which indicates if the current element should be
+/// updated.
+void extend(const std::string& container, const std::string& extension,
+            ElementPtr& element, ElementPtr& other,
+            HierarchyDescriptor& hierarchy, std::string key, size_t idx = 0,
+            bool alter = false);
+
+/// @brief Copy the data up to a nesting level.
+///
+/// The copy is a deep copy so nothing is shared if it is not
+/// under the given nesting level.
+///
+/// @param from the pointer to the element to copy
+/// @param level nesting level (default is 100, 0 means shallow copy,
+/// negative means outbound and perhaps looping forever).
+/// @return a pointer to a fresh copy
+/// @throw raises a BadValue is a null pointer occurs.
+ElementPtr copy(ConstElementPtr from, int level = 100);
+
+/// @brief Compares the data with other using unordered lists
+///
+/// This comparison function handles lists (JSON arrays) as
+/// unordered multi sets (multi means an item can occurs more
+/// than once as soon as it occurs the same number of times).
+bool isEquivalent(ConstElementPtr a, ConstElementPtr b);
+
+/// @brief Pretty prints the data into stream.
+///
+/// This operator converts the @c ConstElementPtr into a string and
+/// inserts it into the output stream @c out with an initial
+/// indentation @c indent and add at each level @c step spaces.
+/// For maps if there is a comment property it is printed first.
+///
+/// @param element A @c ConstElementPtr to pretty print
+/// @param out A @c std::ostream on which the print operation is performed
+/// @param indent An initial number of spaces to add each new line
+/// @param step A number of spaces to add to indentation at a new level
+void prettyPrint(ConstElementPtr element, std::ostream& out,
+                 unsigned indent = 0, unsigned step = 2);
+
+/// @brief Pretty prints the data into string
+///
+/// This operator converts the @c ConstElementPtr into a string with
+/// an initial indentation @c indent and add at each level @c step spaces.
+/// For maps if there is a comment property it is printed first.
+///
+/// @param element A @c ConstElementPtr to pretty print
+/// @param indent An initial number of spaces to add each new line
+/// @param step A number of spaces to add to indentation at a new level
+/// @return a string where element was pretty printed
+std::string prettyPrint(ConstElementPtr element,
+                        unsigned indent = 0, unsigned step = 2);
+
+/// @brief Insert Element::Position as a string into stream.
+///
+/// This operator converts the @c Element::Position into a string and
+/// inserts it into the output stream @c out.
+///
+/// @param out A @c std::ostream object on which the insertion operation is
+/// performed.
+/// @param pos The @c Element::Position structure to insert.
+/// @return A reference to the same @c std::ostream object referenced by
+/// parameter @c out after the insertion operation.
+std::ostream& operator<<(std::ostream& out, const Element::Position& pos);
+
+/// @brief Insert the Element as a string into stream.
+///
+/// This method converts the @c ElementPtr into a string with
+/// @c Element::str() and inserts it into the
+/// output stream @c out.
+///
+/// This function overloads the global operator<< to behave as described in
+/// ostream::operator<< but applied to @c ElementPtr objects.
+///
+/// @param out A @c std::ostream object on which the insertion operation is
+/// performed.
+/// @param e The @c ElementPtr object to insert.
+/// @return A reference to the same @c std::ostream object referenced by
+/// parameter @c out after the insertion operation.
+std::ostream& operator<<(std::ostream& out, const Element& e);
+
+bool operator==(const Element& a, const Element& b);
+bool operator!=(const Element& a, const Element& b);
+bool operator<(const Element& a, const Element& b);
+
+}  // namespace data
+}  // namespace isc
+
+#endif // ISC_DATA_H
+
+// Local Variables:
+// mode: c++
+// End:
diff --git a/src/lib/cc/dhcp_config_error.h b/src/lib/cc/dhcp_config_error.h
new file mode 100644
index 0000000..1337dd8
--- /dev/null
+++ b/src/lib/cc/dhcp_config_error.h
@@ -0,0 +1,72 @@
+// Copyright (C) 2017 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef DHCP_CONFIG_ERROR_H
+#define DHCP_CONFIG_ERROR_H
+
+#include <exceptions/exceptions.h>
+
+namespace isc {
+
+/// @brief Evaluation error exception raised when trying to parse.
+///
+/// This exception is expected to be thrown when parsing of the input
+/// configuration has failed. This exception is used by parsers.
+class ParseError : public isc::Exception {
+ public:
+ ParseError(const char* file, size_t line, const char* what) :
+    isc::Exception(file, line, what) { };
+};
+
+/// An exception that is thrown if an error occurs while configuring
+/// any server.
+/// By convention when this exception is thrown there is a position
+/// between parentheses so the code style should be like this:
+///
+/// try {
+///     ...
+/// } catch (const ConfigError&) {
+///     throw;
+/// } catch (const std::exception& ex) {
+///    isc_throw(ConfigError, "message" << ex.what()
+///              << " (" << getPosition(what) << ")");
+/// }
+
+/// @todo: move this header into simple_parser.h
+/// @todo: create an isc_throw like macro to add the
+/// position more easily.
+/// @todo: replace all references to DhcpConfigError with ConfigError,
+///        then remove DhcpConfigError.
+class ConfigError : public isc::Exception {
+public:
+
+    /// @brief constructor
+    ///
+    /// @param file name of the file, where exception occurred
+    /// @param line line of the file, where exception occurred
+    /// @param what text description of the issue that caused exception
+    ConfigError(const char* file, size_t line, const char* what)
+        : isc::Exception(file, line, what) {}
+};
+
+namespace dhcp {
+
+/// @brief To be removed. Please use ConfigError instead.
+class DhcpConfigError : public isc::Exception {
+public:
+    /// @brief constructor
+    ///
+    /// @param file name of the file, where exception occurred
+    /// @param line line of the file, where exception occurred
+    /// @param what text description of the issue that caused exception
+    DhcpConfigError(const char* file, size_t line, const char* what)
+        : isc::Exception(file, line, what) {}
+};
+
+}; // end of isc::dhcp namespace
+}; // end of isc namespace
+
+#endif // DHCP_CONFIG_ERROR_H
diff --git a/src/lib/cc/element_value.h b/src/lib/cc/element_value.h
new file mode 100644
index 0000000..ff48561
--- /dev/null
+++ b/src/lib/cc/element_value.h
@@ -0,0 +1,117 @@
+// Copyright (C) 2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef ELEMENT_VALUE_H
+#define ELEMENT_VALUE_H
+
+#include <asiolink/io_address.h>
+#include <cc/data.h>
+#include <string>
+
+namespace isc {
+namespace data {
+
+/// @brief Template class for converting a value encapsulated in the
+/// @c Element object into a simple type.
+///
+/// The @c Element object provides a set of accessors to retrieve
+/// values of different types it encapsulates. These methods
+/// however can't be always used in template methods and classes.
+///
+/// Consider a template function which returns a value of a type
+/// specified as template argument. In order to convert a value
+/// held in the @c Element object it would have to conditionally
+/// call this object's accessors to return the value of the
+/// appropriate type. This would however fail to compile because
+/// the compiler would check for all possible value types returned
+/// by the @c Element accessors and report an error for those that
+/// don't cast to the returned type.
+///
+/// This class provides a mechanism to extract the value of the
+/// appropriate type from the @c Element object within the
+/// template function. It comes with a number of class specializations
+/// for various data types to be returned. The default implementation
+/// calls @c Element::intValue and casts it to the returned type.
+/// There are class specializations for @c double, @c bool and
+/// @c string.
+///
+/// @tparam T Type of the value to be extracted.
+template<typename T>
+class ElementValue {
+public:
+
+    /// @brief Function operator extracting an @c Element value as
+    /// integer.
+    ///
+    /// @param el Element holding a value to be extracted.
+    T operator()(ConstElementPtr el) const {
+        return (static_cast<T>(el->intValue()));
+    }
+};
+
+/// @brief The @c ElementValue specialization for double.
+template<>
+class ElementValue<double> {
+public:
+
+    /// @brief Function operator extracting an @c Element value as
+    /// double.
+    ///
+    /// @param el Element holding a value to be extracted.
+    double operator()(ConstElementPtr el) const {
+        return (el->doubleValue());
+    }
+};
+
+/// @brief The @c ElementValue specialization for boolean.
+template<>
+class ElementValue<bool> {
+public:
+
+    /// @brief Function operator extracting an @c Element value as
+    /// boolean.
+    ///
+    /// @param el Element holding a value to be extracted.
+    bool operator()(ConstElementPtr el) const {
+        return (el->boolValue());
+    }
+
+};
+
+/// @brief The @c ElementValue specialization for string.
+template<>
+class ElementValue<std::string> {
+public:
+
+    /// @brief Function operator extracting an @c Element value as
+    /// string.
+    ///
+    /// @param el Element holding a value to be extracted.
+    std::string operator()(ConstElementPtr el) const {
+        return (el->stringValue());
+    }
+};
+
+/// @brief The @c ElementValue specialization for IOAddress.
+template<>
+class ElementValue<asiolink::IOAddress> {
+public:
+
+    /// @brief Function operator extracting an @c Element value as
+    /// IOAddress.
+    ///
+    /// @note This does NOT support empty string value.
+    ///
+    /// @param el Element holding a value to be extracted.
+    asiolink::IOAddress operator()(ConstElementPtr el) const {
+        return (asiolink::IOAddress(el->stringValue()));
+    }
+};
+
+} // end of namespace isc::data
+} // end of namespace isc
+
+#endif // ELEMENT_VALUE_H
diff --git a/src/lib/cc/json_feed.cc b/src/lib/cc/json_feed.cc
new file mode 100644
index 0000000..7cd1e31
--- /dev/null
+++ b/src/lib/cc/json_feed.cc
@@ -0,0 +1,563 @@
+// Copyright (C) 2017-2021 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/data.h>
+#include <cc/json_feed.h>
+#include <functional>
+
+using namespace isc::data;
+using namespace isc::util;
+
+namespace isc {
+namespace config {
+
+const int JSONFeed::RECEIVE_START_ST;
+const int JSONFeed::WHITESPACE_BEFORE_JSON_ST;
+const int JSONFeed::EOL_COMMENT_BEFORE_JSON_ST;
+const int JSONFeed::START_COMMENT_BEFORE_JSON_ST;
+const int JSONFeed::C_COMMENT_BEFORE_JSON_ST;
+const int JSONFeed::STOP_COMMENT_BEFORE_JSON_ST;
+const int JSONFeed::JSON_START_ST;
+const int JSONFeed::INNER_JSON_ST;
+const int JSONFeed::STRING_JSON_ST;
+const int JSONFeed::ESCAPE_JSON_ST;
+const int JSONFeed::EOL_COMMENT_ST;
+const int JSONFeed::START_COMMENT_ST;
+const int JSONFeed::C_COMMENT_ST;
+const int JSONFeed::STOP_COMMENT_ST;
+const int JSONFeed::JSON_END_ST;
+const int JSONFeed::FEED_OK_ST;
+const int JSONFeed::FEED_FAILED_ST;
+
+const int JSONFeed::DATA_READ_OK_EVT;
+const int JSONFeed::NEED_MORE_DATA_EVT;
+const int JSONFeed::MORE_DATA_PROVIDED_EVT;
+const int JSONFeed::FEED_OK_EVT;
+const int JSONFeed::FEED_FAILED_EVT;
+
+JSONFeed::JSONFeed()
+    : StateModel(), buffer_(), data_ptr_(0), error_message_(), open_scopes_(0),
+      output_() {
+}
+
+void
+JSONFeed::initModel() {
+    // Initialize dictionaries of events and states.
+    initDictionaries();
+
+    // Set the current state to starting state and enter the run loop.
+    setState(RECEIVE_START_ST);
+
+    // Parsing starts from here.
+    postNextEvent(START_EVT);
+}
+
+void
+JSONFeed::poll() {
+    try {
+        // Process the input data until no more data is available or until
+        // JSON feed ends with matching closing brace.
+        do {
+            getState(getCurrState())->run();
+
+        } while (!isModelDone() && (getNextEvent() != NOP_EVT) &&
+                 (getNextEvent() != NEED_MORE_DATA_EVT));
+    } catch (const std::exception& ex) {
+        abortModel(ex.what());
+    }
+}
+
+bool
+JSONFeed::needData() const {
+    return ((getNextEvent() == NEED_MORE_DATA_EVT) ||
+            (getNextEvent() == START_EVT));
+}
+
+bool
+JSONFeed::feedOk() const {
+    return ((getNextEvent() == END_EVT) &&
+            (getLastEvent() == FEED_OK_EVT));
+}
+
+ElementPtr
+JSONFeed::toElement() const {
+    if (needData()) {
+        isc_throw(JSONFeedError, "unable to retrieve the data form the"
+                  " JSON feed while parsing hasn't finished");
+    }
+    try {
+        return (Element::fromWire(output_));
+
+    } catch (const std::exception& ex) {
+        isc_throw(JSONFeedError, ex.what());
+    }
+}
+
+void
+JSONFeed::postBuffer(const void* buf, const size_t buf_size) {
+    if (buf_size > 0) {
+        // The next event is NEED_MORE_DATA_EVT when the parser wants to
+        // signal that more data is needed. This method is called to supply
+        // more data and thus it should change the next event to
+        // MORE_DATA_PROVIDED_EVT.
+        if (getNextEvent() == NEED_MORE_DATA_EVT) {
+            transition(getCurrState(), MORE_DATA_PROVIDED_EVT);
+        }
+        buffer_.assign(static_cast<const char*>(buf),
+                       static_cast<const char*>(buf) + buf_size);
+        data_ptr_ = 0;
+    }
+}
+
+void
+JSONFeed::defineEvents() {
+    StateModel::defineEvents();
+
+    // Define JSONFeed specific events.
+    defineEvent(DATA_READ_OK_EVT, "DATA_READ_OK_EVT");
+    defineEvent(NEED_MORE_DATA_EVT, "NEED_MORE_DATA_EVT");
+    defineEvent(MORE_DATA_PROVIDED_EVT, "MORE_DATA_PROVIDED_EVT");
+    defineEvent(FEED_OK_EVT, "FEED_OK_EVT");
+    defineEvent(FEED_FAILED_EVT, "FEED_FAILED_EVT");
+}
+
+void
+JSONFeed::verifyEvents() {
+    StateModel::verifyEvents();
+
+    getEvent(DATA_READ_OK_EVT);
+    getEvent(NEED_MORE_DATA_EVT);
+    getEvent(MORE_DATA_PROVIDED_EVT);
+    getEvent(FEED_OK_EVT);
+    getEvent(FEED_FAILED_EVT);
+}
+
+void
+JSONFeed::defineStates() {
+    // Call parent class implementation first.
+    StateModel::defineStates();
+
+    defineState(RECEIVE_START_ST, "RECEIVE_START_ST",
+                std::bind(&JSONFeed::receiveStartHandler, this));
+    defineState(WHITESPACE_BEFORE_JSON_ST, "WHITESPACE_BEFORE_JSON_ST",
+                std::bind(&JSONFeed::whiteSpaceBeforeJSONHandler, this));
+    defineState(EOL_COMMENT_BEFORE_JSON_ST, "EOL_COMMENT_BEFORE_JSON_ST",
+                std::bind(&JSONFeed::eolCommentBeforeJSONHandler, this));
+    defineState(START_COMMENT_BEFORE_JSON_ST, "START_COMMENT_BEFORE_JSON_ST",
+                std::bind(&JSONFeed::startCommentBeforeJSONHandler, this));
+    defineState(C_COMMENT_BEFORE_JSON_ST, "C_COMMENT_BEFORE_JSON_ST",
+                std::bind(&JSONFeed::cCommentBeforeJSONHandler, this));
+    defineState(STOP_COMMENT_BEFORE_JSON_ST, "STOP_COMMENT_BEFORE_JSON_ST",
+                std::bind(&JSONFeed::stopCommentBeforeJSONHandler, this));
+    defineState(INNER_JSON_ST, "INNER_JSON_ST",
+                std::bind(&JSONFeed::innerJSONHandler, this));
+    defineState(STRING_JSON_ST, "STRING_JSON_ST",
+                std::bind(&JSONFeed::stringJSONHandler, this));
+    defineState(ESCAPE_JSON_ST, "ESCAPE_JSON_ST",
+                std::bind(&JSONFeed::escapeJSONHandler, this));
+    defineState(EOL_COMMENT_ST, "EOL_COMMENT_ST",
+                std::bind(&JSONFeed::eolCommentHandler, this));
+    defineState(START_COMMENT_ST, "START_COMMENT_ST",
+                std::bind(&JSONFeed::startCommentHandler, this));
+    defineState(C_COMMENT_ST, "C_COMMENT_ST",
+                std::bind(&JSONFeed::cCommentHandler, this));
+    defineState(STOP_COMMENT_ST, "STOP_COMMENT_ST",
+                std::bind(&JSONFeed::stopCommentHandler, this));
+    defineState(JSON_END_ST, "JSON_END_ST",
+                std::bind(&JSONFeed::endJSONHandler, this));
+}
+
+void
+JSONFeed::feedFailure(const std::string& error_msg) {
+    error_message_ = error_msg;
+    transition(FEED_FAILED_ST, FEED_FAILED_EVT);
+}
+
+void
+JSONFeed::onModelFailure(const std::string& explanation) {
+    if (error_message_.empty()) {
+        error_message_ = explanation;
+    }
+}
+
+bool
+JSONFeed::popNextFromBuffer(char& next) {
+    // If there are any characters in the buffer, pop next.
+    if (!buffer_.empty() && (data_ptr_ < buffer_.size())) {
+        next = buffer_[data_ptr_++];
+        return (true);
+    }
+    return (false);
+}
+
+char
+JSONFeed::getNextFromBuffer() {
+    unsigned int ev = getNextEvent();
+    char c = '\0';
+    // The caller should always provide additional data when the
+    // NEED_MORE_DATA_EVT occurs. If the next event is still
+    // NEED_MORE_DATA_EVT it indicates that the caller hasn't provided
+    // the data.
+    if (ev == NEED_MORE_DATA_EVT) {
+        isc_throw(JSONFeedError,
+                  "JSONFeed requires new data to progress, but no data"
+                  " have been provided. The transaction is aborted to avoid"
+                  " a deadlock.");
+
+    } else {
+        // Try to pop next character from the buffer.
+        const bool data_exist = popNextFromBuffer(c);
+        if (!data_exist) {
+            // There is no more data so it is really not possible that we're
+            // at MORE_DATA_PROVIDED_EVT.
+            if (ev == MORE_DATA_PROVIDED_EVT) {
+                isc_throw(JSONFeedError,
+                          "JSONFeed state indicates that new data have been"
+                          " provided to be parsed, but the transaction buffer"
+                          " contains no new data.");
+
+            } else {
+                // If there is no more data we should set NEED_MORE_DATA_EVT
+                // event to indicate that new data should be provided.
+                transition(getCurrState(), NEED_MORE_DATA_EVT);
+            }
+        }
+    }
+    return (c);
+}
+
+void
+JSONFeed::invalidEventError(const std::string& handler_name,
+                            const unsigned int event) {
+    isc_throw(JSONFeedError, handler_name << ": invalid event "
+                                 << getEventLabel(static_cast<int>(event)));
+}
+
+void
+JSONFeed::receiveStartHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (getNextEvent()) {
+        case START_EVT:
+            switch (c) {
+            case '\t':
+            case '\n':
+            case '\r':
+            case ' ':
+                transition(WHITESPACE_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+                return;
+
+            case '#':
+                transition(EOL_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+                return;
+
+            case '/':
+                transition(START_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+                return;
+
+            case '{':
+            case '[':
+                output_.push_back(c);
+                ++open_scopes_;
+                transition(INNER_JSON_ST, DATA_READ_OK_EVT);
+                return;
+
+            // Cannot start by a string
+            case '"':
+            default:
+                feedFailure("invalid first character " + std::string(1, c));
+                break;
+            }
+            break;
+
+        default:
+            invalidEventError("receiveStartHandler", getNextEvent());
+        }
+    }
+}
+
+void
+JSONFeed::whiteSpaceBeforeJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '\t':
+        case '\n':
+        case '\r':
+        case ' ':
+            transition(getCurrState(), DATA_READ_OK_EVT);
+            break;
+
+        case '#':
+            transition(EOL_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            return;
+
+        case '/':
+            transition(START_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            return;
+
+        case '{':
+        case '[':
+            output_.push_back(c);
+            ++open_scopes_;
+            transition(INNER_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        // Cannot start by a string
+        case '"':
+        default:
+            feedFailure("invalid character " + std::string(1, c));
+        }
+    }
+}
+
+void
+JSONFeed::eolCommentBeforeJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '\n':
+            transition(WHITESPACE_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            postNextEvent(DATA_READ_OK_EVT);
+            break;
+        }
+    }
+}
+
+void
+JSONFeed::startCommentBeforeJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '/':
+            transition(EOL_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '*':
+            transition(C_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            feedFailure("invalid characters /" + std::string(1, c));
+        }
+    }
+}
+
+void
+JSONFeed::cCommentBeforeJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '*':
+            transition(STOP_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            postNextEvent(DATA_READ_OK_EVT);
+            break;
+        }
+    }
+}
+
+void
+JSONFeed::stopCommentBeforeJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '/':
+            transition(WHITESPACE_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '*':
+            transition(getCurrState(), DATA_READ_OK_EVT);
+            break;
+
+        default:
+            transition(C_COMMENT_BEFORE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+        }
+    }
+}
+
+void
+JSONFeed::innerJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch(c) {
+        case '{':
+        case '[':
+            output_.push_back(c);
+            transition(getCurrState(), DATA_READ_OK_EVT);
+            ++open_scopes_;
+            break;
+
+        case '}':
+        case ']':
+            output_.push_back(c);
+            if (--open_scopes_ == 0) {
+                transition(JSON_END_ST, FEED_OK_EVT);
+
+            } else {
+                postNextEvent(DATA_READ_OK_EVT);
+            }
+            break;
+
+        case '"':
+            output_.push_back(c);
+            transition(STRING_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '#':
+            transition(EOL_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '/':
+            transition(START_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            output_.push_back(c);
+            postNextEvent(DATA_READ_OK_EVT);
+        }
+    }
+}
+
+void
+JSONFeed::stringJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        output_.push_back(c);
+
+        switch(c) {
+        case '"':
+            transition(INNER_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '\\':
+            transition(ESCAPE_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            transition(getCurrState(), DATA_READ_OK_EVT);
+        }
+    }
+}
+
+void
+JSONFeed::escapeJSONHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        output_.push_back(c);
+
+        transition(STRING_JSON_ST, DATA_READ_OK_EVT);
+    }
+}
+
+void
+JSONFeed::eolCommentHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '\n':
+            output_.push_back(c);
+            transition(INNER_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            postNextEvent(DATA_READ_OK_EVT);
+            break;
+        }
+    }
+}
+
+void
+JSONFeed::startCommentHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '/':
+            transition(EOL_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '*':
+            transition(C_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            feedFailure("invalid characters /" + std::string(1, c));
+        }
+    }
+}
+
+void
+JSONFeed::cCommentHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '*':
+            transition(STOP_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '\n':
+            output_.push_back(c);
+            postNextEvent(DATA_READ_OK_EVT);
+            break;
+
+        default:
+            postNextEvent(DATA_READ_OK_EVT);
+            break;
+        }
+    }
+}
+
+void
+JSONFeed::stopCommentHandler() {
+    char c = getNextFromBuffer();
+    if (getNextEvent() != NEED_MORE_DATA_EVT) {
+        switch (c) {
+        case '/':
+            transition(INNER_JSON_ST, DATA_READ_OK_EVT);
+            break;
+
+        case '*':
+            transition(getCurrState(), DATA_READ_OK_EVT);
+            break;
+
+        case '\n':
+            output_.push_back(c);
+            transition(C_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+
+        default:
+            transition(C_COMMENT_ST, DATA_READ_OK_EVT);
+            break;
+        }
+    }
+}
+
+void
+JSONFeed::endJSONHandler() {
+    switch (getNextEvent()) {
+    case FEED_OK_EVT:
+        transition(END_ST, END_EVT);
+        break;
+
+    case FEED_FAILED_EVT:
+        abortModel("reading into JSON feed failed");
+        break;
+
+    default:
+        invalidEventError("endJSONHandler", getNextEvent());
+    }
+}
+
+} // end of namespace config
+} // end of namespace isc
diff --git a/src/lib/cc/json_feed.h b/src/lib/cc/json_feed.h
new file mode 100644
index 0000000..abef6b0
--- /dev/null
+++ b/src/lib/cc/json_feed.h
@@ -0,0 +1,351 @@
+// Copyright (C) 2017-2021 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef JSON_FEED_H
+#define JSON_FEED_H
+
+#include <cc/data.h>
+#include <exceptions/exceptions.h>
+#include <util/state_model.h>
+#include <boost/shared_ptr.hpp>
+#include <stdint.h>
+#include <string>
+#include <vector>
+
+namespace isc {
+namespace config {
+
+class JSONFeed;
+
+/// @brief Pointer to the @ref JSONFeed.
+typedef boost::shared_ptr<JSONFeed> JSONFeedPtr;
+
+/// @brief Pointer to the const @ref JSONFeed.
+typedef boost::shared_ptr<const JSONFeed> ConstJSONFeedPtr;
+
+/// @brief A generic exception thrown upon an error in the @ref JSONFeed.
+class JSONFeedError : public Exception {
+public:
+    JSONFeedError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief State model for asynchronous read of data in JSON format.
+///
+/// Kea control channel uses stream sockets for forwarding commands received
+/// by the Kea Control Agent to respective Kea services. The responses may
+/// contain large amounts of data (e.g. lease queries may return thousands
+/// of leases). Such responses rarely fit into a single data buffer and
+/// require multiple calls to receive/read or asynchronous receive/read.
+///
+/// A receiver performing multiple reads from a socket must be able to
+/// locate the boundaries of the command within the data stream. The
+/// @ref JSONFeed state model solves this problem.
+///
+/// When the partial data is read from the stream socket it should be provided
+/// to the @ref JSONFeed using @ref JSONFeed::postBuffer and then the
+/// @ref JSONFeed::poll should be called to start processing the received
+/// data. The actual JSON structure can be preceded by whitespaces. When first
+/// occurrence of one of the '{' or '[' characters is found in the stream it is
+/// considered a beginning of the JSON structure. The model includes an internal
+/// counter of new '{' and '[' occurrences. The counter increases one of these
+/// characters is found. When any of the '}' or ']' is found, the counter
+/// is decreased. When the counter is decreased to 0 it indicates that the
+/// entire JSON structure has been received and processed.
+///
+/// As '{', '}', '[' and ']' can be embedded in JSON strings two states
+/// for strings and escape in strings are required. Note the processing
+/// of escapes is greatly simplified compared to ECMA 404 figure 5.
+///
+/// Added support for '#' to end of line (bash), '//' to end of line (C++)
+/// and '/*' to '*/' (C) comments both before JSON and inside JSON.
+
+/// Note that this mechanism doesn't check if the JSON structure is well
+/// formed. It merely detects the end of the JSON structure if this structure
+/// is well formed. The structure is validated when @ref JSONFeed::toElement
+/// is called to retrieve the data structures encapsulated with
+/// @ref isc::data::Element objects.
+class JSONFeed : public util::StateModel {
+public:
+
+    /// @name States supported by the @ref JSONFeed
+    ///
+    //@{
+
+    /// @brief State indicating a beginning of a feed.
+    static const int RECEIVE_START_ST = SM_DERIVED_STATE_MIN + 1;
+
+    /// @brief Skipping whitespaces before actual JSON.
+    static const int WHITESPACE_BEFORE_JSON_ST = SM_DERIVED_STATE_MIN + 2;
+
+    /// @brief Skipping an end-of-line comment before actual JSON.
+    static const int EOL_COMMENT_BEFORE_JSON_ST = SM_DERIVED_STATE_MIN + 3;
+
+    /// @brief Starting one of the comments beginning with a slash before actual JSON.
+    static const int START_COMMENT_BEFORE_JSON_ST = SM_DERIVED_STATE_MIN + 4;
+
+    /// @brief Skipping a C style comment before actual JSON.
+    static const int C_COMMENT_BEFORE_JSON_ST = SM_DERIVED_STATE_MIN + 5;
+
+    /// @brief Stopping a C style comment before actual JSON.
+    static const int STOP_COMMENT_BEFORE_JSON_ST = SM_DERIVED_STATE_MIN + 6;
+
+    /// @brief Found first opening brace or square bracket.
+    static const int JSON_START_ST = SM_DERIVED_STATE_MIN + 7;
+
+    /// @brief Parsing JSON.
+    static const int INNER_JSON_ST = SM_DERIVED_STATE_MIN + 8;
+
+    /// @brief Parsing JSON string.
+    static const int STRING_JSON_ST = SM_DERIVED_STATE_MIN + 9;
+
+    /// @brief JSON escape next character.
+    static const int ESCAPE_JSON_ST = SM_DERIVED_STATE_MIN + 10;
+
+    /// @brief Skipping an end-of-line comment.
+    static const int EOL_COMMENT_ST = SM_DERIVED_STATE_MIN + 11;
+
+    /// @brief Starting one of the comments beginning with a slash.
+    static const int START_COMMENT_ST = SM_DERIVED_STATE_MIN + 12;
+
+    /// @brief Skipping a C style comment.
+    static const int C_COMMENT_ST = SM_DERIVED_STATE_MIN + 13;
+
+    /// @brief Stopping a C style comment.
+    static const int STOP_COMMENT_ST = SM_DERIVED_STATE_MIN + 14;
+
+    /// @brief Found last closing brace or square bracket.
+    static const int JSON_END_ST = SM_DERIVED_STATE_MIN + 15;
+
+    /// @brief Found opening and closing brace or square bracket.
+    ///
+    /// This doesn't however indicate that the JSON is well formed. It
+    /// only means that matching closing brace or square bracket was
+    /// found.
+    static const int FEED_OK_ST = SM_DERIVED_STATE_MIN + 100;
+
+    /// @brief Invalid syntax detected.
+    ///
+    /// For example, non matching braces or invalid characters found.
+    static const int FEED_FAILED_ST = SM_DERIVED_STATE_MIN + 101;
+
+    //@}
+
+
+    /// @name Events used during data processing.
+    ///
+    //@{
+
+    /// @brief Chunk of data successfully read and parsed.
+    static const int DATA_READ_OK_EVT = SM_DERIVED_EVENT_MIN + 1;
+
+    /// @brief Unable to proceed with parsing until new data is provided.
+    static const int NEED_MORE_DATA_EVT = SM_DERIVED_EVENT_MIN + 2;
+
+    /// @brief New data provided and parsing should continue.
+    static const int MORE_DATA_PROVIDED_EVT = SM_DERIVED_EVENT_MIN + 3;
+
+    /// @brief Found opening brace and the matching closing brace.
+    static const int FEED_OK_EVT = SM_DERIVED_EVENT_MIN + 100;
+
+    /// @brief Invalid syntax detected.
+    static const int FEED_FAILED_EVT = SM_DERIVED_EVENT_MIN + 101;
+
+    //@}
+
+    /// @brief Constructor.
+    JSONFeed();
+
+    /// @brief Initializes state model.
+    ///
+    /// Initializes events and states. It sets the model to @c RECEIVE_START_ST
+    /// and the next event to @c START_EVT.
+    void initModel();
+
+    /// @brief Runs the model as long as data is available.
+    ///
+    /// It processes the input data character by character until it reaches the
+    /// end of the input buffer, in which case it returns. The next event is set
+    /// to @c NEED_MORE_DATA_EVT to indicate the need for providing additional
+    /// data using @ref JSONFeed::postBuffer. This function also returns when
+    /// the end of the JSON structure has been detected or when an error has
+    /// occurred.
+    void poll();
+
+    /// @brief Checks if the model needs additional data to continue.
+    ///
+    /// The caller can use this method to check if the model expects additional
+    /// data to be provided to finish processing input data.
+    ///
+    /// @return true if more data is needed, false otherwise.
+    bool needData() const;
+
+    /// @brief Checks if the data have been successfully processed.
+    bool feedOk() const;
+
+    /// @brief Returns error string when data processing has failed.
+    std::string getErrorMessage() const {
+        return (error_message_);
+    }
+
+    /// @brief Returns the text parsed into the buffer.
+    std::string getProcessedText() const {
+        return (output_);
+    }
+
+    /// @brief Returns processed data as a structure of @ref isc::data::Element
+    /// objects.
+    ///
+    /// @throw JSONFeedError if the received JSON is not well formed.
+    data::ElementPtr toElement() const;
+
+    /// @brief Receives additional data read from a data stream.
+    ///
+    /// A caller invokes this method to pass additional chunk of data received
+    /// from the stream.
+    ///
+    /// @param buf Pointer to a buffer holding additional input data.
+    /// @param buf_size Size of the data in the input buffer.
+    void postBuffer(const void* buf, const size_t buf_size);
+
+
+private:
+
+    /// @brief Make @ref runModel private to make sure that the caller uses
+    /// @ref poll method instead.
+    using StateModel::runModel;
+
+    /// @brief Define events used by the feed.
+    virtual void defineEvents();
+
+    /// @brief Verifies events used by the feed.
+    virtual void verifyEvents();
+
+    /// @brief Defines states of the feed.
+    virtual void defineStates();
+
+    /// @brief Transition to failure state.
+    ///
+    /// This method transitions the model to @ref FEED_FAILED_ST and
+    /// sets next event to FEED_FAILED_EVT.
+    ///
+    /// @param error_msg Error message explaining the failure.
+    void feedFailure(const std::string& error_msg);
+
+    /// @brief A method called when state model fails.
+    ///
+    /// @param explanation Error message explaining the reason for failure.
+    virtual void onModelFailure(const std::string& explanation);
+
+    /// @brief Retrieves next byte of data from the buffer.
+    ///
+    /// During normal operation, when there is no more data in the buffer,
+    /// the NEED_MORE_DATA_EVT is set as next event to signal the need for
+    /// calling @ref JSONFeed::postBuffer.
+    ///
+    /// @throw JSONFeedError If current event is already set to
+    /// NEED_MORE_DATA_EVT or MORE_DATA_PROVIDED_EVT. In the former case, it
+    /// indicates that the caller failed to provide new data using
+    /// @ref JSONFeed::postBuffer. The latter case is highly unlikely
+    /// as it indicates that no new data were provided but the state of the
+    /// parser was changed from NEED_MORE_DATA_EVT or the data were provided
+    /// but the data buffer is empty. In both cases, it is a programming
+    /// error.
+    char getNextFromBuffer();
+
+    /// @brief This method is called when invalid event occurred in a particular
+    /// state.
+    ///
+    /// This method simply throws @ref JSONFeedError informing about invalid
+    /// event occurring for the particular state. The error message includes
+    /// the name of the handler in which the exception has been thrown.
+    /// It also includes the event which caused the exception.
+    ///
+    /// @param handler_name Name of the handler in which the exception is
+    /// thrown.
+    /// @param event An event which caused the exception.
+    ///
+    /// @throw JSONFeedError.
+    void invalidEventError(const std::string& handler_name,
+                           const unsigned int event);
+
+    /// @brief Tries to read next byte from buffer.
+    ///
+    /// @param [out] next A reference to the variable where read data should be
+    /// stored.
+    ///
+    /// @return true if character was successfully read, false otherwise.
+    bool popNextFromBuffer(char& next);
+
+    /// @name State handlers.
+    ///
+    //@{
+
+    /// @brief Handler for RECEIVE_START_ST.
+    void receiveStartHandler();
+
+    /// @brief Handler for WHITESPACE_BEFORE_JSON_ST.
+    void whiteSpaceBeforeJSONHandler();
+
+    /// @brief Handler for EOL_COMMENT_BEFORE_JSON_ST.
+    void eolCommentBeforeJSONHandler();
+
+    /// @brief Handler for START_COMMENT_BEFORE_JSON_ST.
+    void startCommentBeforeJSONHandler();
+
+    /// @brief Handler for C_COMMENT_BEFORE_JSON_ST.
+    void cCommentBeforeJSONHandler();
+
+    /// @brief Handler for STOP_COMMENT_BEFORE_JSON_ST.
+    void stopCommentBeforeJSONHandler();
+
+    /// @brief Handler for the FIRST_BRACE_ST.
+    void innerJSONHandler();
+
+    /// @brief Handler for the STRING_JSON_ST.
+    void stringJSONHandler();
+
+    /// @brief Handler for the ESCAPE_JSON_ST;
+    void escapeJSONHandler();
+
+    /// @brief Handler for EOL_COMMENT_ST.
+    void eolCommentHandler();
+
+    /// @brief Handler for START_COMMENT_ST.
+    void startCommentHandler();
+
+    /// @brief Handler for C_COMMENT_ST.
+    void cCommentHandler();
+
+    /// @brief Handler for STOP_COMMENT_ST.
+    void stopCommentHandler();
+
+    /// @brief Handler for the JSON_END_ST.
+    void endJSONHandler();
+
+    //@}
+
+    /// @brief Internal buffer from which the feed reads data.
+    std::vector<char> buffer_;
+
+    /// @brief Holds pointer to the next byte in the buffer to be read.
+    size_t data_ptr_;
+
+    /// @brief Error message set by @ref onModelFailure.
+    std::string error_message_;
+
+    /// @brief A counter increased when '{' or '[' is found and decreased when
+    /// '}' or ']' is found in the stream.
+    uint64_t open_scopes_;
+
+    /// @brief Holds processed data.
+    std::string output_;
+};
+
+} // end of namespace config
+} // end of namespace isc
+
+#endif // JSON_FEED_H
diff --git a/src/lib/cc/server_tag.cc b/src/lib/cc/server_tag.cc
new file mode 100644
index 0000000..80e5184
--- /dev/null
+++ b/src/lib/cc/server_tag.cc
@@ -0,0 +1,53 @@
+// Copyright (C) 2019-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/server_tag.h>
+#include <exceptions/exceptions.h>
+#include <util/strutil.h>
+#include <boost/algorithm/string.hpp>
+
+namespace isc {
+namespace data {
+
+std::string ServerTag::ALL = "all";
+
+ServerTag::ServerTag()
+    : tag_(ALL) {
+}
+
+ServerTag::ServerTag(const std::string& tag)
+    : tag_(util::str::trim(tag)) {
+    if (tag_.empty()) {
+        isc_throw(BadValue, "server-tag must not be empty");
+
+    } else if (tag_.length() > 256) {
+        isc_throw(BadValue, "server-tag must not be longer than 256 characters");
+    }
+
+    boost::algorithm::to_lower(tag_);
+
+    // ANY has a defined meaning for server selector and must not be used as
+    // a server tag.
+    if (tag_ == "any") {
+        isc_throw(BadValue, "'any' is reserved and must not be used as a server-tag");
+    }
+}
+
+bool
+ServerTag::amAll() const {
+    return (tag_ == ALL);
+}
+
+std::ostream&
+operator<<(std::ostream& os, const ServerTag& server_tag) {
+    os << server_tag.get();
+    return (os);
+}
+
+} // end of namespace isc::data
+} // end of namespace isc
diff --git a/src/lib/cc/server_tag.h b/src/lib/cc/server_tag.h
new file mode 100644
index 0000000..6f80015
--- /dev/null
+++ b/src/lib/cc/server_tag.h
@@ -0,0 +1,82 @@
+// Copyright (C) 2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef SERVER_TAG_H
+#define SERVER_TAG_H
+
+#include <string>
+
+namespace isc {
+namespace data {
+
+/// @brief Represents a server tag.
+///
+/// The server tag is a label identifying a server or all servers which
+/// configuration is stored in the database. The label "all" is reserved
+/// and it means "all servers". A configuration object in the database
+/// associated with this server tag belongs to all servers. The server
+/// tag must not be empty, must not be longer than 256 characters
+/// (excluding leading and terminating whitespaces, which are trimmed)
+/// and must not be set to "any" which has a special meaning for the
+/// server selector.
+class ServerTag {
+public:
+
+    /// @brief Server tag for all servers as text.
+    static std::string ALL;
+
+    /// @brief Default constructor.
+    ///
+    /// Creates server tag for all servers.
+    ServerTag();
+
+    /// @brief Constructor.
+    ///
+    /// @param tag server tag provided as string. The tag is converted to
+    /// lower case.
+    explicit ServerTag(const std::string& tag);
+
+    /// @brief Checks if the server tag is set to "all servers".
+    ///
+    /// @return true if the server tag is set to all servers, false
+    /// otherwise.
+    bool amAll() const;
+
+    /// @brief Returns server tag as string.
+    ///
+    /// @return lower case server tag.
+    std::string get() const {
+        return (tag_);
+    }
+
+    /// @brief Overload of the less operator for using @c ServerTag in sets.
+    ///
+    /// @param other other server tag to compare to.
+    /// @return true if this server tag is less than the other server tag.
+    bool operator<(const ServerTag& other) const {
+        return (tag_ < other.tag_);
+    }
+
+private:
+
+    /// @brief Holds server tag as string.
+    std::string tag_;
+};
+
+/// @brief Insert the @c ServerTag as a string into stream.
+///
+/// @param os stream to insert server tag into.
+/// @param server_tag server tag to be converted to text and
+/// inserted into a stream.
+/// @return Reference to the stream object with inserted server
+/// tag.
+std::ostream&
+operator<<(std::ostream& os, const ServerTag& server_tag);
+
+} // end of namespace isc::data
+} // end of namespace isc
+
+#endif // SERVER_TAG_H
diff --git a/src/lib/cc/simple_parser.cc b/src/lib/cc/simple_parser.cc
new file mode 100644
index 0000000..8140d13
--- /dev/null
+++ b/src/lib/cc/simple_parser.cc
@@ -0,0 +1,369 @@
+// Copyright (C) 2016-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/simple_parser.h>
+#include <asiolink/io_address.h>
+#include <boost/foreach.hpp>
+#include <boost/lexical_cast.hpp>
+#include <cc/data.h>
+#include <string>
+
+using namespace std;
+using namespace isc::asiolink;
+using namespace isc::dhcp;
+using isc::dhcp::DhcpConfigError;
+
+namespace isc {
+namespace data {
+
+void
+SimpleParser::checkRequired(const SimpleRequiredKeywords& required,
+                            ConstElementPtr scope) {
+    for (auto name : required) {
+        if (scope->contains(name)) {
+            continue;
+        }
+        isc_throw(DhcpConfigError, "missing '" << name << "' parameter");
+    }
+}
+
+void
+SimpleParser::checkKeywords(const SimpleKeywords& keywords,
+                            ConstElementPtr scope) {
+    string spurious;
+    for (auto entry : scope->mapValue()) {
+        if (keywords.count(entry.first) == 0) {
+            if (spurious.empty()) {
+                spurious = entry.first;
+            }
+            continue;
+        }
+        Element::types expected = keywords.at(entry.first);
+        if ((expected == Element::any) ||
+            (entry.second->getType() == expected)) {
+            continue;
+        }
+        isc_throw(DhcpConfigError, "'" << entry.first << "' parameter is not "
+                  << (expected == Element::integer ? "an " : "a ")
+                  << Element::typeToName(expected));
+    }
+    if (!spurious.empty()) {
+        isc_throw(DhcpConfigError, "spurious '" << spurious << "' parameter");
+    }
+}
+
+std::string
+SimpleParser::getString(ConstElementPtr scope, const std::string& name) {
+    ConstElementPtr x = scope->get(name);
+    if (!x) {
+        isc_throw(DhcpConfigError,
+                  "missing parameter '" << name << "' ("
+                  << scope->getPosition() << ")");
+    }
+    if (x->getType() != Element::string) {
+        isc_throw(DhcpConfigError,
+                  "invalid type specified for parameter '" << name
+                  << "' (" << x->getPosition() << ")");
+    }
+
+    return (x->stringValue());
+}
+
+int64_t
+SimpleParser::getInteger(ConstElementPtr scope, const std::string& name) {
+    ConstElementPtr x = scope->get(name);
+    if (!x) {
+        isc_throw(DhcpConfigError,
+                  "missing parameter '" << name << "' ("
+                  << scope->getPosition() << ")");
+    }
+    if (x->getType() != Element::integer) {
+        isc_throw(DhcpConfigError,
+                  "invalid type specified for parameter '" << name
+                  << "' (" << x->getPosition() << ")");
+    }
+
+    return (x->intValue());
+}
+
+int64_t
+SimpleParser::getInteger(isc::data::ConstElementPtr scope, const std::string& name,
+                         int64_t min, int64_t max) {
+    int64_t tmp = getInteger(scope, name);
+    if (tmp < min || tmp > max) {
+        isc_throw(OutOfRange,
+                  "The '" << name << "' value (" << tmp
+                  << ") is not within expected range: (" << min << " - " << max
+                  << ")");
+    }
+
+    return (tmp);
+}
+
+bool
+SimpleParser::getBoolean(ConstElementPtr scope, const std::string& name) {
+    ConstElementPtr x = scope->get(name);
+    if (!x) {
+        isc_throw(DhcpConfigError,
+                  "missing parameter '" << name << "' ("
+                  << scope->getPosition() << ")");
+    }
+    if (x->getType() != Element::boolean) {
+        isc_throw(DhcpConfigError,
+                  "invalid type specified for parameter '" << name
+                  << "' (" << x->getPosition() << ")");
+    }
+
+    return (x->boolValue());
+}
+
+IOAddress
+SimpleParser::getAddress(const ConstElementPtr& scope,
+                         const std::string& name) {
+    std::string str = getString(scope, name);
+    try {
+        return (IOAddress(str));
+    } catch (const std::exception& e) {
+        isc_throw(DhcpConfigError, "Failed to convert '" << str
+                  << "' to address: " << e.what() << "("
+                  << getPosition(name, scope) << ")");
+    }
+}
+
+double
+SimpleParser::getDouble(const ConstElementPtr& scope,
+                        const std::string& name) {
+    ConstElementPtr x = scope->get(name);
+    if (!x) {
+        isc_throw(DhcpConfigError,
+                  "missing parameter '" << name << "' ("
+                  << scope->getPosition() << ")");
+    }
+
+    if (x->getType() != Element::real) {
+        isc_throw(DhcpConfigError,
+                  "invalid type specified for parameter '" << name
+                  << "' (" << x->getPosition() << ")");
+    }
+
+    return (x->doubleValue());
+}
+
+
+const data::Element::Position&
+SimpleParser::getPosition(const std::string& name, const data::ConstElementPtr parent) {
+    if (!parent) {
+        return (data::Element::ZERO_POSITION());
+    }
+    ConstElementPtr elem = parent->get(name);
+    if (!elem) {
+        return (parent->getPosition());
+    }
+
+    return (elem->getPosition());
+}
+
+size_t SimpleParser::setDefaults(ElementPtr scope,
+                                 const SimpleDefaults& default_values) {
+    size_t cnt = 0;
+
+    // This is the position representing a default value. As the values
+    // we're inserting here are not present in whatever the config file
+    // came from, we need to make sure it's clearly labeled as default.
+    const Element::Position pos("<default-value>", 0, 0);
+
+    // Let's go over all parameters we have defaults for.
+    BOOST_FOREACH(SimpleDefault def_value, default_values) {
+
+        // Try if such a parameter is there. If it is, let's
+        // skip it, because user knows best *cough*.
+        ConstElementPtr x = scope->get(string(def_value.name_));
+        if (x) {
+            // There is such a value already, skip it.
+            continue;
+        }
+
+        // There isn't such a value defined, let's create the default
+        // value...
+        switch (def_value.type_) {
+        case Element::string: {
+            x.reset(new StringElement(def_value.value_, pos));
+            break;
+        }
+        case Element::integer: {
+            try {
+                int int_value = boost::lexical_cast<int>(def_value.value_);
+                x.reset(new IntElement(int_value, pos));
+            }
+            catch (const std::exception& ex) {
+                isc_throw(BadValue, "Internal error. Integer value expected for: "
+                                    << def_value.name_ << ", value is: "
+                                    << def_value.value_ );
+            }
+
+            break;
+        }
+        case Element::boolean: {
+            bool bool_value;
+            if (def_value.value_ == string("true")) {
+                bool_value = true;
+            } else if (def_value.value_ == string("false")) {
+                bool_value = false;
+            } else {
+                isc_throw(DhcpConfigError,
+                          "Internal error. Boolean value specified as "
+                          << def_value.value_ << ", expected true or false");
+            }
+            x.reset(new BoolElement(bool_value, pos));
+            break;
+        }
+        case Element::real: {
+            double dbl_value = boost::lexical_cast<double>(def_value.value_);
+            x.reset(new DoubleElement(dbl_value, pos));
+            break;
+        }
+        default:
+            // No default values for null, list or map
+            isc_throw(DhcpConfigError,
+                      "Internal error. Incorrect default value type.");
+        }
+
+        // ... and insert it into the provided Element tree.
+        scope->set(def_value.name_, x);
+        ++cnt;
+    }
+
+    return (cnt);
+}
+
+size_t
+SimpleParser::setListDefaults(ConstElementPtr list,
+                              const SimpleDefaults& default_values) {
+    size_t cnt = 0;
+    BOOST_FOREACH(ElementPtr entry, list->listValue()) {
+        cnt += setDefaults(entry, default_values);
+    }
+    return (cnt);
+}
+
+size_t
+SimpleParser::deriveParams(ConstElementPtr parent,
+                           ElementPtr child,
+                           const ParamsList& params) {
+    if ( (parent->getType() != Element::map) ||
+         (child->getType() != Element::map)) {
+        return (0);
+    }
+
+    size_t cnt = 0;
+    BOOST_FOREACH(string param, params) {
+        ConstElementPtr x = parent->get(param);
+        if (!x) {
+            // Parent doesn't define this parameter, so there's
+            // nothing to derive from
+            continue;
+        }
+
+        if (child->get(param)) {
+            // Child defines this parameter already. There's
+            // nothing to do here.
+            continue;
+        }
+
+        // Copy the parameters to the child scope.
+        child->set(param, x);
+        cnt++;
+    }
+
+    return (cnt);
+}
+
+const util::Triplet<uint32_t>
+SimpleParser::parseIntTriplet(const ConstElementPtr& scope,
+                              const std::string& name) {
+    // Initialize as some compilers complain otherwise.
+    uint32_t value = 0;
+    bool has_value = false;
+    uint32_t min_value = 0;
+    bool has_min = false;
+    uint32_t max_value = 0;
+    bool has_max = false;
+    if (scope->contains(name)) {
+        value = getInteger(scope, name);
+        has_value = true;
+    }
+    if (scope->contains("min-" + name)) {
+        min_value = getInteger(scope, "min-" + name);
+        has_min = true;
+    }
+    if (scope->contains("max-" + name)) {
+        max_value = getInteger(scope, "max-" + name);
+        has_max = true;
+    }
+    if (!has_value && !has_min && !has_max) {
+        return (util::Triplet<uint32_t>());
+    }
+    if (has_value) {
+        if (!has_min && !has_max) {
+            // default only.
+            min_value = value;
+            max_value = value;
+        } else if (!has_min) {
+            // default and max.
+            min_value = value;
+        } else if (!has_max) {
+            // default and min.
+            max_value = value;
+        }
+    } else if (has_min) {
+        // min only.
+        if (!has_max) {
+            value = min_value;
+            max_value = min_value;
+        } else {
+            // min and max.
+            isc_throw(DhcpConfigError, "have min-" << name << " and max-"
+                      << name << " but no " << name << " (default) in "
+                      << scope->getPosition());
+        }
+    } else {
+        // max only.
+        min_value = max_value;
+        value = max_value;
+    }
+    // Check that min <= max.
+    if (min_value > max_value) {
+        if (has_min && has_max) {
+            isc_throw(DhcpConfigError, "the value of min-" << name << " ("
+                      << min_value << ") is not less than max-" << name << " ("
+                      << max_value << ")");
+        } else if (has_min) {
+            // Only min and default so min > default.
+            isc_throw(DhcpConfigError, "the value of min-" << name << " ("
+                      << min_value << ") is not less than (default) " << name
+                      << " (" << value << ")");
+        } else {
+            // Only default and max so default > max.
+            isc_throw(DhcpConfigError, "the value of (default) " << name
+                      << " (" << value << ") is not less than max-" << name
+                      << " (" << max_value << ")");
+        }
+    }
+    // Check that value is between min and max.
+    if ((value < min_value) || (value > max_value)) {
+        isc_throw(DhcpConfigError, "the value of (default) " << name << " ("
+                  << value << ") is not between min-" << name << " ("
+                  << min_value << ") and max-" << name << " ("
+                  << max_value << ")");
+    }
+
+    return (util::Triplet<uint32_t>(min_value, value, max_value));
+}
+
+} // end of isc::dhcp namespace
+} // end of isc namespace
diff --git a/src/lib/cc/simple_parser.h b/src/lib/cc/simple_parser.h
new file mode 100644
index 0000000..cb78802
--- /dev/null
+++ b/src/lib/cc/simple_parser.h
@@ -0,0 +1,339 @@
+// Copyright (C) 2016-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef SIMPLE_PARSER_H
+#define SIMPLE_PARSER_H
+
+#include <asiolink/io_address.h>
+#include <cc/data.h>
+#include <cc/dhcp_config_error.h>
+#include <util/triplet.h>
+#include <map>
+#include <vector>
+#include <string>
+#include <stdint.h>
+#include <limits>
+
+namespace isc {
+namespace data {
+
+/// This array defines a single entry of default values.
+struct SimpleDefault {
+    SimpleDefault(const char* name, isc::data::Element::types type, const char* value)
+        :name_(name), type_(type), value_(value) {}
+    std::string name_;
+    const isc::data::Element::types type_;
+    const char* value_;
+};
+
+/// This specifies all required keywords.
+typedef std::vector<std::string> SimpleRequiredKeywords;
+
+/// This specifies all accepted keywords with their types.
+typedef std::map<std::string, isc::data::Element::types> SimpleKeywords;
+
+/// This specifies all default values in a given scope (e.g. a subnet).
+typedef std::vector<SimpleDefault> SimpleDefaults;
+
+/// This defines a list of all parameters that are derived (or inherited) between
+/// contexts.
+typedef std::vector<std::string> ParamsList;
+
+
+/// @brief A simple parser
+///
+/// This class is intended to be a simpler replacement for DhcpConfigParser.
+/// This class has been initially created to facilitate DHCPv4 and
+/// DHCPv6 servers' configuration parsing. Thus examples provided
+/// herein are related to DHCP configuration. Nevertheless, this is a
+/// generic class to be used in other modules too.
+///
+/// The simplification comes from several factors:
+/// - no build/commit nonsense. There's a single step:
+///   CfgStorage parse(ConstElementPtr json)
+///   that converts JSON configuration into an object and returns it.
+/// - no state kept. This greatly simplifies the parsers (no contexts, no child
+///   parsers list, no separate storage for uint32, strings etc. In fact,
+///   this base class is purely static. However, some derived classes may store
+///   some state. Implementors are advised to store as little state as possible.
+/// - no optional parameters (all are mandatory). This simplifies the parser,
+///   but introduces a new step before parsing where we insert the default
+///   values into client configuration before parsing. This is actually a good
+///   thing, because we now have a clear picture of the default parameters as
+///   they're defined in a single place (the DhcpConfigParser had the defaults
+///   spread out in multiple files in multiple directories).
+class SimpleParser {
+public:
+
+    /// @brief Checks that all required keywords are present.
+    ///
+    /// This method throws an exception when a required
+    /// entry is not present in the given scope.
+    ///
+    /// @param required Required keywords.
+    /// @param scope Specified parameters which are checked.
+    /// @throw DhcpConfigError if a required parameter is not present.
+    static void checkRequired(const SimpleRequiredKeywords& required,
+                              isc::data::ConstElementPtr scope);
+
+    /// @brief Checks acceptable keywords with their expected type.
+    ///
+    /// This methods throws an exception when a not acceptable keyword
+    /// is found or when an acceptable entry does not have the expected type.
+    ///
+    /// @param keywords The @c SimpleKeywords keywords and types map.
+    /// @param scope Specified parameters which are checked.
+    /// @throw DhcpConfigError if a not acceptable keyword is found.
+    /// @throw DhcpConfigError if an acceptable entry does not have
+    /// the expected type.
+    static void checkKeywords(const SimpleKeywords& keywords,
+                              isc::data::ConstElementPtr scope);
+
+    /// @brief Derives (inherits) parameters from parent scope to a child
+    ///
+    /// This method derives parameters from the parent scope to the child,
+    /// if there are no values specified in the child scope. For example,
+    /// this method can be used to derive timers from global scope (e.g. for
+    /// the whole DHCPv6 server) to a subnet scope. This method checks
+    /// if the child scope doesn't have more specific values defined. If
+    /// it doesn't, then the value from parent scope is copied over.
+    ///
+    /// @param parent scope to copy from (e.g. global)
+    /// @param child scope to copy from (e.g. subnet)
+    /// @param params names of the parameters to copy
+    /// @return number of parameters copied
+    static size_t deriveParams(isc::data::ConstElementPtr parent,
+                               isc::data::ElementPtr child,
+                               const ParamsList& params);
+
+    /// @brief Sets the default values
+    ///
+    /// This method sets the default values for parameters that are not
+    /// defined. The list of default values is specified by default_values.
+    /// If not present, those will be inserted into the scope. If
+    /// a parameter is already present, the default value will not
+    /// be inserted.
+    ///
+    /// @param scope default values will be inserted here
+    /// @param default_values list of default values
+    /// @return number of parameters inserted
+    static size_t setDefaults(isc::data::ElementPtr scope,
+                              const SimpleDefaults& default_values);
+
+    /// @brief Sets the default values for all entries in a list
+    ///
+    /// This is a simple utility method that iterates over all
+    /// parameters in a list and calls setDefaults for each
+    /// entry.
+    ///
+    /// @param list list to be iterated over
+    /// @param default_values list of default values
+    /// @return number of parameters inserted
+    static size_t setListDefaults(isc::data::ConstElementPtr list,
+                                  const SimpleDefaults& default_values);
+
+    /// @brief Utility method that returns position of an element
+    ///
+    /// It's mostly useful for logging. If the element is missing
+    /// the parent position is returned or ZERO_POSITION if parent
+    /// is null.
+    ///
+    /// @param name position of that element will be returned
+    /// @param parent parent element (optional)
+    /// @return position of the element specified.
+    static const data::Element::Position&
+    getPosition(const std::string& name, const data::ConstElementPtr parent);
+
+    /// @brief Returns a string parameter from a scope
+    ///
+    /// Unconditionally returns a parameter.
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return a string value of the parameter
+    /// @throw DhcpConfigError if the parameter is not there or is not of
+    /// appropriate type
+    static std::string getString(isc::data::ConstElementPtr scope,
+                                 const std::string& name);
+
+    /// @brief Returns an integer parameter from a scope
+    ///
+    /// Unconditionally returns a parameter.
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return an integer value of the parameter
+    /// @throw DhcpConfigError if the parameter is not there or is not of
+    /// appropriate type
+    static int64_t getInteger(isc::data::ConstElementPtr scope,
+                              const std::string& name);
+
+    /// @brief Returns an integer parameter from a scope and checks its range
+    ///
+    /// Unconditionally returns a parameter. Checks that the value specified
+    /// is in min =< X =< max range.
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @param min minimum allowed value
+    /// @param max maximum allowed value
+    /// @return an integer value of the parameter
+    /// @throw DhcpConfigError if the parameter is not there or is not of
+    /// appropriate type.
+    /// @throw OutOfRange if the parameter is out of range
+    static int64_t getInteger(isc::data::ConstElementPtr scope,
+                              const std::string& name,
+                              int64_t min, int64_t max);
+
+    /// @brief Returns a boolean parameter from a scope
+    ///
+    /// Unconditionally returns a parameter.
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return a boolean value of the parameter
+    /// @throw DhcpConfigError if the parameter is not there or is not of
+    /// appropriate type
+    static bool getBoolean(isc::data::ConstElementPtr scope,
+                           const std::string& name);
+
+
+    /// @brief Returns a IOAddress parameter from a scope
+    ///
+    /// Unconditionally returns a parameter.
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return an IOAddress representing the value of the parameter
+    /// @throw DhcpConfigError if the parameter is not there or is not of
+    /// appropriate type (or its conversion to IOAddress fails due to not
+    /// being a proper address).
+    static isc::asiolink::IOAddress
+    getAddress(const ConstElementPtr& scope, const std::string& name);
+
+    /// @brief Returns a floating point parameter from a scope
+    ///
+    /// Unconditionally returns a parameter.
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return a double value of the parameter
+    /// @throw DhcpConfigError if the parameter is not there or is not
+    /// an Element::real
+    static double getDouble(const ConstElementPtr& scope,
+                            const std::string& name);
+
+protected:
+
+    /// @brief Returns an integer value with range checking from a scope
+    ///
+    /// This template should be instantiated in parsers when useful
+    ///
+    /// @tparam int_type the integer type e.g. uint32_t
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter for error report
+    /// @return a value of int_type
+    /// @throw DhcpConfigError if the parameter is not there, is not of
+    /// appropriate type or is out of type value range
+    template <typename int_type> int_type
+    getIntType(isc::data::ConstElementPtr scope,
+               const std::string& name) {
+        int64_t val_int = getInteger(scope, name);
+        if ((val_int < std::numeric_limits<int_type>::min()) ||
+            (val_int > std::numeric_limits<int_type>::max())) {
+          isc_throw(isc::dhcp::DhcpConfigError,
+                    "out of range value (" << val_int
+                    << ") specified for parameter '" << name
+                    << "' (" << getPosition(name, scope) << ")");
+        }
+        return (static_cast<int_type>(val_int));
+    }
+
+    /// @brief Returns a converted value from a scope
+    ///
+    /// This template should be instantiated in parsers when useful
+    ///
+    /// @tparam target_type the type of the result
+    /// @tparam convert the conversion function std::string -> target_type
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter for error report
+    /// @param type_name name of target_type for error report
+    /// @return a converted value of target_type
+    /// @throw DhcpConfigError if the parameter is not there, is not of
+    /// appropriate type or can not be converted
+    template <typename target_type,
+              target_type convert(const std::string&)> target_type
+    getAndConvert(isc::data::ConstElementPtr scope,
+                  const std::string& name,
+                  const std::string& type_name) {
+        std::string str = getString(scope, name);
+        try {
+            return (convert(str));
+        } catch (const std::exception&) {
+            isc_throw(isc::dhcp::DhcpConfigError,
+                      "invalid " << type_name << " (" << str
+                      << ") specified for parameter '" << name
+                      << "' (" << getPosition(name, scope) << ")");
+        }
+    }
+
+public:
+    /// @brief Returns a value converted to uint32_t
+    ///
+    /// Instantiation of getIntType() to uint32_t
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return an uint32_t value
+    /// @throw isc::dhcp::DhcpConfigError when it is not an uint32_t
+    uint32_t getUint32(isc::data::ConstElementPtr scope,
+                       const std::string& name) {
+        return (getIntType<uint32_t>(scope, name));
+    }
+
+    /// @brief Returns a value converted to uint16_t
+    ///
+    /// Instantiation of getIntType() to uint16_t
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return an uint16_t value
+    /// @throw isc::dhcp::DhcpConfigError when it is not an uint16_t
+    uint16_t getUint16(isc::data::ConstElementPtr scope,
+                       const std::string& name) {
+        return (getIntType<uint16_t>(scope, name));
+    }
+
+    /// @brief Get an uint8_t value
+    ///
+    /// Instantiation of getIntType() to uint8_t
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter
+    /// @return uint8_t value
+    /// @throw isc::dhcp::DhcpConfigError when it is not an uint8_t
+    uint8_t getUint8(ConstElementPtr scope, const std::string& name) {
+        return (getIntType<uint8_t>(scope, name));
+    }
+
+    /// @brief Parses an integer triplet
+    ///
+    /// Parses an integer triplet parameter of the form:
+    ///
+    ///    min-{name}, {name}, max-{name}
+    ///
+    /// @param scope Data element holding e.g. shared network configuration
+    /// to be parsed.
+    /// @param name Base name of the parameter.
+    /// @return A triplet with the parsed value.
+    const isc::util::Triplet<uint32_t> parseIntTriplet(const data::ConstElementPtr& scope,
+                                                       const std::string& name);
+};
+
+}
+}
+
+#endif
diff --git a/src/lib/cc/stamped_element.cc b/src/lib/cc/stamped_element.cc
new file mode 100644
index 0000000..3c53b38
--- /dev/null
+++ b/src/lib/cc/stamped_element.cc
@@ -0,0 +1,50 @@
+// Copyright (C) 2018-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/stamped_element.h>
+
+namespace isc {
+namespace data {
+
+StampedElement::StampedElement()
+    : BaseStampedElement(), server_tags_() {
+}
+
+bool
+StampedElement::hasServerTag(const ServerTag& server_tag) const {
+    return (server_tags_.count(server_tag) > 0);
+}
+
+void
+StampedElement::delServerTag(const std::string& server_tag) {
+    if (!server_tags_.erase(ServerTag(server_tag))) {
+        isc_throw(NotFound, "can't find server tag '" << server_tag << "' to delete");
+    }
+}
+
+bool
+StampedElement::hasAllServerTag() const {
+    return (hasServerTag(ServerTag(ServerTag::ALL)));
+}
+
+
+ElementPtr
+StampedElement::getMetadata() const {
+    ElementPtr metadata = Element::createMap();
+    ElementPtr tags = Element::createList();
+
+    for (auto server_tag : server_tags_) {
+        tags->add(Element::create(server_tag.get()));
+    }
+
+    metadata->set("server-tags", tags);
+    return (metadata);
+}
+
+} // end of namespace isc::data
+} // end of namespace isc
diff --git a/src/lib/cc/stamped_element.h b/src/lib/cc/stamped_element.h
new file mode 100644
index 0000000..c676826
--- /dev/null
+++ b/src/lib/cc/stamped_element.h
@@ -0,0 +1,91 @@
+// Copyright (C) 2018-2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef STAMPED_ELEMENT_H
+#define STAMPED_ELEMENT_H
+
+#include <cc/base_stamped_element.h>
+#include <cc/server_tag.h>
+#include <set>
+
+namespace isc {
+namespace data {
+
+/// @brief This class represents configuration element which is
+/// associated with database identifier, modification timestamp
+/// and servers.
+///
+/// Classes storing Kea configuration should derive from this object
+/// to track ids and modification times of the configuration objects.
+/// This is specifically required by the Kea Configuration Backend
+/// feature which stores and fetches configuration from the database.
+/// The configuration elements must be accessible by their database
+/// identifiers and modification times.
+///
+/// @note This class is not derived from @c Element and should not
+/// be confused with the classes being derived from @c Element class.
+/// Those classes are used to represent JSON structures, whereas this
+/// class represents data fetched from the database.
+///
+/// @todo Find a better name for @c StampedElement.
+class StampedElement : public BaseStampedElement {
+public:
+
+    /// @brief Constructor.
+    ///
+    /// Sets timestamp to the current time.
+    StampedElement();
+
+    /// @brief Adds new server tag.
+    ///
+    /// @param server_tag new server tag.
+    /// @throw BadValue if the server tag length exceeds 256 characters.
+    void setServerTag(const std::string& server_tag) {
+        server_tags_.insert(ServerTag(server_tag));
+    }
+
+    /// @brief Deletes server tag.
+    ///
+    /// Remove the first occurrence of the given server tag.
+    ///
+    /// @param server_tag server tag to delete.
+    /// @throw NotFound if the server tag cannot be found.
+    void delServerTag(const std::string& server_tag);
+
+    /// @brief Returns server tags.
+    ///
+    /// @return Server tags.
+    std::set<ServerTag> getServerTags() const {
+        return (server_tags_);
+    }
+
+    /// @brief Checks if the element has the given server tag.
+    ///
+    /// @param server_tag Server tag to be found.
+    /// @return true if the server tag was found, false otherwise.
+    bool hasServerTag(const ServerTag& server_tag) const;
+
+    /// @brief Checks if the element has 'all' server tag.
+    ///
+    /// @return true if the server tag was found, false otherwise.
+    bool hasAllServerTag() const;
+
+    /// @brief Returns an object representing metadata to be returned
+    /// with objects from the configuration backend.
+    ///
+    /// @return Pointer to the metadata element.
+    isc::data::ElementPtr getMetadata() const;
+
+private:
+
+    /// @brief Holds server tags.
+    std::set<ServerTag> server_tags_;
+};
+
+} // end of namespace isc::data
+} // end of namespace isc
+
+#endif
diff --git a/src/lib/cc/stamped_value.cc b/src/lib/cc/stamped_value.cc
new file mode 100644
index 0000000..b6554ea
--- /dev/null
+++ b/src/lib/cc/stamped_value.cc
@@ -0,0 +1,193 @@
+// Copyright (C) 2018-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/stamped_value.h>
+#include <exceptions/exceptions.h>
+#include <boost/lexical_cast.hpp>
+
+namespace isc {
+namespace data {
+
+StampedValue::StampedValue(const std::string& name)
+    : StampedElement(), name_(name), value_() {
+}
+
+StampedValue::StampedValue(const std::string& name, const ElementPtr& value)
+    : StampedElement(), name_(name), value_(value) {
+    validateConstruct();
+}
+
+StampedValue::StampedValue(const std::string& name, const std::string& value)
+    : StampedElement(), name_(name), value_(Element::create(value)) {
+    validateConstruct();
+}
+
+StampedValuePtr
+StampedValue::create(const std::string& name) {
+    return (StampedValuePtr(new StampedValue(name)));
+}
+
+StampedValuePtr
+StampedValue::create(const std::string& name, const ElementPtr& value) {
+    return (StampedValuePtr(new StampedValue(name, value)));
+}
+
+StampedValuePtr
+StampedValue::create(const std::string& name, const std::string& value) {
+    return (StampedValuePtr(new StampedValue(name, value)));
+}
+
+StampedValuePtr
+StampedValue::create(const std::string& name, const std::string& value,
+                     Element::types parameter_type) {
+    StampedValuePtr stamped_value;
+
+    try {
+        switch (parameter_type) {
+        case Element::string:
+            stamped_value = StampedValue::create(name, value);
+            break;
+
+        case Element::integer:
+            stamped_value = StampedValue::create(name,
+                Element::create(boost::lexical_cast<int64_t>(value)));
+            break;
+
+        case Element::boolean:
+            // We only allow "1" and "0" as input to this function.
+            if ((value != "0") && (value != "1")) {
+                isc_throw(BadValue, "StampedValue: invalid value " << value
+                          << " specified as boolean. Expected \"0\" or \"1\"");
+            }
+            stamped_value = StampedValue::create(name,
+                Element::create((value == "0") ? false : true));
+            break;
+
+        case Element::real:
+            stamped_value = StampedValue::create(name,
+                Element::create(boost::lexical_cast<double>(value)));
+            break;
+
+        default:
+            // Invalid data type provided as argument.
+            isc_throw(TypeError, "StampedValue: unsupported type '"
+                      << Element::typeToName(parameter_type)
+                      << " of the parameter '" << name);
+        }
+
+    } catch (const boost::bad_lexical_cast& ex) {
+        // Failed to cast the value to a given type.
+        isc_throw(BadValue, "StampedValue: the value of the parameter '"
+                  << Element::typeToName(parameter_type)
+                  << "' can't be converted to "
+                  << Element::typeToName(parameter_type)
+                  << " type");
+    }
+
+    return (stamped_value);
+}
+
+int
+StampedValue::getType() const {
+    if (!value_) {
+        isc_throw(InvalidOperation, "StampedValue: attempt to retrieve the "
+                  "type of the null value for the '" << name_
+                  << "' parameter");
+    }
+
+    return (value_->getType());
+}
+
+std::string
+StampedValue::getValue() const {
+    validateAccess(Element::string);
+
+    try {
+        switch (static_cast<Element::types>(value_->getType())) {
+        case Element::string:
+            return (value_->stringValue());
+        case Element::integer:
+            return (boost::lexical_cast<std::string>(value_->intValue()));
+        case Element::boolean:
+            return (value_->boolValue() ? "1" : "0");
+        case Element::real:
+            {
+                std::string repr =
+                    boost::lexical_cast<std::string>(value_->doubleValue());
+                if (repr.find_first_of('.') == std::string::npos) {
+                    repr += ".0";
+                }
+                return (repr);
+            }
+        default:
+            // Impossible condition.
+            isc_throw(TypeError, "StampedValue: invalid type of the '"
+                      << name_ << "' parameter");
+        }
+
+    } catch (const boost::bad_lexical_cast& ex) {
+        isc_throw(BadValue, "StampedValue: unable to convert the value of "
+                  "the parameter '" << name_ << "' to string");
+    }
+    // unreachable
+    return (value_->stringValue());
+}
+
+int64_t
+StampedValue::getIntegerValue() const {
+    validateAccess(Element::integer);
+    return (value_->intValue());
+}
+
+bool
+StampedValue::getBoolValue() const {
+    validateAccess(Element::boolean);
+    return (value_->boolValue());
+}
+
+double
+StampedValue::getDoubleValue() const {
+    validateAccess(Element::real);
+    return (value_->doubleValue());
+}
+
+void
+StampedValue::validateConstruct() const {
+    if (!value_) {
+        isc_throw(BadValue, "StampedValue: provided value of the '"
+                  << name_ << "' parameter is NULL");
+    }
+
+    if ((value_->getType() != Element::string) &&
+        (value_->getType() != Element::integer) &&
+        (value_->getType() != Element::boolean) &&
+        (value_->getType() != Element::real)) {
+        isc_throw(TypeError, "StampedValue: provided value of the '"
+                  << name_ << "' parameter has invalid type: "
+                  << Element::typeToName(static_cast<Element::types>(value_->getType())));
+    }
+}
+
+void
+StampedValue::validateAccess(Element::types type) const {
+    if (!value_) {
+        isc_throw(InvalidOperation, "StampedValue: attempt to get null value "
+                  "of the '" << name_ << "' parameter");
+    }
+
+    if ((type != Element::string) && (type != value_->getType())) {
+        isc_throw(TypeError, "StampedValue: attempt to access a '"
+                  << name_ << "' parameter as " << Element::typeToName(type)
+                  << ", but this parameter has "
+                  << Element::typeToName(static_cast<Element::types>(value_->getType()))
+                  << " type");
+    }
+}
+
+} // end of namespace isc::data
+} // end of namespace isc
diff --git a/src/lib/cc/stamped_value.h b/src/lib/cc/stamped_value.h
new file mode 100644
index 0000000..2120593
--- /dev/null
+++ b/src/lib/cc/stamped_value.h
@@ -0,0 +1,237 @@
+// Copyright (C) 2018-2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef STAMPED_VALUE_H
+#define STAMPED_VALUE_H
+
+#include <cc/data.h>
+#include <cc/stamped_element.h>
+#include <boost/multi_index/hashed_index.hpp>
+#include <boost/multi_index/mem_fun.hpp>
+#include <boost/multi_index/ordered_index.hpp>
+#include <boost/multi_index_container.hpp>
+#include <boost/shared_ptr.hpp>
+#include <cstdint>
+#include <string>
+
+namespace isc {
+namespace data {
+
+class StampedValue;
+
+/// @brief Pointer to the stamped value.
+typedef boost::shared_ptr<StampedValue> StampedValuePtr;
+
+/// @brief This class represents a named configuration parameter,
+/// e.g. global parameter of the DHCP server.
+///
+/// Global configuration elements having simple types, e.g. DHCP
+/// timers, need to be associatied with modification timestamps.
+/// This association is made by deriving from @c StampedElement.
+/// The values can be strings, integers, booleans or real numbers.
+///
+/// Because the strings are more flexible, configuration elements
+/// are always held as strings in the configuration backends. This
+/// class reflects a single value held in the database. The value
+/// can be return in its orginal type or can be returned as a
+/// string. Also the null values are allowed.
+class StampedValue : public StampedElement {
+public:
+
+    /// @brief Constructor creating a null value.
+    ///
+    /// @param name Name of the value.
+    StampedValue(const std::string& name);
+
+    /// @brief Constructor creating a value from the @c Element.
+    ///
+    /// @param name Name of the value.
+    /// @param value Value encapsulated in the @c Element object.
+    ///
+    /// @throw BadValue if the value is null.
+    /// @throw TypeError if the value is neither a string, integer,
+    /// bool nor real.
+    StampedValue(const std::string& name, const ElementPtr& value);
+
+    /// @brief Constructor creating a string value.
+    ///
+    /// Creates stamped value from a string.
+    ///
+    /// @param name Name of the value.
+    /// @param value Value to be set.
+    StampedValue(const std::string& name, const std::string& value);
+
+    /// @brief Factory function creating a null value.
+    ///
+    /// @param name Name of the value.
+    static StampedValuePtr create(const std::string& name);
+
+    /// @brief Factory function creating a value from the @c Element.
+    ///
+    /// @param name Name of the value.
+    /// @param value Value encapsulated in the @c Element object.
+    ///
+    /// @throw BadValue if the value is null.
+    /// @throw TypeError if the value is neither a string, integer,
+    /// bool nor real.
+    static StampedValuePtr create(const std::string& name,
+                                  const ElementPtr& value);
+
+    /// @brief Factory function creating a string value.
+    ///
+    /// Creates stamped value from a string.
+    ///
+    /// @param name Name of the value.
+    /// @param value Value to be set.
+    static StampedValuePtr create(const std::string& name,
+                                  const std::string& value);
+
+    /// @brief Factory function which attempts to convert provided
+    /// string value to a given type.
+    ///
+    /// This factory function is useful in cases when the value is
+    /// read as a string from a database. The string value has to
+    /// be converted to the appropriate data type. The type is also
+    /// known from the database.
+    ///
+    /// @param name Name of the value.
+    /// @param value Value given as string to be converted.
+    /// @param type Type of the value to convert to.
+    static StampedValuePtr create(const std::string& name,
+                                  const std::string& value,
+                                  Element::types type);
+
+    /// @brief Returns a type of the value.
+    ///
+    /// @return Type of the value as integer. It can be compared
+    /// with the @c Element::getType() output.
+    /// @throw InvalidOperation if the value is null.
+    int getType() const;
+
+    /// @brief Returns value name.
+    ///
+    /// @return Value name.
+    std::string getName() const {
+        return (name_);
+    }
+
+    /// @brief Returns value as string.
+    ///
+    /// It is allowed to call this function for all supported data
+    /// types. They are converted to a string. For example, a real
+    /// number of 1.4 will be returned as "1.4". The boolean true
+    /// value will be returned as "1" etc.
+    ///
+    /// @return Stored value as string.
+    /// @throw InvalidOperation if the value is null.
+    std::string getValue() const;
+
+    /// @brief Checks if the value is null.
+    ///
+    /// @return true if the value is null, false otherwise.
+    bool amNull() const {
+        return (!value_);
+    }
+
+    /// @brief Returns value as signed integer.
+    ///
+    /// @return Stored value as a signed integer.
+    /// @throw TypeError if the value is not of @c Element::integer
+    /// type.
+    int64_t getIntegerValue() const;
+
+    /// @brief Returns value as a boolean.
+    ///
+    /// @return Stored value as a boolean.
+    /// @throw TypeError if the value is not of @c Element::boolean
+    /// type.
+    bool getBoolValue() const;
+
+    /// @brief Returns value as a real number.
+    ///
+    /// @return Stored value as a real number.
+    /// @throw TypeError if the value is not of @c Element::real
+    /// type.
+    double getDoubleValue() const;
+
+    /// @brief Returns the value as @c Element.
+    ConstElementPtr getElementValue() const {
+        return (value_);
+    }
+
+private:
+
+    /// @brief Checks if the values passed to the constructors
+    /// were correct.
+    ///
+    /// This is called from the constructors.
+    ///
+    /// @throw BadValue if the value is null.
+    /// @throw TypeError if the value type is neither a string,
+    /// integer, boolean nor real.
+    void validateConstruct() const;
+
+    /// @brief Checks if the value is accessed correctly.
+    ///
+    /// This is called from the accessors of this class.
+    ///
+    /// @param type Type of the value expected by the accessor
+    /// function.
+    ///
+    /// @throw InvalidOperation if the accessed value is null.
+    /// @throw TypeError if the expected type is not a string
+    /// and it doesn't match the value type.
+    void validateAccess(Element::types type) const;
+
+    /// @brief Name of the value.
+    std::string name_;
+
+    /// @brief Stored value.
+    ElementPtr value_;
+};
+
+/// @name Definition of the multi index container for @c StampedValue.
+///
+//@{
+
+/// @brief Tag for the index for access by value name.
+struct StampedValueNameIndexTag { };
+
+/// @brief Tag for the index for access by modification time.
+struct StampedValueModificationTimeIndexTag { };
+
+/// @brief Multi index container for @c StampedValue.
+typedef boost::multi_index_container<
+    StampedValuePtr,
+    boost::multi_index::indexed_by<
+        // Index used to access value by name.
+        boost::multi_index::hashed_non_unique<
+            boost::multi_index::tag<StampedValueNameIndexTag>,
+            boost::multi_index::const_mem_fun<
+                StampedValue,
+                std::string,
+                &StampedValue::getName
+            >
+        >,
+
+        // Index used to access value by modification time.
+        boost::multi_index::ordered_non_unique<
+            boost::multi_index::tag<StampedValueModificationTimeIndexTag>,
+            boost::multi_index::const_mem_fun<
+                BaseStampedElement,
+                boost::posix_time::ptime,
+                &BaseStampedElement::getModificationTime
+            >
+        >
+    >
+> StampedValueCollection;
+
+//@}
+
+} // end of namespace isc::data
+} // end of namespace isc
+
+#endif
diff --git a/src/lib/cc/tests/Makefile.am b/src/lib/cc/tests/Makefile.am
new file mode 100644
index 0000000..2abfb8c
--- /dev/null
+++ b/src/lib/cc/tests/Makefile.am
@@ -0,0 +1,41 @@
+AM_CPPFLAGS = -I$(top_builddir)/src/lib -I$(top_srcdir)/src/lib
+AM_CPPFLAGS += $(BOOST_INCLUDES)
+AM_CXXFLAGS = $(KEA_CXXFLAGS)
+
+if USE_STATIC_LINK
+AM_LDFLAGS = -static
+endif
+
+CLEANFILES = *.gcno *.gcda
+
+TESTS_ENVIRONMENT = \
+	$(LIBTOOL) --mode=execute $(VALGRIND_COMMAND)
+
+TESTS =
+if HAVE_GTEST
+TESTS += run_unittests
+run_unittests_SOURCES = command_interpreter_unittests.cc
+run_unittests_SOURCES += data_unittests.cc
+run_unittests_SOURCES += data_file_unittests.cc
+run_unittests_SOURCES += element_value_unittests.cc
+run_unittests_SOURCES += json_feed_unittests.cc
+run_unittests_SOURCES += server_tag_unittest.cc
+run_unittests_SOURCES += simple_parser_unittest.cc
+run_unittests_SOURCES += stamped_element_unittest.cc
+run_unittests_SOURCES += stamped_value_unittest.cc
+run_unittests_SOURCES += user_context_unittests.cc
+run_unittests_SOURCES += run_unittests.cc
+run_unittests_CPPFLAGS = $(AM_CPPFLAGS) $(GTEST_INCLUDES)
+run_unittests_LDFLAGS = $(AM_LDFLAGS) $(GTEST_LDFLAGS)
+
+run_unittests_LDADD =  $(top_builddir)/src/lib/cc/libkea-cc.la
+run_unittests_LDADD += $(top_builddir)/src/lib/asiolink/libkea-asiolink.la
+run_unittests_LDADD += $(top_builddir)/src/lib/log/libkea-log.la
+run_unittests_LDADD += $(top_builddir)/src/lib/util/unittests/libutil_unittests.la
+run_unittests_LDADD += $(top_builddir)/src/lib/util/libkea-util.la
+run_unittests_LDADD += $(top_builddir)/src/lib/exceptions/libkea-exceptions.la
+run_unittests_LDADD += $(LOG4CPLUS_LIBS) $(BOOST_LIBS) $(GTEST_LDADD)
+
+endif
+
+noinst_PROGRAMS = $(TESTS)
diff --git a/src/lib/cc/tests/Makefile.in b/src/lib/cc/tests/Makefile.in
new file mode 100644
index 0000000..07458a7
--- /dev/null
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+	      dashes="$$skipped"; \
+	  fi; \
+	  report=""; \
+	  if test "$$failed" -ne 0 && test -n "$(PACKAGE_BUGREPORT)"; then \
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+	  echo "$${col}$$dashes$${std}"; \
+	  test "$$failed" -eq 0; \
+	else :; fi
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+distdir-am: $(DISTFILES)
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+.PRECIOUS: Makefile
+
+
+# Tell versions [3.59,3.63) of GNU make to not export all variables.
+# Otherwise a system limit (for SysV at least) may be exceeded.
+.NOEXPORT:
diff --git a/src/lib/cc/tests/command_interpreter_unittests.cc b/src/lib/cc/tests/command_interpreter_unittests.cc
new file mode 100644
index 0000000..12b3eab
--- /dev/null
+++ b/src/lib/cc/tests/command_interpreter_unittests.cc
@@ -0,0 +1,240 @@
+// Copyright (C) 2009-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <gtest/gtest.h>
+
+#include <cc/command_interpreter.h>
+#include <config/tests/data_def_unittests_config.h>
+#include <log/logger_name.h>
+
+#include <boost/scoped_ptr.hpp>
+
+#include <fstream>
+
+using namespace isc::data;
+using namespace isc::config;
+using namespace std;
+
+namespace {
+
+
+/// @brief Convenience method for creating elements from JSON string
+///
+/// @param str string to be converted
+/// @return Element structure
+ElementPtr
+el(const std::string& str) {
+    return (Element::fromJSON(str));
+}
+
+// This test verifies that that createAnswer method is able to generate
+// various answers.
+TEST(CommandInterpreterTest, createAnswer) {
+    ConstElementPtr answer;
+
+    // By default the answer is a successful one.
+    answer = createAnswer();
+    EXPECT_EQ("{ \"result\": 0 }", answer->str());
+
+    // Let's check if we can generate an error.
+    answer = createAnswer(1, "error");
+    EXPECT_EQ("{ \"result\": 1, \"text\": \"error\" }", answer->str());
+
+    // This is expected to throw. When status code is non-zero (indicating error),
+    // textual explanation is mandatory.
+    EXPECT_THROW(createAnswer(1, ElementPtr()), CtrlChannelError);
+    EXPECT_THROW(createAnswer(1, Element::create(1)), CtrlChannelError);
+
+    // Let's check if answer can be generate with some data in it.
+    ConstElementPtr arg = el("[ \"just\", \"some\", \"data\" ]");
+    answer = createAnswer(0, arg);
+    EXPECT_EQ("{ \"arguments\": [ \"just\", \"some\", \"data\" ], \"result\": 0 }",
+              answer->str());
+}
+
+// This test checks whether parseAnswer is able to handle good and malformed
+// answers.
+TEST(CommandInterpreterTest, parseAnswer) {
+    ConstElementPtr answer;
+    ConstElementPtr arg;
+    int rcode;
+
+    EXPECT_THROW(parseAnswer(rcode, ElementPtr()), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("1")), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("[]")), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("{  }")), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("{ \"something\": 1 }")), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("{ \"result\": [ 0 ] }")), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("{ \"result\": [ 1 ] }")), CtrlChannelError);
+    EXPECT_THROW(parseAnswer(rcode, el("{ \"result\": [ 1, 1 ] }")), CtrlChannelError);
+
+    answer = el("{ \"result\": 0 }");
+    arg = parseAnswer(rcode, answer);
+    EXPECT_EQ(0, rcode);
+    EXPECT_TRUE(isNull(arg));
+
+    answer = el("{ \"result\": 1, \"text\": \"error\" }");
+    arg = parseAnswer(rcode, answer);
+    EXPECT_EQ(1, rcode);
+    EXPECT_EQ("error", arg->stringValue());
+
+    answer = el("{ \"result\": 0, \"arguments\": [ \"just\", \"some\", \"data\" ] }");
+    arg = parseAnswer(rcode, answer);
+    EXPECT_EQ(0, rcode);
+    EXPECT_EQ("[ \"just\", \"some\", \"data\" ]", arg->str());
+}
+
+// This checks whether we can convert an answer to easily printable form.
+TEST(CommandInterpreterTest, answerToText) {
+    ConstElementPtr answer;
+
+    // Doing jolly good here.
+    answer = el("{ \"result\": 0 }");
+    EXPECT_EQ("success(0)", answerToText(answer));
+
+    // Sometimes things don't go according to plan.
+    answer = el("{ \"result\": 1, \"text\": \"ho lee fuk sum ting wong\" }");
+    EXPECT_EQ("failure(1), text=ho lee fuk sum ting wong", answerToText(answer));
+}
+
+// This test checks whether createCommand function is able to create commands
+// with and without parameters.
+TEST(CommandInterpreterTest, createCommand) {
+    ConstElementPtr command;
+    ConstElementPtr arg;
+    string service;
+
+    command = createCommand("my_command");
+    ASSERT_EQ("{ \"command\": \"my_command\" }", command->str());
+
+    arg = el("1");
+    command = createCommand("my_command", arg);
+    ASSERT_EQ("{ \"arguments\": 1, \"command\": \"my_command\" }",
+              command->str());
+
+    arg = el("[ \"a\", \"b\" ]");
+    command = createCommand("my_cmd", arg);
+    ASSERT_EQ("{ \"arguments\": [ \"a\", \"b\" ], \"command\": \"my_cmd\" }",
+              command->str());
+
+    arg = el("{ \"a\": \"map\" }");
+    command = createCommand("foo", arg);
+    ASSERT_EQ("{ \"arguments\": { \"a\": \"map\" }, \"command\": \"foo\" }",
+              command->str());
+
+    command = createCommand("my_command", "my_service");
+    ASSERT_EQ("{ \"command\": \"my_command\", "
+              "\"service\": [ \"my_service\" ] }",
+              command->str());
+
+    arg = el("1");
+    command = createCommand("my_command", arg, "my_service");
+    ASSERT_EQ("{ \"arguments\": 1, \"command\": \"my_command\", "
+              "\"service\": [ \"my_service\" ] }",
+              command->str());
+
+    arg = el("[ \"a\", \"b\" ]");
+    command = createCommand("my_cmd", arg, "my_server");
+    ASSERT_EQ("{ \"arguments\": [ \"a\", \"b\" ], "
+              "\"command\": \"my_cmd\", "
+              "\"service\": [ \"my_server\" ] }",
+              command->str());
+
+    arg = el("{ \"a\": \"map\" }");
+    command = createCommand("foo", arg, "bar");
+    ASSERT_EQ("{ \"arguments\": { \"a\": \"map\" }, "
+              "\"command\": \"foo\", "
+              "\"service\": [ \"bar\" ] }",
+              command->str());
+}
+
+// This test checks whether parseCommand function is able to parse various valid
+// and malformed commands.
+TEST(CommandInterpreterTest, parseCommand) {
+    ConstElementPtr arg;
+    std::string cmd;
+
+    // should throw
+    EXPECT_THROW(parseCommand(arg, ElementPtr()), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("1")), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("{  }")), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("{ \"not a command\": 1 }")), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("{ \"command\": 1 }")), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("{ \"command\": [] }")), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("{ \"command\": [ 1 ] }")), CtrlChannelError);
+    EXPECT_THROW(parseCommand(arg, el("{ \"command\": \"my_command\", "
+                                      "\"unknown\": \"xyz\" }")), CtrlChannelError);
+
+    cmd = parseCommand(arg, el("{ \"command\": \"my_command\" }"));
+    EXPECT_EQ("my_command", cmd);
+    EXPECT_FALSE(arg);
+
+    // Include "service" to verify that it is not rejected.
+    cmd = parseCommand(arg, el("{ \"command\": \"my_command\", \"arguments\": 1, "
+                               "  \"service\": [ \"dhcp4\" ] }"));
+    ASSERT_TRUE(arg);
+    EXPECT_EQ("my_command", cmd);
+    EXPECT_EQ("1", arg->str());
+
+    parseCommand(arg, el("{ \"command\": \"my_command\", \"arguments\": "
+                         "[ \"some\", \"argument\", \"list\" ] }"));
+    EXPECT_EQ("my_command", cmd);
+    ASSERT_TRUE(arg);
+    EXPECT_EQ("[ \"some\", \"argument\", \"list\" ]", arg->str());
+
+}
+
+// This test checks whether parseCommandWithArgs function is able to parse
+// various valid and malformed commands.
+TEST(CommandInterpreterTest, parseCommandWithArgs) {
+    ConstElementPtr arg;
+    std::string cmd;
+
+    // Arguments are required.
+    EXPECT_THROW(parseCommandWithArgs(arg, el("{ \"command\": \"my_command\" }")),
+                 CtrlChannelError);
+
+    // Arguments must be a map.
+    EXPECT_THROW(parseCommandWithArgs(arg, el("{ \"command\": \"my_command\", "
+                                              "\"arguments\": [ 1, 2, 3 ] }")),
+                 CtrlChannelError);
+
+    // Arguments must not be empty.
+    EXPECT_THROW(parseCommandWithArgs(arg, el("{ \"command\": \"my_command\", "
+                                              "\"arguments\": { } }")),
+                 CtrlChannelError);
+
+    // Command with unsupported parameter is rejected.
+    EXPECT_THROW(parseCommandWithArgs(arg, el("{ \"command\": \"my_command\", "
+                                              "  \"arguments\": { \"arg1\": \"value1\" }, "
+                                              "  \"unsupported\": 1 }")),
+                 CtrlChannelError);
+
+
+    // Specifying arguments in non empty map should be successful.
+    EXPECT_NO_THROW(
+        cmd = parseCommandWithArgs(arg, el("{ \"command\": \"my_command\", "
+                                           "  \"arguments\": { \"arg1\": \"value1\" } }"))
+    );
+    ASSERT_TRUE(arg);
+    ASSERT_EQ(Element::map, arg->getType());
+    auto arg1 = arg->get("arg1");
+    ASSERT_TRUE(arg1);
+    ASSERT_EQ(Element::string, arg1->getType());
+    EXPECT_EQ("value1", arg1->stringValue());
+    EXPECT_EQ("my_command", cmd);
+
+    // The "service" parameter should be allowed.
+    EXPECT_NO_THROW(parseCommandWithArgs(arg, el("{ \"command\": \"my_command\", "
+                                                 "  \"service\": [ \"dhcp4\" ], "
+                                                 "  \"arguments\": { \"arg1\": \"value1\" } }"))
+    );
+
+}
+
+}
diff --git a/src/lib/cc/tests/data_file_unittests.cc b/src/lib/cc/tests/data_file_unittests.cc
new file mode 100644
index 0000000..a7f1b8d
--- /dev/null
+++ b/src/lib/cc/tests/data_file_unittests.cc
@@ -0,0 +1,98 @@
+// Copyright (C) 2014-2018 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <exceptions/exceptions.h>
+#include <gtest/gtest.h>
+#include <cc/data.h>
+#include <fstream>
+
+using namespace isc;
+using namespace isc::data;
+
+namespace {
+
+/// @brief Test class for testing Daemon class
+class DataFileTest : public ::testing::Test {
+public:
+
+    /// @brief writes specified text to a file
+    ///
+    /// That is an auxiliary function used in fileRead() tests.
+    ///
+    /// @param content text to be written to disk
+    void writeFile(const std::string& content) {
+        // Write sample content to disk
+        static_cast<void>(remove(TEMP_FILE));
+        std::ofstream write_me(TEMP_FILE);
+        EXPECT_TRUE(write_me.is_open());
+        write_me << content;
+        write_me.close();
+    }
+
+    /// destructor
+    ~DataFileTest() {
+        static_cast<void>(remove(TEMP_FILE));
+    }
+
+    /// Name of the temporary file
+    static const char* TEMP_FILE;
+};
+
+/// Temporary file name used in some tests
+const char* DataFileTest::TEMP_FILE="temp-file.json";
+
+// Test checks whether a text file can be read from disk.
+TEST_F(DataFileTest, readFileMultiline) {
+
+    const char* no_endline = "{ \"abc\": 123 }";
+    const char* with_endline = "{\n \"abc\":\n 123\n }\n";
+
+    // That's what we expect
+    ElementPtr exp = Element::fromJSON(no_endline);
+
+    // Write sample content to disk
+    writeFile(no_endline);
+
+    // Check that the read content is correct
+    EXPECT_TRUE(exp->equals(*Element::fromJSONFile(TEMP_FILE)));
+
+    // Write sample content to disk
+    writeFile(with_endline);
+
+    // Check that the read content is correct
+    EXPECT_TRUE(exp->equals(*Element::fromJSONFile(TEMP_FILE)));
+}
+
+// Test checks whether comments in file are ignored as expected.
+TEST_F(DataFileTest, readFileComments) {
+    const char* commented_content = "# This is a comment\n"
+        "{ \"abc\":\n"
+        "# a comment comment\n"
+        "1 }\n";
+
+    // That's what we expect
+    ElementPtr exp = Element::fromJSON("{ \"abc\": 1 }");
+
+    // Write sample content to disk
+    writeFile(commented_content);
+
+    // Check that the read will fail (without comment elimination)
+    EXPECT_THROW(Element::fromJSONFile(TEMP_FILE), JSONError);
+
+    // Check that the read content is correct (with comment elimination)
+    EXPECT_NO_THROW(Element::fromJSONFile(TEMP_FILE, true));
+    EXPECT_TRUE(exp->equals(*Element::fromJSONFile(TEMP_FILE, true)));
+}
+
+// This test checks that missing file will generate an exception.
+TEST_F(DataFileTest, readFileError) {
+
+    // Check that the read content is correct
+    EXPECT_THROW(Element::fromJSONFile("no-such-file.txt"), isc::InvalidOperation);
+}
+
+};
diff --git a/src/lib/cc/tests/data_unittests.cc b/src/lib/cc/tests/data_unittests.cc
new file mode 100644
index 0000000..5aed9a4
--- /dev/null
+++ b/src/lib/cc/tests/data_unittests.cc
@@ -0,0 +1,2230 @@
+// Copyright (C) 2009-2022 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <gtest/gtest.h>
+#include <boost/foreach.hpp>
+#include <boost/pointer_cast.hpp>
+#include <boost/assign/std/vector.hpp>
+#include <climits>
+
+#include <cc/data.h>
+#include <util/unittests/check_valgrind.h>
+
+using namespace isc::data;
+
+#include <sstream>
+#include <iostream>
+using std::oct;
+#include <iomanip>
+using std::setfill;
+using std::setw;
+using std::string;
+
+namespace {
+
+TEST(Position, str) {
+    Element::Position position("kea.conf", 30, 20);
+    EXPECT_EQ("kea.conf:30:20", position.str());
+
+    Element::Position position2("another.conf", 123, 24);
+    EXPECT_EQ("another.conf:123:24", position2.str());
+}
+
+TEST(Element, type) {
+    // this tests checks whether the getType() function returns the
+    // correct type
+    IntElement int_el = IntElement(1);
+    EXPECT_EQ(int_el.getType(), Element::integer);
+    DoubleElement double_el = DoubleElement(1.0);
+    EXPECT_EQ(double_el.getType(), Element::real);
+    BoolElement bool_el = BoolElement(true);
+    EXPECT_EQ(bool_el.getType(), Element::boolean);
+    StringElement str_el = StringElement("foo");
+    EXPECT_EQ(str_el.getType(), Element::string);
+    ListElement list_el = ListElement();
+    EXPECT_EQ(list_el.getType(), Element::list);
+    MapElement map_el = MapElement();
+    EXPECT_EQ(map_el.getType(), Element::map);
+
+}
+
+TEST(Element, TypeNameConversion) {
+    EXPECT_EQ(Element::integer, Element::nameToType("integer"));
+    EXPECT_EQ(Element::real, Element::nameToType("real"));
+    EXPECT_EQ(Element::boolean, Element::nameToType("boolean"));
+    EXPECT_EQ(Element::string, Element::nameToType("string"));
+    EXPECT_EQ(Element::list, Element::nameToType("list"));
+    EXPECT_EQ(Element::map, Element::nameToType("map"));
+    EXPECT_EQ(Element::null, Element::nameToType("null"));
+    EXPECT_EQ(Element::any, Element::nameToType("any"));
+    EXPECT_THROW(Element::nameToType("somethingunknown"), TypeError);
+
+    EXPECT_EQ("integer", Element::typeToName(Element::integer));
+    EXPECT_EQ("real", Element::typeToName(Element::real));
+    EXPECT_EQ("boolean", Element::typeToName(Element::boolean));
+    EXPECT_EQ("string", Element::typeToName(Element::string));
+    EXPECT_EQ("list", Element::typeToName(Element::list));
+    EXPECT_EQ("map", Element::typeToName(Element::map));
+    EXPECT_EQ("null", Element::typeToName(Element::null));
+    EXPECT_EQ("any", Element::typeToName(Element::any));
+    EXPECT_EQ("unknown", Element::typeToName((Element::types)123));
+}
+
+TEST(Element, from_and_to_json) {
+    // a set of inputs that are the same when converted to json and
+    // back to a string (tests for inputs that have equivalent, but
+    // different string representations when converted back are below)
+    ConstElementPtr el;
+    std::vector<std::string> sv;
+
+    sv.push_back("12");
+    sv.push_back("1.1");
+    sv.push_back("true");
+    sv.push_back("false");
+    sv.push_back("\"asdf\"");
+    sv.push_back("null");
+    sv.push_back("[ 1, 2, 3, 4 ]");
+    sv.push_back("{ \"name\": \"foo\", \"value\": 56176 }");
+    sv.push_back("[ { \"a\": 1, \"b\": \"c\" }, { \"a\": 2, \"b\": \"d\" } ]");
+    sv.push_back("8.23");
+    sv.push_back("123.456");
+    sv.push_back("null");
+    sv.push_back("-1");
+    sv.push_back("-1.234");
+    sv.push_back("-123.456");
+    // We should confirm that our string handling is 8-bit clean.
+    // At one point we were using char-length data and comparing to EOF,
+    // which means that character '\xFF' would not parse properly.
+    sv.push_back("\"\\u00ff\"");
+
+    BOOST_FOREACH(const std::string& s, sv) {
+        // Test two types of fromJSON(): with string and istream.
+        for (unsigned i = 0; i < 2; ++i) {
+            // test << operator, which uses Element::str()
+            if (i == 0) {
+                el = Element::fromJSON(s);
+            } else {
+                std::istringstream iss(s);
+                el = Element::fromJSON(iss);
+            }
+            std::ostringstream stream;
+            stream << *el;
+            EXPECT_EQ(s, stream.str());
+
+            // test toWire(ostream), which should also be the same now
+            std::ostringstream wire_stream;
+            el->toWire(wire_stream);
+            EXPECT_EQ(s, wire_stream.str());
+        }
+    }
+
+    // some parse errors
+    try {
+        Element::fromJSON("{1}");
+    } catch (const isc::data::JSONError& pe) {
+        std::string s = std::string(pe.what());
+        EXPECT_EQ("String expected in <string>:1:3", s);
+    }
+
+    sv.clear();
+    sv.push_back("{1}");
+    //ElementPtr ep = Element::fromJSON("\"aaa\nbbb\"err");
+    //std::cout << ep << std::endl;
+    sv.push_back("\n\nTrue");
+    sv.push_back("\n\ntru");
+    sv.push_back("{ \n \"aaa\nbbb\"err:");
+    sv.push_back("{ \t\n \"aaa\nbbb\"\t\n\n:\n true, \"\\\"");
+    sv.push_back("{ \"a\": None}");
+    sv.push_back("");
+    sv.push_back("NULL");
+    sv.push_back("nul");
+    sv.push_back("hello\"foobar\"");
+    sv.push_back("\"foobar\"hello");
+    sv.push_back("[]hello");
+    sv.push_back("{}hello");
+    // String not delimited correctly
+    sv.push_back("\"hello");
+    sv.push_back("hello\"");
+    // Bad unicode
+    sv.push_back("\"\\u123\"");
+    sv.push_back("\"\\u1234\"");
+    sv.push_back("\"\\u0123\"");
+    sv.push_back("\"\\u00ag\"");
+    sv.push_back("\"\\u00BH\"");
+
+    BOOST_FOREACH(std::string s, sv) {
+        EXPECT_THROW(el = Element::fromJSON(s), isc::data::JSONError);
+    }
+
+    // some json specific format tests, here the str() output is
+    // different from the string input
+    // +100 is incorrect according to the ECMA 404 JSON standard.
+    // Keeping it as it will be reversed.
+    // EXPECT_EQ("100", Element::fromJSON("+100")->str());
+    EXPECT_EQ("100.0", Element::fromJSON("1e2")->str());
+    EXPECT_EQ("100.0", Element::fromJSON("+1e2")->str());
+    EXPECT_EQ("-100.0", Element::fromJSON("-1e2")->str());
+
+    EXPECT_NO_THROW({
+       EXPECT_EQ("9223372036854775807", Element::fromJSON("9223372036854775807")->str());
+    });
+    EXPECT_NO_THROW({
+       EXPECT_EQ("-9223372036854775808", Element::fromJSON("-9223372036854775808")->str());
+    });
+    EXPECT_THROW({
+       EXPECT_NE("9223372036854775808", Element::fromJSON("9223372036854775808")->str());
+    }, JSONError);
+
+    EXPECT_EQ("0.01", Element::fromJSON("1e-2")->str());
+    EXPECT_EQ("0.01", Element::fromJSON(".01")->str());
+    EXPECT_EQ("-0.01", Element::fromJSON("-1e-2")->str());
+    EXPECT_EQ("1.2", Element::fromJSON("1.2")->str());
+    EXPECT_EQ("1.0", Element::fromJSON("1.0")->str());
+    EXPECT_EQ("120.0", Element::fromJSON("1.2e2")->str());
+    EXPECT_EQ("100.0", Element::fromJSON("1.0e2")->str());
+    EXPECT_EQ("100.0", Element::fromJSON("1.0E2")->str());
+    EXPECT_EQ("0.01", Element::fromJSON("1.0e-2")->str());
+    EXPECT_EQ("0.012", Element::fromJSON("1.2e-2")->str());
+    EXPECT_EQ("0.012", Element::fromJSON("1.2E-2")->str());
+    EXPECT_EQ("\"\"", Element::fromJSON("  \n \t \r \f \b \"\" \n \f \t \r \b")->str());
+    EXPECT_EQ("{  }", Element::fromJSON("{  \n  \r \t  \b \f }")->str());
+    EXPECT_EQ("[  ]", Element::fromJSON("[  \n  \r \f \t  \b  ]")->str());
+
+    // number overflows
+    EXPECT_THROW(Element::fromJSON("12345678901234567890")->str(), JSONError);
+    EXPECT_THROW(Element::fromJSON("1.1e12345678901234567890")->str(), JSONError);
+    EXPECT_THROW(Element::fromJSON("-1.1e12345678901234567890")->str(), JSONError);
+    EXPECT_THROW(Element::fromJSON("1e12345678901234567890")->str(), JSONError);
+    EXPECT_THROW(Element::fromJSON("1e50000")->str(), JSONError);
+    // number underflow
+    // EXPECT_THROW(Element::fromJSON("1.1e-12345678901234567890")->str(), JSONError);
+
+}
+
+template <typename T>
+void
+testGetValueInt() {
+    T el;
+    int64_t i;
+    int32_t i32;
+    uint32_t ui32;
+    long l;
+    long long ll;
+    double d;
+    bool b;
+    std::string s;
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+
+    el = Element::create(1);
+    EXPECT_NO_THROW({
+       EXPECT_EQ(1, el->intValue());
+    });
+    EXPECT_THROW(el->doubleValue(), TypeError);
+    EXPECT_THROW(el->boolValue(), TypeError);
+    EXPECT_THROW(el->stringValue(), TypeError);
+    EXPECT_THROW(el->listValue(), TypeError);
+    EXPECT_THROW(el->mapValue(), TypeError);
+    EXPECT_TRUE(el->getValue(i));
+    EXPECT_FALSE(el->getValue(d));
+    EXPECT_FALSE(el->getValue(b));
+    EXPECT_FALSE(el->getValue(s));
+    EXPECT_FALSE(el->getValue(v));
+    EXPECT_FALSE(el->getValue(m));
+    EXPECT_EQ(1, i);
+
+    el = Element::create(9223372036854775807LL);
+    EXPECT_NO_THROW({
+       EXPECT_EQ(9223372036854775807LL, el->intValue());
+    });
+    EXPECT_TRUE(el->getValue(i));
+    EXPECT_EQ(9223372036854775807LL, i);
+
+    ll = 9223372036854775807LL;
+    el = Element::create(ll);
+    EXPECT_NO_THROW({
+       EXPECT_EQ(ll, el->intValue());
+    });
+    EXPECT_TRUE(el->getValue(i));
+    EXPECT_EQ(ll, i);
+
+    i32 = 2147483647L;
+    el = Element::create(i32);
+    EXPECT_NO_THROW({
+       EXPECT_EQ(i32, el->intValue());
+    });
+    EXPECT_TRUE(el->getValue(i));
+    EXPECT_EQ(i32, i);
+
+    ui32 = 4294967295L;
+    el = Element::create(ui32);
+    EXPECT_NO_THROW({
+       EXPECT_EQ(ui32, el->intValue());
+    });
+    EXPECT_TRUE(el->getValue(i));
+    EXPECT_EQ(ui32, i);
+
+    l = 2147483647L;
+    el = Element::create(l);
+    EXPECT_NO_THROW({
+       EXPECT_EQ(l, el->intValue());
+    });
+    EXPECT_TRUE(el->getValue(i));
+    EXPECT_EQ(l, i);
+}
+
+template <typename T>
+void
+testGetValueDouble() {
+    T el;
+    int64_t i;
+    double d;
+    bool b;
+    std::string s;
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+
+    el = Element::create(1.1);
+    EXPECT_THROW(el->intValue(), TypeError);
+    EXPECT_NO_THROW(el->doubleValue());
+    EXPECT_THROW(el->boolValue(), TypeError);
+    EXPECT_THROW(el->stringValue(), TypeError);
+    EXPECT_THROW(el->listValue(), TypeError);
+    EXPECT_THROW(el->mapValue(), TypeError);
+    EXPECT_FALSE(el->getValue(i));
+    EXPECT_TRUE(el->getValue(d));
+    EXPECT_FALSE(el->getValue(b));
+    EXPECT_FALSE(el->getValue(s));
+    EXPECT_FALSE(el->getValue(v));
+    EXPECT_FALSE(el->getValue(m));
+    EXPECT_EQ(1.1, d);
+}
+
+template <typename T>
+void
+testGetValueBool() {
+    T el;
+    int64_t i;
+    double d;
+    bool b;
+    std::string s;
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+
+    el = Element::create(true);
+    EXPECT_THROW(el->intValue(), TypeError);
+    EXPECT_THROW(el->doubleValue(), TypeError);
+    EXPECT_NO_THROW(el->boolValue());
+    EXPECT_THROW(el->stringValue(), TypeError);
+    EXPECT_THROW(el->listValue(), TypeError);
+    EXPECT_THROW(el->mapValue(), TypeError);
+    EXPECT_FALSE(el->getValue(i));
+    EXPECT_FALSE(el->getValue(d));
+    EXPECT_TRUE(el->getValue(b));
+    EXPECT_FALSE(el->getValue(s));
+    EXPECT_FALSE(el->getValue(v));
+    EXPECT_FALSE(el->getValue(m));
+    EXPECT_EQ(true, b);
+}
+
+template <typename T>
+void
+testGetValueString() {
+    T el;
+    int64_t i;
+    double d;
+    bool b;
+    std::string s;
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+
+    el = Element::create("foo");
+    EXPECT_THROW(el->intValue(), TypeError);
+    EXPECT_THROW(el->doubleValue(), TypeError);
+    EXPECT_THROW(el->boolValue(), TypeError);
+    EXPECT_NO_THROW(el->stringValue());
+    EXPECT_THROW(el->listValue(), TypeError);
+    EXPECT_THROW(el->mapValue(), TypeError);
+    EXPECT_FALSE(el->getValue(i));
+    EXPECT_FALSE(el->getValue(d));
+    EXPECT_FALSE(el->getValue(b));
+    EXPECT_TRUE(el->getValue(s));
+    EXPECT_FALSE(el->getValue(v));
+    EXPECT_FALSE(el->getValue(m));
+    EXPECT_EQ("foo", s);
+}
+
+template <typename T>
+void
+testGetValueList() {
+    T el;
+    int64_t i;
+    double d;
+    bool b;
+    std::string s;
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+
+    el = Element::createList();
+    EXPECT_THROW(el->intValue(), TypeError);
+    EXPECT_THROW(el->doubleValue(), TypeError);
+    EXPECT_THROW(el->boolValue(), TypeError);
+    EXPECT_THROW(el->stringValue(), TypeError);
+    EXPECT_NO_THROW(el->listValue());
+    EXPECT_THROW(el->mapValue(), TypeError);
+    EXPECT_FALSE(el->getValue(i));
+    EXPECT_FALSE(el->getValue(d));
+    EXPECT_FALSE(el->getValue(b));
+    EXPECT_FALSE(el->getValue(s));
+    EXPECT_TRUE(el->getValue(v));
+    EXPECT_FALSE(el->getValue(m));
+    EXPECT_EQ("[  ]", el->str());
+}
+
+template <typename T>
+void
+testGetValueMap() {
+    T el;
+    int64_t i;
+    double d;
+    bool b;
+    std::string s;
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+
+    el = Element::createMap();
+    EXPECT_THROW(el->intValue(), TypeError);
+    EXPECT_THROW(el->doubleValue(), TypeError);
+    EXPECT_THROW(el->boolValue(), TypeError);
+    EXPECT_THROW(el->stringValue(), TypeError);
+    EXPECT_THROW(el->listValue(), TypeError);
+    EXPECT_NO_THROW(el->mapValue());
+    EXPECT_FALSE(el->getValue(i));
+    EXPECT_FALSE(el->getValue(d));
+    EXPECT_FALSE(el->getValue(b));
+    EXPECT_FALSE(el->getValue(s));
+    EXPECT_FALSE(el->getValue(v));
+    EXPECT_TRUE(el->getValue(m));
+    EXPECT_EQ("{  }", el->str());
+}
+
+TEST(Element, create_and_value_throws) {
+    // this test checks whether elements throw exceptions if the
+    // incorrect type is requested
+    ElementPtr el;
+    ConstElementPtr cel;
+    int64_t i = 0;
+    double d = 0.0;
+    bool b = false;
+    std::string s("asdf");
+    std::vector<ElementPtr> v;
+    std::map<std::string, ConstElementPtr> m;
+    ConstElementPtr tmp;
+
+    testGetValueInt<ElementPtr>();
+    testGetValueInt<ConstElementPtr>();
+
+    el = Element::create(1);
+    i = 2;
+    EXPECT_TRUE(el->setValue(i));
+    EXPECT_EQ(2, el->intValue());
+    EXPECT_FALSE(el->setValue(d));
+    EXPECT_FALSE(el->setValue(b));
+    EXPECT_FALSE(el->setValue(s));
+    EXPECT_FALSE(el->setValue(v));
+    EXPECT_FALSE(el->setValue(m));
+    EXPECT_THROW(el->get(1), TypeError);
+    EXPECT_THROW(el->set(1, el), TypeError);
+    EXPECT_THROW(el->add(el), TypeError);
+    EXPECT_THROW(el->remove(1), TypeError);
+    EXPECT_THROW(el->size(), TypeError);
+    EXPECT_THROW(el->empty(), TypeError);
+    EXPECT_THROW(el->get("foo"), TypeError);
+    EXPECT_THROW(el->set("foo", el), TypeError);
+    EXPECT_THROW(el->remove("foo"), TypeError);
+    EXPECT_THROW(el->contains("foo"), TypeError);
+    EXPECT_FALSE(el->find("foo", tmp));
+
+    testGetValueDouble<ElementPtr>();
+    testGetValueDouble<ConstElementPtr>();
+
+    el = Element::create(1.1);
+    d = 2.2;
+    EXPECT_TRUE(el->setValue(d));
+    EXPECT_EQ(2.2, el->doubleValue());
+    EXPECT_FALSE(el->setValue(i));
+    EXPECT_FALSE(el->setValue(b));
+    EXPECT_FALSE(el->setValue(s));
+    EXPECT_FALSE(el->setValue(v));
+    EXPECT_FALSE(el->setValue(m));
+    EXPECT_THROW(el->get(1), TypeError);
+    EXPECT_THROW(el->set(1, el), TypeError);
+    EXPECT_THROW(el->add(el), TypeError);
+    EXPECT_THROW(el->remove(1), TypeError);
+    EXPECT_THROW(el->size(), TypeError);
+    EXPECT_THROW(el->empty(), TypeError);
+    EXPECT_THROW(el->get("foo"), TypeError);
+    EXPECT_THROW(el->set("foo", el), TypeError);
+    EXPECT_THROW(el->remove("foo"), TypeError);
+    EXPECT_THROW(el->contains("foo"), TypeError);
+    EXPECT_FALSE(el->find("foo", tmp));
+
+    testGetValueBool<ElementPtr>();
+    testGetValueBool<ConstElementPtr>();
+
+    el = Element::create(true);
+    b = false;
+    EXPECT_TRUE(el->setValue(b));
+    EXPECT_FALSE(el->boolValue());
+    EXPECT_FALSE(el->setValue(i));
+    EXPECT_FALSE(el->setValue(d));
+    EXPECT_FALSE(el->setValue(s));
+    EXPECT_FALSE(el->setValue(v));
+    EXPECT_FALSE(el->setValue(m));
+    EXPECT_THROW(el->get(1), TypeError);
+    EXPECT_THROW(el->set(1, el), TypeError);
+    EXPECT_THROW(el->add(el), TypeError);
+    EXPECT_THROW(el->remove(1), TypeError);
+    EXPECT_THROW(el->size(), TypeError);
+    EXPECT_THROW(el->empty(), TypeError);
+    EXPECT_THROW(el->get("foo"), TypeError);
+    EXPECT_THROW(el->set("foo", el), TypeError);
+    EXPECT_THROW(el->remove("foo"), TypeError);
+    EXPECT_THROW(el->contains("foo"), TypeError);
+    EXPECT_FALSE(el->find("foo", tmp));
+
+    testGetValueString<ElementPtr>();
+    testGetValueString<ConstElementPtr>();
+
+    el = Element::create("foo");
+    s = "bar";
+    EXPECT_TRUE(el->setValue(s));
+    EXPECT_EQ("bar", el->stringValue());
+    EXPECT_FALSE(el->setValue(i));
+    EXPECT_FALSE(el->setValue(b));
+    EXPECT_FALSE(el->setValue(d));
+    EXPECT_FALSE(el->setValue(v));
+    EXPECT_FALSE(el->setValue(m));
+    EXPECT_THROW(el->get(1), TypeError);
+    EXPECT_THROW(el->set(1, el), TypeError);
+    EXPECT_THROW(el->add(el), TypeError);
+    EXPECT_THROW(el->remove(1), TypeError);
+    EXPECT_THROW(el->size(), TypeError);
+    EXPECT_THROW(el->empty(), TypeError);
+    EXPECT_THROW(el->get("foo"), TypeError);
+    EXPECT_THROW(el->set("foo", el), TypeError);
+    EXPECT_THROW(el->remove("foo"), TypeError);
+    EXPECT_THROW(el->contains("foo"), TypeError);
+    EXPECT_FALSE(el->find("foo", tmp));
+
+    testGetValueList<ElementPtr>();
+    testGetValueList<ConstElementPtr>();
+
+    el = Element::createList();
+    EXPECT_TRUE(el->empty());
+    v.push_back(Element::create(1));
+    EXPECT_TRUE(el->setValue(v));
+    EXPECT_FALSE(el->empty());
+    EXPECT_EQ("[ 1 ]", el->str());
+
+    testGetValueMap<ElementPtr>();
+    testGetValueMap<ConstElementPtr>();
+
+    el = Element::createMap();
+    EXPECT_NO_THROW(el->set("foo", Element::create("bar")));
+    EXPECT_EQ("{ \"foo\": \"bar\" }", el->str());
+}
+
+// Helper for escape check; it puts the given string in a StringElement,
+// then checks for the following conditions:
+// stringValue() must be same as input
+// toJSON() output must be escaped
+// fromJSON() on the previous output must result in original input
+void
+escapeHelper(const std::string& input, const std::string& expected) {
+    StringElement str_element = StringElement(input);
+    EXPECT_EQ(input, str_element.stringValue());
+    std::stringstream os;
+    str_element.toJSON(os);
+    EXPECT_EQ(expected, os.str());
+    ElementPtr str_element2 = Element::fromJSON(os.str());
+    EXPECT_EQ(str_element.stringValue(), str_element2->stringValue());
+}
+
+TEST(Element, escape) {
+    // Test whether quotes are escaped correctly when creating direct
+    // String elements.
+    escapeHelper("foo\"bar", "\"foo\\\"bar\"");
+    escapeHelper("foo\\bar", "\"foo\\\\bar\"");
+    escapeHelper("foo\bbar", "\"foo\\bbar\"");
+    escapeHelper("foo\fbar", "\"foo\\fbar\"");
+    escapeHelper("foo\nbar", "\"foo\\nbar\"");
+    escapeHelper("foo\rbar", "\"foo\\rbar\"");
+    escapeHelper("foo\tbar", "\"foo\\tbar\"");
+    escapeHelper("foo\u001fbar", "\"foo\\u001fbar\"");
+    // Bad escapes
+    EXPECT_THROW(Element::fromJSON("\\a"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\"), JSONError);
+    // Can't have escaped quotes outside strings
+    EXPECT_THROW(Element::fromJSON("\\\"\\\""), JSONError);
+    // Unicode use lower u and 4 hexa, only 00 prefix is supported
+    EXPECT_THROW(Element::fromJSON("\\U0020"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u002"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u0123"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u1023"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u00ag"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u00ga"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u00BH"), JSONError);
+    EXPECT_THROW(Element::fromJSON("\\u00HB"), JSONError);
+    // Inside strings is OK
+    EXPECT_NO_THROW(Element::fromJSON("\"\\\"\\\"\""));
+    // A whitespace test
+    EXPECT_NO_THROW(Element::fromJSON("\"  \n  \r \t \f  \n \n    \t\""));
+    // Escape for forward slash is optional
+    ASSERT_NO_THROW(Element::fromJSON("\"foo\\/bar\""));
+    EXPECT_EQ("foo/bar", Element::fromJSON("\"foo\\/bar\"")->stringValue());
+    // Control characters
+    StringElement bell("foo\abar");
+    EXPECT_EQ("\"foo\\u0007bar\"", bell.str());
+    // 8 bit escape
+    StringElement ab("foo\253bar");
+    EXPECT_EQ("\"foo\\u00abbar\"", ab.str());
+    ASSERT_NO_THROW(Element::fromJSON("\"foo\\u00abbar\""));
+    EXPECT_TRUE(ab.equals(*Element::fromJSON("\"foo\\u00abbar\"")));
+    ASSERT_NO_THROW(Element::fromJSON("\"foo\\u00ABbar\""));
+    EXPECT_TRUE(ab.equals(*Element::fromJSON("\"foo\\u00ABbar\"")));
+    StringElement f1("foo\361bar");
+    EXPECT_EQ("\"foo\\u00f1bar\"", f1.str());
+    ASSERT_NO_THROW(Element::fromJSON("\"foo\\u00f1bar\""));
+    EXPECT_TRUE(f1.equals(*Element::fromJSON("\"foo\\u00f1bar\"")));
+    ASSERT_NO_THROW(Element::fromJSON("\"foo\\u00F1bar\""));
+    EXPECT_TRUE(f1.equals(*Element::fromJSON("\"foo\\u00F1bar\"")));
+}
+
+// This test verifies that strings are copied.
+TEST(Element, stringCopy) {
+    // StringElement constructor copies its string argument.
+    std::string foo = "foo";
+    ElementPtr elem = ElementPtr(new StringElement(foo));
+    EXPECT_EQ(foo, elem->stringValue());
+    foo[1] = 'O';
+    EXPECT_EQ("fOo", foo);
+    EXPECT_NE(foo, elem->stringValue());
+
+    // Map keys are copied too.
+    ElementPtr map = ElementPtr(new MapElement());
+    std::string bar = "bar";
+    map->set(bar, ElementPtr(new IntElement(1)));
+    ConstElementPtr item = map->get("bar");
+    ASSERT_TRUE(item);
+    EXPECT_EQ(1, item->intValue());
+    bar[0] = 'B';
+    EXPECT_EQ("Bar", bar);
+    EXPECT_TRUE(map->get("bar"));
+    EXPECT_FALSE(map->get(bar));
+}
+
+// This test verifies that a backslash can be used in element content
+// when the element is created using constructor.
+TEST(Element, backslash1) {
+    string input = "SMSBoot\\x64";// One slash passed to elem constructor...
+    string exp = "SMSBoot\\x64";  // ... should result in one slash in the actual option.
+
+    StringElement elem(input);
+    EXPECT_EQ(exp, elem.stringValue());
+}
+
+// This test verifies that a backslash can be used in element content
+// when the element is created using fromJSON.
+TEST(Element, backslash2) {
+    string input = "\"SMSBoot\\\\x64\""; // Two slashes put in the config file...
+    string exp = "SMSBoot\\x64"; // ... should result in one slash in the actual option.
+
+    ElementPtr elem = Element::fromJSON(input);
+    EXPECT_EQ(exp, elem->stringValue());
+}
+
+TEST(Element, ListElement) {
+    // this function checks the specific functions for ListElements
+    ElementPtr el = Element::fromJSON("[ 1, \"bar\", 3 ]");
+    EXPECT_EQ(el->get(0)->intValue(), 1);
+    EXPECT_EQ(el->get(1)->stringValue(), "bar");
+    EXPECT_EQ(el->get(2)->intValue(), 3);
+
+    el->set(0, Element::fromJSON("\"foo\""));
+    EXPECT_EQ(el->get(0)->stringValue(), "foo");
+
+    el->add(Element::create(56176));
+    EXPECT_EQ(el->get(3)->intValue(), 56176);
+
+    el->remove(1);
+    el->remove(1);
+    EXPECT_EQ(el->str(), "[ \"foo\", 56176 ]");
+
+    // hmm, it errors on EXPECT_THROW(el->get(3), std::out_of_range)
+    EXPECT_ANY_THROW(el->get(3));
+
+    el->add(Element::create(32));
+    EXPECT_EQ(32, el->get(2)->intValue());
+
+    // boundary condition tests for set()
+    el->set(2, Element::create(0)); // update the last entry of the list
+    EXPECT_EQ(0, el->get(2)->intValue());
+    // attempt of set beyond the range of list should trigger an exception.
+    EXPECT_ANY_THROW(el->set(3, Element::create(0)));
+}
+
+TEST(Element, MapElement) {
+    // this function checks the specific functions for ListElements
+    ElementPtr el = Element::fromJSON("{ \"name\": \"foo\", \"value1\": \"bar\", \"value2\": { \"number\": 42 } }");
+    ConstElementPtr el2;
+
+    EXPECT_EQ(el->get("name")->stringValue(), "foo");
+    EXPECT_EQ(el->get("value2")->getType(), Element::map);
+
+    EXPECT_TRUE(isNull(el->get("value3")));
+
+    EXPECT_FALSE(el->empty());
+
+    el->set("value3", Element::create(56176));
+    EXPECT_EQ(el->get("value3")->intValue(), 56176);
+
+    el->remove("value3");
+    EXPECT_TRUE(isNull(el->get("value3")));
+
+    EXPECT_EQ(el->find("value2/number")->intValue(), 42);
+    EXPECT_TRUE(isNull(el->find("value2/nothing/")));
+
+    EXPECT_EQ(el->find("value1")->stringValue(), "bar");
+    EXPECT_EQ(el->find("value1/")->stringValue(), "bar");
+
+    EXPECT_TRUE(el->find("value1", el2));
+    EXPECT_EQ("bar", el2->stringValue());
+    EXPECT_FALSE(el->find("name/error", el2));
+
+    // A map element whose (only) element has the maximum length of tag.
+    string long_maptag("0123456789abcdef1123456789abcdef2123456789abcdef"
+                       "3123456789abcdef4123456789abcdef5123456789abcdef"
+                       "6123456789abcdef7123456789abcdef8123456789abcdef"
+                       "9123456789abcdefa123456789abcdefb123456789abcdef"
+                       "c123456789abcdefd123456789abcdefe123456789abcdef"
+                       "f123456789abcde");
+
+    EXPECT_EQ(255, long_maptag.length()); // check prerequisite
+    el = Element::fromJSON("{ \"" + long_maptag + "\": \"bar\"}");
+    EXPECT_EQ("bar", el->find(long_maptag)->stringValue());
+
+    el = Element::createMap();
+    el->set(long_maptag, Element::create("bar"));
+    EXPECT_EQ("bar", el->find(long_maptag)->stringValue());
+
+    // A one-byte longer tag should still be allowed
+    long_maptag.push_back('f');
+    el = Element::fromJSON("{ \"" + long_maptag + "\": \"bar\"}");
+    el->set(long_maptag, Element::create("bar"));
+    EXPECT_EQ("bar", el->find(long_maptag)->stringValue());
+
+    // Null pointer value
+    el.reset(new MapElement());
+    ConstElementPtr null_ptr;
+    el->set("value", null_ptr);
+    EXPECT_FALSE(el->get("value"));
+    EXPECT_EQ("{ \"value\": None }", el->str());
+}
+
+TEST(Element, to_and_from_wire) {
+    // Wire format is now plain JSON.
+    EXPECT_EQ("1", Element::create(1)->toWire());
+    EXPECT_EQ("1.1", Element::create(1.1)->toWire());
+    EXPECT_EQ("true", Element::create(true)->toWire());
+    EXPECT_EQ("false", Element::create(false)->toWire());
+    EXPECT_EQ("null", Element::create()->toWire());
+    EXPECT_EQ("\"a string\"", Element::create("a string")->toWire());
+    EXPECT_EQ("[ \"a\", \"list\" ]", Element::fromJSON("[ \"a\", \"list\" ]")->toWire());
+    EXPECT_EQ("{ \"a\": \"map\" }", Element::fromJSON("{ \"a\": \"map\" }")->toWire());
+
+    EXPECT_EQ("1", Element::fromWire("1")->str());
+
+    std::stringstream ss;
+    ss << "1";
+    EXPECT_EQ("1", Element::fromWire(ss, 1)->str());
+
+    // Some malformed JSON input
+    EXPECT_THROW(Element::fromJSON("{ "), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\" "), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\": "), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\": \"b\""), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\": {"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\": {}"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\": []"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\": [ }"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{\":"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("]"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("[ 1, 2, }"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("[ 1, 2, {}"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("[ 1, 2, { ]"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("[ "), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{{}}"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{[]}"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("{ \"a\", \"b\" }"), isc::data::JSONError);
+    EXPECT_THROW(Element::fromJSON("[ \"a\": \"b\" ]"), isc::data::JSONError);
+}
+
+ConstElementPtr
+efs(const std::string& str) {
+    return (Element::fromJSON(str));
+}
+
+TEST(Element, equals) {
+    EXPECT_EQ(*efs("1"), *efs("1"));
+    EXPECT_NE(*efs("1"), *efs("2"));
+    EXPECT_NE(*efs("1"), *efs("\"1\""));
+    EXPECT_NE(*efs("1"), *efs("[]"));
+    EXPECT_NE(*efs("1"), *efs("true"));
+    EXPECT_NE(*efs("1"), *efs("{}"));
+    EXPECT_EQ(*efs("1.1"), *efs("1.1"));
+    EXPECT_NE(*efs("1.0"), *efs("1"));
+    EXPECT_NE(*efs("1.1"), *efs("\"1\""));
+    EXPECT_NE(*efs("1.1"), *efs("[]"));
+    EXPECT_NE(*efs("1.1"), *efs("true"));
+    EXPECT_NE(*efs("1.1"), *efs("{}"));
+
+    EXPECT_EQ(*efs("true"), *efs("true"));
+    EXPECT_NE(*efs("true"), *efs("false"));
+    EXPECT_NE(*efs("true"), *efs("1"));
+    EXPECT_NE(*efs("true"), *efs("\"1\""));
+    EXPECT_NE(*efs("true"), *efs("[]"));
+    EXPECT_NE(*efs("true"), *efs("{}"));
+
+    EXPECT_EQ(*efs("\"foo\""), *efs("\"foo\""));
+    EXPECT_NE(*efs("\"foo\""), *efs("\"bar\""));
+    EXPECT_NE(*efs("\"foo\""), *efs("1"));
+    EXPECT_NE(*efs("\"foo\""), *efs("\"1\""));
+    EXPECT_NE(*efs("\"foo\""), *efs("true"));
+    EXPECT_NE(*efs("\"foo\""), *efs("[]"));
+    EXPECT_NE(*efs("\"foo\""), *efs("{}"));
+
+    EXPECT_EQ(*efs("[]"), *efs("[]"));
+    EXPECT_EQ(*efs("[ 1, 2, 3 ]"), *efs("[ 1, 2, 3 ]"));
+    EXPECT_EQ(*efs("[ \"a\", [ true, 1], 2.2 ]"), *efs("[ \"a\", [ true, 1], 2.2 ]"));
+    EXPECT_NE(*efs("[ \"a\", [ true, 1], 2.2 ]"), *efs("[ \"a\", [ true, 2], 2.2 ]"));
+    EXPECT_NE(*efs("[]"), *efs("[1]"));
+    EXPECT_NE(*efs("[]"), *efs("1"));
+    EXPECT_NE(*efs("[]"), *efs("\"1\""));
+    EXPECT_NE(*efs("[]"), *efs("{}"));
+
+    EXPECT_EQ(*efs("{}"), *efs("{}"));
+    EXPECT_EQ(*efs("{ \"foo\": \"bar\" }"), *efs("{ \"foo\": \"bar\" }"));
+    EXPECT_EQ(*efs("{ \"item1\": 1, \"item2\": [ \"a\", \"list\" ], \"item3\": { \"foo\": \"bar\" } }"), *efs("{ \"item1\": 1, \"item2\": [ \"a\", \"list\" ], \"item3\": { \"foo\": \"bar\" } }"));
+    EXPECT_NE(*efs("{ \"item1\": 1, \"item2\": [ \"a\", \"list\" ], \"item3\": { \"foo\": \"bar\" } }"), *efs("{ \"item1\": 1, \"item2\": [ \"a\", \"list\" ], \"item3\": { \"foo\": \"bar2\" } }"));
+    EXPECT_NE(*efs("{ \"item1\": 1, \"item2\": [ \"a\", \"list\" ], \"item3\": { \"foo\": \"bar\" } }"), *efs("{ \"item1\": 1, \"item2\": [ \"a\", \"list\", 1 ], \"item3\": { \"foo\": \"bar\" } }"));
+    EXPECT_NE(*efs("{ \"foo\": \"bar\" }"), *efs("1"));
+    EXPECT_NE(*efs("{ \"foo\": \"bar\" }"), *efs("\"1\""));
+    EXPECT_NE(*efs("{ \"foo\": \"bar\" }"), *efs("[]"));
+    EXPECT_NE(*efs("{ \"foo\": \"bar\" }"), *efs("{}"));
+    EXPECT_NE(*efs("{ \"foo\": \"bar\" }"), *efs("{ \"something\": \"different\" }"));
+
+    EXPECT_EQ(*efs("null"), *Element::create());
+}
+
+TEST(Element, removeIdentical) {
+    ElementPtr a = Element::createMap();
+    ConstElementPtr b = Element::createMap();
+    ConstElementPtr c = Element::createMap();
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1 }");
+    b = Element::fromJSON("{ \"a\": 1 }");
+    c = Element::createMap();
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    b = Element::createMap();
+    c = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    b = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    c = Element::createMap();
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    b = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 3 ] }");
+    c = Element::fromJSON("{ \"b\": [ 1, 2 ] }");
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::createMap();
+    c = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    c = Element::createMap();
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": { \"b\": \"d\" } }");
+    c = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": 2, \"c\": 3 }");
+    b = Element::fromJSON("{ \"c\": 3, \"b\": 2 }");
+    c = Element::fromJSON("{ \"a\": 1 }");
+    removeIdentical(a, b);
+    EXPECT_EQ(*a, *c);
+
+    EXPECT_THROW(removeIdentical(Element::create(1), Element::create(2)), TypeError);
+}
+
+TEST(Element, constRemoveIdentical) {
+    ConstElementPtr a = Element::createMap();
+    ConstElementPtr b = Element::createMap();
+    ConstElementPtr c = Element::createMap();
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": 1 }");
+    b = Element::fromJSON("{ \"a\": 1 }");
+    c = Element::createMap();
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    b = Element::createMap();
+    c = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    b = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    c = Element::createMap();
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 2 ] }");
+    b = Element::fromJSON("{ \"a\": 1, \"b\": [ 1, 3 ] }");
+    c = Element::fromJSON("{ \"b\": [ 1, 2 ] }");
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::createMap();
+    c = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    c = Element::createMap();
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": { \"b\": \"d\" } }");
+    c = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": 2, \"c\": 3 }");
+    b = Element::fromJSON("{ \"c\": 3, \"b\": 2 }");
+    c = Element::fromJSON("{ \"a\": 1 }");
+    EXPECT_EQ(*removeIdentical(a, b), *c);
+
+    // removeIdentical() is overloaded so force the first argument to const
+    ConstElementPtr bad = Element::create(1);
+    EXPECT_THROW(removeIdentical(bad, Element::create(2)), TypeError);
+}
+
+TEST(Element, merge) {
+    ElementPtr a = Element::createMap();
+    ElementPtr b = Element::createMap();
+    ConstElementPtr c = Element::createMap();
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("1");
+    b = Element::createMap();
+    EXPECT_THROW(merge(a, b), TypeError);
+
+    a = Element::createMap();
+    b = Element::fromJSON("{ \"a\": 1 }");
+    c = Element::fromJSON("{ \"a\": 1 }");
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::createMap();
+    b = Element::fromJSON("{ \"a\": 1 }");
+    c = Element::fromJSON("{ \"a\": 1 }");
+    merge(b, a);
+    EXPECT_EQ(*b, *c);
+
+    a = Element::fromJSON("{ \"a\": 1 }");
+    b = Element::fromJSON("{ \"a\": 2 }");
+    c = Element::fromJSON("{ \"a\": 2 }");
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1 }");
+    b = Element::fromJSON("{ \"a\": 2 }");
+    c = Element::fromJSON("{ \"a\": 1 }");
+    merge(b, a);
+    EXPECT_EQ(*b, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": { \"b\": \"d\" } }");
+    c = Element::fromJSON("{ \"a\": { \"b\": \"d\" } }");
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": { \"b\": \"d\" } }");
+    c = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    merge(b, a);
+    EXPECT_EQ(*b, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": null }");
+    c = Element::fromJSON("{  }");
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    b = Element::fromJSON("{ \"a\": null }");
+    c = Element::fromJSON("{ \"a\": { \"b\": \"c\" } }");
+    merge(b, a);
+    EXPECT_EQ(*b, *c);
+
+    // And some tests with multiple values
+    a = Element::fromJSON("{ \"a\": 1, \"b\": true, \"c\": null }");
+    b = Element::fromJSON("{ \"a\": 1, \"b\": null, \"c\": \"a string\" }");
+    c = Element::fromJSON("{ \"a\": 1, \"c\": \"a string\" }");
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": true, \"c\": null }");
+    b = Element::fromJSON("{ \"a\": 1, \"b\": null, \"c\": \"a string\" }");
+    c = Element::fromJSON("{ \"a\": 1, \"b\": true }");
+    merge(b, a);
+    EXPECT_EQ(*b, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": 2, \"c\": 3 }");
+    b = Element::fromJSON("{ \"a\": 3, \"b\": 2, \"c\": 1 }");
+    c = Element::fromJSON("{ \"a\": 3, \"b\": 2, \"c\": 1 }");
+    merge(a, b);
+    EXPECT_EQ(*a, *c);
+
+    a = Element::fromJSON("{ \"a\": 1, \"b\": 2, \"c\": 3 }");
+    b = Element::fromJSON("{ \"a\": 3, \"b\": 2, \"c\": 1 }");
+    c = Element::fromJSON("{ \"a\": 1, \"b\": 2, \"c\": 3 }");
+    merge(b, a);
+    EXPECT_EQ(*b, *c);
+
+}
+
+// This test checks copy.
+TEST(Element, copy) {
+    // Null pointer
+    ElementPtr elem;
+    EXPECT_THROW(copy(elem, 0), isc::BadValue);
+    EXPECT_THROW(copy(elem), isc::BadValue);
+    EXPECT_THROW(copy(elem, -1), isc::BadValue);
+
+    // Basic types
+    elem.reset(new IntElement(1));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("1")));
+    EXPECT_EQ("1", elem->str());
+    ElementPtr copied;
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+
+    elem.reset(new DoubleElement(1.0));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("1.0")));
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+
+    elem.reset(new BoolElement(true));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("true")));
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+
+    elem.reset(new NullElement());
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("null")));
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+
+    elem.reset(new StringElement("foo"));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("\"foo\"")));
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+    ASSERT_NO_THROW(elem->setValue(std::string("bar")));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("\"bar\"")));
+    EXPECT_FALSE(elem->equals(*copied));
+
+    elem.reset(new ListElement());
+    ElementPtr item = ElementPtr(new IntElement(1));
+    elem->add(item);
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("[ 1 ]")));
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+    ElementPtr deep;
+    ASSERT_NO_THROW(deep = copy(elem));
+    EXPECT_TRUE(elem->equals(*deep));
+    ASSERT_NO_THROW(item = elem->getNonConst(0));
+    ASSERT_NO_THROW(item->setValue(2));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("[ 2 ]")));
+    EXPECT_TRUE(elem->equals(*copied));
+    EXPECT_FALSE(elem->equals(*deep));
+
+    elem.reset(new MapElement());
+    item.reset(new StringElement("bar"));
+    elem->set("foo", item);
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("{ \"foo\": \"bar\" }")));
+    ASSERT_NO_THROW(copied = copy(elem, 0));
+    EXPECT_TRUE(elem->equals(*copied));
+    ASSERT_NO_THROW(deep = copy(elem));
+    EXPECT_TRUE(elem->equals(*deep));
+    ASSERT_NO_THROW(item->setValue(std::string("Bar")));
+    EXPECT_TRUE(elem->equals(*Element::fromJSON("{ \"foo\": \"Bar\" }")));
+    EXPECT_TRUE(elem->equals(*copied));
+    EXPECT_FALSE(elem->equals(*deep));
+
+    // Complex example
+    std::string input = "{ \n"
+        "\"integer\": 1,\n"
+        "\"double\": 1.0,\n"
+        "\"boolean\": true,\n"
+        "\"null\": null,\n"
+        "\"string\": \"foobar\",\n"
+        "\"list\": [ 1, 2 ],\n"
+        "\"map\": { \"foo\": \"bar\" } }\n";
+    ConstElementPtr complex;
+    ASSERT_NO_THROW(complex = Element::fromJSON(input));
+    ASSERT_NO_THROW(copied = copy(complex, 0));
+    EXPECT_TRUE(copied->equals(*complex));
+    ASSERT_NO_THROW(deep = copy(complex));
+    EXPECT_TRUE(deep->equals(*complex));
+    ElementPtr shallow;
+    ASSERT_NO_THROW(shallow = copy(complex, 1));
+    EXPECT_TRUE(shallow->equals(*complex));
+    // Try to modify copies
+    ASSERT_NO_THROW(item = deep->get("list")->getNonConst(1));
+    ASSERT_NO_THROW(item->setValue(3));
+    EXPECT_FALSE(deep->equals(*complex));
+    EXPECT_TRUE(shallow->equals(*complex));
+    ASSERT_NO_THROW(item = boost::const_pointer_cast<Element>(shallow->get("string")));
+    ASSERT_NO_THROW(item->setValue(std::string("FooBar")));
+    EXPECT_FALSE(shallow->equals(*complex));
+    EXPECT_TRUE(copied->equals(*complex));
+}
+
+// This test checks the isEquivalent function.
+TEST(Element, isEquivalent) {
+    // All are different but a is equivalent to b
+    string texta = "{ \"a\": 1, \"b\": [ ], \"c\": [ 1, 1, 2 ] }";
+    string textb = "{ \"b\": [ ], \"a\": 1, \"c\": [ 1, 2, 1 ] }";
+    string textc = "{ \"a\": 2, \"b\": [ ], \"c\": [ 1, 1, 2 ] }";
+    string textd = "{ \"a\": 1, \"c\": [ ], \"b\": [ 1, 1, 2 ] }";
+    string texte = "{ \"a\": 1, \"b\": [ ], \"c\": [ 1, 2, 2 ] }";
+
+    ElementPtr a = Element::fromJSON(texta);
+    ElementPtr b = Element::fromJSON(textb);
+    ElementPtr c = Element::fromJSON(textc);
+    ElementPtr d = Element::fromJSON(textd);
+    ElementPtr e = Element::fromJSON(texte);
+
+    EXPECT_TRUE(isEquivalent(a, b));
+    EXPECT_NE(a, b);
+    EXPECT_FALSE(isEquivalent(a, c));
+    EXPECT_FALSE(isEquivalent(a, d));
+    EXPECT_FALSE(isEquivalent(a, e));
+
+    // Verifies isEquivalent handles cycles
+    if (isc::util::unittests::runningOnValgrind()) {
+        ElementPtr l = Element::createList();
+        l->add(l);
+        EXPECT_THROW(isEquivalent(l, l), isc::BadValue);
+    }
+}
+
+// This test checks the pretty print function.
+TEST(Element, prettyPrint) {
+
+    // default step is 2, order is alphabetic, no \n at the end
+    string text = "{\n"
+        "  \"boolean\": true,\n"
+        "  \"comment\": \"this is an exception\",\n"
+        "  \"empty-list\": [ ],\n"
+        "  \"empty-map\": { },\n"
+        "  \"integer\": 1,\n"
+        "  \"list\": [ 1, 2, 3 ],\n"
+        "  \"map\": {\n"
+        "    \"item\": null\n"
+        "  },\n"
+        "  \"string\": \"foobar\"\n"
+        "}";
+    ElementPtr json = Element::fromJSON(text);
+    string pprinted = prettyPrint(json);
+    EXPECT_EQ(text, pprinted);
+}
+
+// This test checks whether it is possible to ignore comments. It also checks
+// that the comments are ignored only when told to.
+TEST(Element, preprocessor) {
+
+    string no_comment = "{ \"a\": 1,\n"
+                        " \"b\": 2}";
+
+    string head_comment = "# this is a comment, ignore me\n"
+                          "{ \"a\": 1,\n"
+                          " \"b\": 2}";
+
+    string mid_comment = "{ \"a\": 1,\n"
+                         "# this is a comment, ignore me\n"
+                         " \"b\": 2}";
+
+    string tail_comment = "{ \"a\": 1,\n"
+                          " \"b\": 2}"
+                          "# this is a comment, ignore me\n";
+
+    string dbl_head_comment = "# this is a comment, ignore me\n"
+                              "# second line, still ignored\n"
+                              "{ \"a\": 1,\n"
+                              " \"b\": 2}";
+
+    string dbl_mid_comment = "{ \"a\": 1,\n"
+                             "# this is a comment, ignore me\n"
+                             "# second line, still ignored\n"
+                             " \"b\": 2}";
+
+    string dbl_tail_comment = "{ \"a\": 1,\n"
+                              " \"b\": 2}"
+                              "# this is a comment, ignore me\n"
+                              "# second line, still ignored\n";
+
+    // This is what we expect in all cases.
+    ElementPtr exp = Element::fromJSON(no_comment);
+
+    // Let's convert them all and see that the result it the same every time
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(head_comment, true)));
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(mid_comment, true)));
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(tail_comment, true)));
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(dbl_head_comment, true)));
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(dbl_mid_comment, true)));
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(dbl_tail_comment, true)));
+
+    // With preprocessing disabled, it should fail all around
+    EXPECT_THROW(Element::fromJSON(head_comment), JSONError);
+    EXPECT_THROW(Element::fromJSON(mid_comment), JSONError);
+    EXPECT_THROW(Element::fromJSON(tail_comment), JSONError);
+    EXPECT_THROW(Element::fromJSON(dbl_head_comment), JSONError);
+    EXPECT_THROW(Element::fromJSON(dbl_mid_comment), JSONError);
+    EXPECT_THROW(Element::fromJSON(dbl_tail_comment), JSONError);
+
+    // For coverage
+    std::istringstream iss(no_comment);
+    EXPECT_TRUE(exp->equals(*Element::fromJSON(iss, true)));
+}
+
+TEST(Element, getPosition) {
+    std::istringstream ss("{\n"
+                          "    \"a\":  2,\n"
+                          "    \"b\":true,\n"
+                          "    \"cy\": \"a string\",\n"
+                          "    \"dyz\": {\n"
+                          "\n"
+                          "      \"e\": 3,\n"
+                          "        \"f\": null\n"
+                          "\n"
+                          "    },\n"
+                          "    \"g\": [ 5, 6,\n"
+                          "             7 ]\n"
+                          "}\n");
+
+    // Create a JSON string holding different type of values. Some of the
+    // values in the config string are not aligned, so as we can check that
+    // the position is set correctly for the elements.
+    ElementPtr top = Element::fromJSON(ss, string("kea.conf"));
+    ASSERT_TRUE(top);
+
+    // Element "a"
+    ConstElementPtr level1_el = top->get("a");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(2, level1_el->getPosition().line_);
+    EXPECT_EQ(11, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "b"
+    level1_el = top->get("b");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(3, level1_el->getPosition().line_);
+    EXPECT_EQ(9, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "cy"
+    level1_el = top->get("cy");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(4, level1_el->getPosition().line_);
+    EXPECT_EQ(11, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "dyz"
+    level1_el = top->get("dyz");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(5, level1_el->getPosition().line_);
+    EXPECT_EQ(13, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "e" is a sub element of "dyz".
+    ConstElementPtr level2_el = level1_el->get("e");
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(7, level2_el->getPosition().line_);
+    EXPECT_EQ(12, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+
+    // Element "f" is also a sub element of "dyz"
+    level2_el = level1_el->get("f");
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(8, level2_el->getPosition().line_);
+    EXPECT_EQ(14, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+
+    // Element "g" is a list.
+    level1_el = top->get("g");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(11, level1_el->getPosition().line_);
+    // Position indicates where the values start (excluding the "[" character)"
+    EXPECT_EQ(11, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // First element from the list.
+    level2_el = level1_el->get(0);
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(11, level2_el->getPosition().line_);
+    EXPECT_EQ(12, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+
+    // Second element from the list.
+    level2_el = level1_el->get(1);
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(11, level2_el->getPosition().line_);
+    EXPECT_EQ(15, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+
+    // Third element from the list.
+    level2_el = level1_el->get(2);
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(12, level2_el->getPosition().line_);
+    EXPECT_EQ(14, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+
+}
+
+// Tests whether position is returned properly for a commented input JSON text.
+TEST(Element, getPositionCommented) {
+    std::istringstream ss("{\n"
+                          "    \"a\":  2,\n"
+                          "# comment\n"
+                          "    \"cy\": \"a string\",\n"
+                          "    \"dyz\": {\n"
+                          "# another comment\n"
+                          "      \"e\": 3,\n"
+                          "        \"f\": null\n"
+                          "\n"
+                          "    } }\n");
+
+    // Create a JSON string holding different type of values. Some of the
+    // values in the config string are not aligned, so as we can check that
+    // the position is set correctly for the elements.
+    ElementPtr top = Element::fromJSON(ss, string("kea.conf"), true);
+    ASSERT_TRUE(top);
+
+    // Element "a"
+    ConstElementPtr level1_el = top->get("a");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(2, level1_el->getPosition().line_);
+    EXPECT_EQ(11, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "cy"
+    level1_el = top->get("cy");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(4, level1_el->getPosition().line_);
+    EXPECT_EQ(11, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "dyz"
+    level1_el = top->get("dyz");
+    ASSERT_TRUE(level1_el);
+    EXPECT_EQ(5, level1_el->getPosition().line_);
+    EXPECT_EQ(13, level1_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level1_el->getPosition().file_);
+
+    // Element "e" is a sub element of "dyz".
+    ConstElementPtr level2_el = level1_el->get("e");
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(7, level2_el->getPosition().line_);
+    EXPECT_EQ(12, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+
+    // Element "f" is also a sub element of "dyz"
+    level2_el = level1_el->get("f");
+    ASSERT_TRUE(level2_el);
+    EXPECT_EQ(8, level2_el->getPosition().line_);
+    EXPECT_EQ(14, level2_el->getPosition().pos_);
+    EXPECT_EQ("kea.conf", level2_el->getPosition().file_);
+}
+
+TEST(Element, empty) {
+
+    // Let's try Map first
+    ElementPtr m = Element::createMap();
+    EXPECT_TRUE(m->empty());
+    m->set("something", Element::create(123));
+    EXPECT_FALSE(m->empty());
+    m->remove("something");
+    EXPECT_TRUE(m->empty());
+
+    // Now do the same with list
+    ElementPtr l = Element::createList();
+    EXPECT_TRUE(l->empty());
+    l->add(Element::create(123));
+    EXPECT_FALSE(l->empty());
+    l->remove(0);
+    EXPECT_TRUE(l->empty());
+}
+
+TEST(Element, sortIntegers) {
+    ElementPtr l(Element::fromJSON("[5, 7, 4, 2, 8, 6, 1, 9, 0, 3]"));
+    ElementPtr expected(Element::fromJSON("[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]"));
+    boost::dynamic_pointer_cast<ListElement>(l)->sort();
+    EXPECT_EQ(*l, *expected);
+}
+
+TEST(Element, sortFloatingPoint) {
+    ElementPtr l(Element::fromJSON("[2.1, 3.2, 2.1, 2.2, 4.1, 3.2, 1.1, 4.2, 0.1, 1.2]"));
+    ElementPtr expected(Element::fromJSON("[0.1, 1.1, 1.2, 2.1, 2.1, 2.2, 3.2, 3.2, 4.1, 4.2]"));
+    boost::dynamic_pointer_cast<ListElement>(l)->sort();
+    EXPECT_EQ(*l, *expected);
+}
+
+TEST(Element, sortBooleans) {
+    ElementPtr l(Element::fromJSON("[false, true, false, true]"));
+    ElementPtr expected(Element::fromJSON("[false, false, true, true]"));
+    boost::dynamic_pointer_cast<ListElement>(l)->sort();
+    EXPECT_EQ(*l, *expected);
+}
+
+TEST(Element, sortStrings) {
+    ElementPtr l(Element::fromJSON(R"(["hello", "world", "lorem", "ipsum", "dolor", "sit", "amet"])"));
+    ElementPtr expected(Element::fromJSON(R"(["amet", "dolor", "hello", "ipsum", "lorem", "sit", "world"])"));
+    boost::dynamic_pointer_cast<ListElement>(l)->sort();
+    EXPECT_EQ(*l, *expected);
+}
+
+TEST(Element, sortMaps) {
+    ElementPtr e1(Element::fromJSON(R"({"id": 1, "subnet": "10.0.2.0/24"})"));
+    ElementPtr e2(Element::fromJSON(R"({"id": 2, "subnet": "10.0.1.0/24"})"));
+    ElementPtr l;
+
+    // Test sorting by "id". Order shouldn't change.
+    l = Element::createList();
+    l->add(e1);
+    l->add(e2);
+    boost::dynamic_pointer_cast<ListElement>(l)->sort("id");
+    ASSERT_EQ(l->size(), 2);
+    EXPECT_EQ(*l->get(0), *e1);
+    EXPECT_EQ(*l->get(1), *e2);
+
+    // Test sorting by "id". Order should change.
+    l = Element::createList();
+    l->add(e2);
+    l->add(e1);
+    boost::dynamic_pointer_cast<ListElement>(l)->sort("id");
+    ASSERT_EQ(l->size(), 2);
+    EXPECT_EQ(*l->get(0), *e1);
+    EXPECT_EQ(*l->get(1), *e2);
+
+    // Test sorting by "subnet". Order should change.
+    l = Element::createList();
+    l->add(e1);
+    l->add(e2);
+    boost::dynamic_pointer_cast<ListElement>(l)->sort("subnet");
+    ASSERT_EQ(l->size(), 2);
+    EXPECT_EQ(*l->get(0), *e2);
+    EXPECT_EQ(*l->get(1), *e1);
+
+    // Test sorting by "subnet". Order shouldn't change.
+    l = Element::createList();
+    l->add(e2);
+    l->add(e1);
+    boost::dynamic_pointer_cast<ListElement>(l)->sort("subnet");
+    ASSERT_EQ(l->size(), 2);
+    EXPECT_EQ(*l->get(0), *e2);
+    EXPECT_EQ(*l->get(1), *e1);
+}
+
+TEST(Element, removeEmptyContainersRecursively) {
+    ElementPtr e(Element::fromJSON(R"(
+{
+  "list": [
+    {
+      "nested-list": [
+        {
+          "nestedx2-list": [
+            {}
+          ]
+        }
+      ]
+    }
+  ],
+  "map": {
+    "nested-map": {
+      "nestedx2-map": {}
+    }
+  },
+  "simple-list": {},
+  "simple-map": {}
+}
+)"));
+    e->removeEmptyContainersRecursively();
+    EXPECT_EQ(*e, *Element::fromJSON("{}"));
+
+    e = Element::fromJSON(R"(
+{
+  "list": [
+    {
+      "value": "not empty anymore",
+      "nested-list": [
+        {
+          "nestedx2-list": [
+            {}
+          ]
+        }
+      ]
+    }
+  ],
+  "map": {
+    "value": "not empty anymore",
+    "nested-map": {
+      "nestedx2-map": {}
+    }
+  },
+  "simple-list": {},
+  "simple-map": {}
+}
+)");
+    e->removeEmptyContainersRecursively();
+    EXPECT_EQ(*e, *Element::fromJSON(R"(
+{
+  "list": [
+    {
+      "value": "not empty anymore"
+    }
+  ],
+  "map": {
+    "value": "not empty anymore"
+  }
+}
+)"));
+}
+
+/// @brief Function which creates an imaginary configuration hierarchy used to
+/// test mergeDiffAdd, mergeDiffDel and extend.
+///
+/// @param any Flag which indicates if traversing the hierarchy should use exact
+/// element match or not.
+isc::data::HierarchyDescriptor createHierarchy(bool any = false) {
+    auto const& element_empty = [](ElementPtr& element) {
+        for (auto const& kv : element->mapValue()) {
+            auto const& key = kv.first;
+            if (key != "id") {
+                return (false);
+            }
+        }
+        return (true);
+    };
+    auto const& element_match = [](ElementPtr& left, ElementPtr& right) -> bool {
+        return (left->get("id")->intValue() == right->get("id")->intValue());
+    };
+    auto const& element_any_match = [](ElementPtr&, ElementPtr&) -> bool {
+        return (true);
+    };
+    auto const& element_is_key = [](const std::string& key) -> bool {
+        return (key == "id");
+    };
+    isc::data::HierarchyDescriptor hierarchy = {
+        { { "root", { element_match, element_empty, element_is_key } } },
+        { { "elements", { element_match, element_empty, element_is_key } },
+          { "elements-other", { element_match, element_empty, element_is_key } } }
+    };
+    if (any) {
+        hierarchy = {
+            { { "root", { element_any_match, element_empty, element_is_key } } },
+            { { "elements", { element_any_match, element_empty, element_is_key } },
+              { "elements-other", { element_any_match, element_empty, element_is_key } } }
+        };
+    }
+    return (hierarchy);
+}
+
+/// @brief Test which checks that mergeDiffAdd throws if called with wrong
+/// element types.
+TEST(Element, mergeDiffAddBadParams) {
+    {
+        SCOPED_TRACE("root bad scalars");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(true);
+        ElementPtr right = Element::create("false");
+        ASSERT_THROW(mergeDiffAdd(left, right, hierarchy, ""), TypeError);
+    }
+    {
+        SCOPED_TRACE("map bad elements");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::createList());
+        right->set("elements", Element::createMap());
+        ASSERT_THROW(mergeDiffAdd(left, right, hierarchy, "root"), TypeError);
+    }
+    {
+        SCOPED_TRACE("list bad elements");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::createMap());
+        right_right->set("id", Element::create(0));
+        right_right->set("elements", Element::createList());
+        left->add(left_left);
+        right->add(right_right);
+        ASSERT_THROW(mergeDiffAdd(left, right, hierarchy, "root"), TypeError);
+    }
+}
+
+/// @brief Test which checks that mergeDiffAdd works as expected.
+TEST(Element, mergeDiffAdd) {
+    {
+        SCOPED_TRACE("scalar bool");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(true);
+        ElementPtr right = Element::create(false);
+        EXPECT_NE(left->boolValue(), right->boolValue());
+        mergeDiffAdd(left, right, hierarchy, "");
+        EXPECT_EQ(left->boolValue(), right->boolValue());
+        std::string expected_str("false");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar int");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(1);
+        ElementPtr right = Element::create(2);
+        EXPECT_NE(left->intValue(), right->intValue());
+        mergeDiffAdd(left, right, hierarchy, "");
+        EXPECT_EQ(left->intValue(), right->intValue());
+        std::string expected_str("2");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar double");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(0.1);
+        ElementPtr right = Element::create(0.2);
+        EXPECT_NE(left->doubleValue(), right->doubleValue());
+        mergeDiffAdd(left, right, hierarchy, "");
+        EXPECT_EQ(left->doubleValue(), right->doubleValue());
+        std::string expected_str("0.2");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar string");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create("left");
+        ElementPtr right = Element::create("right");
+        EXPECT_NE(left->stringValue(), right->stringValue());
+        mergeDiffAdd(left, right, hierarchy, "");
+        EXPECT_EQ(left->stringValue(), right->stringValue());
+        std::string expected_str("\"right\"");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar in map");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::create("left"));
+        left->set("other-elements", Element::create("other"));
+        // scalar element which is updated
+        right->set("elements", Element::create("right"));
+        // scalar element which is added
+        right->set("new-elements", Element::create("new"));
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffAdd(left, right, hierarchy, "");
+        std::string expected_str("{ \"elements\": \"right\", \"new-elements\": \"new\", \"other-elements\": \"other\" }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar in list");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        left->add(Element::create("left"));
+        left->add(Element::create("other"));
+        left->add(Element::create("test"));
+        // scalar element which is added
+        right->add(Element::create("right"));
+        // scalar element which is added
+        right->add(Element::create("new"));
+        // scalar element which already exists but is still added
+        right->add(Element::create("test"));
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffAdd(left, right, hierarchy, "");
+        std::string expected_str("[ \"left\", \"other\", \"test\", \"right\", \"new\", \"test\" ]");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar and list and map in map");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::create("left"));
+        left_left->set("other-elements", Element::create("other"));
+        // scalar element used as key
+        right_right->set("id", Element::create(0));
+        // scalar element which is updated
+        right_right->set("elements", Element::create("right"));
+        // scalar element which is added
+        right_right->set("new-elements", Element::create("new"));
+        ElementPtr left_other_left = Element::createMap();
+        ElementPtr right_other_right = Element::createMap();
+        left_other_left->set("id", Element::create(1));
+        left_other_left->set("elements", Element::create("other-left"));
+        // scalar element used as key
+        right_other_right->set("id", Element::create(2));
+        // scalar element which is added
+        right_other_right->set("elements", Element::create("other-right"));
+        left->set("elements", left_left);
+        left->set("left-other-elements", left_other_left);
+        // map element which is added
+        right->set("right-other-elements", right_other_right);
+        // map element which is updated
+        right->set("elements", right_right);
+        left_other_left = Element::createList();
+        right_other_right = Element::createList();
+        left_other_left->add(Element::create("left-other-left"));
+        left_other_left->add(Element::create("left-other-left-other"));
+        left_other_left->add(Element::create("other-other"));
+        // scalar element which is added
+        right_other_right->add(Element::create("right-other-right"));
+        // scalar element which is added
+        right_other_right->add(Element::create("right-other-right-other"));
+        // scalar element which already exists but is still added
+        right_other_right->add(Element::create("other-other"));
+        left->set("other", left_other_left);
+        // list element which is updated
+        right->set("other", right_other_right);
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffAdd(left, right, hierarchy, "root");
+        std::string expected_str("{ \"elements\": { \"elements\": \"right\", \"id\": 0, \"new-elements\": \"new\", \"other-elements\": \"other\" }, "
+                                   "\"left-other-elements\": { \"elements\": \"other-left\", \"id\": 1 }, "
+                                   "\"other\": [ \"left-other-left\", \"left-other-left-other\", \"other-other\", \"right-other-right\", \"right-other-right-other\", \"other-other\" ], "
+                                   "\"right-other-elements\": { \"elements\": \"other-right\", \"id\": 2 } }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar and list and map in list");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::create("left"));
+        left_left->set("other-elements", Element::create("other"));
+        // scalar element used as key
+        right_right->set("id", Element::create(0));
+        // scalar element which is updated
+        right_right->set("elements", Element::create("right"));
+        // scalar element which is added
+        right_right->set("new-elements", Element::create("new"));
+        ElementPtr left_other_left = Element::createMap();
+        ElementPtr right_other_right = Element::createMap();
+        left_other_left->set("id", Element::create(1));
+        left_other_left->set("elements", Element::create("other-left"));
+        // scalar element used as key
+        right_other_right->set("id", Element::create(2));
+        // scalar element which is added
+        right_other_right->set("elements", Element::create("other-right"));
+        left->add(left_left);
+        left->add(left_other_left);
+        // map element which is added
+        right->add(right_other_right);
+        // map element which is updated
+        right->add(right_right);
+        left_other_left = Element::createList();
+        right_other_right = Element::createList();
+        left_other_left->add(Element::create("left-other-left"));
+        left_other_left->add(Element::create("left-other-left-other"));
+        left_other_left->add(Element::create("other-other"));
+        // scalar element which is added
+        right_other_right->add(Element::create("right-other-right"));
+        // scalar element which is added
+        right_other_right->add(Element::create("right-other-right-other"));
+        // scalar element which already exists but is still added
+        right_other_right->add(Element::create("other-other"));
+        left_left->set("other", left_other_left);
+        // list element which is updated
+        right_right->set("other", right_other_right);
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffAdd(left, right, hierarchy, "root");
+        std::string expected_str("[ { \"elements\": \"right\", \"id\": 0, \"new-elements\": \"new\", "
+                                     "\"other\": [ \"left-other-left\", \"left-other-left-other\", \"other-other\", \"right-other-right\", \"right-other-right-other\", \"other-other\" ], "
+                                     "\"other-elements\": \"other\" }, "
+                                   "{ \"elements\": \"other-left\", \"id\": 1 }, "
+                                   "{ \"elements\": \"other-right\", \"id\": 2 } ]");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+}
+
+/// @brief Test which checks that mergeDiffDel throws if called with wrong
+/// element types.
+TEST(Element, mergeDiffDelBadParams) {
+    {
+        SCOPED_TRACE("root bad scalars");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(true);
+        ElementPtr right = Element::create("false");
+        ASSERT_THROW(mergeDiffDel(left, right, hierarchy, ""), TypeError);
+    }
+    {
+        SCOPED_TRACE("map bad elements");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::createList());
+        right->set("elements", Element::createMap());
+        ASSERT_THROW(mergeDiffDel(left, right, hierarchy, "root"), TypeError);
+    }
+    {
+        SCOPED_TRACE("list bad elements");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::createMap());
+        right_right->set("id", Element::create(0));
+        right_right->set("elements", Element::createList());
+        left->add(left_left);
+        right->add(right_right);
+        ASSERT_THROW(mergeDiffDel(left, right, hierarchy, "root"), TypeError);
+    }
+}
+
+/// @brief Test which checks that mergeDiffDel works as expected.
+TEST(Element, mergeDiffDel) {
+    {
+        SCOPED_TRACE("scalar bool");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(true);
+        ElementPtr right = Element::create(false);
+        EXPECT_NE(left->boolValue(), right->boolValue());
+        mergeDiffDel(left, right, hierarchy, "");
+        EXPECT_EQ(left->getType(), Element::null);
+    }
+    {
+        SCOPED_TRACE("scalar int");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(1);
+        ElementPtr right = Element::create(2);
+        EXPECT_NE(left->intValue(), right->intValue());
+        mergeDiffDel(left, right, hierarchy, "");
+        EXPECT_EQ(left->getType(), Element::null);
+    }
+    {
+        SCOPED_TRACE("scalar double");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(0.1);
+        ElementPtr right = Element::create(0.2);
+        EXPECT_NE(left->doubleValue(), right->doubleValue());
+        mergeDiffDel(left, right, hierarchy, "");
+        EXPECT_EQ(left->getType(), Element::null);
+    }
+    {
+        SCOPED_TRACE("scalar string");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create("left");
+        ElementPtr right = Element::create("right");
+        EXPECT_NE(left->stringValue(), right->stringValue());
+        mergeDiffDel(left, right, hierarchy, "");
+        EXPECT_EQ(left->getType(), Element::null);
+    }
+    {
+        SCOPED_TRACE("scalar in map");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::create("left"));
+        left->set("other-elements", Element::create("other"));
+        // scalar element which is removed
+        right->set("elements", Element::create("right"));
+        // scalar element which does not exist and does nothing
+        right->set("new-elements", Element::create("new"));
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffDel(left, right, hierarchy, "root");
+        std::string expected_str("{ \"other-elements\": \"other\" }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar in list");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        left->add(Element::create("left"));
+        left->add(Element::create("other"));
+        left->add(Element::create("other-left"));
+        left->add(Element::create("new"));
+        // scalar element which does not exist and does nothing
+        right->add(Element::create("right"));
+        // scalar element which is removed
+        right->add(Element::create("other"));
+        // scalar element which does not exist and does nothing
+        right->add(Element::create("other-right"));
+        // scalar element which is removed
+        right->add(Element::create("new"));
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffDel(left, right, hierarchy, "");
+        std::string expected_str("[ \"left\", \"other-left\" ]");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar and list and map in map");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::create("left"));
+        left_left->set("other-elements", Element::create("other"));
+        // scalar element used as key
+        right_right->set("id", Element::create(0));
+        // scalar element which is removed
+        right_right->set("elements", Element::create("right"));
+        // scalar element which does not exist and does nothing
+        right_right->set("new-elements", Element::create("new"));
+        ElementPtr left_other_left = Element::createMap();
+        ElementPtr right_other_right = Element::createMap();
+        left_other_left->set("id", Element::create(1));
+        left_other_left->set("elements", Element::create("other-left"));
+        // scalar element used as key
+        right_other_right->set("id", Element::create(2));
+        // scalar element which does not exist and does nothing
+        right_other_right->set("elements", Element::create("other-right"));
+        left->set("elements", left_left);
+        left->set("left-other-elements", left_other_left);
+        // map element which does not exist and does nothing
+        right->set("right-other-elements", right_other_right);
+        // map element which is updated
+        right->set("elements", right_right);
+        left_other_left = Element::createList();
+        right_other_right = Element::createList();
+        left_other_left->add(Element::create("left-other-left"));
+        left_other_left->add(Element::create("other"));
+        left_other_left->add(Element::create("left-other-left-other"));
+        left_other_left->add(Element::create("new"));
+        // scalar element which does not exist and does nothing
+        right_other_right->add(Element::create("right-other-right"));
+        // scalar element which is removed
+        right_other_right->add(Element::create("other"));
+        // scalar element which does not exist and does nothing
+        right_other_right->add(Element::create("right-other-right-other"));
+        // scalar element which is removed
+        right_other_right->add(Element::create("new"));
+        left->set("other", left_other_left);
+        // list element which is updated
+        right->set("other", right_other_right);
+        left_left = Element::createMap();
+        right_right = Element::createMap();
+        left_left->set("id", Element::create(3));
+        left_left->set("elements", Element::create("new-left"));
+        left_left->set("other-elements", Element::create("new-other"));
+        left->set("elements-other", left_left);
+        // scalar element used as key
+        right_right->set("id", Element::create(3));
+        // map element which is not removed because it is contained in a map and
+        // the key can not be removed
+        right->set("elements-other", right_right);
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffDel(left, right, hierarchy, "root");
+        std::string expected_str("{ \"elements\": { \"id\": 0, \"other-elements\": \"other\" }, "
+                                   "\"elements-other\": { \"elements\": \"new-left\", \"id\": 3, \"other-elements\": \"new-other\" }, "
+                                   "\"left-other-elements\": { \"elements\": \"other-left\", \"id\": 1 }, "
+                                   "\"other\": [ \"left-other-left\", \"left-other-left-other\" ] }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar and list and map in list");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::create("left"));
+        left_left->set("other-elements", Element::create("other"));
+        // scalar element used as key
+        right_right->set("id", Element::create(0));
+        // scalar element which is removed
+        right_right->set("elements", Element::create("right"));
+        // scalar element which does not exist and does nothing
+        right_right->set("new-elements", Element::create("new"));
+        ElementPtr left_other_left = Element::createMap();
+        ElementPtr right_other_right = Element::createMap();
+        left_other_left->set("id", Element::create(1));
+        left_other_left->set("elements", Element::create("other-left"));
+        // scalar element used as key
+        right_other_right->set("id", Element::create(2));
+        // scalar element which does not exist and does nothing
+        right_other_right->set("elements", Element::create("other-right"));
+        left->add(left_left);
+        left->add(left_other_left);
+        // map element which does not exist and does nothing
+        right->add(right_other_right);
+        // map element which is updated
+        right->add(right_right);
+        left_other_left = Element::createList();
+        right_other_right = Element::createList();
+        left_other_left->add(Element::create("left-other-left"));
+        left_other_left->add(Element::create("other"));
+        left_other_left->add(Element::create("left-other-left-other"));
+        left_other_left->add(Element::create("new"));
+        // scalar element which does not exist and does nothing
+        right_other_right->add(Element::create("right-other-right"));
+        // scalar element which is removed
+        right_other_right->add(Element::create("other"));
+        // scalar element which does not exist and does nothing
+        right_other_right->add(Element::create("right-other-right-other"));
+        // scalar element which is removed
+        right_other_right->add(Element::create("new"));
+        left_left->set("other", left_other_left);
+        // list element which is updated
+        right_right->set("other", right_other_right);
+        left_left = Element::createMap();
+        right_right = Element::createMap();
+        left_left->set("id", Element::create(3));
+        left_left->set("elements", Element::create("new-left"));
+        left_left->set("other-elements", Element::create("new-other"));
+        left->add(left_left);
+        // scalar element used as key
+        right_right->set("id", Element::create(3));
+        // map element which is removed by key
+        // the key can not be removed
+        right->add(right_right);
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        mergeDiffDel(left, right, hierarchy, "root");
+        std::string expected_str("[ { \"id\": 0, \"other\": [ \"left-other-left\", \"left-other-left-other\" ], \"other-elements\": \"other\" }, "
+                                   "{ \"elements\": \"other-left\", \"id\": 1 } ]");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+}
+
+/// @brief Test which checks that extend throws if called with wrong element
+/// types.
+TEST(Element, extendBadParam) {
+    {
+        SCOPED_TRACE("root bad scalars");
+        isc::data::HierarchyDescriptor hierarchy;
+        ElementPtr left = Element::create(true);
+        ElementPtr right = Element::create("false");
+        ASSERT_THROW(extend("elements", "", left, right, hierarchy, ""), TypeError);
+    }
+    {
+        SCOPED_TRACE("map bad elements");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::createList());
+        right->set("elements", Element::createMap());
+        ASSERT_THROW(extend("elements", "", left, right, hierarchy, "root"), TypeError);
+    }
+    {
+        SCOPED_TRACE("list bad elements");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy();
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::createMap());
+        right_right->set("id", Element::create(0));
+        right_right->set("elements", Element::createList());
+        left->add(left_left);
+        right->add(right_right);
+        ASSERT_THROW(extend("elements", "", left, right, hierarchy, "root"), TypeError);
+    }
+}
+
+/// @brief Test which checks that extend works as expected.
+TEST(Element, extend) {
+    {
+        SCOPED_TRACE("scalar in map but alter flag is not set");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy(true);
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::create("left"));
+        left->set("other-elements", Element::create("other"));
+        // scalar element which is not updated
+        right->set("elements", Element::create("right"));
+        // scalar element which is extended
+        right->set("new-elements", Element::create("new"));
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        extend("root", "new-elements", left, right, hierarchy, "root", 0, false);
+        std::string expected_str("{ \"elements\": \"left\", \"other-elements\": \"other\" }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar in map");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy(true);
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        left->set("elements", Element::create("left"));
+        left->set("other-elements", Element::create("other"));
+        // scalar element which is not updated
+        right->set("elements", Element::create("right"));
+        // scalar element which is extended
+        right->set("new-elements", Element::create("new"));
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        extend("root", "new-elements", left, right, hierarchy, "root", 0, true);
+        std::string expected_str("{ \"elements\": \"left\", \"new-elements\": \"new\", \"other-elements\": \"other\" }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar in map in map");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy(true);
+        ElementPtr left = Element::createMap();
+        ElementPtr right = Element::createMap();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::create("left"));
+        left_left->set("other-elements", Element::create("other"));
+        // scalar element used as key
+        right_right->set("id", Element::create(1));
+        // scalar element which is not updated
+        right_right->set("elements", Element::create("right"));
+        // scalar element which is extended
+        right_right->set("new-elements", Element::create("new"));
+        left->set("elements", left_left);
+        // map element which is used for extension
+        right->set("elements", right_right);
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        extend("root", "new-elements", left, right, hierarchy, "root");
+        std::string expected_str("{ \"elements\": { \"elements\": \"left\", \"id\": 0, \"new-elements\": \"new\", \"other-elements\": \"other\" } }");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+    {
+        SCOPED_TRACE("scalar in map in list");
+        isc::data::HierarchyDescriptor hierarchy;
+        hierarchy = createHierarchy(true);
+        ElementPtr left = Element::createList();
+        ElementPtr right = Element::createList();
+        ElementPtr left_left = Element::createMap();
+        ElementPtr right_right = Element::createMap();
+        left_left->set("id", Element::create(0));
+        left_left->set("elements", Element::create("left"));
+        left_left->set("other-elements", Element::create("other"));
+        // scalar element used as key
+        right_right->set("id", Element::create(1));
+        // scalar element which is not updated
+        right_right->set("elements", Element::create("right"));
+        // scalar element which is extended
+        right_right->set("new-elements", Element::create("new"));
+        left->add(left_left);
+        // map element which is used for extension
+        right->add(right_right);
+        ASSERT_FALSE(isc::data::isEquivalent(left, right));
+        extend("root", "new-elements", left, right, hierarchy, "root");
+        std::string expected_str("[ { \"elements\": \"left\", \"id\": 0, \"new-elements\": \"new\", \"other-elements\": \"other\" } ]");
+        ElementPtr expected = Element::fromJSON(expected_str);
+        EXPECT_TRUE(isc::data::isEquivalent(left, expected))
+            << "Actual: " << left->str()
+            << "\nExpected: " << expected->str();
+    }
+}
+
+}  // namespace
diff --git a/src/lib/cc/tests/element_value_unittests.cc b/src/lib/cc/tests/element_value_unittests.cc
new file mode 100644
index 0000000..e284440
--- /dev/null
+++ b/src/lib/cc/tests/element_value_unittests.cc
@@ -0,0 +1,43 @@
+// Copyright (C) 2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <cc/element_value.h>
+#include <gtest/gtest.h>
+
+using namespace isc::data;
+
+namespace {
+
+// This test verifies that integer value can be extracted.
+TEST(ElementValue, intValue) {
+    EXPECT_EQ(5, ElementValue<int>()(Element::create(5)));
+    EXPECT_THROW(ElementValue<int>()(Element::create("hola!")),
+                 TypeError);
+}
+
+// This test verifies that double value can be extracted.
+TEST(ElementValue, doubleValue) {
+    EXPECT_EQ(1.4, ElementValue<double>()(Element::create(1.4)));
+    EXPECT_THROW(ElementValue<double>()(Element::create("hola!")),
+                 TypeError);
+}
+
+// This test verifies that boolean value can be extracted.
+TEST(ElementValue, boolValue) {
+    EXPECT_TRUE(ElementValue<bool>()(Element::create(true)));
+    EXPECT_THROW(ElementValue<bool>()(Element::create("hola!")),
+                 TypeError);
+}
+
+// This test verifies that string value can be extracted.
+TEST(ElementValue, stringValue) {
+    EXPECT_EQ("hola!", ElementValue<std::string>()(Element::create("hola!")));
+    EXPECT_THROW(ElementValue<std::string>()(Element::create(false)),
+                 TypeError);
+}
+
+}
diff --git a/src/lib/cc/tests/json_feed_unittests.cc b/src/lib/cc/tests/json_feed_unittests.cc
new file mode 100644
index 0000000..84739f7
--- /dev/null
+++ b/src/lib/cc/tests/json_feed_unittests.cc
@@ -0,0 +1,449 @@
+// Copyright (C) 2017-2021 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <cc/data.h>
+#include <cc/json_feed.h>
+#include <gtest/gtest.h>
+#include <sstream>
+#include <string>
+
+using namespace isc::config;
+using namespace isc::data;
+
+namespace {
+
+/// @brief Test fixture class for @ref JSONFeed class.
+class JSONFeedTest : public ::testing::Test {
+public:
+
+    /// @brief Constructor.
+    ///
+    /// Initializes @ref json_map_ and @ref json_list_ which hold reference
+    /// JSON structures.
+    JSONFeedTest()
+        : json_map_(), json_list_() {
+        ElementPtr m = Element::fromJSON(createJSON());
+        ElementPtr l = Element::createList();
+        l->add(m);
+        json_map_ = m;
+        json_list_ = l;
+    }
+
+    /// @brief Creates a JSON map holding 20 elements.
+    ///
+    /// Each map value is a list of 20 elements.
+    std::string createJSON() const {
+        // Create a list of 20 elements.
+        ElementPtr list_element = Element::createList();
+        for (unsigned i = 0; i < 20; ++i) {
+            std::ostringstream s;
+            s << "list_element" << i;
+            list_element->add(Element::create(s.str()));
+        }
+
+        // Create a map of 20 elements. Each map element holds a list
+        // of 20 elements.
+        ElementPtr map_element = Element::createMap();
+        for (unsigned i = 0; i < 20; ++i) {
+            std::ostringstream s;
+            s << "map_element" << i;
+            map_element->set(s.str(), list_element);
+        }
+
+        return (prettyPrint(map_element));
+    }
+
+    /// @brief Test that the JSONFeed correctly recognizes the beginning
+    /// and the end of the JSON structure.
+    ///
+    /// @param input_json A string holding an input JSON structure.
+    /// @param expected_output A structure holding expected output from the
+    /// @ref JSONFeed::toElement.
+    void testRead(const std::string& input_json,
+                  const ConstElementPtr& expected_output) {
+        JSONFeed feed;
+        ASSERT_NO_THROW(feed.initModel());
+
+        // Post the data into the feed in 10 bytes long chunks.
+        size_t chunk = 10;
+
+        for (size_t i = 0; i < input_json.size(); i += chunk) {
+            bool done = false;
+            // When we're near the end of the data stream, the chunk length may
+            // vary.
+            if (i + chunk >= input_json.size()) {
+                chunk = input_json.size() - i;
+                done = true;
+            }
+            // Feed the parser with a data chunk and parse it.
+            feed.postBuffer(&input_json[i], chunk);
+            feed.poll();
+            if (!done) {
+                ASSERT_TRUE(feed.needData());
+            }
+        }
+
+        // Convert parsed/collected data in the feed into the structure of
+        // elements.
+        ConstElementPtr element_from_feed = feed.toElement();
+        EXPECT_TRUE(element_from_feed->equals(*expected_output));
+    }
+
+    /// @brief Test that the JSONFeed correctly recognizes the beginning
+    /// and the end of the JSON structure.
+    ///
+    /// @param input_json A string holding an input JSON structure.
+    /// @param expected_output A string holding expected output from the
+    /// @ref JSONFeed::getProcessedText.
+    void testRead(const std::string& input_json,
+                  const std::string& expected_output) {
+        JSONFeed feed;
+        ASSERT_NO_THROW(feed.initModel());
+
+        // Post the data into the feed in 10 bytes long chunks.
+        size_t chunk = 10;
+
+        for (size_t i = 0; i < input_json.size(); i += chunk) {
+            bool done = false;
+            // When we're near the end of the data stream, the chunk length may
+            // vary.
+            if (i + chunk >= input_json.size()) {
+                chunk = input_json.size() - i;
+                done = true;
+            }
+            // Feed the parser with a data chunk and parse it.
+            feed.postBuffer(&input_json[i], chunk);
+            feed.poll();
+            if (!done) {
+                ASSERT_TRUE(feed.needData());
+            }
+        }
+
+        EXPECT_EQ(expected_output, feed.getProcessedText());
+    }
+
+    /// @brief Test that the @ref JSONFeed signals an error when the input
+    /// string holds invalid data.
+    ///
+    /// @param input_json A string holding an input JSON structure.
+    /// @param err_msg A string holding an expected error message.
+    void testInvalidRead(const std::string& input_json,
+                         const std::string& err_msg) {
+        JSONFeed feed;
+        ASSERT_NO_THROW(feed.initModel());
+
+        ASSERT_NO_THROW(feed.postBuffer(&input_json[0], input_json.size()));
+        ASSERT_NO_THROW(feed.poll());
+
+        EXPECT_FALSE(feed.needData());
+        EXPECT_FALSE(feed.feedOk());
+
+        EXPECT_EQ(err_msg, feed.getErrorMessage());
+    }
+
+    /// @brief JSON map holding a number of lists.
+    ConstElementPtr json_map_;
+
+    /// @brief JSON list holding a map of lists.
+    ConstElementPtr json_list_;
+
+};
+
+// This test verifies that toElement should not be called before
+// the feed detects the end of the data stream.
+TEST_F(JSONFeedTest, toElementTooSoon) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "{\n";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_TRUE(feed.needData());
+    EXPECT_THROW(feed.toElement(), JSONFeedError);
+}
+
+// This test verifies that toElement checks JSON syntax as a side effect.
+TEST_F(JSONFeedTest, badJSON) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "{\n]\n";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_FALSE(feed.needData());
+    EXPECT_THROW(feed.toElement(), JSONFeedError);
+}
+
+// This test verifies that a JSON structure starting with '{' is accepted
+// and parsed.
+TEST_F(JSONFeedTest, startWithBrace) {
+    std::string json = createJSON();
+    testRead(json, json_map_);
+}
+
+// This test verifies that a JSON structure starting with '[' is accepted
+// and parsed.
+TEST_F(JSONFeedTest, startWithSquareBracket) {
+    std::string json = createJSON();
+    json = std::string("[") + json + std::string("]");
+    testRead(json, json_list_);
+}
+
+// This test verifies that input JSON can be preceded with whitespaces.
+TEST_F(JSONFeedTest, startWithWhitespace) {
+    std::string json = createJSON();
+    json = std::string("  \r\r\t  ") + json;
+    testRead(json, json_map_);
+}
+
+// This test verifies that an empty map is accepted and parsed.
+TEST_F(JSONFeedTest, emptyMap) {
+    std::string json = "{}";
+    testRead(json, Element::createMap());
+}
+
+// This test verifies that an empty list is accepted and parsed.
+TEST_F(JSONFeedTest, emptyList) {
+    std::string json = "[  ]";
+    testRead(json, Element::createList());
+}
+
+// This test verifies that an error is signalled when a JSON structure
+// is preceded by invalid character.
+TEST_F(JSONFeedTest, unexpectedFirstCharacter) {
+    std::string json = "a {}";
+    std::string err_msg = "invalid first character a";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that an error is signalled when a JSON structure
+// is preceded by white spaces and an invalid character.
+TEST_F(JSONFeedTest, unexpectedCharacter) {
+    std::string json = " a {}";
+    std::string err_msg = "invalid character a";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that an error is signalled when the JSON structure
+// begins by a string.
+TEST_F(JSONFeedTest, stringFirst) {
+    std::string json = "\"foo\"";
+    std::string err_msg = "invalid first character \"";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that an error is signalled when the JSON structure
+// begins by white spaces followed by a string.
+TEST_F(JSONFeedTest, stringBefore) {
+    std::string json = " \"foo\"";
+    std::string err_msg = "invalid character \"";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that an error is signalled when a JSON structure
+// lacks an opening brace character.
+TEST_F(JSONFeedTest, noOpeningBrace) {
+    std::string json = "\"x\": \"y\" }";
+    std::string err_msg = "invalid first character \"";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that an error is signalled when a JSON structure
+// lacks an opening square bracket.
+TEST_F(JSONFeedTest, noOpeningSquareBracket) {
+    std::string json = "1, 2 ]";
+    std::string err_msg = "invalid first character 1";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that a string is correctly handled
+TEST_F(JSONFeedTest, string) {
+    std::string json = "{ \"braces\": \"}}}}\" }";
+    ElementPtr expected = Element::createMap();
+    expected->set("braces", Element::create("}}}}"));
+    testRead(json, expected);
+}
+
+// This test verifies that a string with escapes is correctly handled
+TEST_F(JSONFeedTest, escape) {
+    std::string json = "{ \"escapes\": \"\\n\\t\\\"\\\\\" }";
+    ElementPtr expected = Element::createMap();
+    expected->set("escapes", Element::create("\n\t\"\\"));
+    testRead(json, expected);
+}
+
+// This test verifies that white spaces before JSON are ignored.
+TEST_F(JSONFeedTest, whiteSpaceBefore) {
+    std::string json = " \n  [ ]\n";
+    std::string expected = "[ ]";
+    testRead(json, expected);
+}
+
+// This test verifies that bash style comments before JSON are ignored.
+TEST_F(JSONFeedTest, bashCommentBefore) {
+    std::string json = "# ahah\n  # foo\"bar\n{ }\n";
+    std::string expected = "{ }";
+    testRead(json, expected);
+}
+
+// This test verifies that C++ style comments before JSON are ignored.
+TEST_F(JSONFeedTest, cppCommentBefore) {
+    std::string json = "// ahah\n  // foo\"bar\n[ 12 ]\n";
+    std::string expected = "[ 12 ]";
+    testRead(json, expected);
+}
+
+// This test verifies that multi-line comments before JSON are ignored.
+TEST_F(JSONFeedTest, multiLineCommentBefore) {
+    std::string json = "/* ahah\n \"// foo*bar**/\n { \"foo\": \"bar\" }\n";
+    std::string expected = "{ \"foo\": \"bar\" }";
+    testRead(json, expected);
+}
+
+// This test verifies that an error is signalled when a slash does not
+// begin a C++ or C style comment before JSON.
+TEST_F(JSONFeedTest, badCommentBefore) {
+    std::string json = "/# foo\n [ ]\n";
+    std::string err_msg = "invalid characters /#";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that bash style comments are ignored.
+TEST_F(JSONFeedTest, bashComments) {
+    std::string json = "{ # ahah\n \"foo\": # value?\n \"bar\" }";
+    std::string expected = "{ \n \"foo\": \n \"bar\" }";
+    testRead(json, expected);
+}
+
+// This test verifies that C++ style comments are ignored.
+TEST_F(JSONFeedTest, cppComments) {
+    std::string json = "[ // ahah\n \"foo\", /// value?\n \"bar\" ]";
+    std::string expected = "[ \n \"foo\", \n \"bar\" ]";
+    testRead(json, expected);
+}
+
+// This test verifies that multi-line comments are ignored.
+TEST_F(JSONFeedTest, multiLineComments) {
+    std::string json = "{ /* ahah\n \"// foo*bar**/\n \"foo\": \"bar\" }\n";
+    std::string expected = "{ \n\n \"foo\": \"bar\" }";
+    testRead(json, expected);
+}
+
+// This test verifies that an error is signalled a slash does not begin
+// a C++ or C style comment.
+TEST_F(JSONFeedTest, badComment) {
+    std::string json = "[ /# foo\n ]\n";
+    std::string err_msg = "invalid characters /#";
+    testInvalidRead(json, err_msg);
+}
+
+// This test verifies that trailing garbage is ignored.
+TEST_F(JSONFeedTest, trailing) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "[ 1, 2] 3, 4]";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_FALSE(feed.needData());
+    EXPECT_TRUE(feed.feedOk());
+    std::string expected = "[ 1, 2]";
+    EXPECT_EQ(expected, feed.getProcessedText());
+}
+
+// Example from DHCPv4 unit tests.
+TEST_F(JSONFeedTest, bashComment4) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "{ \"Dhcp4\": { \"interfaces-config\": {"
+        "  \"interfaces\": [ \"*\" ]"
+        "},\n"
+        "# this is a comment\n"
+        "\"rebind-timer\": 2000, \n"
+        "# lots of comments here\n"
+        "# and here\n"
+        "\"renew-timer\": 1000, \n"
+        "\"subnet4\": [ { "
+        "    \"pools\": [ { \"pool\": \"192.0.2.1 - 192.0.2.100\" } ],"
+        "    \"subnet\": \"192.0.2.0/24\", "
+        "    \"interface\": \"eth0\""
+        " } ],"
+        "\"valid-lifetime\": 4000 } }";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_FALSE(feed.needData());
+    EXPECT_TRUE(feed.feedOk());
+    EXPECT_NO_THROW(feed.toElement());
+}
+
+// Example from DHCPv4 unit tests.
+TEST_F(JSONFeedTest, bashCommentsInline4) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "{ \"Dhcp4\": { \"interfaces-config\": {"
+        "  \"interfaces\": [ \"*\" ]"
+        "},\n"
+        "\"rebind-timer\": 2000, # everything after # is ignored\n"
+        "\"renew-timer\": 1000, # this will be ignored, too\n"
+        "\"subnet4\": [ { "
+        "    \"pools\": [ { \"pool\": \"192.0.2.1 - 192.0.2.100\" } ],"
+        "    \"subnet\": \"192.0.2.0/24\", "
+        "    \"interface\": \"eth0\""
+        " } ],"
+        "\"valid-lifetime\": 4000 } }";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_FALSE(feed.needData());
+    EXPECT_TRUE(feed.feedOk());
+    EXPECT_NO_THROW(feed.toElement());
+}
+
+// Example from DHCPv6 unit tests.
+TEST_F(JSONFeedTest, cppComments6) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "{ \"Dhcp6\": { \"interfaces-config\": {"
+        "  \"interfaces\": [ \"*\" ]"
+        "},\n"
+        "\"preferred-lifetime\": 3000, // this is a comment \n"
+        "\"rebind-timer\": 2000, // everything after // is ignored\n"
+        "\"renew-timer\": 1000, // this will be ignored, too\n"
+        "\"subnet6\": [ { "
+        "    \"pools\": [ { \"pool\": \"2001:db8:1::/64\" } ],"
+        "    \"subnet\": \"2001:db8:1::/48\", "
+        "    \"interface\": \"eth0\""
+        " } ],"
+        "\"valid-lifetime\": 4000 } }";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_FALSE(feed.needData());
+    EXPECT_TRUE(feed.feedOk());
+    EXPECT_NO_THROW(feed.toElement());
+}
+
+// Example from DHCPv6 unit tests.
+TEST_F(JSONFeedTest, multilineComments6) {
+    JSONFeed feed;
+    ASSERT_NO_THROW(feed.initModel());
+    std::string json = "{ \"Dhcp6\": { \"interfaces-config\": {"
+        "  \"interfaces\": [ \"*\" ]"
+        "},\n"
+        "\"preferred-lifetime\": 3000, /* this is a C style comment\n"
+        "that\n can \n span \n multiple \n lines */ \n"
+        "\"rebind-timer\": 2000,\n"
+        "\"renew-timer\": 1000, \n"
+        "\"subnet6\": [ { "
+        "    \"pools\": [ { \"pool\": \"2001:db8:1::/64\" } ],"
+        "    \"subnet\": \"2001:db8:1::/48\", "
+        "    \"interface\": \"eth0\""
+        " } ],"
+        "\"valid-lifetime\": 4000 } }";
+    feed.postBuffer(&json[0], json.size());
+    feed.poll();
+    EXPECT_FALSE(feed.needData());
+    EXPECT_TRUE(feed.feedOk());
+    EXPECT_NO_THROW(feed.toElement());
+}
+
+} // end of anonymous namespace.
diff --git a/src/lib/cc/tests/run_unittests.cc b/src/lib/cc/tests/run_unittests.cc
new file mode 100644
index 0000000..40c051f
--- /dev/null
+++ b/src/lib/cc/tests/run_unittests.cc
@@ -0,0 +1,20 @@
+// Copyright (C) 2009-2015 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <gtest/gtest.h>
+#include <util/unittests/run_all.h>
+#include <log/logger_support.h>
+
+int
+main(int argc, char* argv[]) {
+    ::testing::InitGoogleTest(&argc, argv);
+
+    isc::log::initLogger();
+
+    return (isc::util::unittests::run_all());
+}
diff --git a/src/lib/cc/tests/server_tag_unittest.cc b/src/lib/cc/tests/server_tag_unittest.cc
new file mode 100644
index 0000000..523be74
--- /dev/null
+++ b/src/lib/cc/tests/server_tag_unittest.cc
@@ -0,0 +1,97 @@
+// Copyright (C) 2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <cc/server_tag.h>
+#include <exceptions/exceptions.h>
+#include <boost/scoped_ptr.hpp>
+#include <gtest/gtest.h>
+#include <string>
+
+using namespace isc;
+using namespace isc::data;
+
+namespace {
+
+// This test verifies that the constructors of the ServerTag class
+// work properly.
+TEST(ServerTagTest, constructors) {
+    boost::scoped_ptr<ServerTag> tag;
+
+    {
+        SCOPED_TRACE("default constructor for all servers");
+        ASSERT_NO_THROW(tag.reset(new ServerTag()));
+        EXPECT_EQ(ServerTag::ALL, tag->get());
+        EXPECT_TRUE(tag->amAll());
+    }
+
+    {
+        SCOPED_TRACE("all servers");
+        ASSERT_NO_THROW(tag.reset(new ServerTag(ServerTag::ALL)));
+        EXPECT_EQ(ServerTag::ALL, tag->get());
+        EXPECT_TRUE(tag->amAll());
+    }
+
+    {
+        SCOPED_TRACE("no whitespace");
+        ASSERT_NO_THROW(tag.reset(new ServerTag("xyz")));
+        EXPECT_EQ("xyz", tag->get());
+        EXPECT_FALSE(tag->amAll());
+    }
+
+    {
+        SCOPED_TRACE("leading whitespace");
+        ASSERT_NO_THROW(tag.reset(new ServerTag("  left")));
+        EXPECT_EQ("left", tag->get());
+        EXPECT_FALSE(tag->amAll());
+    }
+
+    {
+        SCOPED_TRACE("terminating whitespace");
+        ASSERT_NO_THROW(tag.reset(new ServerTag("right  ")));
+        EXPECT_EQ("right", tag->get());
+        EXPECT_FALSE(tag->amAll());
+    }
+
+    {
+        SCOPED_TRACE("leading and terminating whitespace");
+        ASSERT_NO_THROW(tag.reset(new ServerTag("  both left-right  ")));
+        EXPECT_EQ("both left-right", tag->get());
+        EXPECT_FALSE(tag->amAll());
+    }
+
+    {
+        SCOPED_TRACE("upper to lower case");
+        ASSERT_NO_THROW(tag.reset(new ServerTag("UPPER CASE TAG")));
+        EXPECT_EQ("upper case tag", tag->get());
+        EXPECT_FALSE(tag->amAll());
+    }
+}
+
+// This test verifies that malformed server tags are rejected.
+TEST(ServerTagTest, malformed) {
+    {
+        SCOPED_TRACE("empty tag");
+        EXPECT_THROW(ServerTag(""), BadValue);
+    }
+
+    {
+        SCOPED_TRACE("only whitespaces");
+        EXPECT_THROW(ServerTag("   "), BadValue);
+    }
+
+    {
+        SCOPED_TRACE("too long tag, max is 256");
+        EXPECT_THROW(ServerTag(std::string(257, 'c')), BadValue);
+    }
+
+    {
+        SCOPED_TRACE("use reserved keyword any as a tag");
+        EXPECT_THROW(ServerTag("any"), BadValue);
+    }
+}
+
+}
diff --git a/src/lib/cc/tests/simple_parser_unittest.cc b/src/lib/cc/tests/simple_parser_unittest.cc
new file mode 100644
index 0000000..58aa40d
--- /dev/null
+++ b/src/lib/cc/tests/simple_parser_unittest.cc
@@ -0,0 +1,364 @@
+// Copyright (C) 2016-2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <stdint.h>
+#include <cc/simple_parser.h>
+#include <gtest/gtest.h>
+
+using namespace isc;
+using namespace isc::data;
+using namespace isc::asiolink;
+using isc::dhcp::DhcpConfigError;
+
+/// This list defines required keywords.
+const SimpleRequiredKeywords REQUIRED_KEYWORDS = { "foobar" };
+
+/// This table defines keywords and types.
+const SimpleKeywords KEYWORDS = {
+    { "id",     Element::integer },
+    { "prefix", Element::string },
+    { "map",    Element::map },
+    { "any",    Element::any }
+};
+
+/// This table defines sample default values. Although these are DHCPv6
+/// specific, the mechanism is generic and can be used by any other component.
+const SimpleDefaults SAMPLE_DEFAULTS = {
+    { "renew-timer",        Element::integer, "900" },
+    { "rebind-timer",       Element::integer, "1800" },
+    { "preferred-lifetime", Element::integer, "3600" },
+    { "valid-lifetime",     Element::integer, "7200" }
+};
+
+/// This list defines parameters that can be inherited from one scope
+/// to another. Although these are DHCPv6 specific, the mechanism is generic and
+/// can be used by any other component.
+const ParamsList SAMPLE_INHERITS = {
+    "renew-timer",
+    "rebind-timer",
+    "preferred-lifetime",
+    "valid-lifetime"
+};
+
+/// @brief Simple Parser test fixture class
+class SimpleParserTest : public ::testing::Test {
+public:
+    /// @brief Checks if specified map has an integer parameter with expected value
+    ///
+    /// @param map map to be checked
+    /// @param param_name name of the parameter to be checked
+    /// @param exp_value expected value of the parameter.
+    void checkIntegerValue(const ConstElementPtr& map, const std::string& param_name,
+                           int64_t exp_value) {
+
+        // First check if the passed element is a map.
+        ASSERT_EQ(Element::map, map->getType());
+
+        // Now try to get the element being checked
+        ConstElementPtr elem = map->get(param_name);
+        ASSERT_TRUE(elem);
+
+        // Now check if it's indeed integer
+        ASSERT_EQ(Element::integer, elem->getType());
+
+        // Finally, check if its value meets expectation.
+        EXPECT_EQ(exp_value, elem->intValue());
+    }
+};
+
+class SimpleParserClassTest : public SimpleParser {
+public:
+    /// @brief Instantiation of getAndConvert
+    ///
+    /// @param scope specified parameter will be extracted from this scope
+    /// @param name name of the parameter for error report
+    /// @return a bool value
+    bool getAsBool(ConstElementPtr scope, const std::string& name) {
+        return (getAndConvert<bool, toBool>(scope, name, "boolean"));
+    }
+
+    /// @brief Convert to boolean
+    ///
+    /// @param str the string "false" or "true"
+    /// @return false for "false" and true for "true"
+    /// @thrown isc::OutOfRange if not "false" or "true'
+    static bool toBool(const std::string& str) {
+        if (str == "false") {
+            return (false);
+        } else if (str == "true") {
+            return (true);
+        } else {
+            isc_throw(TypeError, "not a boolean: " << str);
+        }
+    }
+};
+
+// This test checks if the checkRequired method works as expected.
+TEST_F(SimpleParserTest, checkRequired) {
+    ConstElementPtr empty = Element::fromJSON("{ }");
+    EXPECT_THROW(SimpleParser::checkRequired(REQUIRED_KEYWORDS, empty),
+                 DhcpConfigError);
+    ConstElementPtr other = Element::fromJSON("{ \"foo\": 1, \"bar\": 2 }");
+    EXPECT_THROW(SimpleParser::checkRequired(REQUIRED_KEYWORDS, other),
+                 DhcpConfigError);
+    ConstElementPtr good = Element::fromJSON("{ \"foobar\": 2 }");
+    EXPECT_NO_THROW(SimpleParser::checkRequired(REQUIRED_KEYWORDS, good));
+}
+
+// This test checks if the checkKeywords method works as expected.
+TEST_F(SimpleParserTest, checkKeywords) {
+    ConstElementPtr empty = Element::fromJSON("{ }");
+    EXPECT_NO_THROW(SimpleParser::checkKeywords(KEYWORDS, empty));
+    ConstElementPtr id = Element::fromJSON("{ \"id\": 1 }");
+    EXPECT_NO_THROW(SimpleParser::checkKeywords(KEYWORDS, id));
+    ConstElementPtr any = Element::fromJSON("{ \"any\": 1 }");
+    EXPECT_NO_THROW(SimpleParser::checkKeywords(KEYWORDS, any));
+    ConstElementPtr bad_id = Element::fromJSON("{ \"id\": true }");
+    EXPECT_THROW(SimpleParser::checkKeywords(KEYWORDS, bad_id),
+                 DhcpConfigError);
+    ConstElementPtr bad_prefix = Element::fromJSON("{ \"prefix\": 12 }");
+    EXPECT_THROW(SimpleParser::checkKeywords(KEYWORDS, bad_prefix),
+                 DhcpConfigError);
+    ConstElementPtr bad_map = Element::fromJSON("{ \"map\": [ ] }");
+    EXPECT_THROW(SimpleParser::checkKeywords(KEYWORDS, bad_map),
+                 DhcpConfigError);
+    ConstElementPtr spurious = Element::fromJSON("{ \"spurious\": 1 }");
+    EXPECT_THROW(SimpleParser::checkKeywords(KEYWORDS, spurious),
+                 DhcpConfigError);
+
+    // Bad type has precedence.
+    ConstElementPtr bad = Element::fromJSON("{ \"spurious\": 1, \"id\": true }");
+    try {
+        SimpleParser::checkKeywords(KEYWORDS, bad);
+        ADD_FAILURE() << "expect exception";
+    } catch (const DhcpConfigError& ex) {
+        EXPECT_EQ("'id' parameter is not an integer", std::string(ex.what()));
+    } catch (...) {
+        ADD_FAILURE() << "expect DhcpConfigError";
+    }
+}
+
+// This test checks if the parameters can be inherited from the global
+// scope to the subnet scope.
+TEST_F(SimpleParserTest, deriveParams) {
+    ElementPtr global = Element::fromJSON("{ \"renew-timer\": 1,"
+                                          "  \"rebind-timer\": 2,"
+                                          "  \"preferred-lifetime\": 3,"
+                                          "  \"valid-lifetime\": 4"
+                                          "}");
+    ElementPtr subnet = Element::fromJSON("{ \"renew-timer\": 100 }");
+
+    // we should inherit 3 parameters. Renew-timer should remain intact,
+    // as it was already defined in the subnet scope.
+    size_t num;
+    EXPECT_NO_THROW(num = SimpleParser::deriveParams(global, subnet,
+                                                     SAMPLE_INHERITS));
+    EXPECT_EQ(3, num);
+
+    // Check the values. 3 of them are inherited, while the fourth one
+    // was already defined in the subnet, so should not be inherited.
+    checkIntegerValue(subnet, "renew-timer", 100);
+    checkIntegerValue(subnet, "rebind-timer", 2);
+    checkIntegerValue(subnet, "preferred-lifetime", 3);
+    checkIntegerValue(subnet, "valid-lifetime", 4);
+}
+
+// This test checks if global defaults are properly set for DHCPv6.
+TEST_F(SimpleParserTest, setDefaults) {
+
+    ElementPtr empty = Element::fromJSON("{ }");
+    size_t num = 0;
+
+    EXPECT_NO_THROW(num = SimpleParser::setDefaults(empty, SAMPLE_DEFAULTS));
+
+    // We expect at least 4 parameters to be inserted.
+    EXPECT_GE(num, 3);
+
+    checkIntegerValue(empty, "valid-lifetime", 7200);
+    checkIntegerValue(empty, "preferred-lifetime", 3600);
+    checkIntegerValue(empty, "rebind-timer", 1800);
+    checkIntegerValue(empty, "renew-timer", 900);
+}
+
+// This test checks if global defaults are properly set for DHCPv6.
+TEST_F(SimpleParserTest, setListDefaults) {
+
+    ElementPtr empty = Element::fromJSON("[{}, {}, {}]");
+    size_t num;
+
+    EXPECT_NO_THROW(num = SimpleParser::setListDefaults(empty, SAMPLE_DEFAULTS));
+
+    // We expect at least 12 parameters to be inserted (3 entries, with
+    // 4 parameters inserted in each)
+    EXPECT_EQ(12, num);
+
+    ASSERT_EQ(Element::list, empty->getType());
+    ASSERT_EQ(3, empty->size());
+
+    ConstElementPtr first = empty->get(0);
+    ConstElementPtr second = empty->get(1);
+    ConstElementPtr third = empty->get(2);
+
+    checkIntegerValue(first, "valid-lifetime", 7200);
+    checkIntegerValue(first, "preferred-lifetime", 3600);
+    checkIntegerValue(first, "rebind-timer", 1800);
+    checkIntegerValue(first, "renew-timer", 900);
+
+    checkIntegerValue(second, "valid-lifetime", 7200);
+    checkIntegerValue(second, "preferred-lifetime", 3600);
+    checkIntegerValue(second, "rebind-timer", 1800);
+    checkIntegerValue(second, "renew-timer", 900);
+
+    checkIntegerValue(third, "valid-lifetime", 7200);
+    checkIntegerValue(third, "preferred-lifetime", 3600);
+    checkIntegerValue(third, "rebind-timer", 1800);
+    checkIntegerValue(third, "renew-timer", 900);
+}
+
+// This test exercises the getIntType template
+TEST_F(SimpleParserTest, getIntType) {
+
+    SimpleParserClassTest parser;
+
+    // getIntType checks it can be found
+    ElementPtr not_found = Element::fromJSON("{ \"bar\": 1 }");
+    EXPECT_THROW(parser.getUint8(not_found, "foo"), DhcpConfigError);
+
+    // getIntType checks if it is an integer
+    ElementPtr not_int = Element::fromJSON("{ \"foo\": \"xyz\" }");
+    EXPECT_THROW(parser.getUint8(not_int, "foo"), DhcpConfigError);
+
+    // getIntType checks bounds
+    ElementPtr negative = Element::fromJSON("{ \"foo\": -1 }");
+    EXPECT_THROW(parser.getUint8(negative, "foo"), DhcpConfigError);
+    ElementPtr too_large = Element::fromJSON("{ \"foo\": 1024 }");
+    EXPECT_THROW(parser.getUint8(too_large, "foo"), DhcpConfigError);
+
+    // checks if getIntType can return the expected value
+    ElementPtr hundred = Element::fromJSON("{ \"foo\": 100 }");
+    uint8_t val = 0;
+    EXPECT_NO_THROW(val = parser.getUint8(hundred, "foo"));
+    EXPECT_EQ(100, val);
+}
+
+// This test exercises the getInteger with range checking
+TEST_F(SimpleParserTest, getInteger) {
+
+    // The value specified is 100.
+    ElementPtr json = Element::fromJSON("{ \"bar\": 100 }");
+    int64_t x;
+
+    // Positive case: we expect value in range 0..200. All ok.
+    EXPECT_NO_THROW(x = SimpleParser::getInteger(json, "bar", 0, 200));
+    EXPECT_EQ(100, x);
+
+    // Border checks: 100 for 100..200 range is still ok.
+    EXPECT_NO_THROW(x = SimpleParser::getInteger(json, "bar", 100, 200));
+    // Border checks: 100 for 1..100 range is still ok.
+    EXPECT_NO_THROW(x = SimpleParser::getInteger(json, "bar", 1, 100));
+
+    // Out of expected range. Should throw.
+    EXPECT_THROW(x = SimpleParser::getInteger(json, "bar", 101, 200), OutOfRange);
+    EXPECT_THROW(x = SimpleParser::getInteger(json, "bar", 1, 99), OutOfRange);
+}
+
+// This test exercises the getAndConvert template
+TEST_F(SimpleParserTest, getAndConvert) {
+
+    SimpleParserClassTest parser;
+
+    // getAndConvert checks it can be found
+    ElementPtr not_found = Element::fromJSON("{ \"bar\": \"true\" }");
+    EXPECT_THROW(parser.getAsBool(not_found, "foo"), DhcpConfigError);
+
+    // getAndConvert checks if it is a string
+    ElementPtr not_bool = Element::fromJSON("{ \"foo\": 1 }");
+    EXPECT_THROW(parser.getAsBool(not_bool, "foo"), DhcpConfigError);
+
+    // checks if getAndConvert can return the expected value
+    ElementPtr a_bool = Element::fromJSON("{ \"foo\": \"false\" }");
+    bool val = true;
+    EXPECT_NO_THROW(val = parser.getAsBool(a_bool, "foo"));
+    EXPECT_FALSE(val);
+
+    // getAndConvert checks conversion
+    ElementPtr bad_bool = Element::fromJSON("{ \"foo\": \"bar\" }");
+    EXPECT_THROW(parser.getAsBool(bad_bool, "bar"), DhcpConfigError);
+}
+
+// This test exercises the getIOAddress
+TEST_F(SimpleParserTest, getIOAddress) {
+
+    SimpleParserClassTest parser;
+
+    // getAddress checks it can be found
+    ElementPtr not_found = Element::fromJSON("{ \"bar\": 1 }");
+    EXPECT_THROW(parser.getAddress(not_found, "foo"), DhcpConfigError);
+
+    // getAddress checks if it is a string
+    ElementPtr not_addr = Element::fromJSON("{ \"foo\": 1234 }");
+    EXPECT_THROW(parser.getAddress(not_addr, "foo"), DhcpConfigError);
+
+    // checks if getAddress can return the expected value of v4 address
+    ElementPtr v4 = Element::fromJSON("{ \"foo\": \"192.0.2.1\" }");
+    IOAddress val("::");
+    EXPECT_NO_THROW(val = parser.getAddress(v4, "foo"));
+    EXPECT_EQ("192.0.2.1" , val.toText());
+
+    // checks if getAddress can return the expected value of v4 address
+    ElementPtr v6 = Element::fromJSON("{ \"foo\": \"2001:db8::1\" }");
+    EXPECT_NO_THROW(val = parser.getAddress(v6, "foo"));
+    EXPECT_EQ("2001:db8::1" , val.toText());
+}
+
+// This test exercises getDouble()
+TEST_F(SimpleParserTest, getDouble) {
+
+    SimpleParserClassTest parser;
+    std::string json =
+    "{\n"
+    "  \"string\" : \"12.3\",\n"
+    "  \"bool\" : true, \n"
+    "  \"int\" : 777, \n"
+    "  \"map\" : {}, \n"
+    "  \"list\" : [], \n"
+    "  \"zero\" : 0.0, \n"
+    "  \"fraction\" : .75, \n"
+    "  \"negative\" : -1.45, \n"
+    "  \"positive\" : 346.7 \n"
+    "}\n";
+
+    // Create our test set of parameters.
+    ElementPtr elems;
+    ASSERT_NO_THROW(elems = Element::fromJSON(json)) << " invalid JSON, test is broken";
+
+    // Verify that a non-existant element is caught.
+    EXPECT_THROW(parser.getDouble(elems, "not-there"), DhcpConfigError);
+
+    // Verify that wrong element types are caught.
+    EXPECT_THROW(parser.getDouble(elems, "string"), DhcpConfigError);
+    EXPECT_THROW(parser.getDouble(elems, "int"), DhcpConfigError);
+    EXPECT_THROW(parser.getDouble(elems, "bool"), DhcpConfigError);
+    EXPECT_THROW(parser.getDouble(elems, "map"), DhcpConfigError);
+    EXPECT_THROW(parser.getDouble(elems, "list"), DhcpConfigError);
+
+    // Verify valid values are correct.
+    double value;
+
+    EXPECT_NO_THROW(value = parser.getDouble(elems, "zero"));
+    EXPECT_EQ(0.0, value);
+
+    EXPECT_NO_THROW(value = parser.getDouble(elems, "fraction"));
+    EXPECT_EQ(.75, value);
+
+    EXPECT_NO_THROW(value = parser.getDouble(elems, "negative"));
+    EXPECT_EQ(-1.45, value);
+
+    EXPECT_NO_THROW(value = parser.getDouble(elems, "positive"));
+    EXPECT_EQ(346.7, value);
+}
diff --git a/src/lib/cc/tests/stamped_element_unittest.cc b/src/lib/cc/tests/stamped_element_unittest.cc
new file mode 100644
index 0000000..1ffcd84
--- /dev/null
+++ b/src/lib/cc/tests/stamped_element_unittest.cc
@@ -0,0 +1,132 @@
+// Copyright (C) 2018-2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/stamped_element.h>
+#include <boost/date_time/gregorian/gregorian.hpp>
+#include <boost/date_time/posix_time/posix_time.hpp>
+#include <gtest/gtest.h>
+
+using namespace isc::data;
+
+namespace {
+
+// Tests that the modification timestamp is by default set to current
+// time and the identifier is set to 0.
+TEST(StampedElementTest, create) {
+    StampedElement element;
+
+    // Default identifier is 0.
+    EXPECT_EQ(0, element.getId());
+
+    // By default there is no server tag.
+    EXPECT_TRUE(element.getServerTags().empty());
+
+    // Checking that the delta between now and the timestamp is within
+    // 5s range should be sufficient.
+    boost::posix_time::time_duration delta =
+        boost::posix_time::second_clock::local_time() -
+        element.getModificationTime();
+    EXPECT_LT(delta.seconds(), 5);
+}
+
+// Tests that default id can be overridden by a new value.
+TEST(StampedElementTest, setId) {
+    StampedElement element;
+    element.setId(123);
+    EXPECT_EQ(123, element.getId());
+}
+
+// Tests that the modification timestamp can be set to an arbitrary
+// value.
+TEST(StampedElementTest, setModificationTime) {
+    boost::posix_time::ptime
+        modification_time(boost::gregorian::date(2002, boost::date_time::Jan, 10),
+                          boost::posix_time::time_duration(1,2,3));
+    StampedElement element;
+    element.setModificationTime(modification_time);
+    EXPECT_TRUE(element.getModificationTime() == modification_time);
+}
+
+// Tests that updating modification timestamp sets it to the current
+// time.
+TEST(StampedElementTest, update) {
+    boost::posix_time::ptime
+        modification_time(boost::gregorian::date(2002, boost::date_time::Jan, 10),
+                          boost::posix_time::time_duration(1,2,3));
+    StampedElement element;
+    element.setModificationTime(modification_time);
+    element.updateModificationTime();
+
+    // Checking that the delta between now and the timestamp is within
+    // 5s range should be sufficient.
+    boost::posix_time::time_duration delta =
+        boost::posix_time::second_clock::local_time() -
+        element.getModificationTime();
+    EXPECT_LT(delta.seconds(), 5);
+}
+
+// Tests that one or more server tag can be specified.
+TEST(StampedElementTest, setServerTag) {
+    StampedElement element;
+    element.setServerTag("foo");
+    EXPECT_EQ(1, element.getServerTags().size());
+    EXPECT_EQ("foo", element.getServerTags().begin()->get());
+
+    element.setServerTag("bar");
+    EXPECT_EQ(2, element.getServerTags().size());
+
+    EXPECT_TRUE(element.hasServerTag(ServerTag("foo")));
+    EXPECT_TRUE(element.hasServerTag(ServerTag("bar")));
+    EXPECT_FALSE(element.hasServerTag(ServerTag("xyz")));
+    EXPECT_FALSE(element.hasAllServerTag());
+
+    element.setServerTag(ServerTag::ALL);
+    EXPECT_TRUE(element.hasAllServerTag());
+}
+
+// Tests that a server tag can be deleted.
+TEST(StampedElementTest, delServerTag) {
+    StampedElement element;
+    EXPECT_THROW(element.delServerTag("foo"), isc::NotFound);
+    element.setServerTag("foo");
+    element.setServerTag("bar");
+
+    ASSERT_EQ(2, element.getServerTags().size());
+    EXPECT_TRUE(element.hasServerTag(ServerTag("foo")));
+    EXPECT_TRUE(element.hasServerTag(ServerTag("bar")));
+
+    EXPECT_NO_THROW(element.delServerTag("foo"));
+    ASSERT_EQ(1, element.getServerTags().size());
+    EXPECT_TRUE(element.hasServerTag(ServerTag("bar")));
+
+    EXPECT_NO_THROW(element.delServerTag("bar"));
+    EXPECT_EQ(0, element.getServerTags().size());
+    EXPECT_THROW(element.delServerTag("bar"), isc::NotFound);
+}
+
+
+// Test that metadata can be created from the StampedElement.
+TEST(StampedElementTest, getMetadata) {
+    StampedElement element;
+    element.setServerTag("world");
+    auto metadata = element.getMetadata();
+    ASSERT_TRUE(metadata);
+    ASSERT_EQ(Element::map, metadata->getType());
+
+    auto server_tags_element = metadata->get("server-tags");
+    ASSERT_TRUE(server_tags_element);
+    EXPECT_EQ(Element::list, server_tags_element->getType());
+    EXPECT_EQ(1, server_tags_element->size());
+
+    auto server_tag_element = server_tags_element->get(0);
+    ASSERT_TRUE(server_tag_element);
+    EXPECT_EQ(Element::string, server_tag_element->getType());
+    EXPECT_EQ("world", server_tag_element->stringValue());
+}
+
+}
diff --git a/src/lib/cc/tests/stamped_value_unittest.cc b/src/lib/cc/tests/stamped_value_unittest.cc
new file mode 100644
index 0000000..3673825
--- /dev/null
+++ b/src/lib/cc/tests/stamped_value_unittest.cc
@@ -0,0 +1,175 @@
+// Copyright (C) 2018-2019 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+
+#include <cc/stamped_value.h>
+#include <exceptions/exceptions.h>
+#include <boost/scoped_ptr.hpp>
+#include <gtest/gtest.h>
+
+using namespace isc;
+using namespace isc::data;
+
+namespace {
+
+// Tests that the stamped value can be created with a NULL value.
+TEST(StampedValueTest, createNull) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar"));
+
+    EXPECT_TRUE(value->amNull());
+
+    EXPECT_THROW(value->getType(), InvalidOperation);
+    EXPECT_THROW(value->getValue(), InvalidOperation);
+    EXPECT_THROW(value->getIntegerValue(), InvalidOperation);
+    EXPECT_THROW(value->getBoolValue(), InvalidOperation);
+    EXPECT_THROW(value->getDoubleValue(), InvalidOperation);
+}
+
+// Tests that stamped value from string can be created.
+TEST(StampedValueTest, createFromString) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", Element::create("foo")));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::string, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ("foo", value->getValue());
+
+    EXPECT_THROW(value->getIntegerValue(), TypeError);
+    EXPECT_THROW(value->getBoolValue(), TypeError);
+    EXPECT_THROW(value->getDoubleValue(), TypeError);
+}
+
+// Tests that the stamped value can be created from string using the
+// factory function variant that takes parameter type as an argument.
+TEST(StampedValueTest, convertStringToString) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", "foo", Element::string));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::string, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ("foo", value->getValue());
+}
+
+// Tests that stamped value from integer can be created.
+TEST(StampedValueTest, createFromInteger) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", Element::create(static_cast<int64_t>(5))));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::integer, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ("5", value->getValue());
+    int64_t signed_integer;
+    ASSERT_NO_THROW(signed_integer = value->getIntegerValue());
+    EXPECT_EQ(5, signed_integer);
+
+    EXPECT_THROW(value->getBoolValue(), TypeError);
+    EXPECT_THROW(value->getDoubleValue(), TypeError);
+}
+
+// Tests that stamped value can be converted from string to integer.
+TEST(StampedValueTest, convertStringToInteger) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", "123", Element::integer));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::integer, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ(123, value->getIntegerValue());
+
+    EXPECT_THROW(StampedValue::create("bar", "hoho", Element::integer), BadValue);
+}
+
+// Tests that stamped value from bool can be created.
+TEST(StampedValueTest, createFromBool) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", Element::create(static_cast<bool>(true))));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::boolean, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ("1", value->getValue());
+    bool bool_value = false;
+    ASSERT_NO_THROW(bool_value = value->getBoolValue());
+    EXPECT_TRUE(bool_value);
+
+    EXPECT_THROW(value->getIntegerValue(), TypeError);
+    EXPECT_THROW(value->getDoubleValue(), TypeError);
+}
+
+// Tests that stamped value can be converted from string to boolean.
+TEST(StampedValueTest, convertStringToBoolean) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", "1", Element::boolean));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::boolean, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_TRUE(value->getBoolValue());
+
+    ASSERT_NO_THROW(value = StampedValue::create("foo", "0", Element::boolean));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::boolean, value->getType());
+    EXPECT_EQ("foo", value->getName());
+    EXPECT_FALSE(value->getBoolValue());
+
+    EXPECT_THROW(StampedValue::create("bar", "888", Element::boolean), BadValue);
+}
+
+// Tests that stamped value from real can be created.
+TEST(StampedValueTest, createFromDouble) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", Element::create(static_cast<double>(1.45))));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::real, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ("1.45", value->getValue());
+    double double_value = 0;
+    ASSERT_NO_THROW(double_value = value->getDoubleValue());
+    EXPECT_EQ(1.45, double_value);
+
+    EXPECT_THROW(value->getIntegerValue(), TypeError);
+    EXPECT_THROW(value->getBoolValue(), TypeError);
+}
+
+// Tests that stamped value from real can handle a round value.
+TEST(StampedValueTest, createFromDoubleRound) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", Element::create(static_cast<double>(7.0))));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::real, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ("7.0", value->getValue());
+    double double_value = 0;
+    ASSERT_NO_THROW(double_value = value->getDoubleValue());
+    EXPECT_EQ(7.0, double_value);
+
+    EXPECT_THROW(value->getIntegerValue(), TypeError);
+    EXPECT_THROW(value->getBoolValue(), TypeError);
+}
+
+// Tests that stamped value can be converted from string to real.
+TEST(StampedValueTest, convertStringToDouble) {
+    StampedValuePtr value;
+    ASSERT_NO_THROW(value = StampedValue::create("bar", "1.67", Element::real));
+    EXPECT_FALSE(value->amNull());
+    EXPECT_EQ(Element::real, value->getType());
+    EXPECT_EQ("bar", value->getName());
+    EXPECT_EQ(1.67, value->getDoubleValue());
+
+    EXPECT_THROW(StampedValue::create("bar", "hoho", Element::real), BadValue);
+}
+
+// Tests that the value must have an allowed type.
+TEST(StampedValueTest, createFailures) {
+    EXPECT_THROW(StampedValue::create("bar", ElementPtr()), BadValue);
+    EXPECT_THROW(StampedValue::create("bar", Element::createMap()), TypeError);
+    EXPECT_THROW(StampedValue::create("bar", Element::createList()), TypeError);
+
+    EXPECT_THROW(StampedValue::create("bar", "1", Element::map), TypeError);
+    EXPECT_THROW(StampedValue::create("bar", "1", Element::list), TypeError);
+    EXPECT_THROW(StampedValue::create("bar", "1", Element::null), TypeError);
+}
+
+}
diff --git a/src/lib/cc/tests/user_context_unittests.cc b/src/lib/cc/tests/user_context_unittests.cc
new file mode 100644
index 0000000..e88b421
--- /dev/null
+++ b/src/lib/cc/tests/user_context_unittests.cc
@@ -0,0 +1,132 @@
+// Copyright (C) 2018-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <cc/user_context.h>
+#include <gtest/gtest.h>
+
+using namespace isc::data;
+
+namespace {
+
+ElementPtr gen() {
+    std::string content = "{ \"foo\": 1, \"bar\": \"xyz\" }";
+    return (Element::fromJSON(content));
+}
+
+TEST(UserContext, setget) {
+    UserContext parent;
+    EXPECT_FALSE(parent.getContext());
+    ConstElementPtr map = gen();
+    parent.setContext(map);
+    ConstElementPtr ctx = parent.getContext();
+    EXPECT_EQ(*ctx, *map);
+}
+
+TEST(UserContext, null) {
+    UserContext parent;
+    ElementPtr map = gen();
+    parent.contextToElement(map);
+    ElementPtr expected = gen();
+    EXPECT_EQ(*expected, *map);
+}
+
+TEST(UserContext, notMap) {
+    UserContext parent;
+    ConstElementPtr ctx = Element::create("foo");
+    parent.setContext(ctx);
+    ElementPtr map = gen();
+    parent.contextToElement(map);
+    ElementPtr expected = gen();
+    expected->set("user-context", ctx);
+    EXPECT_EQ(*expected, *map);
+}
+
+TEST(UserContext, empty) {
+    UserContext parent;
+    ConstElementPtr ctx = Element::createMap();
+    parent.setContext(ctx);
+    ElementPtr map = gen();
+    parent.contextToElement(map);
+    ElementPtr expected = gen();
+    expected->set("user-context", ctx);
+    EXPECT_EQ(*expected, *map);
+}
+
+TEST(UserContext, noComment) {
+    UserContext parent;
+    ConstElementPtr ctx = Element::fromJSON("{ \"version\": 1 }");
+    parent.setContext(ctx);
+    ElementPtr map = gen();
+    parent.contextToElement(map);
+    ElementPtr expected = gen();
+    expected->set("user-context", ctx);
+    EXPECT_EQ(*expected, *map);
+};
+
+TEST(UserContext, onlyComment) {
+    UserContext parent;
+    ConstElementPtr ctx = Element::fromJSON("{ \"comment\": \"foobar\" }");
+    parent.setContext(ctx);
+    ElementPtr map = gen();
+    parent.contextToElement(map);
+    ElementPtr expected = gen();
+    expected->set("user-context", ctx);
+    EXPECT_EQ(*expected, *map);
+}
+
+TEST(UserContext, both) {
+    UserContext parent;
+    ConstElementPtr ctx =
+        Element::fromJSON("{ \"comment\": \"foobar\", \"version\": 1 }");
+    parent.setContext(ctx);
+    ElementPtr map = gen();
+    parent.contextToElement(map);
+    ElementPtr expected = gen();
+    expected->set("user-context", ctx);
+    EXPECT_EQ(*expected, *map);
+}
+
+TEST(toElement, notMap) {
+    ConstElementPtr arg = Element::create("foo");
+    ConstElementPtr result = UserContext::toElement(arg);
+    EXPECT_EQ(*result, *arg);
+}
+
+TEST(toElement, empty) {
+    ElementPtr map = gen();
+    ConstElementPtr ctx = Element::createMap();
+    map->set("user-context", ctx);
+    ConstElementPtr result = UserContext::toElement(map);
+    EXPECT_EQ(*result, *map);
+}
+
+TEST(toElement, noComment) {
+    ElementPtr map = gen();
+    ConstElementPtr ctx = Element::fromJSON("{ \"version\": 1 }");
+    map->set("user-context", ctx);
+    ConstElementPtr result = UserContext::toElement(map);
+    EXPECT_EQ(*result, *map);
+}
+
+TEST(toElement, onlyComment) {
+    ElementPtr map = gen();
+    ConstElementPtr ctx = Element::fromJSON("{ \"comment\": \"foobar\" }");
+    map->set("user-context", ctx);
+    ConstElementPtr result = UserContext::toElement(map);
+    EXPECT_EQ(*result, *map);
+}
+
+TEST(toElement, both) {
+    ElementPtr map = gen();
+    ConstElementPtr ctx =
+        Element::fromJSON("{ \"comment\": \"foobar\", \"version\": 1 }");
+    map->set("user-context", ctx);
+    ConstElementPtr result = UserContext::toElement(map);
+    EXPECT_EQ(*result, *map);
+}
+
+}
diff --git a/src/lib/cc/user_context.cc b/src/lib/cc/user_context.cc
new file mode 100644
index 0000000..2ff1984
--- /dev/null
+++ b/src/lib/cc/user_context.cc
@@ -0,0 +1,30 @@
+// Copyright (C) 2017-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#include <config.h>
+#include <cc/user_context.h>
+
+
+namespace isc {
+namespace data {
+
+void
+UserContext::contextToElement(ElementPtr map) const {
+    // Set user-context extracting comment
+    ConstElementPtr context = getContext();
+    if (context) {
+        map->set("user-context", context);
+    }
+}
+
+ElementPtr
+UserContext::toElement(ConstElementPtr map) {
+    ElementPtr result = isc::data::copy(map);
+    return (result);
+}
+
+}; // end of isc::dhcp namespace
+}; // end of isc namespace
diff --git a/src/lib/cc/user_context.h b/src/lib/cc/user_context.h
new file mode 100644
index 0000000..2804c7e
--- /dev/null
+++ b/src/lib/cc/user_context.h
@@ -0,0 +1,59 @@
+// Copyright (C) 2017-2020 Internet Systems Consortium, Inc. ("ISC")
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef USER_CONTEXT_H
+#define USER_CONTEXT_H
+
+#include <cc/data.h>
+#include <boost/shared_ptr.hpp>
+
+namespace isc {
+namespace data {
+
+/// @brief Base class for user context
+///
+/// Many configuration structures allow attaching and storing arbitrary
+/// user data that we call user context. Each of those configuration
+/// structures need to derive from this class or include this class
+/// to handle user context.
+struct UserContext {
+    /// @brief Returns const pointer to the user context.
+    data::ConstElementPtr getContext() const {
+        return (user_context_);
+    }
+
+    /// @brief Sets user context.
+    /// @param ctx user context to be stored.
+    void setContext(const data::ConstElementPtr& ctx) {
+        user_context_ = ctx;
+    }
+
+    /// @brief Merge unparse a user_context object.
+    ///
+    /// Add user-context to map, but only if defined. Omit if it was not.
+    ///
+    /// @param map A pointer to map where the user context will be unparsed.
+    void contextToElement(data::ElementPtr map) const;
+
+    /// @brief Copy an Element map
+    ///
+    /// A previous version of this extracted comments.
+    ///
+    /// @param map A pointer to map.
+    /// @return a copy of map
+    static data::ElementPtr toElement(data::ConstElementPtr map);
+
+protected:
+
+    /// @brief Pointer to the user context (may be NULL)
+    data::ConstElementPtr user_context_;
+};
+
+} // end of isc::dhcp namespace
+} // end of isc namespace
+
+
+#endif // USER_CONTEXT_H