From: Marcin Siodelski <marcin@isc.org>
Date: Wed, 29 Mar 2017 10:06:30 +0000 (+0200)
Subject: [5078] Implemented commands forwarding in Control Agent.
X-Git-Tag: trac5196_base~14^2~10
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0d0288e1bbbe71a6161d228dbaae685bcf3cb831;p=thirdparty%2Fkea.git

[5078] Implemented commands forwarding in Control Agent.
---

diff --git a/src/bin/agent/ca_cfg_mgr.cc b/src/bin/agent/ca_cfg_mgr.cc
index 1ba886b20c..2028edc279 100644
--- a/src/bin/agent/ca_cfg_mgr.cc
+++ b/src/bin/agent/ca_cfg_mgr.cc
@@ -10,6 +10,7 @@
 #include <agent/simple_parser.h>
 #include <cc/simple_parser.h>
 #include <cc/command_interpreter.h>
+#include <exceptions/exceptions.h>
 
 using namespace isc::dhcp;
 using namespace isc::process;
@@ -34,6 +35,20 @@ CtrlAgentCfgContext::CtrlAgentCfgContext(const CtrlAgentCfgContext& orig)
     ctrl_sockets_[TYPE_DHCP6] = orig.ctrl_sockets_[TYPE_DHCP6];
 }
 
+CtrlAgentCfgContext::ServerType
+CtrlAgentCfgContext::toServerType(const std::string& service) {
+    if (service == "dhcp4") {
+        return (CtrlAgentCfgContext::TYPE_DHCP4);
+
+    } else if (service == "dhcp6") {
+        return (CtrlAgentCfgContext::TYPE_DHCP6);
+
+    } else if (service == "d2") {
+        return (CtrlAgentCfgContext::TYPE_D2);
+    }
+
+    isc_throw(isc::BadValue, "invalid service value " << service);
+}
 
 CtrlAgentCfgMgr::CtrlAgentCfgMgr()
     : DCfgMgrBase(DCfgContextBasePtr(new CtrlAgentCfgContext())) {
diff --git a/src/bin/agent/ca_cfg_mgr.h b/src/bin/agent/ca_cfg_mgr.h
index 655d2b5c39..4373d61a09 100644
--- a/src/bin/agent/ca_cfg_mgr.h
+++ b/src/bin/agent/ca_cfg_mgr.h
@@ -11,6 +11,7 @@
 #include <hooks/hooks_config.h>
 #include <process/d_cfg_mgr.h>
 #include <boost/pointer_cast.hpp>
+#include <string>
 
 namespace isc {
 namespace agent {
@@ -42,6 +43,11 @@ public:
     /// @brief Used check that specified ServerType is within valid range.
     static const uint32_t MAX_TYPE_SUPPORTED = TYPE_D2;
 
+    /// @brief Converts service specified as a string to ServerType.
+    ///
+    /// @param service Service value as a string: 'dhcp4', 'dhcp6', 'd2'.
+    static ServerType toServerType(const std::string& service);
+
     /// @brief Creates a clone of this context object.
     ///
     /// Note this method does not do deep copy the information about control sockets.
diff --git a/src/bin/agent/ca_command_mgr.cc b/src/bin/agent/ca_command_mgr.cc
index 5a36d8e954..449ec7fd50 100644
--- a/src/bin/agent/ca_command_mgr.cc
+++ b/src/bin/agent/ca_command_mgr.cc
@@ -4,11 +4,24 @@
 // 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 <agent/ca_cfg_mgr.h>
 #include <agent/ca_command_mgr.h>
+#include <agent/ca_controller.h>
+#include <agent/ca_log.h>
+#include <agent/ca_process.h>
+#include <asiolink/asio_wrapper.h>
+#include <asiolink/io_service.h>
+#include <asiolink/unix_domain_socket.h>
+#include <cc/command_interpreter.h>
 #include <cc/data.h>
 #include <boost/pointer_cast.hpp>
+#include <string>
+#include <vector>
 
+using namespace isc::asiolink;
+using namespace isc::config;
 using namespace isc::data;
+using namespace isc::process;
 
 namespace isc {
 namespace agent {
@@ -25,13 +38,191 @@ CtrlAgentCommandMgr::CtrlAgentCommandMgr()
 
 ConstElementPtr
 CtrlAgentCommandMgr::handleCommand(const std::string& cmd_name,
-                                   const isc::data::ConstElementPtr& params) {
+                                   const isc::data::ConstElementPtr& params,
+                                   const isc::data::ConstElementPtr& original_cmd) {
+    ConstElementPtr answer;
+
+    try {
+        // list-commands is a special case. The Control Agent always supports this
+        // command but most of the time users don't want to list commands supported
+        // by the CA but by one of the Kea servers. The user would indicate that
+        // by specifying 'service' value.
+        if (cmd_name == "list-commands") {
+            if (original_cmd && original_cmd->contains("service")) {
+                ConstElementPtr services = original_cmd->get("service");
+                if (services && !services->empty()) {
+                    // The non-empty control command 'service' parameter exists which
+                    // means we will forward this command to the Kea server. Let's
+                    // cheat that Control Agent doesn't support this command to
+                    // avoid it being handled by CA.
+                    answer = createAnswer(CONTROL_RESULT_COMMAND_UNSUPPORTED,
+                                          "forwarding list-commands command");
+                }
+            }
+        }
+    } catch (const std::exception& ex) {
+        answer = createAnswer(CONTROL_RESULT_ERROR, "invalid service parameter value: "
+                              + std::string(ex.what()));
+    }
+
+    if (!answer) {
+        // Try handling this command on our own.
+        answer = HookedCommandMgr::handleCommand(cmd_name, params, original_cmd);
+    }
+
+    int rcode = 0;
+    static_cast<void>(parseAnswer(rcode, answer));
+
+    // We have tried handling the command on our own but it seems that neither
+    // the Control Agent nor a hook library can handle this command. We need
+    // to try forwarding the command to one of the Kea servers.
+    if (original_cmd && (rcode == CONTROL_RESULT_COMMAND_UNSUPPORTED)) {
+        try {
+            answer = tryForwardCommand(cmd_name, original_cmd);
+
+        } catch (const CommandForwardingError& ex) {
+            // This is apparently some configuration error or client's error.
+            // We have notify the client.
+            answer = createAnswer(CONTROL_RESULT_ERROR, ex.what());
+
+        } catch (const CommandForwardingSkip& ex) {
+            // Command is not intended to be forwarded so do nothing.
+        }
+    }
+
+    // We have a response, so let's wrap it in the list.
     ElementPtr answer_list = Element::createList();
-    answer_list->add(boost::const_pointer_cast<
-                     Element>(HookedCommandMgr::handleCommand(cmd_name, params)));
+    answer_list->add(boost::const_pointer_cast<Element>(answer));
+
     return (answer_list);
 }
 
+ConstElementPtr
+CtrlAgentCommandMgr::tryForwardCommand(const std::string& cmd_name,
+                                       const isc::data::ConstElementPtr& command) {
+    // Context will hold the server configuration.
+    CtrlAgentCfgContextPtr ctx;
+
+    // There is a hierarchy of the objects through which we need to pass to get
+    // the configuration context. We may simplify this at some point but since
+    // we're in the singleton we want to make sure that we're using most current
+    // configuration.
+    boost::shared_ptr<CtrlAgentController> controller =
+        boost::dynamic_pointer_cast<CtrlAgentController>(CtrlAgentController::instance());
+    if (controller) {
+        CtrlAgentProcessPtr process = controller->getCtrlAgentProcess();
+        if (process) {
+            CtrlAgentCfgMgrPtr cfgmgr = process->getCtrlAgentCfgMgr();
+            if (cfgmgr) {
+                ctx = cfgmgr->getCtrlAgentCfgContext();
+            }
+        }
+    }
+
+    // This is highly unlikely but keep the checks just in case someone messes up
+    // in the code.
+    if (!ctx) {
+        isc_throw(CommandForwardingError, "internal server error: unable to retrieve"
+                  " Control Agent configuration information");
+    }
+
+    // If the service is not specified it means that the Control Agent is the
+    // intended receiver of this message. This is not a fatal error, we simply
+    // skip forwarding the command and rely on the internal logic of the
+    // Control Agent to generate response.
+    ConstElementPtr service_elements = command->get("service");
+    if (!service_elements) {
+        isc_throw(CommandForwardingSkip, "service parameter not specified");
+    }
+
+    // If the service exists it must be a list, even though we currently allow
+    // only one service.
+    std::vector<ElementPtr> service_vec;
+    try {
+        service_vec = service_elements->listValue();
+
+    } catch (const std::exception& ex) {
+        isc_throw(CommandForwardingError, "service parameter is not a list");
+    }
+
+    // service list may be empty in which case we treat it as it is not specified.
+    if (service_vec.empty()) {
+        isc_throw(CommandForwardingSkip, "service parameter is empty");
+    }
+
+    // Do not allow more than one service value. This will be allowed in the
+    // future.
+    if (service_vec.size() > 1) {
+        isc_throw(CommandForwardingError, "service parameter must contain 0 or 1"
+                  " service value");
+    }
+
+    // Convert the service to the server type values. Make sure the client
+    // provided right value.
+    CtrlAgentCfgContext::ServerType server_type;
+    try {
+        server_type = CtrlAgentCfgContext::toServerType(service_vec.at(0)->stringValue());
+
+    } catch (const std::exception& ex) {
+        // Invalid value in service list. Can't proceed.
+        isc_throw(CommandForwardingError, ex.what());
+    }
+
+    // Now that we know what service it should be forwarded to, we should
+    // find a matching forwarding socket. If this socket is not configured,
+    // we have to communicate it to the client.
+    ConstElementPtr socket_info = ctx->getControlSocketInfo(server_type);
+    if (!socket_info) {
+        isc_throw(CommandForwardingError, "forwarding socket is not configured"
+                  " for the server type " << service_vec.at(0)->stringValue());
+    }
+
+    // If the configuration does its job properly the socket-name must be
+    // specified and must be a string value.
+    std::string socket_name = socket_info->get("socket-name")->stringValue();
+
+    // Forward command and receive reply.
+    IOService io_service;
+    UnixDomainSocket unix_socket(io_service);
+    size_t receive_len;
+    try {
+        unix_socket.connect(socket_name);
+        std::string wire_command = command->toWire();
+        unix_socket.write(&wire_command[0], wire_command.size());
+        receive_len = unix_socket.receive(&receive_buf_[0], receive_buf_.size());
+
+    } catch (...) {
+        isc_throw(CommandForwardingError, "unable to forward command to the "
+                  + service_vec.at(0)->stringValue() + " service. The server "
+                  "is likely to be offline");
+    }
+
+    // This is really not possible right now, but when we migrate to the
+    // solution using timeouts it is possible that the response is not
+    // received.
+    if (receive_len == 0) {
+        isc_throw(CommandForwardingError, "internal server error: no answer"
+                  " received from the server to the forwarded message");
+    }
+
+    std::string reply(&receive_buf_[0], receive_len);
+
+    ConstElementPtr answer;
+    try {
+        answer = Element::fromJSON(reply);
+
+        LOG_INFO(agent_logger, CTRL_AGENT_COMMAND_FORWARDED)
+            .arg(cmd_name)
+            .arg(service_vec.at(0)->stringValue());
+
+    } catch (const std::exception& ex) {
+        isc_throw(CommandForwardingError, "internal server error: unable to parse"
+                  " server's answer to the forwarded message: " << ex.what());
+    }
+
+    return (answer);
+}
+
 
 } // end of namespace isc::agent
 } // end of namespace isc
diff --git a/src/bin/agent/ca_command_mgr.h b/src/bin/agent/ca_command_mgr.h
index 03de1b12a9..d8c598fb77 100644
--- a/src/bin/agent/ca_command_mgr.h
+++ b/src/bin/agent/ca_command_mgr.h
@@ -8,12 +8,29 @@
 #define CTRL_AGENT_COMMAND_MGR_H
 
 #include <config/hooked_command_mgr.h>
+#include <exceptions/exceptions.h>
 #include <boost/noncopyable.hpp>
 #include <boost/shared_ptr.hpp>
+#include <array>
 
 namespace isc {
 namespace agent {
 
+/// @brief Exception thrown when an error occurred during control command
+/// forwarding.
+class CommandForwardingError : public Exception {
+public:
+    CommandForwardingError(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
+/// @brief Exception thrown when command forwarding has been skipped.
+class CommandForwardingSkip : public Exception {
+public:
+    CommandForwardingSkip(const char* file, size_t line, const char* what) :
+        isc::Exception(file, line, what) { };
+};
+
 /// @brief Command Manager for Control Agent.
 ///
 /// This is an implementation of the Command Manager within Control Agent.
@@ -45,20 +62,55 @@ public:
     ///
     /// @param cmd_name Command name.
     /// @param params Command arguments.
+    /// @param original_cmd Original command being processed.
     ///
     /// @return Pointer to the const data element representing response
     /// to a command.
     virtual isc::data::ConstElementPtr
     handleCommand(const std::string& cmd_name,
-                  const isc::data::ConstElementPtr& params);
+                  const isc::data::ConstElementPtr& params,
+                  const isc::data::ConstElementPtr& orginal_cmd);
 
 private:
+
+    /// @brief Tries to forward received control command to Kea servers.
+    ///
+    /// When the Control Agent was unable to process the control command
+    /// because it doesn't recognize it, the command should be forwarded to
+    /// the specific Kea services listed within a 'service' parameter.
+    ///
+    /// @todo Currently only one service per control command is supported.
+    /// Forwarding to multiple services should be allowed in the future.
+    ///
+    /// This method makes an attempt to forward the control command. If
+    /// the 'service' parameter is not specified or it is empty, the
+    /// command is not forwarded and the @ref CommandForwardingSkip exception
+    /// is thrown. The caller catching this exception should not treat
+    /// this situation as an error but this is normal situation when the
+    /// message is not intended to be forwarded.
+    ///
+    /// All other exceptions should be treated as an error.
+    ///
+    /// @param cmd_name Command name.
+    /// @param command Pointer to the object representing the forwarded command.
+    ///
+    /// @return Response to forwarded command.
+    /// @throw CommandForwardingError when an error occurred during forwarding.
+    /// @throw CommandForwardingSkip when 'service' parameter hasn't been
+    /// specified which means that the command should not be forwarded.
+    isc::data::ConstElementPtr
+    tryForwardCommand(const std::string& cmd_name,
+                      const isc::data::ConstElementPtr& command);
+
     /// @brief Private constructor.
     ///
     /// The instance should be created using @ref CtrlAgentCommandMgr::instance,
     /// thus the constructor is private.
     CtrlAgentCommandMgr();
 
+    /// @brief Buffer into which responses to forwarded commands are stored.
+    std::array<char, 8192> receive_buf_;
+
 };
 
 } // end of namespace isc::agent
diff --git a/src/bin/agent/ca_controller.cc b/src/bin/agent/ca_controller.cc
index a5fce22fd1..02ad66ac9d 100644
--- a/src/bin/agent/ca_controller.cc
+++ b/src/bin/agent/ca_controller.cc
@@ -86,5 +86,10 @@ CtrlAgentController::CtrlAgentController()
 CtrlAgentController::~CtrlAgentController() {
 }
 
+CtrlAgentProcessPtr
+CtrlAgentController::getCtrlAgentProcess() {
+    return (boost::dynamic_pointer_cast<CtrlAgentProcess>(getProcess()));
+}
+
 } // namespace isc::agent
 } // namespace isc
diff --git a/src/bin/agent/ca_controller.h b/src/bin/agent/ca_controller.h
index 2cca081298..fa1c1c3504 100644
--- a/src/bin/agent/ca_controller.h
+++ b/src/bin/agent/ca_controller.h
@@ -7,6 +7,7 @@
 #ifndef CTRL_AGENT_CONTROLLER_H
 #define CTRL_AGENT_CONTROLLER_H
 
+#include <agent/ca_process.h>
 #include <process/d_controller.h>
 
 namespace isc {
@@ -20,6 +21,8 @@ namespace agent {
 class CtrlAgentController : public process::DControllerBase {
 public:
 
+    using DControllerBase::getIOService;
+
     /// @brief Static singleton instance method.
     ///
     /// This method returns the base class singleton instance member.
@@ -32,6 +35,9 @@ public:
     /// @brief Destructor
     virtual ~CtrlAgentController();
 
+    /// @brief Returns pointer to an instance of the underlying process object.
+    CtrlAgentProcessPtr getCtrlAgentProcess();
+
     /// @brief Defines the application name, this is passed into base class
     /// and appears in log statements.
     static const char* agent_app_name_;
diff --git a/src/bin/agent/ca_messages.mes b/src/bin/agent/ca_messages.mes
index 2bdc7371f7..1336dcba41 100644
--- a/src/bin/agent/ca_messages.mes
+++ b/src/bin/agent/ca_messages.mes
@@ -6,6 +6,10 @@
 
 $NAMESPACE isc::agent
 
+% CTRL_AGENT_COMMAND_FORWARDED command %1 successfully forwarded to the service %2
+This informational message is issued when the CA successfully forwards
+the control message to the specified Kea service and receives a response.
+
 % CTRL_AGENT_HTTP_SERVICE_STARTED HTTP service bound to address %1:%2
 This informational message indicates that the server has started HTTP service
 on the specified address and port. All control commands should be sent to this
diff --git a/src/bin/agent/tests/Makefile.am b/src/bin/agent/tests/Makefile.am
index 19b1359146..94e8d941fc 100644
--- a/src/bin/agent/tests/Makefile.am
+++ b/src/bin/agent/tests/Makefile.am
@@ -69,6 +69,7 @@ ca_unittests_LDADD += $(top_builddir)/src/lib/stats/libkea-stats.la
 ca_unittests_LDADD += $(top_builddir)/src/lib/config/libkea-cfgclient.la
 ca_unittests_LDADD += $(top_builddir)/src/lib/dhcp/libkea-dhcp++.la
 ca_unittests_LDADD += $(top_builddir)/src/lib/http/libkea-http.la
+ca_unittests_LDADD += $(top_builddir)/src/lib/asiolink/testutils/libasiolinktest.la
 ca_unittests_LDADD += $(top_builddir)/src/lib/asiolink/libkea-asiolink.la
 ca_unittests_LDADD += $(top_builddir)/src/lib/cc/libkea-cc.la
 ca_unittests_LDADD += $(top_builddir)/src/lib/dns/libkea-dns++.la
diff --git a/src/bin/agent/tests/ca_cfg_mgr_unittests.cc b/src/bin/agent/tests/ca_cfg_mgr_unittests.cc
index a3e6fcaafe..9f5e26c2f9 100644
--- a/src/bin/agent/tests/ca_cfg_mgr_unittests.cc
+++ b/src/bin/agent/tests/ca_cfg_mgr_unittests.cc
@@ -7,6 +7,7 @@
 #include <config.h>
 #include <agent/ca_cfg_mgr.h>
 #include <agent/parser_context.h>
+#include <exceptions/exceptions.h>
 #include <process/testutils/d_test_stubs.h>
 #include <process/d_cfg_mgr.h>
 #include <agent/tests/test_libraries.h>
@@ -27,6 +28,18 @@ public:
     using CtrlAgentCfgMgr::parse;
 };
 
+// Tests conversion of the 'service' parameter to ServerType.
+TEST(CtrlAgentCfgContextTest, toServerType) {
+    EXPECT_EQ(CtrlAgentCfgContext::TYPE_DHCP4,
+              CtrlAgentCfgContext::toServerType("dhcp4"));
+    EXPECT_EQ(CtrlAgentCfgContext::TYPE_DHCP6,
+              CtrlAgentCfgContext::toServerType("dhcp6"));
+    EXPECT_EQ(CtrlAgentCfgContext::TYPE_D2,
+              CtrlAgentCfgContext::toServerType("d2"));
+    EXPECT_THROW(CtrlAgentCfgContext::toServerType("other"),
+                 isc::BadValue);
+}
+
 // Tests construction of CtrlAgentCfgMgr class.
 TEST(CtrlAgentCfgMgr, construction) {
     boost::scoped_ptr<CtrlAgentCfgMgr> cfg_mgr;
diff --git a/src/bin/agent/tests/ca_command_mgr_unittests.cc b/src/bin/agent/tests/ca_command_mgr_unittests.cc
index 8061150adc..8a97f6f684 100644
--- a/src/bin/agent/tests/ca_command_mgr_unittests.cc
+++ b/src/bin/agent/tests/ca_command_mgr_unittests.cc
@@ -5,29 +5,52 @@
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 #include <config.h>
+#include <agent/ca_cfg_mgr.h>
 #include <agent/ca_command_mgr.h>
+#include <agent/ca_controller.h>
+#include <agent/ca_process.h>
+#include <asiolink/asio_wrapper.h>
+#include <asiolink/interval_timer.h>
+#include <asiolink/io_service.h>
+#include <asiolink/testutils/test_server_unix_socket.h>
 #include <cc/command_interpreter.h>
+#include <cc/data.h>
+#include <process/testutils/d_test_stubs.h>
+#include <util/threads/thread.h>
+#include <boost/bind.hpp>
+#include <boost/pointer_cast.hpp>
 #include <gtest/gtest.h>
 
 using namespace isc::agent;
+using namespace isc::asiolink;
 using namespace isc::data;
+using namespace isc::process;
 
 namespace {
 
+/// @brief Test unix socket file name.
+const std::string TEST_SOCKET = "test-socket";
+
+/// @brief Test timeout in ms.
+const long TEST_TIMEOUT = 10000;
+
 /// @brief Test fixture class for @ref CtrlAgentCommandMgr.
 ///
 /// @todo Add tests for various commands, including the cases when the
 /// commands are forwarded to other servers via unix sockets.
 /// Meanwhile, this is just a placeholder for the tests.
-class CtrlAgentCommandMgrTest : public ::testing::Test {
+class CtrlAgentCommandMgrTest : public DControllerTest {
 public:
 
     /// @brief Constructor.
     ///
     /// Deregisters all commands except 'list-commands'.
     CtrlAgentCommandMgrTest()
-        : mgr_(CtrlAgentCommandMgr::instance()) {
+        : DControllerTest(CtrlAgentController::instance),
+          mgr_(CtrlAgentCommandMgr::instance()) {
         mgr_.deregisterAll();
+        removeUnixSocketFile();
+        initProcess();
     }
 
     /// @brief Destructor.
@@ -35,6 +58,7 @@ public:
     /// Deregisters all commands except 'list-commands'.
     virtual ~CtrlAgentCommandMgrTest() {
         mgr_.deregisterAll();
+        removeUnixSocketFile();
     }
 
     /// @brief Verifies received answer
@@ -58,8 +82,128 @@ public:
         }
     }
 
+    /// @brief Returns socket file path.
+    static std::string unixSocketFilePath() {
+        std::ostringstream s;
+        s << TEST_DATA_BUILDDIR << "/" << TEST_SOCKET;
+        return (s.str());
+    }
+
+    /// @brief Removes unix socket descriptor.
+    void removeUnixSocketFile() {
+        static_cast<void>(remove(unixSocketFilePath().c_str()));
+    }
+
+    /// @brief Returns pointer to CtrlAgentProcess instance.
+    CtrlAgentProcessPtr getCtrlAgentProcess() {
+        return (boost::dynamic_pointer_cast<CtrlAgentProcess>(getProcess()));
+    }
+
+    /// @brief Returns pointer to CtrlAgentCfgMgr instance for a process.
+    CtrlAgentCfgMgrPtr getCtrlAgentCfgMgr() {
+        CtrlAgentCfgMgrPtr p;
+        if (getCtrlAgentProcess()) {
+            p = getCtrlAgentProcess()->getCtrlAgentCfgMgr();
+        }
+        return (p);
+    }
+
+    /// @brief Returns a pointer to the configuration context.
+    CtrlAgentCfgContextPtr getCtrlAgentCfgContext() {
+        CtrlAgentCfgContextPtr p;
+        if (getCtrlAgentCfgMgr()) {
+            p = getCtrlAgentCfgMgr()->getCtrlAgentCfgContext();
+        }
+        return (p);
+    }
+
+    /// @brief Adds configuration of the control socket.
+    ///
+    /// @param server_type Server type for which socket configuration is to
+    /// be added.
+    void
+    configureControlSocket(const CtrlAgentCfgContext::ServerType& server_type) {
+        CtrlAgentCfgContextPtr ctx = getCtrlAgentCfgContext();
+        ASSERT_TRUE(ctx);
+
+        ElementPtr control_socket = Element::createMap();
+        control_socket->set("socket-name",
+                            Element::create(unixSocketFilePath()));
+        ctx->setControlSocketInfo(control_socket, server_type);
+    }
+
+    /// @brief Create and bind server side socket.
+    ///
+    /// @param response Stub response to be sent from the server socket to the
+    /// client.
+    void bindServerSocket(const std::string& response) {
+        server_socket_.reset(new test::TestServerUnixSocket(*getIOService(),
+                                                            unixSocketFilePath(),
+                                                            TEST_TIMEOUT,
+                                                            response));
+        server_socket_->bindServerSocket();
+    }
+
+    /// @brief Creates command with no arguments.
+    ///
+    /// @param command_name Command name.
+    /// @param service Service value to be added to the command. If this value
+    /// holds an empty string, the service parameter is not added.
+    ///
+    /// @return Pointer to the instance of the created command.
+    ConstElementPtr createCommand(const std::string& command_name,
+                                  const std::string& service) {
+        ElementPtr command = Element::createMap();
+
+        command->set("command", Element::create(command_name));
+
+        // Only add the 'service' parameter if non-empty.
+        if (!service.empty()) {
+            ElementPtr services = Element::createList();
+            services->add(Element::create(service));
+            command->set("service", services);
+        }
+
+        command->set("arguments", Element::createMap());
+
+        return (command);
+    }
+
+    /// @brief Test forwarding the command.
+    ///
+    /// @param server_type Server for which the client socket should be
+    /// configured.
+    /// @param service Service to be included in the command.
+    /// @param expected_result Expected result in response from the server.
+    /// @param server_response Stub response to be sent by the server.
+    void testForward(const CtrlAgentCfgContext::ServerType& server_type,
+                     const std::string& service,
+                     const int expected_result,
+                     const std::string& server_response = "{ \"result\": 0 }") {
+        // Configure client side socket.
+        configureControlSocket(server_type);
+        // Create server side socket.
+        bindServerSocket(server_response);
+
+        // The client side communication is synchronous. To be able to respond
+        // to this we need to run the server side socket at the same time.
+        // Running IO service in a thread guarantees that the server responds
+        // as soon as it receives the control command.
+        isc::util::thread::Thread(boost::bind(&IOService::run,
+                                              getIOService().get()));
+
+        ConstElementPtr command = createCommand("foo", service);
+        ConstElementPtr answer = mgr_.handleCommand("foo", ConstElementPtr(),
+                                                    command);
+
+        checkAnswer(answer, expected_result);
+    }
+
     /// @brief a convenience reference to control agent command manager
     CtrlAgentCommandMgr& mgr_;
+
+    /// @brief Pointer to the test server unix socket.
+    test::TestServerUnixSocketPtr server_socket_;
 };
 
 /// Just a basic test checking that non-existent command is handled
@@ -67,17 +211,91 @@ public:
 TEST_F(CtrlAgentCommandMgrTest, bogus) {
     ConstElementPtr answer;
     EXPECT_NO_THROW(answer = mgr_.handleCommand("fish-and-chips-please",
+                                                ConstElementPtr(),
                                                 ConstElementPtr()));
-    checkAnswer(answer, isc::config::CONTROL_RESULT_ERROR);
+    checkAnswer(answer, isc::config::CONTROL_RESULT_COMMAND_UNSUPPORTED);
 };
 
 /// Just a basic test checking that 'list-commands' is supported.
 TEST_F(CtrlAgentCommandMgrTest, listCommands) {
     ConstElementPtr answer;
     EXPECT_NO_THROW(answer = mgr_.handleCommand("list-commands",
+                                                ConstElementPtr(),
                                                 ConstElementPtr()));
     checkAnswer(answer, isc::config::CONTROL_RESULT_SUCCESS);
 };
 
+/// Check that control command is successfully forwarded to the DHCPv4 server.
+TEST_F(CtrlAgentCommandMgrTest, forwardToDHCPv4Server) {
+    testForward(CtrlAgentCfgContext::TYPE_DHCP4, "dhcp4",
+                isc::config::CONTROL_RESULT_SUCCESS);
+}
+
+/// Check that control command is successfully forwarded to the DHCPv6 server.
+TEST_F(CtrlAgentCommandMgrTest, forwardToDHCPv6Server) {
+    testForward(CtrlAgentCfgContext::TYPE_DHCP6, "dhcp6",
+                isc::config::CONTROL_RESULT_SUCCESS);
+}
+
+/// Check that control command is not forwarded if the service is not specified.
+TEST_F(CtrlAgentCommandMgrTest, noService) {
+    testForward(CtrlAgentCfgContext::TYPE_DHCP6, "",
+                isc::config::CONTROL_RESULT_COMMAND_UNSUPPORTED);
+}
+
+/// Check that error is returned to the client when the server to which the
+/// command was forwarded sent an invalid message.
+TEST_F(CtrlAgentCommandMgrTest, invalidAnswer) {
+    testForward(CtrlAgentCfgContext::TYPE_DHCP6, "dhcp6",
+                isc::config::CONTROL_RESULT_ERROR,
+                "{ \"result\": 0");
+}
+
+/// Check that error is returned to the client if the forwarding socket is
+/// not configured for the given service.
+TEST_F(CtrlAgentCommandMgrTest, noClientSocket) {
+    ConstElementPtr command = createCommand("foo", "dhcp4");
+    ConstElementPtr answer = mgr_.handleCommand("foo", ConstElementPtr(),
+                                                command);
+
+    checkAnswer(answer, isc::config::CONTROL_RESULT_ERROR);
+}
+
+/// Check that error is returned to the client if the remote server to
+/// which the control command is to be forwarded is not available.
+TEST_F(CtrlAgentCommandMgrTest, noServerSocket) {
+    configureControlSocket(CtrlAgentCfgContext::TYPE_DHCP6);
+
+    ConstElementPtr command = createCommand("foo", "dhcp6");
+    ConstElementPtr answer = mgr_.handleCommand("foo", ConstElementPtr(),
+                                                command);
+
+    checkAnswer(answer, isc::config::CONTROL_RESULT_ERROR);
+}
+
+// Check that list-commands command is forwarded when the service
+// value is specified.
+TEST_F(CtrlAgentCommandMgrTest, forwardListCommands) {
+    // Configure client side socket.
+    configureControlSocket(CtrlAgentCfgContext::TYPE_DHCP4);
+    // Create server side socket.
+    bindServerSocket("{ \"result\" : 3 }");
+
+    // The client side communication is synchronous. To be able to respond
+    // to this we need to run the server side socket at the same time.
+    // Running IO service in a thread guarantees that the server responds
+    // as soon as it receives the control command.
+    isc::util::thread::Thread(boost::bind(&IOService::run,
+                                          getIOService().get()));
+
+    ConstElementPtr command = createCommand("list-commands", "dhcp4");
+    ConstElementPtr answer = mgr_.handleCommand("list-commands", ConstElementPtr(),
+                                                command);
+
+    // Answer of 3 is specific to the stub response we send when the
+    // command is forwarded. So having this value returned means that
+    // the command was forwarded as expected.
+    checkAnswer(answer, 3);
+}
 
 }
diff --git a/src/lib/asiolink/tests/unix_domain_socket_unittest.cc b/src/lib/asiolink/tests/unix_domain_socket_unittest.cc
index 2c7c57fc11..ee9e58e923 100644
--- a/src/lib/asiolink/tests/unix_domain_socket_unittest.cc
+++ b/src/lib/asiolink/tests/unix_domain_socket_unittest.cc
@@ -72,7 +72,7 @@ TEST_F(UnixDomainSocketTest, sendReceive) {
 
     // Setup client side.
     UnixDomainSocket socket(io_service_);
-    ASSERT_NO_THROW(socket.connect(TEST_SOCKET));
+    ASSERT_NO_THROW(socket.connect(unixSocketFilePath()));
 
     // Send "foo".
     const std::string outbound_data = "foo";
@@ -100,7 +100,7 @@ TEST_F(UnixDomainSocketTest, sendReceive) {
 // is not available.
 TEST_F(UnixDomainSocketTest, clientErrors) {
     UnixDomainSocket socket(io_service_);
-    ASSERT_THROW(socket.connect(TEST_SOCKET), UnixDomainSocketError);
+    ASSERT_THROW(socket.connect(unixSocketFilePath()), UnixDomainSocketError);
     const std::string outbound_data = "foo";
     ASSERT_THROW(socket.write(outbound_data.c_str(), outbound_data.size()),
                  UnixDomainSocketError);
@@ -117,7 +117,7 @@ TEST_F(UnixDomainSocketTest, getNative) {
 
     // Setup client side.
     UnixDomainSocket socket(io_service_);
-    ASSERT_NO_THROW(socket.connect(TEST_SOCKET));
+    ASSERT_NO_THROW(socket.connect(unixSocketFilePath()));
     ASSERT_GE(socket.getNative(), 0);
 }
 
diff --git a/src/lib/asiolink/testutils/test_server_unix_socket.cc b/src/lib/asiolink/testutils/test_server_unix_socket.cc
index c4184df890..4959ca39f7 100644
--- a/src/lib/asiolink/testutils/test_server_unix_socket.cc
+++ b/src/lib/asiolink/testutils/test_server_unix_socket.cc
@@ -6,6 +6,7 @@
 
 #include <asiolink/asio_wrapper.h>
 #include <asiolink/testutils/test_server_unix_socket.h>
+#include <boost/bind.hpp>
 
 namespace isc {
 namespace asiolink {
@@ -13,12 +14,14 @@ namespace test {
 
 TestServerUnixSocket::TestServerUnixSocket(IOService& io_service,
                                            const std::string& socket_file_path,
-                                           const long test_timeout)
+                                           const long test_timeout,
+                                           const std::string& custom_response)
     : io_service_(io_service),
       server_endpoint_(socket_file_path),
       server_acceptor_(io_service_.get_io_service()),
       server_socket_(io_service_.get_io_service()),
-      test_timer_(io_service_) {
+      test_timer_(io_service_),
+      custom_response_(custom_response) {
     test_timer_.setup(boost::bind(&TestServerUnixSocket::timeoutHandler, this),
                       test_timeout, IntervalTimer::ONE_SHOT);
 }
@@ -35,9 +38,6 @@ TestServerUnixSocket::bindServerSocket() {
 
 void
 TestServerUnixSocket::acceptHandler(const boost::system::error_code& ec) {
-    if (ec) {
-        ADD_FAILURE() << ec.message();
-    }
     server_socket_.async_read_some(boost::asio::buffer(&raw_buf_[0],
                                                        raw_buf_.size()),
                                    boost::bind(&TestServerUnixSocket::
@@ -47,10 +47,15 @@ TestServerUnixSocket::acceptHandler(const boost::system::error_code& ec) {
 void
 TestServerUnixSocket::readHandler(const boost::system::error_code& ec,
                                   size_t bytes_transferred) {
-    std::string received(&raw_buf_[0], bytes_transferred);
-    std::string response("received " + received);
-    boost::asio::write(server_socket_, boost::asio::buffer(response.c_str(),
-                                                           response.size()));
+    if (!custom_response_.empty()) {
+        boost::asio::write(server_socket_, boost::asio::buffer(custom_response_.c_str(),
+                                                               custom_response_.size()));
+    } else {
+        std::string received(&raw_buf_[0], bytes_transferred);
+        std::string response("received " + received);
+        boost::asio::write(server_socket_, boost::asio::buffer(response.c_str(),
+                                                               response.size()));
+    }
     io_service_.stop();
 }
 
diff --git a/src/lib/asiolink/testutils/test_server_unix_socket.h b/src/lib/asiolink/testutils/test_server_unix_socket.h
index 1e201b06d6..77e556b130 100644
--- a/src/lib/asiolink/testutils/test_server_unix_socket.h
+++ b/src/lib/asiolink/testutils/test_server_unix_socket.h
@@ -10,7 +10,7 @@
 #include <config.h>
 #include <asiolink/interval_timer.h>
 #include <asiolink/io_service.h>
-#include <boost/bind.hpp>
+#include <boost/shared_ptr.hpp>
 #include <gtest/gtest.h>
 #include <array>
 #include <string>
@@ -28,9 +28,11 @@ public:
     /// @param io_service IO service.
     /// @param socket_file_path Socket file path.
     /// @param test_timeout Test timeout in milliseconds.
+    /// @param custom_response Custom response to be sent to the client.
     TestServerUnixSocket(IOService& io_service,
                          const std::string& socket_file_path,
-                         const long test_timeout);
+                         const long test_timeout,
+                         const std::string& custom_response = "");
 
     /// @brief Creates and binds server socket.
     void bindServerSocket();
@@ -59,7 +61,6 @@ private:
 
     /// @brief Server endpoint.
     boost::asio::local::stream_protocol::endpoint server_endpoint_;
-
     /// @brief Server acceptor.
     boost::asio::local::stream_protocol::acceptor server_acceptor_;
 
@@ -71,8 +72,14 @@ private:
 
     /// @brief Asynchronous timer service to detect timeouts.
     IntervalTimer test_timer_;
+
+    /// @brief Holds custom response to be sent to the client.
+    std::string custom_response_;
 };
 
+/// @brief Pointer to the @ref TestServerUnixSocket.
+typedef boost::shared_ptr<TestServerUnixSocket> TestServerUnixSocketPtr;
+
 } // end of namespace isc::asiolink::test
 } // end of namespace isc::asiolink
 } // end of namespace isc
diff --git a/src/lib/cc/command_interpreter.h b/src/lib/cc/command_interpreter.h
index 3420086620..a0bad85d77 100644
--- a/src/lib/cc/command_interpreter.h
+++ b/src/lib/cc/command_interpreter.h
@@ -38,6 +38,9 @@ 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 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 {
diff --git a/src/lib/config/base_command_mgr.cc b/src/lib/config/base_command_mgr.cc
index c148dc5f3d..88b6a290d0 100644
--- a/src/lib/config/base_command_mgr.cc
+++ b/src/lib/config/base_command_mgr.cc
@@ -31,11 +31,33 @@ BaseCommandMgr::registerCommand(const std::string& cmd, CommandHandler handler)
                   << "' is already installed.");
     }
 
-    handlers_.insert(make_pair(cmd, handler));
+    HandlersPair handlers;
+    handlers.handler = handler;
+    handlers_.insert(make_pair(cmd, handlers));
 
     LOG_DEBUG(command_logger, DBG_COMMAND, COMMAND_REGISTERED).arg(cmd);
 }
 
+void
+BaseCommandMgr::registerExtendedCommand(const std::string& cmd,
+                                        ExtendedCommandHandler handler) {
+    if (!handler) {
+        isc_throw(InvalidCommandHandler, "Specified command handler is NULL");
+    }
+
+    HandlerContainer::const_iterator it = handlers_.find(cmd);
+    if (it != handlers_.end()) {
+        isc_throw(InvalidCommandName, "Handler for command '" << cmd
+                  << "' is already installed.");
+    }
+
+    HandlersPair handlers;
+    handlers.extended_handler = handler;
+    handlers_.insert(make_pair(cmd, handlers));
+
+    LOG_DEBUG(command_logger, DBG_COMMAND, COMMAND_EXTENDED_REGISTERED).arg(cmd);
+}
+
 void
 BaseCommandMgr::deregisterCommand(const std::string& cmd) {
     if (cmd == "list-commands") {
@@ -76,7 +98,7 @@ BaseCommandMgr::processCommand(const isc::data::ConstElementPtr& cmd) {
 
         LOG_INFO(command_logger, COMMAND_RECEIVED).arg(name);
 
-        return (handleCommand(name, arg));
+        return (handleCommand(name, arg, cmd));
 
     } catch (const Exception& e) {
         LOG_WARN(command_logger, COMMAND_PROCESS_ERROR2).arg(e.what());
@@ -88,16 +110,20 @@ BaseCommandMgr::processCommand(const isc::data::ConstElementPtr& cmd) {
 
 ConstElementPtr
 BaseCommandMgr::handleCommand(const std::string& cmd_name,
-                              const ConstElementPtr& params) {
+                              const ConstElementPtr& params,
+                              const ConstElementPtr& original_cmd) {
     auto it = handlers_.find(cmd_name);
     if (it == handlers_.end()) {
         // Ok, there's no such command.
-        return (createAnswer(CONTROL_RESULT_ERROR,
+        return (createAnswer(CONTROL_RESULT_COMMAND_UNSUPPORTED,
                              "'" + cmd_name + "' command not supported."));
     }
 
     // Call the actual handler and return whatever it returned
-    return (it->second(cmd_name, params));
+    if (it->second.handler) {
+        return (it->second.handler(cmd_name, params));
+    }
+    return (it->second.extended_handler(cmd_name, params, original_cmd));
 }
 
 isc::data::ConstElementPtr
diff --git a/src/lib/config/base_command_mgr.h b/src/lib/config/base_command_mgr.h
index 97321a5387..19bbae3248 100644
--- a/src/lib/config/base_command_mgr.h
+++ b/src/lib/config/base_command_mgr.h
@@ -81,6 +81,20 @@ public:
     typedef boost::function<isc::data::ConstElementPtr (const std::string& name,
         const isc::data::ConstElementPtr& params)> CommandHandler;
 
+    /// @brief Defines extended command handler type.
+    ///
+    /// This command handler includes third parameter which holds the
+    /// entire command control message. The handler can retrieve
+    /// additional information from this parameter, e.g. 'service'.
+    ///
+    /// @param name name of the commands
+    /// @param params parameters specific to the command
+    /// @param original original control command.
+    /// @return response (created with createAnswer())
+    typedef boost::function<isc::data::ConstElementPtr (const std::string& name,
+        const isc::data::ConstElementPtr& params,
+        const isc::data::ConstElementPtr& original)> ExtendedCommandHandler;
+
     /// @brief Constructor.
     ///
     /// Registers "list-commands" command.
@@ -105,6 +119,19 @@ public:
     /// @param handler Pointer to the method that will handle the command.
     void registerCommand(const std::string& cmd, CommandHandler handler);
 
+    /// @brief Registers specified command handler for a given command.
+    ///
+    /// This variant of the method uses extended command handler which, besides
+    /// command name and arguments, also has a third parameter 'original_cmd'
+    /// in its signature. Such handlers can retrieve additional parameters from
+    /// the command, e.g. 'service' indicating where the command should be
+    /// routed.
+    ///
+    /// @param cmd Name of the command to be handled.
+    /// @param handler Pointer to the method that will handle the command.
+    void registerExtendedCommand(const std::string& cmd,
+                                 ExtendedCommandHandler handler);
+
     /// @brief Deregisters specified command handler.
     ///
     /// @param cmd Name of the command that's no longer handled.
@@ -127,15 +154,24 @@ protected:
     ///
     /// @param cmd_name Command name.
     /// @param params Command arguments.
+    /// @param original_cmd Pointer to the entire command received. It may
+    /// be sometimes useful to retrieve additional parameters from this
+    /// command.
     ///
     /// @return Pointer to the const data element representing response
     /// to a command.
     virtual isc::data::ConstElementPtr
     handleCommand(const std::string& cmd_name,
-                  const isc::data::ConstElementPtr& params);
+                  const isc::data::ConstElementPtr& params,
+                  const isc::data::ConstElementPtr& original_cmd);
+
+    struct HandlersPair {
+        CommandHandler handler;
+        ExtendedCommandHandler extended_handler;
+    };
 
     /// @brief Type of the container for command handlers.
-    typedef std::map<std::string, CommandHandler> HandlerContainer;
+    typedef std::map<std::string, HandlersPair> HandlerContainer;
 
     /// @brief Container for command handlers.
     HandlerContainer handlers_;
diff --git a/src/lib/config/config_messages.mes b/src/lib/config/config_messages.mes
index 215edf90b4..f76ef6cc74 100644
--- a/src/lib/config/config_messages.mes
+++ b/src/lib/config/config_messages.mes
@@ -6,6 +6,11 @@
 
 $NAMESPACE isc::config
 
+% COMMAND_EXTENDED_REGISTERED Command %1 registered
+This debug message indicates that the daemon started supporting specified
+command. The handler for the registered command includes a parameter holding
+entire command to be processed.
+
 % COMMAND_DEREGISTERED Command %1 deregistered
 This debug message indicates that the daemon stopped supporting specified
 command. This command can no longer be issued. If the command socket is
diff --git a/src/lib/config/hooked_command_mgr.cc b/src/lib/config/hooked_command_mgr.cc
index be3c1cb04d..2a32f10b38 100644
--- a/src/lib/config/hooked_command_mgr.cc
+++ b/src/lib/config/hooked_command_mgr.cc
@@ -44,7 +44,8 @@ HookedCommandMgr::HookedCommandMgr()
 
 ConstElementPtr
 HookedCommandMgr::handleCommand(const std::string& cmd_name,
-                                const ConstElementPtr& params) {
+                                const ConstElementPtr& params,
+                                const ConstElementPtr& original_cmd) {
     if (!callout_handle_) {
         isc_throw(Unexpected, "callout handle not configured for the Command "
                   "Manager: this is a programming error");
@@ -52,6 +53,7 @@ HookedCommandMgr::handleCommand(const std::string& cmd_name,
 
     std::string final_cmd_name = cmd_name;
     ConstElementPtr final_params = boost::const_pointer_cast<Element>(params);
+    ConstElementPtr final_cmd = original_cmd;
 
     ConstElementPtr hook_response;
     if (HooksManager::calloutsPresent(Hooks.hook_index_control_command_receive_)) {
@@ -59,13 +61,11 @@ HookedCommandMgr::handleCommand(const std::string& cmd_name,
         // Delete previously set arguments.
         callout_handle_->deleteAllArguments();
 
-        // Being in this function we don't have access to the original data
-        // object holding the whole command (name and arguments). Let's
-        // recreate it.
-        ConstElementPtr original_command = createCommand(cmd_name, params);
+        ConstElementPtr command = original_cmd ? original_cmd :
+            createCommand(cmd_name, params);
 
         // And pass it to the hook library.
-        callout_handle_->setArgument("command", original_command);
+        callout_handle_->setArgument("command", command);
         callout_handle_->setArgument("response", hook_response);
 
         HooksManager::callCallouts(Hooks.hook_index_control_command_receive_,
@@ -89,6 +89,7 @@ HookedCommandMgr::handleCommand(const std::string& cmd_name,
         ConstElementPtr hook_command;
         callout_handle_->getArgument("command", hook_command);
         final_cmd_name = parseCommand(final_params, hook_command);
+        final_cmd = hook_command;
     }
 
     // If we're here it means that the callouts weren't called or the 'skip'
@@ -96,7 +97,8 @@ HookedCommandMgr::handleCommand(const std::string& cmd_name,
     // is being processed. Anyhow, we need to handle the command using local
     // Command Mananger.
     ConstElementPtr response = BaseCommandMgr::handleCommand(final_cmd_name,
-                                                             final_params);
+                                                             final_params,
+                                                             final_cmd);
 
     // For the 'list-commands' case we will have to combine commands supported
     // by the hook libraries with the commands that this Command Manager supports.
diff --git a/src/lib/config/hooked_command_mgr.h b/src/lib/config/hooked_command_mgr.h
index ab7cdebd04..7d2c36f93e 100644
--- a/src/lib/config/hooked_command_mgr.h
+++ b/src/lib/config/hooked_command_mgr.h
@@ -48,12 +48,14 @@ protected:
     ///
     /// @param cmd_name Command name.
     /// @param params Command arguments.
+    /// @param original_cmd Original command received.
     ///
     /// @return Pointer to the const data element representing response
     /// to a command.
     virtual isc::data::ConstElementPtr
     handleCommand(const std::string& cmd_name,
-                  const isc::data::ConstElementPtr& params);
+                  const isc::data::ConstElementPtr& params,
+                  const isc::data::ConstElementPtr& original_cmd);
 
     /// @brief Pointer to a callout handle used by this class.
     isc::hooks::CalloutHandlePtr callout_handle_;
diff --git a/src/lib/config/tests/command_mgr_unittests.cc b/src/lib/config/tests/command_mgr_unittests.cc
index e73ebbb7bc..95e736379e 100644
--- a/src/lib/config/tests/command_mgr_unittests.cc
+++ b/src/lib/config/tests/command_mgr_unittests.cc
@@ -222,7 +222,7 @@ TEST_F(CommandMgrTest, bogusCommand) {
     ASSERT_TRUE(answer);
     int status_code;
     parseAnswer(status_code, answer);
-    EXPECT_EQ(CONTROL_RESULT_ERROR, status_code);
+    EXPECT_EQ(CONTROL_RESULT_COMMAND_UNSUPPORTED, status_code);
 }
 
 // Test checks whether handlers installation is sanitized. In particular,