[master] Merge branch 'trac2994' (Initial hooks for DHCPv4 server)

Conflicts:
	ChangeLog
	src/bin/dhcp4/dhcp4_messages.mes
	src/bin/dhcp4/dhcp4_srv.cc
	src/bin/dhcp4/dhcp4_srv.h

ChangeLog

+645.	[func]		tomek
+	Added initial set of hooks (pk4_receive, subnet4_select,
+	lease4_select, pkt4_send) to the DHCPv6 server.
+	(Trac #2994, git be65cfba939a6a7abd3c93931ce35c33d3e8247b)
+
 644.	[func]		marcin
 	b10-dhcp4, b10-dhcp6: Implemented selection of the interfaces
 	that server listens on, using Configuration Manager. It is

doc/devel/mainpage.dox

@@ -37,6 +37,8 @@
  * <a href="http://bind10.isc.org/">BIND10 webpage (http://bind10.isc.org)</a>
  * @section hooksFramework Hooks Framework
  * - @subpage hooksComponentDeveloperGuide
+ * - @subpage dhcpv4Hooks
+ * - @subpage dhcpv6Hooks
  *
  * @section dnsMaintenanceGuide DNS Maintenance Guide
  * - Authoritative DNS (todo)
@@ -48,11 +50,12 @@
  *   - @subpage dhcpv4Session
  *   - @subpage dhcpv4ConfigParser
  *   - @subpage dhcpv4ConfigInherit
+ *   - @subpage dhcpv4Other
  * - @subpage dhcp6
  *   - @subpage dhcpv6Session
  *   - @subpage dhcpv6ConfigParser
  *   - @subpage dhcpv6ConfigInherit
- *   - @subpage dhcpv6Hooks
+ *   - @subpage dhcpv6Other
  * - @subpage libdhcp
  *   - @subpage libdhcpIntro
  *   - @subpage libdhcpRelay

src/bin/dhcp4/dhcp4.dox

@@ -79,4 +79,8 @@ See \ref dhcpv6ConfigParser.
 Configuration inheritance in DHCPv4 follows exactly the same logic as its DHCPv6
 counterpart. See \ref dhcpv6ConfigInherit.
 
+@section dhcpv4Other Other DHCPv4 topics
+
+ For hooks API support in DHCPv4, see @ref dhcpv4Hooks.
+
 */

src/bin/dhcp4/dhcp4_hooks.dox

+// Copyright (C) 2013  Internet Systems Consortium, Inc. ("ISC")
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+// OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+/**
+ @page dhcpv4Hooks The Hooks API for the DHCPv4 Server
+
+ @section dhcpv4HooksIntroduction Introduction
+ BIND10 features an API (the "Hooks" API) that allows user-written code to
+ be integrated into BIND 10 and called at specific points in its processing.
+ An overview of the API and a tutorial for writing such code can be found in
+ the @ref hooksDevelopersGuide.  Information for BIND 10 maintainers can be
+ found in the @ref hooksComponentDeveloperGuide.
+
+ This manual is more specialised and is aimed at developers of hook
+ code for the DHCPv4 server. It describes each hook point, what the callouts
+ attached to the hook are able to do, and the arguments passed to the
+ callouts.  Each entry in this manual has the following information:
+
+ - Name of the hook point.
+ - Arguments for the callout.  As well as the argument name and data type, the
+   information includes the direction, which can be one of:
+   - @b in - the server passes values to the callout but ignored any data
+     returned.
+   - @b out - the callout is expected to set this value.
+   - <b>in/out</b> - the server passes a value to the callout and uses whatever
+     value the callout sends back.  Note that the callout may choose not to
+     do any modification, in which case the server will use whatever value
+     it sent to the callout.
+ - Description of the hook. This explains where in the processing the hook
+   is located, the possible actions a callout attached to this hook could take,
+   and a description of the data passed to the callouts.
+ - Skip flag action: the action taken by the server if a callout chooses to set
+    the "skip" flag.
+
+@section dhcpv4HooksHookPoints Hooks in the DHCPv4 Server
+
+The following list is ordered by appearance of specific hook points during
+packet processing. Hook points that are not specific to packet processing
+(e.g. lease expiration) will be added to the end of this list.
+
+ @subsection dhcpv4HooksPkt4Receive pkt4_receive
+
+ - @b Arguments:
+   - name: @b query4, type: isc::dhcp::Pkt4Ptr, direction: <b>in/out</b>
+
+ - @b Description: this callout is executed when an incoming DHCPv4
+   packet is received and its content is parsed. The sole argument -
+   query4 - contains a pointer to an isc::dhcp::Pkt4 object that contains
+   all information regarding incoming packet, including its source and
+   destination addresses, interface over which it was received, a list
+   of all options present within and relay information.  All fields of
+   the Pkt4 object can be modified at this time, except data_. (data_
+   contains the incoming packet as raw buffer. By the time this hook is
+   reached, that information has already parsed and is available though
+   other fields in the Pkt4 object.  For this reason, it doesn't make
+   sense to modify it.)
+
+ - <b>Skip flag action</b>: If any callout sets the skip flag, the server will
+   drop the packet and start processing the next one.  The reason for the drop
+   will be logged if logging is set to the appropriate debug level.
+
+@subsection dhcpv4HooksSubnet4Select subnet4_select
+
+ - @b Arguments:
+   - name: @b query4, type: isc::dhcp::Pkt4Ptr, direction: <b>in/out</b>
+   - name: @b subnet4, type: isc::dhcp::Subnet4Ptr, direction: <b>in/out</b>
+   - name: @b subnet4collection, type: const isc::dhcp::Subnet4Collection *, direction: <b>in</b>
+
+ - @b Description: this callout is executed when a subnet is being
+   selected for the incoming packet. All parameters and addresses
+   will be assigned from that subnet. A callout can select a
+   different subnet if it wishes so, the list of all subnets currently
+   configured being provided as 'subnet4collection'. The list itself must
+   not be modified.
+
+ - <b>Skip flag action</b>: If any callout installed on 'subnet4_select'
+   sets the skip flag, the server will not select any subnet. Packet processing
+   will continue, but will be severely limited (i.e. only global options
+   will be assigned).
+
+@subsection dhcpv4HooksLeaseSelect lease4_select
+
+ - @b Arguments:
+   - name: @b subnet4, type: isc::dhcp::Subnet4Ptr, direction: <b>in</b>
+   - name: @b fake_allocation, type: bool, direction: <b>in</b>
+   - name: @b lease4, type: isc::dhcp::Lease4Ptr, direction: <b>in/out</b>
+
+ - @b Description: this callout is executed after the server engine
+   has selected a lease for client's request but before the lease
+   has been inserted into the database. Any modifications made to the
+   isc::dhcp::Lease4 object will be stored in the lease's record in the
+   database. The callout should make sure that any modifications are
+   sanity checked as the server will use that data as is with no further
+   checking.\n\n The server processes lease requests for DISCOVER and
+   REQUEST in a very similar way. The only major difference is that
+   for DISCOVER the lease is just selected, but not inserted into
+   the database.  It is possible to distinguish between DISCOVER and
+   REQUEST by checking value of the fake_allocation flag: a value of true
+   means that the lease won't be inserted into the database (DISCOVER),
+   a value of false means that it will (REQUEST).
+
+ - <b>Skip flag action</b>: If any callout installed on 'lease4_select'
+   sets the skip flag, the server will not assign any lease. Packet
+   processing will continue, but client will not get an address.
+
+@subsection dhcpv4HooksPkt4Send pkt4_send
+
+ - @b Arguments:
+   - name: @b response4, type: isc::dhcp::Pkt4Ptr, direction: <b>in/out</b>
+
+ - @b Description: this callout is executed when server's response
+   is about to be send back to the client. The sole argument - response4 -
+   contains a pointer to an isc::dhcp::Pkt4 object that contains the
+   packet, with set source and destination addresses, interface over which
+   it will be send, list of all options and relay information.  All fields
+   of the Pkt4 object can be modified at this time, except bufferOut_.
+   (This is scratch space used for constructing the packet after all
+   pkt4_send callouts are complete, so any changes to that field will
+   be overwritten.)
+
+ - <b>Skip flag action</b>: if any callout sets the skip flag, the server
+   will drop this response packet. However, the original request packet
+   from a client was processed, so server's state was most likely changed
+   (e.g. lease was allocated). Setting this flag merely stops the change
+   being communicated to the client.
+
+*/

src/bin/dhcp4/dhcp4_log.h

@@ -38,6 +38,9 @@ const int DBG_DHCP4_COMMAND = DBGLVL_COMMAND;
 // Trace basic operations within the code.
 const int DBG_DHCP4_BASIC = DBGLVL_TRACE_BASIC;
 
+// Trace hook related operations
+const int DBG_DHCP4_HOOKS = DBGLVL_TRACE_BASIC;
+
 // Trace detailed operations, including errors raised when processing invalid
 // packets.  (These are not logged at severities of WARN or higher for fear
 // that a set of deliberately invalid packets set to the server could overwhelm

src/bin/dhcp4/dhcp4_messages.mes

@@ -42,7 +42,7 @@ This critical error message indicates that the initial DHCPv4
 configuration has failed. The server will start, but nothing will be
 served until the configuration has been corrected.
 
-% DHCP4_CONFIG_NEW_SUBNET A new subnet has been added to configuration: %1
+% DHCP4_CONFIG_NEW_SUBNET a new subnet has been added to configuration: %1
 This is an informational message reporting that the configuration has
 been extended to include the specified IPv4 subnet.
 
@@ -70,6 +70,25 @@ This message is printed when DHCPv4 server disables an interface from being
 used to receive DHCPv4 traffic. Sockets on this interface will not be opened
 by the Interface Manager until interface is enabled.
 
+% DHCP4_HOOK_PACKET_RCVD_SKIP received DHCPv4 packet was dropped, because a callout set the skip flag.
+This debug message is printed when a callout installed on the pkt4_receive
+hook point sets the skip flag. For this particular hook point, the
+setting of the flag instructs the server to drop the packet.
+
+% DHCP4_HOOK_PACKET_SEND_SKIP prepared DHCPv6 response was not sent, because a callout set skip flag.
+This debug message is printed when a callout installed on the pkt4_send
+hook point sets the skip flag. For this particular hook point, the setting
+of the flag instructs the server to drop the packet. This means that
+the client will not get any response, even though the server processed
+client's request and acted on it (e.g. possibly allocated a lease).
+
+% DHCP4_HOOK_SUBNET4_SELECT_SKIP no subnet was selected, because a callout set skip flag.
+This debug message is printed when a callout installed on the
+subnet4_select hook point sets the skip flag. For this particular hook
+point, the setting of the flag instructs the server not to choose a
+subnet, an action that severely limits further processing; the server
+will be only able to offer global options - no addresses will be assigned.
+
 % DHCP4_LEASE_ADVERT lease %1 advertised (client client-id %2, hwaddr %3)
 This debug message indicates that the server successfully advertised
 a lease. It is up to the client to choose one server out of othe advertised

src/bin/dhcp4/dhcp4_srv.cc

@@ -30,6 +30,8 @@
 #include <dhcpsrv/subnet.h>
 #include <dhcpsrv/utils.h>
 #include <dhcpsrv/addr_utilities.h>
+#include <hooks/hooks_manager.h>
+#include <hooks/callout_handle.h>
 
 #include <boost/algorithm/string/erase.hpp>
 
@@ -39,9 +41,30 @@
 using namespace isc;
 using namespace isc::asiolink;
 using namespace isc::dhcp;
+using namespace isc::hooks;
 using namespace isc::log;
 using namespace std;
 
+/// Structure that holds registered hook indexes
+struct Dhcp6Hooks {
+    int hook_index_pkt4_receive_;   ///< index for "pkt4_receive" hook point
+    int hook_index_subnet4_select_; ///< index for "subnet4_select" hook point
+    int hook_index_pkt4_send_;      ///< index for "pkt4_send" hook point
+
+    /// Constructor that registers hook points for DHCPv6 engine
+    Dhcp6Hooks() {
+        hook_index_pkt4_receive_   = HooksManager::registerHook("pkt4_receive");
+        hook_index_subnet4_select_ = HooksManager::registerHook("subnet4_select");
+        hook_index_pkt4_send_      = HooksManager::registerHook("pkt4_send");
+    }
+};
+
+// Declare a Hooks object. As this is outside any function or method, it
+// will be instantiated (and the constructor run) when the module is loaded.
+// As a result, the hook indexes will be defined before any method in this
+// module is called.
+Dhcp6Hooks Hooks;
+
 namespace isc {
 namespace dhcp {
 
@@ -59,7 +82,10 @@ static const char* SERVER_ID_FILE = "b10-dhcp4-serverid";
 
 Dhcpv4Srv::Dhcpv4Srv(uint16_t port, const char* dbconfig, const bool use_bcast,
                      const bool direct_response_desired)
-    : port_(port), use_bcast_(use_bcast) {
+: serverid_(), shutdown_(true), alloc_engine_(), port_(port), 
+    use_bcast_(use_bcast), hook_index_pkt4_receive_(-1), 
+    hook_index_subnet4_select_(-1), hook_index_pkt4_send_(-1) {
+
     LOG_DEBUG(dhcp4_logger, DBG_DHCP4_START, DHCP4_OPEN_SOCKET).arg(port);
     try {
         // First call to instance() will create IfaceMgr (it's a singleton)
@@ -104,6 +130,13 @@ Dhcpv4Srv::Dhcpv4Srv(uint16_t port, const char* dbconfig, const bool use_bcast,
         // Instantiate allocation engine
         alloc_engine_.reset(new AllocEngine(AllocEngine::ALLOC_ITERATIVE, 100));
 
+        // Register hook points
+        hook_index_pkt4_receive_   = Hooks.hook_index_pkt4_receive_;
+        hook_index_subnet4_select_ = Hooks.hook_index_subnet4_select_;
+        hook_index_pkt4_send_      = Hooks.hook_index_pkt4_send_;
+
+        /// @todo call loadLibraries() when handling configuration changes
+
     } catch (const std::exception &e) {
         LOG_ERROR(dhcp4_logger, DHCP4_SRV_CONSTRUCT_ERROR).arg(e.what());
         shutdown_ = true;
@@ -123,6 +156,16 @@ Dhcpv4Srv::shutdown() {
     shutdown_ = true;
 }
 
+Pkt4Ptr
+Dhcpv4Srv::receivePacket(int timeout) {
+    return (IfaceMgr::instance().receive4(timeout));
+}
+
+void
+Dhcpv4Srv::sendPacket(const Pkt4Ptr& packet) {
+    IfaceMgr::instance().send(packet);
+}
+
 bool
 Dhcpv4Srv::run() {
     while (!shutdown_) {
@@ -135,7 +178,7 @@ Dhcpv4Srv::run() {
         Pkt4Ptr rsp;
 
         try {
-            query = IfaceMgr::instance().receive4(timeout);
+            query = receivePacket(timeout);
         } catch (const std::exception& e) {
             LOG_ERROR(dhcp4_logger, DHCP4_PACKET_RECEIVE_FAIL).arg(e.what());
         }
@@ -157,6 +200,31 @@ Dhcpv4Srv::run() {
             LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA, DHCP4_QUERY_DATA)
                       .arg(query->toText());
 
+            // Let's execute all callouts registered for packet_received
+            if (HooksManager::calloutsPresent(hook_index_pkt4_receive_)) {
+                CalloutHandlePtr callout_handle = getCalloutHandle(query);
+
+                // Delete previously set arguments
+                callout_handle->deleteAllArguments();
+
+                // Pass incoming packet as argument
+                callout_handle->setArgument("query4", query);
+
+                // Call callouts
+                HooksManager::callCallouts(hook_index_pkt4_receive_,
+                                           *callout_handle);
+
+                // Callouts decided to skip the next processing step. The next
+                // processing step would to process the packet, so skip at this
+                // stage means drop.
+                if (callout_handle->getSkip()) {
+                    LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_RCVD_SKIP);
+                    continue;
+                }
+
+                callout_handle->getArgument("query4", query);
+            }
+
             try {
                 switch (query->getType()) {
                 case DHCPDISCOVER:
@@ -221,13 +289,39 @@ Dhcpv4Srv::run() {
                 rsp->setIface(query->getIface());
                 rsp->setIndex(query->getIndex());
 
+                // Execute all callouts registered for packet6_send
+                if (HooksManager::calloutsPresent(hook_index_pkt4_send_)) {
+                    CalloutHandlePtr callout_handle = getCalloutHandle(query);
+
+                    // Delete all previous arguments
+                    callout_handle->deleteAllArguments();
+
+                    // Clear skip flag if it was set in previous callouts
+                    callout_handle->setSkip(false);
+
+                    // Set our response
+                    callout_handle->setArgument("response4", rsp);
+
+                    // Call all installed callouts
+                    HooksManager::callCallouts(hook_index_pkt4_send_,
+                                               *callout_handle);
+
+                    // Callouts decided to skip the next processing step. The next
+                    // processing step would to send the packet, so skip at this
+                    // stage means "drop response".
+                    if (callout_handle->getSkip()) {
+                        LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_PACKET_SEND_SKIP);
+                        continue;
+                    }
+                }
+
                 LOG_DEBUG(dhcp4_logger, DBG_DHCP4_DETAIL_DATA,
                           DHCP4_RESPONSE_DATA)
                           .arg(rsp->getType()).arg(rsp->toText());
 
                 if (rsp->pack()) {
                     try {
-                        IfaceMgr::instance().send(rsp);
+                        sendPacket(rsp);
                     } catch (const std::exception& e) {
                         LOG_ERROR(dhcp4_logger, DHCP4_PACKET_SEND_FAIL).arg(e.what());
                     }
@@ -515,12 +609,15 @@ Dhcpv4Srv::assignLease(const Pkt4Ptr& question, Pkt4Ptr& answer) {
     // allocation.
     bool fake_allocation = (question->getType() == DHCPDISCOVER);
 
+    CalloutHandlePtr callout_handle = getCalloutHandle(question);
+
     // Use allocation engine to pick a lease for this client. Allocation engine
     // will try to honour the hint, but it is just a hint - some other address
     // may be used instead. If fake_allocation is set to false, the lease will
     // be inserted into the LeaseMgr as well.
     Lease4Ptr lease = alloc_engine_->allocateAddress4(subnet, client_id, hwaddr,
-                                                      hint, fake_allocation);
+                                                      hint, fake_allocation,
+                                                      callout_handle);
 
     if (lease) {
         // We have a lease! Let's set it in the packet and send it back to
@@ -633,6 +730,9 @@ Dhcpv4Srv::getNetmaskOption(const Subnet4Ptr& subnet) {
 
 Pkt4Ptr
 Dhcpv4Srv::processDiscover(Pkt4Ptr& discover) {
+
+    sanityCheck(discover, FORBIDDEN);
+
     Pkt4Ptr offer = Pkt4Ptr
         (new Pkt4(DHCPOFFER, discover->getTransid()));
 
@@ -783,17 +883,50 @@ Dhcpv4Srv::serverReceivedPacketName(uint8_t type) {
 Subnet4Ptr
 Dhcpv4Srv::selectSubnet(const Pkt4Ptr& question) {
 
+    Subnet4Ptr subnet;
     // Is this relayed message?
     IOAddress relay = question->getGiaddr();
-    if (relay.toText() == "0.0.0.0") {
+    static const IOAddress notset("0.0.0.0");
 
+    if (relay != notset) {
         // Yes: Use relay address to select subnet
-        return (CfgMgr::instance().getSubnet4(relay));
+        subnet = CfgMgr::instance().getSubnet4(relay);
     } else {
 
         // No: Use client's address to select subnet
-        return (CfgMgr::instance().getSubnet4(question->getRemoteAddr()));
+        subnet = CfgMgr::instance().getSubnet4(question->getRemoteAddr());
+    }
+
+    /// @todo Implement getSubnet4(interface-name)
+
+    // Let's execute all callouts registered for packet_received
+    if (HooksManager::calloutsPresent(hook_index_subnet4_select_)) {
+        CalloutHandlePtr callout_handle = getCalloutHandle(question);
+
+        // We're reusing callout_handle from previous calls
+        callout_handle->deleteAllArguments();
+
+        // Set new arguments
+        callout_handle->setArgument("query4", question);
+        callout_handle->setArgument("subnet4", subnet);
+        callout_handle->setArgument("subnet4collection", CfgMgr::instance().getSubnets4());
+
+        // Call user (and server-side) callouts
+        HooksManager::callCallouts(hook_index_subnet4_select_, *callout_handle);
+
+        // Callouts decided to skip this step. This means that no subnet will be
+        // selected. Packet processing will continue, but it will be severly limited
+        // (i.e. only global options will be assigned)
+        if (callout_handle->getSkip()) {
+            LOG_DEBUG(dhcp4_logger, DBG_DHCP4_HOOKS, DHCP4_HOOK_SUBNET4_SELECT_SKIP);
+            return (Subnet4Ptr());
+        }
+
+        // Use whatever subnet was specified by the callout
+        callout_handle->getArgument("subnet4", subnet);
     }
+
+    return (subnet);
 }
 
 void
@@ -819,6 +952,49 @@ Dhcpv4Srv::sanityCheck(const Pkt4Ptr& pkt, RequirementLevel serverid) {
         // do nothing here
         ;
     }
+
+    // If there is HWAddress set and it is non-empty, then we're good
+    if (pkt->getHWAddr() && !pkt->getHWAddr()->hwaddr_.empty()) {
+        return;
+    }
+
+    // There has to be something to uniquely identify the client:
+    // either non-zero MAC address or client-id option present (or both)
+    OptionPtr client_id = pkt->getOption(DHO_DHCP_CLIENT_IDENTIFIER);
+
+    // If there's no client-id (or a useless one is provided, i.e. 0 length)
+    if (!client_id || client_id->len() == client_id->getHeaderLen()) {
+        isc_throw(RFCViolation, "Missing or useless client-id and no HW address "
+                  " provided in message "
+                  << serverReceivedPacketName(pkt->getType()));
+    }
+}
+
+isc::hooks::CalloutHandlePtr Dhcpv4Srv::getCalloutHandle(const Pkt4Ptr& pkt) {
+    // This method returns a CalloutHandle for a given packet. It is guaranteed
+    // to return the same callout_handle (so user library contexts are
+    // preserved). This method works well if the server processes one packet
+    // at a time. Once the server architecture is extended to cover parallel
+    // packets processing (e.g. delayed-ack, some form of buffering etc.), this
+    // method has to be extended (e.g. store callouts in a map and use pkt as
+    // a key). Additional code would be required to release the callout handle
+    // once the server finished processing.
+
+    CalloutHandlePtr callout_handle;
+    static Pkt4Ptr old_pointer;
+
+    if (!callout_handle ||
+        old_pointer != pkt) {
+        // This is the first packet or a different packet than previously
+        // passed to getCalloutHandle()
+
+        // Remember the pointer to this packet
+        old_pointer = pkt;
+
+        callout_handle = HooksManager::createCalloutHandle();
+    }
+
+    return (callout_handle);
 }
 
 void

src/bin/dhcp4/dhcp4_srv.h

@@ -20,6 +20,7 @@
 #include <dhcp/option.h>
 #include <dhcpsrv/subnet.h>
 #include <dhcpsrv/alloc_engine.h>
+#include <hooks/callout_handle.h>
 
 #include <boost/noncopyable.hpp>
 
@@ -336,6 +337,18 @@ protected:
     /// initiate server shutdown procedure.
     volatile bool shutdown_;
 
+    /// @brief dummy wrapper around IfaceMgr::receive4
+    ///
+    /// This method is useful for testing purposes, where its replacement
+    /// simulates reception of a packet. For that purpose it is protected.
+    virtual Pkt4Ptr receivePacket(int timeout);
+
+    /// @brief dummy wrapper around IfaceMgr::send()
+    ///
+    /// This method is useful for testing purposes, where its replacement
+    /// simulates transmission of a packet. For that purpose it is protected.
+    virtual void sendPacket(const Pkt4Ptr& pkt);
+
 private:
 
     /// @brief Constructs netmask option based on subnet4
@@ -353,6 +366,17 @@ private:
     uint16_t port_;  ///< UDP port number on which server listens.
     bool use_bcast_; ///< Should broadcast be enabled on sockets (if true).
 
+    /// @brief returns callout handle for specified packet
+    ///
+    /// @param pkt packet for which the handle should be returned
+    ///
+    /// @return a callout handle to be used in hooks related to said packet
+    isc::hooks::CalloutHandlePtr getCalloutHandle(const Pkt4Ptr& pkt);
+
+    /// Indexes for registered hook points
+    int hook_index_pkt4_receive_;
+    int hook_index_subnet4_select_;
+    int hook_index_pkt4_send_;
 };
 
 }; // namespace isc::dhcp

src/bin/dhcp6/dhcp6.dox

@@ -92,4 +92,8 @@
 
  @todo Add section about setting up options and their definitions with bindctl.
 
+ @section dhcpv6Other Other DHCPv6 topics
+
+ For hooks API support in DHCPv6, see @ref dhcpv6Hooks.
+
  */

src/bin/dhcp6/dhcp6_hooks.dox

@@ -110,8 +110,10 @@ packet processing. Hook points that are not specific to packet processing
    means that the lease won't be inserted into the database (SOLICIT),
    a value of false means that it will (REQUEST).
 
- - <b>Skip flag action</b>: the "skip" flag is ignored by the server on this
-   hook.
+ - <b>Skip flag action</b>: If any callout installed on 'lease6_select'
+   sets the skip flag, the server will not assign that particular lease.
+   Packet processing will continue and the client may get other addresses
+   or prefixes if it requested more than one address and/or prefix.
 
 @subsection dhcpv6HooksPkt6Send pkt6_send
 

src/bin/dhcp6/dhcp6_messages.mes

@@ -76,23 +76,25 @@ used to receive DHCPv6 traffic. Sockets on this interface will not be opened
 by the Interface Manager until interface is enabled.
 
 % DHCP6_HOOK_PACKET_RCVD_SKIP received DHCPv6 packet was dropped, because a callout set skip flag.
-This debug message is printed when a callout installed on pkt6_received
-hook point sets skip flag. For this particular hook point, the setting
-of the flag by a callout instructs the server to drop the packet.
+This debug message is printed when a callout installed on the pkt6_receive
+hook point sets the skip flag. For this particular hook point, the
+setting of the flag by a callout instructs the server to drop the packet.
 
-% DHCP6_HOOK_PACKET_SEND_SKIP Prepared DHCPv6 response was not sent, because a callout set skip flag.
-This debug message is printed when a callout installed on pkt6_send
-hook point sets skip flag. For this particular hook point, the setting
+% DHCP6_HOOK_PACKET_SEND_SKIP prepared DHCPv6 response was not sent, because a callout set skip flag.
+This debug message is printed when a callout installed on the pkt6_send
+hook point sets the skip flag. For this particular hook point, the setting
 of the flag by a callout instructs the server to drop the packet. This
 effectively means that the client will not get any response, even though
 the server processed client's request and acted on it (e.g. possibly
 allocated a lease).
 
-% DHCP6_HOOK_SUBNET6_SELECT_SKIP No subnet was selected, because a callout set skip flag.
-This debug message is printed when a callout installed on subnet6_select
-hook point sets a skip flag. It means that the server was told that no subnet
-should be selected. This severely limits further processing - server will be only
-able to offer global options. No addresses or prefixes could be assigned.
+% DHCP6_HOOK_SUBNET6_SELECT_SKIP no subnet was selected, because a callout set skip flag.
+This debug message is printed when a callout installed on the
+subnet6_select hook point sets the skip flag. For this particular hook
+point, the setting of the flag instructs the server not to choose a
+subnet, an action that severely limits further processing; the server
+will be only able to offer global options - no addresses or prefixes
+will be assigned.
 
 % DHCP6_LEASE_ADVERT lease %1 advertised (client duid=%2, iaid=%3)
 This debug message indicates that the server successfully advertised
@@ -193,10 +195,10 @@ actions and committal of changes failed.  The message has been output in
 response to a non-BIND 10 exception being raised.  Additional messages
 may give further information.
 
-The most likely cause of this is that the specification file for the server
-(which details the allowable contents of the configuration) is not correct for
-this version of BIND 10.  This former may be the result of an interrupted
-installation of an update to BIND 10.
+The most likely cause of this is that the specification file for the