[master] Merge branch 'trac2983' (4 extra hooks for DHCPv4)

Conflicts:
	ChangeLog

ChangeLog

+667.	[func]		tomek
+	Additional hooks (buffer4_receive, lease4_renew,
+	lease4_release, buffer4_send) added to the DHCPv4 server.
+	(Trac #2983, git fd47f18f898695b98623a63a0a1c68d2e4b37568)
+
 666.	[func]		vorner
 	The CmdCtl's command "print_settings" was removed. It served no real
 	purpose and was just experimental leftover from early development.

src/bin/dhcp4/dhcp4_hooks.dox

@@ -49,22 +49,45 @@ 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 dhcpv4HooksBuffer4Receive buffer4_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
+   buffer is received, before its content is parsed. The sole argument
+   - query4 - contains a pointer to an isc::dhcp::Pkt4 object that
+   contains raw information regarding incoming packet, including its
+   source and destination addresses, interface over which it was
+   received, and a raw buffer stored in data_ field. None of the
+   packet fields (op_, hlen_, chaddr_, etc.) are set yet. Callouts
+   installed on this hook point can modify the incoming buffer. The
+   server will parse the buffer afterwards.
+
+ - <b>Skip flag action</b>: If any callout sets the skip flag, the server will
+   skip the buffer parsing. In such case there is an expectation that
+   the callout will parse the buffer and create option objects (see
+   isc::dhcp::Pkt4::addOption()). Otherwise the server will find out
+   that some mandatory options are missing (e.g. DHCP Message Type) and
+   will drop the packet. If you want to have the capability to drop
+   a message, it is better to use skip flag in pkt4_receive callout.
+
  @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.)
+   packet is received and its content has been 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_. (By the time this hook is reached, the contents
+   of the data_ field has been already parsed and stored in other
+   fields. Therefore, the modification in the data_ field has no
+   effect.)
 
  - <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
@@ -97,42 +120,97 @@ packet processing. Hook points that are not specific to packet processing
    - 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).
+   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 sanity check all modifications 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 indicates that the
+   lease won't be inserted into the database (DISCOVER), a value of
+   false indicates 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 dhcpv4HooksLeaseRenew lease4_renew
+
+ - @b Arguments:
+   - name: @b subnet4, type: isc::dhcp::Subnet4Ptr, direction: <b>in</b>
+   - name: @b clientid, type: isc::dhcp::ClientId, direction: <b>in</b>
+   - name: @b hwaddr, type: isc::dhcp::HWAddr, direction: <b>in</b>
+   - name: @b lease4, type: isc::dhcp::Lease4Ptr, direction: <b>in/out</b>
+
+ - @b Description: this callout is executed when the server engine
+   is about to renew a lease, as a result of receiving REQUEST/Renewing
+   packet. The lease4 argument points to Lease4 object that contains
+   the updated values. Callout can modify those values. Care should be taken
+   as the server will attempt to update the lease in the database without
+   any additional checks.
+
+ - <b>Skip flag action</b>: If any callout installed on 'lease4_renew'
+   sets the skip flag, the server will not update the lease and will
+   use old values instead.
+
+@subsection dhcpv4HooksLeaseRelease lease4_release
+
+ - @b Arguments:
+   - name: @b query4, type: isc::dhcp::Pkt4Ptr, direction: <b>in</b>
+   - name: @b lease4, type: isc::dhcp::Lease4Ptr, direction: <b>in</b>
+
+ - @b Description: this callout is executed when the server engine
+   is about to release a lease, as a result of receiving RELEASE packet.
+   The lease4 argument points to Lease4 object that contains the lease to
+   be released. It doesn't make sense to modify it at this time.
+
+ - <b>Skip flag action</b>: If any callout installed on 'lease4_release'
+   sets the skip flag, the server will not delete the lease. It will be
+   kept in the database and will go through the regular expiration/reuse
+   process.
+
 @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 -
+   is about to be sent 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_.
+   packet, with source and destination addresses set, interface over which
+   it will be sent, and a list of all options and relay information.  All fields
+   of the Pkt4 object can be modified at this time, except buffer_out_.
    (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 not construct raw buffer. The expectation is that if the callout
+   set skip flag, it is responsible for constructing raw form on its own.
+   Otherwise the output packet will be sent with zero length.
+
+@subsection dhcpv4HooksBuffer4Send buffer4_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 sent back to the client. The sole argument - response4 -
+   contains a pointer to an isc::dhcp::Pkt4 object that contains the
+   packet, with source and destination addresses set, interface over which
+   it will be sent, and a list of all options and relay information. The raw
+   on-wire form is already prepared in buffer_out_ (see isc::dhcp::Pkt4::getBuffer())
+   It doesn't make any sense to modify packet fields or options content
+   at this time, because they were already used to construct on-wire buffer.
+
  - <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_messages.mes

@@ -70,6 +70,24 @@ 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_BUFFER_RCVD_SKIP received DHCPv4 buffer was dropped because a callout set the skip flag.
+This debug message is printed when a callout installed on buffer4_receive
+hook point set the skip flag. For this particular hook point, the
+setting of the flag by a callout instructs the server to drop the packet.
+
+% DHCP4_HOOK_BUFFER_SEND_SKIP prepared DHCPv4 response was dropped because a callout set the skip flag.
+This debug message is printed when a callout installed on buffer4_send
+hook point set the skip flag. For this particular hook point, the
+setting of the flag by a callout instructs the server to drop the packet.
+Server completed all the processing (e.g. may have assigned, updated
+or released leases), but the response will not be send to the client.
+
+% DHCP4_HOOK_LEASE4_RELEASE_SKIP DHCPv4 lease was not released because a callout set the skip flag.
+This debug message is printed when a callout installed on lease4_release
+hook point set the skip flag. For this particular hook point, the
+setting of the flag by a callout instructs the server to not release
+a lease.
+
 % 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
@@ -138,6 +156,10 @@ This is a general catch-all message indicating that the processing of a
 received packet failed.  The reason is given in the message.  The server
 will not send a response but will instead ignore the packet.
 
+% DHCP4_PACKET_DROP_NO_TYPE packet received on interface %1 dropped, because of missing msg-type option
+This is a debug message informing that incoming DHCPv4 packet did not
+have mandatory DHCP message type option and thus was dropped.
+
 % DHCP4_PACKET_RECEIVED %1 (type %2) packet received on interface %3
 A debug message noting that the server has received the specified type of
 packet on the specified interface.  Note that a packet marked as UNKNOWN

src/bin/dhcp6/dhcp6_messages.mes

@@ -118,7 +118,7 @@ hook point set 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_BUFFER_SEND_SKIP prepared DHCPv6 response was dropped because a callout set the skip flag.
-This debug message is printed when a callout installed on buffer6_receive
+This debug message is printed when a callout installed on buffer6_send
 hook point set the skip flag. For this particular hook point, the
 setting of the flag by a callout instructs the server to drop the packet.
 Server completed all the processing (e.g. may have assigned, updated

src/bin/dhcp6/tests/hooks_unittest.cc

@@ -285,10 +285,6 @@ public:
     /// @return always 0
     static int
     buffer6_receive_skip(CalloutHandle& callout_handle) {
-
-        Pkt6Ptr pkt;
-        callout_handle.getArgument("query6", pkt);
-
         callout_handle.setSkip(true);
 
         // Carry on as usual
@@ -561,7 +557,7 @@ TEST_F(HooksDhcpv6SrvTest, simple_buffer6_receive) {
     // Server will now process to run its normal loop, but instead of calling
     // IfaceMgr::receive6(), it will read all packets from the list set by
     // fakeReceive()
-    // In particular, it should call registered pkt6_receive callback.
+    // In particular, it should call registered buffer6_receive callback.
     srv_->run();
 
     // Check that the callback called is indeed the one we installed
@@ -577,7 +573,7 @@ TEST_F(HooksDhcpv6SrvTest, simple_buffer6_receive) {
     EXPECT_TRUE(expected_argument_names == callback_argument_names_);
 }
 
-// Checks if callouts installed on pkt6_received is able to change
+// Checks if callouts installed on buffer6_receive is able to change
 // the values and the parameters are indeed used by the server.
 TEST_F(HooksDhcpv6SrvTest, valueChange_buffer6_receive) {
 

src/lib/dhcp/pkt4.cc

@@ -33,7 +33,8 @@ namespace dhcp {
 const IOAddress DEFAULT_ADDRESS("0.0.0.0");
 
 Pkt4::Pkt4(uint8_t msg_type, uint32_t transid)
-     :local_addr_(DEFAULT_ADDRESS),
+     :buffer_out_(DHCPV4_PKT_HDR_LEN),
+      local_addr_(DEFAULT_ADDRESS),
       remote_addr_(DEFAULT_ADDRESS),
       iface_(""),
       ifindex_(0),
@@ -48,8 +49,7 @@ Pkt4::Pkt4(uint8_t msg_type, uint32_t transid)
       ciaddr_(DEFAULT_ADDRESS),
       yiaddr_(DEFAULT_ADDRESS),
       siaddr_(DEFAULT_ADDRESS),
-      giaddr_(DEFAULT_ADDRESS),
-      bufferOut_(DHCPV4_PKT_HDR_LEN)
+      giaddr_(DEFAULT_ADDRESS)
 {
     memset(sname_, 0, MAX_SNAME_LEN);
     memset(file_, 0, MAX_FILE_LEN);
@@ -58,7 +58,8 @@ Pkt4::Pkt4(uint8_t msg_type, uint32_t transid)
 }
 
 Pkt4::Pkt4(const uint8_t* data, size_t len)
-     :local_addr_(DEFAULT_ADDRESS),
+     :buffer_out_(0), // not used, this is RX packet
+      local_addr_(DEFAULT_ADDRESS),
       remote_addr_(DEFAULT_ADDRESS),
       iface_(""),
       ifindex_(0),
@@ -72,8 +73,7 @@ Pkt4::Pkt4(const uint8_t* data, size_t len)
       ciaddr_(DEFAULT_ADDRESS),
       yiaddr_(DEFAULT_ADDRESS),
       siaddr_(DEFAULT_ADDRESS),
-      giaddr_(DEFAULT_ADDRESS),
-      bufferOut_(0) // not used, this is RX packet
+      giaddr_(DEFAULT_ADDRESS)
 {
     if (len < DHCPV4_PKT_HDR_LEN) {
         isc_throw(OutOfRange, "Truncated DHCPv4 packet (len=" << len
@@ -111,25 +111,25 @@ Pkt4::pack() {
     try {
         size_t hw_len = hwaddr_->hwaddr_.size();
 
-        bufferOut_.writeUint8(op_);
-        bufferOut_.writeUint8(hwaddr_->htype_);
-        bufferOut_.writeUint8(hw_len < MAX_CHADDR_LEN ? 
+        buffer_out_.writeUint8(op_);
+        buffer_out_.writeUint8(hwaddr_->htype_);
+        buffer_out_.writeUint8(hw_len < MAX_CHADDR_LEN ?
                               hw_len : MAX_CHADDR_LEN);
-        bufferOut_.writeUint8(hops_);
-        bufferOut_.writeUint32(transid_);
-        bufferOut_.writeUint16(secs_);
-        bufferOut_.writeUint16(flags_);
-        bufferOut_.writeUint32(ciaddr_);
-        bufferOut_.writeUint32(yiaddr_);
-        bufferOut_.writeUint32(siaddr_);
-        bufferOut_.writeUint32(giaddr_);
+        buffer_out_.writeUint8(hops_);
+        buffer_out_.writeUint32(transid_);
+        buffer_out_.writeUint16(secs_);
+        buffer_out_.writeUint16(flags_);
+        buffer_out_.writeUint32(ciaddr_);
+        buffer_out_.writeUint32(yiaddr_);
+        buffer_out_.writeUint32(siaddr_);
+        buffer_out_.writeUint32(giaddr_);
 
 
         if (hw_len <= MAX_CHADDR_LEN) {
             // write up to 16 bytes of the hardware address (CHADDR field is 16
             // bytes long in DHCPv4 message).
-            bufferOut_.writeData(&hwaddr_->hwaddr_[0], 
-                                 (hw_len < MAX_CHADDR_LEN ? 
+            buffer_out_.writeData(&hwaddr_->hwaddr_[0],
+                                 (hw_len < MAX_CHADDR_LEN ?
                                   hw_len : MAX_CHADDR_LEN) );
             hw_len = MAX_CHADDR_LEN - hw_len;
         } else {
@@ -138,20 +138,20 @@ Pkt4::pack() {
 
         // write (len) bytes of padding
         vector<uint8_t> zeros(hw_len, 0);
-        bufferOut_.writeData(&zeros[0], hw_len);
-        // bufferOut_.writeData(chaddr_, MAX_CHADDR_LEN);
+        buffer_out_.writeData(&zeros[0], hw_len);
+        // buffer_out_.writeData(chaddr_, MAX_CHADDR_LEN);
 
-        bufferOut_.writeData(sname_, MAX_SNAME_LEN);
-        bufferOut_.writeData(file_, MAX_FILE_LEN);
+        buffer_out_.writeData(sname_, MAX_SNAME_LEN);
+        buffer_out_.writeData(file_, MAX_FILE_LEN);
 
         // write DHCP magic cookie
-        bufferOut_.writeUint32(DHCP_OPTIONS_COOKIE);
+        buffer_out_.writeUint32(DHCP_OPTIONS_COOKIE);
 
-        LibDHCP::packOptions(bufferOut_, options_);
+        LibDHCP::packOptions(buffer_out_, options_);
 
         // add END option that indicates end of options
         // (End option is very simple, just a 255 octet)
-         bufferOut_.writeUint8(DHO_END);
+         buffer_out_.writeUint8(DHO_END);
      } catch(const Exception& e) {
         // An exception is thrown and message will be written to Logger
          isc_throw(InvalidOperation, e.what());
@@ -259,7 +259,7 @@ void Pkt4::setType(uint8_t dhcp_type) {
 }
 
 void Pkt4::repack() {
-    bufferOut_.writeData(&data_[0], data_.size());
+    buffer_out_.writeData(&data_[0], data_.size());
 }
 
 std::string

src/lib/dhcp/pkt4.h

@@ -70,7 +70,7 @@ public:
     ///
     /// Prepares on-wire format of message and all its options.
     /// Options must be stored in options_ field.
-    /// Output buffer will be stored in bufferOut_.
+    /// Output buffer will be stored in buffer_out_.
     ///
     /// @throw InvalidOperation if packing fails
     void
@@ -103,7 +103,7 @@ public:
     ///
     /// This is mostly a diagnostic function. It is being used for sending
     /// received packet. Received packet is stored in bufferIn_, but
-    /// transmitted data is stored in bufferOut_. If we want to send packet
+    /// transmitted data is stored in buffer_out_. If we want to send packet
     /// that we just received, a copy between those two buffers is necessary.
     void repack();
 
@@ -307,11 +307,12 @@ public:
     /// is only valid till Pkt4 object is valid.
     ///
     /// RX packet or TX packet before pack() will return buffer with
-    /// zero length
+    /// zero length. This buffer is returned as non-const, so hooks
+    /// framework (and user's callouts) can modify them if needed
     ///
     /// @return reference to output buffer
-    const isc::util::OutputBuffer&
-    getBuffer() const { return (bufferOut_); };
+    isc::util::OutputBuffer&
+    getBuffer() { return (buffer_out_); };
 
     /// @brief Add an option.
     ///
@@ -489,6 +490,38 @@ public:
     /// @throw isc::Unexpected if timestamp update failed
     void updateTimestamp();
 
+    /// Output buffer (used during message transmission)
+    ///
+    /// @warning This public member is accessed by derived
+    /// classes directly. One of such derived classes is
+    /// @ref perfdhcp::PerfPkt4. The impact on derived clasess'
+    /// behavior must be taken into consideration before making
+    /// changes to this member such as access scope restriction or
+    /// data format change etc. This field is also public, because
+    /// it may be modified by callouts (which are written in C++ now,
+    /// but we expect to also have them in Python, so any accesibility
+    /// methods would overly complicate things here and degrade
+    /// performance).
+    isc::util::OutputBuffer buffer_out_;
+
+    /// @brief That's the data of input buffer used in RX packet.
+    ///
+    /// @note Note that InputBuffer does not store the data itself, but just
+    /// expects that data will be valid for the whole life of InputBuffer.
+    /// Therefore we need to keep the data around.
+    ///
+    /// @warning This public member is accessed by derived
+    /// classes directly. One of such derived classes is
+    /// @ref perfdhcp::PerfPkt4. The impact on derived clasess'
+    /// behavior must be taken into consideration before making
+    /// changes to this member such as access scope restriction or
+    /// data format change etc. This field is also public, because
+    /// it may be modified by callouts (which are written in C++ now,
+    /// but we expect to also have them in Python, so any accesibility
+    /// methods would overly complicate things here and degrade
+    /// performance).
+    std::vector<uint8_t> data_;
+
 private:
 
     /// @brief Generic method that validates and sets HW address.
@@ -591,29 +624,6 @@ protected:
 
     // end of real DHCPv4 fields
 
-    /// output buffer (used during message transmission)
-    ///
-    /// @warning This protected member is accessed by derived
-    /// classes directly. One of such derived classes is
-    /// @ref perfdhcp::PerfPkt4. The impact on derived clasess'
-    /// behavior must be taken into consideration before making
-    /// changes to this member such as access scope restriction or
-    /// data format change etc.
-    isc::util::OutputBuffer bufferOut_;
-
-    /// that's the data of input buffer used in RX packet. Note that
-    /// InputBuffer does not store the data itself, but just expects that
-    /// data will be valid for the whole life of InputBuffer. Therefore we
-    /// need to keep the data around.
-    ///
-    /// @warning This protected member is accessed by derived
-    /// classes directly. One of such derived classes is
-    /// @ref perfdhcp::PerfPkt4. The impact on derived clasess'
-    /// behavior must be taken into consideration before making
-    /// changes to this member such as access scope restriction or
-    /// data format change etc.
-    std::vector<uint8_t> data_;
-
     /// collection of options present in this message
     ///
     /// @warning This protected member is accessed by derived

src/lib/dhcpsrv/alloc_engine.cc

@@ -31,11 +31,13 @@ namespace {
 /// Structure that holds registered hook indexes
 struct AllocEngineHooks {
     int hook_index_lease4_select_; ///< index for "lease4_receive" hook point
+    int hook_index_lease4_renew_;  ///< index for "lease4_renew" hook point
     int hook_index_lease6_select_; ///< index for "lease6_receive" hook point
 
     /// Constructor that registers hook points for AllocationEngine
     AllocEngineHooks() {
         hook_index_lease4_select_ = HooksManager::registerHook("lease4_select");
+        hook_index_lease4_renew_  = HooksManager::registerHook("lease4_renew");
         hook_index_lease6_select_ = HooksManager::registerHook("lease6_select");
     }
 };
@@ -351,7 +353,8 @@ AllocEngine::allocateAddress4(const SubnetPtr& subnet,
         if (existing) {
             // We have a lease already. This is a returning client, probably after
             // its reboot.
-            existing = renewLease4(subnet, clientid, hwaddr, existing, fake_allocation);
+            existing = renewLease4(subnet, clientid, hwaddr, existing, callout_handle,
+                                   fake_allocation);
             if (existing) {
                 return (existing);
             }
@@ -365,7 +368,8 @@ AllocEngine::allocateAddress4(const SubnetPtr& subnet,
             if (existing) {
                 // we have a lease already. This is a returning client, probably after
                 // its reboot.
-                existing = renewLease4(subnet, clientid, hwaddr, existing, fake_allocation);
+                existing = renewLease4(subnet, clientid, hwaddr, existing, callout_handle,
+                                       fake_allocation);
                 // @todo: produce a warning. We haven't found him using MAC address, but
                 // we found him using client-id
                 if (existing) {
@@ -463,8 +467,19 @@ Lease4Ptr AllocEngine::renewLease4(const SubnetPtr& subnet,
                                    const ClientIdPtr& clientid,
                                    const HWAddrPtr& hwaddr,
                                    const Lease4Ptr& lease,
+                                   const isc::hooks::CalloutHandlePtr& callout_handle,
                                    bool fake_allocation /* = false */) {
 
+    if (!lease) {
+        isc_throw(InvalidOperation, "Lease4 must be specified");
+    }
+
+    // Let's keep the old data. This is essential if we are using memfile
+    // (the lease returned points directly to the lease4 object in the database)
+    // We'll need it if we want to skip update (i.e. roll back renewal)
+    /// @todo: remove this once #3083 is implemented
+    Lease4 old_values = *lease;
+
     lease->subnet_id_ = subnet->getID();
     lease->hwaddr_ = hwaddr->hwaddr_;
     lease->client_id_ = clientid;
@@ -473,10 +488,48 @@ Lease4Ptr AllocEngine::renewLease4(const SubnetPtr& subnet,
     lease->t2_ = subnet->getT2();
     lease->valid_lft_ = subnet->getValid();
 
-    if (!fake_allocation) {
+    bool skip = false;
+    // Execute all callouts registered for packet6_send
+    if (HooksManager::getHooksManager().calloutsPresent(Hooks.hook_index_lease4_renew_)) {
+
+        // Delete all previous arguments
+        callout_handle->deleteAllArguments();
+
+        // Subnet from which we do the allocation. Convert the general subnet
+        // pointer to a pointer to a Subnet4.  Note that because we are using
+        // boost smart pointers here, we need to do the cast using the boost
+        // version of dynamic_pointer_cast.
+        Subnet4Ptr subnet4 = boost::dynamic_pointer_cast<Subnet4>(subnet);
+
+        // Pass the parameters
+        callout_handle->setArgument("subnet4", subnet4);
+        callout_handle->setArgument("clientid", clientid);
+        callout_handle->setArgument("hwaddr", hwaddr);
+
+        // Pass the lease to be updated
+        callout_handle->setArgument("lease4", lease);
+
+        // Call all installed callouts
+        HooksManager::callCallouts(Hooks.hook_index_lease4_renew_, *callout_handle);
+
+        // Callouts decided to skip the next processing step. The next
+        // processing step would to actually renew the lease, so skip at this
+        // stage means "keep the old lease as it is".
+        if (callout_handle->getSkip()) {
+            skip = true;
+            LOG_DEBUG(dhcpsrv_logger, DHCPSRV_DBG_HOOKS, DHCPSRV_HOOK_LEASE4_RENEW_SKIP);
+        }
+    }
+
+    if (!fake_allocation && !skip) {
         // for REQUEST we do update the lease
         LeaseMgrFactory::instance().updateLease4(lease);
     }
+    if (skip) {
+        // Rollback changes (really useful only for memfile)
+        /// @todo: remove this once #3083 is implemented
+        *lease = old_values;
+    }
 
     return (lease);
 }

src/lib/dhcpsrv/alloc_engine.h

@@ -218,6 +218,8 @@ protected:
     /// @param clientid client identifier
     /// @param hwaddr client's hardware address
     /// @param lease lease to be renewed
+    /// @param callout_handle a callout handle (used in hooks). A lease callouts
+    ///        will be executed if this parameter is passed.
     /// @param fake_allocation is this real i.e. REQUEST (false) or just picking
     ///        an address for DISCOVER that is not really allocated (true)
     Lease4Ptr
@@ -225,6 +227,7 @@ protected:
                 const ClientIdPtr& clientid,
                 const HWAddrPtr& hwaddr,
                 const Lease4Ptr& lease,
+                const isc::hooks::CalloutHandlePtr& callout_handle,
                 bool fake_allocation /* = false */);
 
     /// @brief Allocates an IPv6 lease

src/lib/dhcpsrv/dhcpsrv_messages.mes

@@ -141,6 +141,12 @@ hook point sets the skip flag. It means that the server was told that
 no lease4 should be assigned. The server will not put that lease in its
 database and the client will get a NAK packet.
 
+% DHCPSRV_HOOK_LEASE4_RENEW_SKIP DHCPv4 lease was not renewed because a callout set the skip flag.
+This debug message is printed when a callout installed on lease4_renew
+hook point set the skip flag. For this particular hook point, the setting
+of the flag by a callout instructs the server to not renew a lease. The
+server will use existing lease as it is, without extending its lifetime.
+
 % DHCPSRV_HOOK_LEASE6_SELECT_SKIP Lease6 (non-temporary) creation was skipped, because of callout skip flag.
 This debug message is printed when a callout installed on lease6_select
 hook point sets the skip flag. It means that the server was told that

src/lib/dhcpsrv/tests/alloc_engine_unittest.cc

@@ -1017,6 +1017,8 @@ TEST_F(AllocEngine4Test, requestReuseExpiredLease4) {
 // called
 TEST_F(AllocEngine4Test, renewLease4) {
     boost::scoped_ptr<AllocEngine> engine;
+    CalloutHandlePtr callout_handle = HooksManager::createCalloutHandle();
+
     ASSERT_NO_THROW(engine.reset(new AllocEngine(AllocEngine::ALLOC_ITERATIVE, 100)));
     ASSERT_TRUE(engine);
 
@@ -1037,7 +1039,8 @@ TEST_F(AllocEngine4Test, renewLease4) {
     // Lease was assigned 45 seconds ago and is valid for 100 seconds. Let's
     // renew it.
     ASSERT_FALSE(lease->expired());
-    lease = engine->renewLease4(subnet_, clientid_, hwaddr_, lease, false);
+    lease = engine->renewLease4(subnet_, clientid_, hwaddr_, lease,
+                                callout_handle, false);
     // Check that he got that single lease
     ASSERT_TRUE(lease);
     EXPECT_EQ(addr.toText(), lease->addr_.toText());
@@ -1278,6 +1281,10 @@ TEST_F(HookAllocEngine6Test, change_lease6_select) {