[2765] Invoke error handler if the interface opening failed.

src/bin/dhcp4/dhcp4_messages.mes

@@ -147,6 +147,10 @@ IPv4 DHCP server but it is not running.
 A debug message issued during startup, this indicates that the IPv4 DHCP
 server is about to open sockets on the specified port.
 
+% DHCP4_OPEN_SOCKET_FAIL failed to create socket: %1
+A warning message issued when IfaceMgr fails to open and bind a socket. The reason
+for the failure is appended as an argument of the log message.
+
 % DHCP4_PACKET_PARSE_FAIL failed to parse incoming packet: %1
 The IPv4 DHCP server has received a packet that it is unable to
 interpret. The reason why the packet is invalid is included in the message.

src/bin/dhcp4/dhcp4_srv.cc

@@ -1241,7 +1241,9 @@ Dhcpv4Srv::openActiveSockets(const uint16_t port,
     // sockets are marked active or inactive.
     // @todo Optimization: we should not reopen all sockets but rather select
     // those that have been affected by the new configuration.
-    if (!IfaceMgr::instance().openSockets4(port, use_bcast)) {
+    isc::dhcp::IfaceMgrErrorMsgCallback error_handler =
+        boost::bind(&Dhcpv4Srv::ifaceMgrSocket4ErrorHandler, _1);
+    if (!IfaceMgr::instance().openSockets4(port, use_bcast, error_handler)) {
         LOG_WARN(dhcp4_logger, DHCP4_NO_SOCKETS_OPEN);
     }
 }
@@ -1335,6 +1337,11 @@ Dhcpv4Srv::unpackOptions(const OptionBuffer& buf,
     return (offset);
 }
 
+void
+Dhcpv4Srv::ifaceMgrSocket4ErrorHandler(const std::string& errmsg) {
+    // Log the reason for socket opening failure and return.
+    LOG_WARN(dhcp4_logger, DHCP4_OPEN_SOCKET_FAIL).arg(errmsg);
+}
 
 }   // namespace dhcp
 }   // namespace isc

src/bin/dhcp4/dhcp4_srv.h

@@ -381,6 +381,15 @@ private:
     /// @return Option that contains netmask information
     static OptionPtr getNetmaskOption(const Subnet4Ptr& subnet);
 
+    /// @brief Implements the error handler for socket open failure.
+    ///
+    /// This callback function is installed on the @c isc::dhcp::IfaceMgr
+    /// when IPv4 sockets are being open. When socket fails to open for
+    /// any reason, this function is called. It simply logs the error message.
+    ///
+    /// @param errmsg An error message containing a cause of the failure.
+    static void ifaceMgrSocket4ErrorHandler(const std::string& errmsg);
+
     /// @brief Allocation Engine.
     /// Pointer to the allocation engine that we are currently using
     /// It must be a pointer, because we will support changing engines

src/bin/dhcp4/tests/dhcp4_srv_unittest.cc

@@ -191,6 +191,26 @@ TEST_F(Dhcpv4SrvTest, basic) {
     EXPECT_TRUE(naked_srv->getServerID());
 }
 
+// This test verifies that exception is not thrown when an error occurs during
+// opening sockets. This test forces an error by adding a fictious interface
+// to the IfaceMgr. An attempt to open socket on this interface must always
+// fail. The DHCPv4 installs the error handler function to prevent exceptions
+// being thrown from the openSockets4 function.
+// @todo The server tests for socket should be extended but currently the
+// ability to unit test the sockets code is somewhat limited.
+TEST_F(Dhcpv4SrvTest, openActiveSockets) {
+    ASSERT_NO_THROW(CfgMgr::instance().activateAllIfaces());
+
+    Iface iface("bogusiface", 255);
+    iface.flag_loopback_ = false;
+    iface.flag_up_ = true;
+    iface.flag_running_ = true;
+    iface.inactive4_ = false;
+    iface.addAddress(IOAddress("192.0.0.0"));
+    IfaceMgr::instance().addInterface(iface);
+    ASSERT_NO_THROW(Dhcpv4Srv::openActiveSockets(DHCP4_SERVER_PORT, false));
+}
+
 // This test verifies that the destination address of the response
 // message is set to giaddr, when giaddr is set to non-zero address
 // in the received message.

src/bin/dhcp4/tests/dhcp4_test_utils.cc

@@ -44,6 +44,7 @@ Dhcpv4SrvTest::Dhcpv4SrvTest()
     pool_ = Pool4Ptr(new Pool4(IOAddress("192.0.2.100"), IOAddress("192.0.2.110")));
     subnet_->addPool(pool_);
 
+    CfgMgr::instance().deleteActiveIfaces();
     CfgMgr::instance().deleteSubnets4();
     CfgMgr::instance().addSubnet4(subnet_);
 

src/lib/dhcp/iface_mgr.h

@@ -424,7 +424,7 @@ public:
     /// @return true if direct response is supported.
     bool isDirectResponseSupported() const;
 
-    /// @brief Returns interface with specified interface index
+    /// @brief Returns interfac specified interface index
     ///
     /// @param ifindex index of searched interface
     ///
@@ -732,6 +732,15 @@ public:
     /// not having address assigned.
     void setMatchingPacketFilter(const bool direct_response_desired = false);
 
+    /// @brief Adds an interface to list of known interfaces.
+    ///
+    /// @param iface reference to Iface object.
+    /// @note This function must be public because it has to be callable
+    /// from unit tests.
+    void addInterface(const Iface& iface) {
+        ifaces_.push_back(iface);
+    }
+
     /// A value of socket descriptor representing "not specified" state.
     static const int INVALID_SOCKET = -1;
 
@@ -776,13 +785,6 @@ protected:
     /// @return socket descriptor
     int openSocket6(Iface& iface, const isc::asiolink::IOAddress& addr, uint16_t port);
 
-    /// @brief Adds an interface to list of known interfaces.
-    ///
-    /// @param iface reference to Iface object.
-    void addInterface(const Iface& iface) {
-        ifaces_.push_back(iface);
-    }
-
     /// @brief Detects network interfaces.
     ///
     /// This method will eventually detect available interfaces. For now