Add default virtual destructors to base classes with virtual functions

Without this fix, the openvpn3-linux build is broken whenever a
dependency enables -Wnon-virtual-dtor (which protobuf 27.3
currently does on Arch Linux). The openvpn3-linux build treats
warnings as errors.

Jira: OVPN3-1242
Signed-off-by: Razvan Cojocaru <razvan.cojocaru@openvpn.com>
(cherry picked from commit 6217fa0e1a)

openvpn/buffer/bufcomplete.hpp

@@ -32,8 +32,9 @@ namespace openvpn {
 class BufferComplete
 {
   public:
-    /* each advance/get method returns false if message is incomplete */
+    virtual ~BufferComplete() = default;
 
+    /* each advance/get method returns false if message is incomplete */
     bool advance(size_t size)
     {
         while (size)

openvpn/buffer/buffer.hpp

@@ -214,7 +214,17 @@ class ConstBufferType
     {
     }
 
-    // const index into array
+    /**
+     * @brief Needed because this class has virtual member functions and is
+     *        intended as a base class.
+     */
+    virtual ~ConstBufferType() = default;
+
+    /**
+     * @brief Const indexing operator for ConstBufferType.
+     * @param index Index of the element to access.
+     * @return Const reference to the element at the specified index.
+     */
     const T &operator[](const size_t index) const
     {
         if (index >= size_)

openvpn/buffer/buflimit.hpp

@@ -43,6 +43,8 @@ class BufferLimit
         reset();
     }
 
+    virtual ~BufferLimit() = default;
+
     void set_max(const T max_lines_arg,
                  const T max_bytes_arg)
     {

openvpn/client/clilife.hpp

@@ -34,6 +34,8 @@ class ClientLifeCycle : public RC<thread_unsafe_refcount>
   public:
     struct NotifyCallback
     {
+        virtual ~NotifyCallback() = default;
+
         virtual void cln_stop() = 0;
         virtual void cln_pause(const std::string &reason) = 0;
         virtual void cln_resume() = 0;

openvpn/client/cliproto.hpp

@@ -81,6 +81,8 @@ namespace openvpn::ClientProto {
 
 struct NotifyCallback
 {
+    virtual ~NotifyCallback() = default;
+
     virtual void client_proto_terminate() = 0;
     virtual void client_proto_connected()
     {

openvpn/client/remotelist.hpp

@@ -112,6 +112,8 @@ class RemoteList : public RC<thread_unsafe_refcount>
     {
         typedef RCPtr<ConnBlockFactory> Ptr;
 
+        virtual ~ConnBlockFactory() = default;
+
         virtual ConnBlock::Ptr new_conn_block(const OptionList::Ptr &opt) = 0;
     };
 
@@ -229,6 +231,8 @@ class RemoteList : public RC<thread_unsafe_refcount>
 
     struct RemoteOverride
     {
+        virtual ~RemoteOverride() = default;
+
         virtual Item::Ptr get() = 0;
     };
 
@@ -311,6 +315,8 @@ class RemoteList : public RC<thread_unsafe_refcount>
 
         struct NotifyCallback
         {
+            virtual ~NotifyCallback() = default;
+
             // client callback when resolve operation is complete
             virtual void bulk_resolve_done() = 0;
         };

openvpn/ssl/proto.hpp

@@ -161,6 +161,8 @@ enum
 class ProtoContextCallbackInterface
 {
   public:
+    virtual ~ProtoContextCallbackInterface() = default;
+
     /**
      * Sends out bytes to the network.
      */

openvpn/transport/reconnect_notify.hpp

@@ -26,6 +26,8 @@ namespace openvpn {
 class ReconnectNotify
 {
   public:
+    virtual ~ReconnectNotify() = default;
+
     // When a connection is close to timeout, the core will call this
     // method.  If it returns false, the core will disconnect with a
     // CONNECTION_TIMEOUT event.  If true, the core will enter a PAUSE

openvpn/transport/socket_protect.hpp

@@ -35,6 +35,8 @@ namespace openvpn {
 class BaseSocketProtect
 {
   public:
+    virtual ~BaseSocketProtect() = default;
+
     virtual bool socket_protect(openvpn_io::detail::socket_type socket, IP::Addr endpoint) = 0;
 };
 

openvpn/tun/client/tunbase.hpp

@@ -70,6 +70,8 @@ struct TunClient : public virtual RC<thread_unsafe_refcount>
 // special events, and progress notifications.
 struct TunClientParent
 {
+    virtual ~TunClientParent() = default;
+
     virtual void tun_recv(BufferAllocated &buf) = 0;
     virtual void tun_error(const Error::Type fatal_err, const std::string &err_text) = 0;