Fixes #458

include/mqtt/async_client.hpp

@@ -251,6 +251,12 @@ class async_client : public client<Socket, PacketIdBytes> {
     void unsuback() = delete;
 
 protected:
+    // Ensure that only code that knows the *exact* type of an object
+    // inheriting from this abstract base class can destruct it.
+    // This avoids issues of the destructor not triggering destruction
+    // of derived classes, and any member variables contained in them.
+    // Note: Not virtual to avoid need for a vtable when possible.
+    ~async_client() = default;
 
     async_client(
         as::io_context& ioc,

include/mqtt/client.hpp

@@ -927,6 +927,14 @@ class client : public endpoint<std::mutex, std::lock_guard, PacketIdBytes> {
         if (ping_duration_ms_ != 0) tim_ping_.cancel();
     }
 
+protected:
+    // Ensure that only code that knows the *exact* type of an object
+    // inheriting from this abstract base class can destruct it.
+    // This avoids issues of the destructor not triggering destruction
+    // of derived classes, and any member variables contained in them.
+    // Note: Not virtual to avoid need for a vtable when possible.
+    ~client() = default;
+
 private:
     std::shared_ptr<Socket> socket_;
     as::io_context& ioc_;

include/mqtt/sync_client.hpp

@@ -250,6 +250,12 @@ class sync_client : public client<Socket, PacketIdBytes> {
     void async_unsuback() = delete;
 
 protected:
+    // Ensure that only code that knows the *exact* type of an object
+    // inheriting from this abstract base class can destruct it.
+    // This avoids issues of the destructor not triggering destruction
+    // of derived classes, and any member variables contained in them.
+    // Note: Not virtual to avoid need for a vtable when possible.
+    ~sync_client() = default;
 
     sync_client(
         as::io_context& ioc,