State

class TCPOctetStream;
class TCPState;

class TCPConnection 
{
public:
	TCPConnection();
	/*
	*/
	void ActiveOpen();
	void PassiveOpen();
	void Close();
	/*
	*/
	void Send();
	void Acknowledge();
	void Synchronize();
	/*
	*/
	void ProcessOctet(TCPOctetStream*)
	{

	}
private:
	friend class TCPState;
	void ChangeState(TCPState*);
private:
	TCPState* _state;
};

class TCPState 
{
public:
	virtual void Transmit(TCPConnection*, TCPOctetStream*);
	virtual void ActiveOpen(TCPConnection*);
	virtual void PassiveOpen(TCPConnection*);
	virtual void Close(TCPConnection*);
	virtual void Synchronize(TCPConnection*);
	virtual void Acknowledge(TCPConnection*);
	virtual void Send(TCPConnection*);
protected:
	void ChangeState(TCPConnection*, TCPState*);
};

class TCPClosed : public TCPState 
{
public:
	static TCPState* Instance(){ return new TCPState(); }

	virtual void ActiveOpen(TCPConnection*);
	virtual void PassiveOpen(TCPConnection*);
	// ...
};

/*
*/
TCPConnection::TCPConnection () 
{
	_state = TCPClosed::Instance();
}
/*
*/
void TCPConnection::ChangeState (TCPState* s) 
{
	_state = s;
}
/*
*/
void TCPConnection::ActiveOpen () 
{
	_state->ActiveOpen(this);
}
/*
*/
void TCPConnection::PassiveOpen () 
{
	_state->PassiveOpen(this);
}
/*
*/
void TCPConnection::Close () 
{
	_state->Close(this);
}
/*
*/
void TCPConnection::Acknowledge () 
{
	_state->Acknowledge(this);
}
/*
*/
void TCPConnection::Synchronize () 
{
	_state->Synchronize(this);
}
/*
*/
void TCPState::Transmit (TCPConnection*, TCPOctetStream*) { }
void TCPState::ActiveOpen (TCPConnection*) { }
void TCPState::PassiveOpen (TCPConnection*) { }
void TCPState::Close (TCPConnection*) { }
void TCPState::Synchronize (TCPConnection*) { }
void TCPState::Acknowledge (TCPConnection*) { }
void TCPState::Send (TCPConnection*) { }
/*
*/
void TCPState::ChangeState (TCPConnection* t, TCPState* s) 
{
	t->ChangeState(s);
}
/*
*/

/*
*/
class TCPEstablished : public TCPState 
{
public:
	static TCPState* Instance(){ return NULL; }

	virtual void Transmit(TCPConnection*, TCPOctetStream*);
	virtual void Close(TCPConnection*);
};
/*
*/
class TCPListen : public TCPState 
{
public:
	static TCPState* Instance(){ return NULL; }

	virtual void Send(TCPConnection*);
	// ...
};
/*
*/
void TCPClosed::ActiveOpen (TCPConnection* t) 
{
	// send SYN, receive SYN, ACK, etc.

	ChangeState(t, TCPEstablished::Instance());
}
/*
*/
void TCPClosed::PassiveOpen (TCPConnection* t) 
{
	ChangeState(t, TCPListen::Instance());
}
/*
*/
void TCPEstablished::Close (TCPConnection* t) 
{
	// send FIN, receive ACK of FIN

	ChangeState(t, TCPListen::Instance());
}
/*
*/
void TCPEstablished::Transmit (
							   TCPConnection* t, TCPOctetStream* o
							   ) 
{
								   t->ProcessOctet(o);
}
/*
*/
void TCPListen::Send (TCPConnection* t) 
{
	// send SYN, receive SYN, ACK, etc.

	ChangeState(t, TCPEstablished::Instance());
}
/*
*/