IEG4180 Tutorial 3 Shaoquan Zhang

Announcement The deadline of the project 1 is extended to 11pm, 12/02/2011 Follow the requirement of the marking scheme

Outline Stream socket programming I/O modes in Unix

Stream Socket Programming Stream socket Q: When is the three-way handshake happened? A: When the client calls the function connect(), the TCP connection is built before the accept(). The function accept() selects one from the established connection queue.

TCP Connection Backlog TCP Connection Queue – For a given listening socket, the kernel maintains two queues for client sockets: An incomplete connection queue: three-way handshake is not completed yet; A completed connection queue: three-way handshake is completed. – listen(socket s, int backlog) backlog: the maximum of the sum of two queue lengths Problem: SYN attack

Accept() By default, when the completed queue is empty, the function will be blocked. Methods: – poll() : accept() becomes non-blocking – select(): accept() is called only when the completed queue is not empty – Multithread – Message driven

Message-driven Accept() SOCKET s=socket(); bind(); WSAAsyncSelect(s, m_hWnd, wMsg, FD_ACCEPT); //turn the socket s into a message-driven socket //m_hWnd: handle to window that will process the message //wMsg: message identifier; FD_ACCEPT: events to handle listen(s, 5);

Message Flow

WindowProc() HRESULT CNetProbeDlg::WindowProc(UINT message, WPARAM wParam, LPARAM lParam) { if(message==wMsg) { SOCKET s = (SOCKET)wParam; int event = WSAGETSELECTEVENT(lParam); switch(event){ case FD_ACCEPT: OnAccept(s); break; case FD_READ: OnRead(s); //receive data break; } } return CDialog::WindowProc(message, wParam, lParam); } message events to handle void CNetProbeDlg::OnAccept(SOCKET s) { SOCKET newsfd = accept(s,…); WSAAsyncSelect(newsfd, m_hWnd, wMsg, FD_READ); //turn the new socket into a message-driven one; handle the recv() }

Add WindowProc() class review -> dialog class propertyoverrides

Unix I/O Modes Blocking I/O Non-blocking I/O I/O multiplexing (select and poll) Asynchronous I/O For a socket input operation, there are two steps: 1. wait data to arrive 2. copy data from kernel’s buffer to the process

Blocking I/O Acknowledgement: following pictures come from UNIX Networking Programming

Non-blocking I/O

I/O Multiplexing

Asynchronous I/O

Backup Host AHost B