Shulou(Shulou.com)06/02 Report--

This article mainly introduces "what are the knowledge points of Socket programming". In the daily operation, I believe many people have doubts about the knowledge points of Socket programming. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the questions of "what are the knowledge points of Socket programming?" Next, please follow the editor to study!

What is TCP/IP, UDP?

TCP/IP (Transmission Control Protocol/Internet Protocol), the transmission control protocol / internetwork protocol, is an industry standard protocol set designed for the wide area network (WANs).

UDP (User Data Protocol, user Datagram Protocol) is the protocol corresponding to TCP. It belongs to one of the TCP/IP protocol families.

Here is a diagram that shows the relationship between these protocols.

Figure 1

The TCP/IP protocol family includes the transport layer, the network layer and the link layer. Now you know the relationship between TCP/IP and UDP.

Where is Socket?

In figure 1, we don't see the shadow of Socket, so where is it? Still use the picture to speak, it is clear at a glance.

Figure 2

So Socket is here.

What is Socket?

Socket is the middle software abstraction layer for the communication between the application layer and the TCP/IP protocol family, and it is a group of interfaces. In the design pattern, Socket is actually a facade pattern, which hides the complex TCP/IP protocol family behind the Socket interface. For users, a simple set of interfaces is all, allowing Socket to organize the data to comply with the specified protocol.

Can you use them?

Our predecessors have done a lot for us, and the communication between networks is much easier, but after all, there is still a lot of work to be done. When I heard about Socket programming in the past, I thought it was a relatively advanced programming knowledge, but as long as I found out how Socket programming works, the mystery was lifted.

A scene in life. If you want to call a friend, dial first, and the friend will pick up the phone when he hears the ringtone, and then you and your friend will have a connection and can talk. When the exchange is over, hang up the phone and end the conversation. The scenes in life explain how this works. Maybe the TCP/IP protocol family was born in life, but not necessarily.

Figure 3

Let's start with the server side. The server initializes Socket, then binds to the port (bind), listen the port, calls accept blocking, and waits for the client to connect. At this point, if a client initializes a Socket and then connects to the server (connect), if the connection is successful, the connection between the client and the server is established. The client sends a data request, the server receives the request and processes the request, then sends the response data to the client, the client reads the data, * closes the connection, and an interaction ends.

Let me give you a simple example here. We are following the path of the TCP protocol (see figure 2). The example is written in MFC and runs with the following interface:

Figure 4

Figure 5

Enter the IP address of the server and the sent data on the client side, then press the send button, the server receives the data, and then responds to the client side. The client reads the response data and displays it on the interface.

Here are the functions that receive and send data:

Int Receive (SOCKET fd,char * szText,int len) {int cnt; int rc; cnt=len; while (cnt > 0) {rc=recv (fd,szText,cnt,0); if (rc==SOCKET_ERROR) {return-1 } if (rc==0) return len-cnt; szText+=rc; cnt-=rc;} return len;} int Send (SOCKET fd,char * szText,int len) {int cnt; int rc; cnt=len While (cnt > 0) {rc=send (fd,szText,cnt,0); if (rc==SOCKET_ERROR) {return-1;} if (rc==0) return len-cnt; szText+=rc; cnt-=rc } return len;}

Server side:

On the server side, the main task is to start Socket and listen on threads.

# define DEFAULT_PORT 2000 void CServerDlg::OnStart () {sockaddr_in local; DWORD dwThreadID = 0; the port set for local.sin_family=AF_INET; / / is DEFAULT_PORT. Local.sin_port=htons (DEFAULT_PORT); / / the IP address is set to INADDR_ANY, which allows the system to automatically obtain the local IP address. Local.sin_addr.S_un.S_addr=INADDR_ANY; / / initialize Socket m_Listening = socket (AF_INET,SOCK_STREAM,0); if (m_Listening = = INVALID_SOCKET) {return } / / bind the local address to the created socket if (bind (m_Listening, (LPSOCKADDR) & local,sizeof (local)) = = SOCKET_ERROR) {closesocket (m_Listening); return;} / / create a listening thread, which can also respond to actions on the interface. M_hListenThread =:: CreateThread (NULL,0,ListenThread,this,0,&dwThreadID); m_StartBtn.EnableWindow (FALSE); m_StopBtn.EnableWindow (TRUE);}

Listener thread function:

DWORD WINAPI CServerDlg::ListenThread (LPVOID lpparam) {CServerDlg* pDlg = (CServerDlg*) lpparam; if (pDlg = = NULL) return 0; SOCKET Listening = pDlg- > masking listing; / / start listening for client connections. If (listen (Listening,40) = = SOCKET_ERROR) {return 0;} char szBuf [Max _ PATH]; / / initialize memset (szBuf,0,MAX_PATH); while (1) {SOCKET ConnectSocket; sockaddr_in ClientAddr Int nLen = sizeof (sockaddr); / / blocking until there is a client connection, otherwise more CPU resources are wasted. ConnectSocket = accept (Listening, (sockaddr*) & ClientAddr,&nLen); / / all to the IP address of the client. Char * pAddrname = inet_ntoa (ClientAddr.sin_addr); pDlg- > Receive (ConnectSocket,szBuf,100); / / request data is displayed on the interface. PDlg- > SetRequestText (szBuf); strcat (szBuf, ": I am an old cat, received ("); strcat (szBuf,pAddrname); strcat (szBuf, ")"); / / send response data pDlg- > Send (ConnectSocket,szBuf,100) to the client;} return 0;}

The server has been listening to whether there is a client connection, if there is a connection, process the client's request, give a response, and then continue to monitor.

Client:

Sending function of the client:

# define DEFAULT_PORT 2000 void CClientDlg::OnSend () {DWORD dwIP = 0; TCHAR szText [Max _ PATH]; memset (szText,0,MAX_PATH); m_IP.GetWindowText (szText,MAX_PATH); / / convert the IP address in string form to the form required by the IN_ADDR structure. DwIP = inet_addr (szText); m_RequestEdit.GetWindowText (szText,MAX_PATH); sockaddr_in local; SOCKET socketTmp; / / must be AF_INET, indicating that the socket communicates in the Internet domain local.sin_family=AF_INET; / / port number local.sin_port=htons (DEFAULT_PORT); / / the IP address of the server. Local.sin_addr.S_un.S_addr=dwIP; / initialize Socket socketTmp=socket (AF_INET,SOCK_STREAM,0); / / connect to the server if (connect (socketTmp, (LPSOCKADDR) & local,sizeof (local)) < 0) {closesocket (socketTmp); MessageBox ("failed to connect to the server.") ; return;} / / send a request that simply sends only 100bytes, and also specifies 100bytes on the server side. Send (socketTmp,szText,100); / / reads the data returned by the server. Memset (szText,0,MAX_PATH); / / receives a response from the server. Receive (socketTmp,szText,100); TCHAR szMessage [Max _ PATH]; memset (szMessage,0,MAX_PATH); strcat (szMessage,szText); / / display response data on the interface. M_ReplyBtn.SetWindowText (szMessage); closesocket (socketTmp);}

The client communicates once with a single function. Why is the IP address 127.0.0.1 here? With this IP address, the server and client can run on the same machine, which makes debugging much easier. Of course, you can run the Server program on your friend's machine (I have tested it on the local area network) and run the Client program on your own machine. Of course, the IP address entered should be the IP address of your friend's machine.

At this point, the study of "what are the knowledge points of Socket programming" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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