Socket message flow introduction and C code implementation, socket message flow code

Socket message flow introduction and C code implementation, socket message flow code

In actual software development, socket programming is often involved, that is, using socket to complete message interaction and command execution. This article uses a C program to explain the entire message execution process of the socket in Linux.

C program example

/*************************************** * ******************************** All Rights Reserved (C) 2015, Zhou Zhaoxiong. ** File name: TestSocket. c * File ID: none * Content summary: test the entire process from socket creation to completion * Other Instructions: none * Current version: V1.0 * Author: Zhou Zhaoxiong * completion date: 20150608 *************************************** * *******************************/# include <stdio. h> # include <stdlib. h> # include <string. h> # include <errno. h> # include <netinet/in. h> # include <sys/socket. h> // macro definition # define INVALID_SOCKET-1 # define SOCKET_ERROR-1 # define BUFFER_LEN 1024 # define SERVERPORT 89 99 # define IPADDR "10.116.32.10" // redefine the Data Type typedef unsigned char UINT8; typedef signed int INT32; typedef unsigned int UINT32; typedef INT32 SOCKET; typedef struct sockaddr_in SOCKADDR_IN; typedef struct sockaddr * PSOCKADDR; // global variable UINT8 g_iStart = 0; UINT8 g_iFinish = 0; /*************************************** * ******************************** function description: main function * input parameter: none * output parameter: none * return value: none * Other Description: No * modify date version number modifier modify content *-- ----------------------------------------------------------------- * 20150608 V1.0 Zhou Zhaoxiong create ********************************* * ***********************************/INT32 main () {INT32 iRet =-1; INT32 status = 0; INT32 iTempVar = 0; UINT32 iLenth = 0; UINT8 szBuffer [BUFFER_LEN] = {0}; SOCKET sockefd = INVALID_SOCKET; SOCKET clientSocketfd = {0}; SOCKADDR_IN local_address = {0}; SOCKADDR_IN c Lient_addrss = {0}; pthread_t tid = pthread_self (); while (1) {// create socket close (sockefd); sockefd = socket (AF_INET, SOCK_STREAM, 0 ); if (INVALID_SOCKET = sockefd) {continue;} // bind the specified IP address and port local_address.sin_family = AF_INET; region = htons (SERVERPORT); region = inet_addr (IPADDR); status = SOCKET_ERROR; iTempVar = 1; if (setsockopt (sockefd, SOL_SOCKET, SO _ REUSEADDR, (int *) & iTempVar, sizeof (iTempVar) =-1) {printf ("setsockopt SO_REUSEADDR FAILED! ERROR [% d] ERRORINFO [% s] \ n ", errno, strerror (errno); close (sockefd); continue;} status = bind (sockefd, (PSOCKADDR) & local_address, sizeof (SOCKADDR_IN); // bind the specified IP address and port if (status = SOCKET_ERROR) {close (sockefd); printf ("FAILED to bind ipaddr: % s! \ N ", IPADDR); continue;} else {printf (" Succeeded to bind ipaddr: % s, port: % d! \ N ", IPADDR, SERVERPORT); break ;}// enable listening iRet = listen (sockefd, 10); if (iRet <0) {printf ("FAILED to stratup the listener! \ N "); return-1 ;}// obtain the while (1) {iLenth = sizeof (client_addrss) from the listener queue cyclically; clientSocketfd = accept (sockefd, (struct sockaddr *) & client_addrss, & iLenth); if (clientSocketfd = INVALID_SOCKET) {printf ("The client socket is invalid! \ N "); continue;} printf (" ------------------------------------------ \ n "); printf (" Accept msg from SendMsgTool successfully! \ N "); memset (szBuffer, 0x00, sizeof (szBuffer); iLenth = recv (clientSocketfd, szBuffer, BUFFER_LEN-1, 0); if (iLenth <= 0) {printf ("Server receive data failed! Strerror = % s. \ n ", strerror (errno); continue;} printf (" Receive data: % s \ n ", szBuffer); if (0 = strncmp (szBuffer, "start test. \ r \ n ", strlen (" start test. \ r \ n ") {g_iStart = 1; // print the message UINT8 szCmd [1024] = {0}; sprintf (szCmd, "This is a test for SOCKET! \ N "); printf (" The command is: % s \ n ", szCmd); g_iFinish = 1; // set The end ID to 1} while (1) {if (1 = g_iFinish) {memset (szBuffer, 0x00, sizeof (szBuffer); sprintf (szBuffer, "task completed \ r \ n "); if (send (clientSocketfd, szBuffer, strlen (szBuffer), 0) <0) // Send the message that ends this session {printf ("send close msg failed! \ N ");} else {printf (" Send close msg OK! \ N ");} printf (" ------------------------------------------ \ n "); g_iFinish = 0; g_iStart = 0; break ;}} return 0 ;}

Detailed procedures
Through the above code, we can see that the entire message flow of the socket is:
Step 1: Create a socket.
Step 2: bind the specified IP address and port. If binding fails, skip to the first step.
Step 3: Start the listener. If no message is monitored, the program remains in the listening State. If the message is listened to, execute the next step.
Step 4: cyclically retrieve messages from the listener queue and perform related operations based on the message content.
Step 5: after the operation is completed, the relevant message is returned to the message sending module.

Multiple socket functions are involved in the entire process, including close, socket, inet_addr, setsockopt, bind, listen, accept, recv, and send, for more information about these functions, visit the internet.

Makefile content
This program is compiled and run in Linux. The content of the makefile file is:

TestSocket : TestSocket.c    gcc -c -g TestSocket.c    gcc -g -o release/TestSocket TestSocket.o    rm *.o

Program running result
A self-developed message sending Tool sends three messages to the program consecutively. The result is as follows:

zhou@Linux:~/zhouzhaoxiong/TestSocket/release> TestSocketSucceeded to bind ipaddr:10.116.32.139, port:8999!------------------------------------------Accept msg from SendMsgTool successfully!Receive data: start test.The command is: This is a test for SOCKET!Send close msg OK!------------------------------------------------------------------------------------Accept msg from SendMsgTool successfully!Receive data: start test.The command is: This is a test for SOCKET!Send close msg OK!------------------------------------------------------------------------------------Accept msg from SendMsgTool successfully!Receive data: start test.The command is: This is a test for SOCKET!Send close msg OK!------------------------------------------

As you can see, after the program is successfully bound to an IP address and port, it remains in the listening state. As long as a message is sent, it will perform subsequent message processing.

Summary
Socket has a long history and is also widely used in actual software development projects. As a qualified software development engineer, you must master the usage methods.

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