Socket programming (multi process)

Using multiple processes to achieve multiple clients and a server CS Model

【 Last one 】： A client and a server model

Using parent-child processes , The parent process listens to accept new connections , Child processes handle new connections . The parent process is also responsible for recycling the child process
accept and read Blocking function , Will be interrupted by the signal , This should not be considered an error , Need to add a judgment ：errno=EINTER

The server code is as follows , The client code remains unchanged

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>
#include<sys/types.h>
#include<arpa/inet.h>
#include<unistd.h>
#include<netinet/in.h>
#include <sys/wait.h>
#include <errno.h>

// Signal processing functions 
void waitchild()
{
    
	pid_t wpid;
	while(1)
	{
    
		wpid = waitpid(-1, NULL, WNOHANG);
		if(wpid > 0)
		{
    
			printf("child exit\n");
		}
		else if(wpid == 0 || wpid == -1)
		{
    
			break;
		}
	}
}

int main()
{
    
	int lfd = socket(AF_INET, SOCK_STREAM, 0);
	if(lfd < 0)
	{
    
		perror("socket error");
		return -1;
	}
	
	struct sockaddr_in serv;
	bzero(&serv, sizeof(serv));
	serv.sin_family = AF_INET;
	serv.sin_port = htons(8888);
	serv.sin_addr.s_addr = htonl(INADDR_ANY);
	int ret = bind(lfd, (struct sockaddr*)&serv, sizeof(serv));
	if(ret < 0)
	{
    
		perror("bind error");
		return -1;
	}
	
	listen(lfd, 128);

	// Blocking SIGCHLD The signal , Avoid generating signals before the handler is registered 
	sigset_t mask;
	sigemptyset(&mask);
	sigaddset(&mask, SIGCHLD);
	sigprocmask(SIG_BLOCK, &mask, NULL);

	struct sockaddr_in client;
	socklen_t len;
	int cfd;
	char ip[16];
	pid_t pid;
       	while(1)
	{
    
		len = sizeof(client);
		cfd = accept(lfd, (struct sockaddr*)&client, &len);
		if(errno == EINTR)
		{
    
			cfd = accept(lfd, (struct sockaddr*)&client, &len);
		}
		memset(ip, 0, sizeof(ip));
		printf("client: ip == [%s], port == [%d]\n", inet_ntop(AF_INET, &client.sin_addr.s_addr, ip, sizeof(ip)), ntohs(client.sin_port));
		printf("lfd == [%d], cfd == [%d]\n", lfd, cfd);
		
		pid = fork();
		if(pid < 0)
		{
    
			perror("fork error\n");
			exit(-1);
		}
		else if(pid > 0)
		{
    
			close(cfd);
			// Register callback function 
			struct sigaction act;
			act.sa_handler = waitchild;
			act.sa_flags = 0;
			sigemptyset(&act.sa_mask);
			sigaction(SIGCHLD, &act, NULL);

			// Release right SIGCHLD Signal blocking 
			sigprocmask(SIG_UNBLOCK, &mask, NULL);
		}
		else
		{
    
			close(lfd);
			int n = 0;
			char buf[1024];
			while(1)
			{
    
				memset(buf, 0, sizeof(buf));
				n = read(cfd, buf, sizeof(buf));
				if(n <= 0)
				{
    
					printf("read error or client close\n");
					break;
				}
				// Parent process and created child process client They don't affect each other （ Read share write copy ）
				//printf("client: ip == [%s], port == [%d]\n", inet_ntop(AF_INET, &client.sin_addr.s_addr, ip, sizeof(ip)), ntohs(client.sin_port));
				printf("port == [%d]: n == [%d], buf == [%s]\n", ntohs(client.sin_port), n, buf);

				for(int i=0; i<n; i++)
				{
    
					buf[i] = toupper(buf[i]);
				}

				write(cfd, buf, n);
			}
			close(cfd);
			// Avoid creating child processes after the communication is over 
			exit(0);
		}
	}
	close(lfd);
	return 0;
}

【 Next 】: Multithreaded version