echo_mpserv.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <sys/wait.h>
#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30

void read_childproc(int sig)
{
	int status;
	pid_t pid = waitpid(-1, &status, WNOHANG);
	if(WIFEXITED(status))
	{
		printf("Removed proc fid : %d \n", pid);
		printf("child send : %d \n", WEXITSTATUS(status));
	}
}

void error_handling(char *message)
{
	fputs(message, stderr);
	fputc('\n', stderr);
	exit(1);
}

int main(int argc, char const *argv[])
{
	int serv_sock,clnt_sock;
	struct sockaddr_in serv_adr,clnt_adr;

	pid_t pid;
	struct sigaction act;
	socklen_t adr_sz;
	int str_len,state;
	char buf[BUF_SIZE];
	if(argc != 2)
	{
		printf("Usage : %s <port> \n", argv[0]);
		exit(1);
	}

	act.sa_handler = read_childproc;
	sigemptyset(&act.sa_mask);
	act.sa_flags = 0;
    state = sigaction(SIGCHLD, &act, 0);

    serv_sock = socket(PF_INET, SOCK_STREAM, 0);
    memset(&serv_adr,0, sizeof(serv_adr));
    serv_adr.sin_family = AF_INET;
    serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_adr.sin_port = htons(atoi(argv[1]));

    if(bind(serv_sock, (struct sockaddr*)&serv_adr, sizeof(serv_adr))==-1)
    	error_handling("bind() error");
    if(listen(serv_sock,5) == -1)
    	error_handling("listen() error");

    while(1)
    {
    	adr_sz = sizeof(clnt_adr);
    	clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_adr, &adr_sz);
    	if(clnt_sock == -1)
    		continue;
    	else
    		puts("new client connected......");

    	pid = fork();
    	if(pid == -1)//fork failed
    	{
    		close(clnt_sock);
    		continue;
    	}
    	if(pid == 0)//child process
    	{
            close(serv_sock);
            while((str_len =read(clnt_sock, buf, BUF_SIZE))!=0)
            	write(clnt_sock,buf,str_len);

            close(clnt_sock);
            puts("client disconnected...");
            return 0;
    	}
    	else
    		close(clnt_sock);
    }

    close(serv_sock);
    return 0;
}