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

#define ERR_EXIT(m) \
	do \
	{ \
		perror(m);	\
		exit(EXIT_FAILURE);\
	}while(0)

int main(void)
{
	int sockfds[2];
	//全雙工的父子程序或有親緣關係程序的通訊
	if(socketpair(PF_UNIX, sock_STREAM, 0, sockfds)<0)
	{
		ERR_EXIT("socketpair");
	}

	pid_t pid;
	pid = fork();
	if(pid==-1)
	{
		ERR_EXIT("fork");
	}
	if(pid>0)//父程序
	{
		int val =0;
		close(sockfds[1]);
		while(1)
		{
			++val;
			printf("sending data: %d\n",val);
			write(sockfds[0], &val, sizeof(val));
			read(sockfds[0], &val, sizeof(val));
			printf("recv data: %d\n",val);
			sleep(1);
		}
	}
	else if(pid ==0)//子程序
	{
		int val;
		close(sockfds[0]);
		while(1)
		{
			read(sockfds[1], &val, sizeof(val));
			++val;
			write(sockfds[1], &val, sizeof(val));
		}
	}
	return 0;
}