/*********************************************************************************
 *      Copyright:  (C) 2025 LingYun IoT System Studio
 *                  All rights reserved.
 *
 *       Filename:  pipe.c
 *    Description:  This file pipe example program
 *
 *        Version:  1.0.0(11/07/2025)
 *         Author:  Guo Wenxue <guowenxue@gmail.com>
 *      ChangeLog:  1, Release initial version on "11/07/2025 11:26:33 AM"
 *
 ********************************************************************************/
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>

#define MSG_STR "This message is from parent: Hello, child process!"

int main(int argc, char **argv)
{
    int             pipe_fd[2];
    int             rv;
    int             pid;
    char            buf[512];
    int             wstatus;

    if( pipe(pipe_fd) < 0)
    {
        printf("Create pipe failure: %s\n", strerror(errno));
        return -1;
    }

    if( (pid=fork()) < 0 )
    {
        printf("Create child process failure: %s\n", strerror(errno));
        return -2;
    }
    else if(pid == 0)
    {
        /* child process close write endpoint, then read data from parent process */
        close(pipe_fd[1]);

        memset(buf, 0, sizeof(buf));
        rv=read(pipe_fd[0], buf, sizeof(buf));
        if(rv < 0 )
        {
            printf("Child process read from pipe failure: %s\n", strerror(errno));
            return -3;
        }

        printf("Child process read %d bytes data from pipe: \"%s\"\n", rv, buf);
        return 0;
    }

    /* parent process close read endpoint, then write data to child process */
    close(pipe_fd[0]);
    if( write(pipe_fd[1], MSG_STR, strlen(MSG_STR)) < 0)
    {
        printf("Parent process write data to pipe failure: %s\n", strerror(errno));
        return -3;
    }

    printf("Parent start wait child process exit...\n");
    wait(&wstatus);

    return 0;
}