// Ivan Novick
// Feb 3, 2008
// pipe_write_read.c
// basic opening of a pipe, forking a child process, then the child writes to parent over the pipe

#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int pipe_fd[2];
pid_t me;
pid_t parent;
char buffer[512];

int main(int argc, char** argv)
{
    // create a pipe 
    if (pipe(pipe_fd)) { fprintf(stderr, "pipe creation failed, exiting...\n"); exit(1); }

    int fork_return = fork();
    if (fork_return < 0) { fprintf(stderr, "fork failed, exiting...\n"); exit(2); }   

    // obtain the pid of this process and the parent
    pid_t me = getpid();
    pid_t par = getppid();
    printf("PID: %d, PARENT: %d\n", (int)me, (int)par);

    // determine if this is the parent or child process
    if (fork_return == 0) 
    {
        // if fork returned 0, this is the child
        sprintf(buffer, "Hi parent, my pid is %d", me);

        // actually write to the pipe now
        size_t amount = write(pipe_fd[1], buffer, strlen(buffer) + 1);

        printf("wrote to pipe %d bytes\n", (int)amount);
    }
    else 
    {
        // fork returned > 0 this is the parent process

        // actually read from the pipe now
        ssize_t amount = read(pipe_fd[0], buffer, sizeof(buffer));

        printf("read from pipe %d bytes\n", (int)amount);
        printf("in parent, message from child over pipe: %s\n", buffer);
    }
    return 0;
}