Named Fifo Select Bug

fifo.c

#include <errno.h>
#include <sys/select.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdbool.h>
#include <unistd.h>
#include <string.h>

int main() {
    // Open export fifo
    int fd = open("./foo-fifo", O_RDWR | O_CREAT);
    if (fd < 0) { // Failed to open
        perror("error opening fifo");
    }

    // Read or write fifo until "quit" is in buffer 
    while (true) {
        fd_set read_fds;
        fd_set write_fds;

        FD_ZERO(&read_fds);
        FD_SET(fd, &read_fds);

        FD_ZERO(&write_fds);
        FD_SET(fd, &write_fds);

        int num_fds = select(fd+1, &read_fds, &write_fds, NULL, NULL);
        if (num_fds < 0) { // Failed to select
            perror("failed to select fifo fd");
        } else if (num_fds == 0) { // Timeout
            continue;
        }

        // If read
        if (FD_ISSET(fd, &read_fds)) {
            char buf[1000] = "";

            if (read(fd, buf, sizeof(buf)) < 0) {
                perror("error reading fifo");
            }

            printf("read: \"%s\"\n", buf);

            if (strcmp(buf, "quit\n") == 0) {
                break;
            }
        }

        // If write
        if (FD_ISSET(fd, &write_fds)) {
            char *buf = "foo";

            if (write(fd, buf, sizeof(buf)) < 0) {
                perror("error writing fifo");
            }

            printf("write: \"%s\"\n", buf);
        }
    }

    // Close fifo
    if (close(fd) < 0) { // Failed to close
        perror("failed to close export fifo");
    }

    return 0;
}