bug: the fifo file remains present even after the daemon dies - c

Question

I created a daemon that creates a fifo file with a default name and then is being blocked waiting for messages on that fifo. When an interactive process (even from the shell an echo "..." > file_filo) write data to that fifo, the daemon wakes up and writes the received data to a journal file along with the time when the writing was done. The code (daemon.fifo file) creates a daemon.fifo file in the current directory and can be written anywhere in that file.
code:
#include "ourhdr.h"
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>
// gcc -Wall -O tema_daemon_fifo.c liblab.a -o tema_daemon_fifo
int main()
{
// 1 = keep the current directory (will contain the log and the fifo)
// 0 = close the standard input/output streams for the daemon
int daemonized = daemon(1, 0);
if (daemonized != 0)
err_sys("daemon error");
char* fifo_file = "daemon.fifo";
int r = mkfifo(fifo_file, 0700);
if (r != 0)
{
if (errno != EEXIST)
{
err_sys("mkfifo error");
}
}
int fifo_fd = open(fifo_file, O_RDONLY);
if (fifo_fd < 0)
{
err_sys("open-fifo error");
}
int stop_loop = 0;
char buff[1024];
do
{
int c = read(fifo_fd, buff, 1024);
if (c >= 0)
{
if (c >= 4 && strncmp("exit", buff, 4) == 0)
{
stop_loop = 1;
}
if (c > 0)
{
int file_fd = open("daemon.txt", O_WRONLY | O_CREAT | O_APPEND, 0700);
if (file_fd >= 0)
{
time_t t = time(0);
char* timestamp = ctime(&t);
r = write(file_fd, timestamp, strlen(timestamp));
if (r < 0)
err_sys("write timestamp error");
r = write(file_fd, buff, c);
if (r < 0)
err_sys("write buff error");
close(file_fd);
}
else
{
err_sys("open-log error");
}
}
}
else
{
err_sys("read error");
}
} while (stop_loop == 0);
close(fifo_fd);
return 0;
}
problem (bug): Normally the daemon.fifo file through which you can write to the daemon should only exist if there is also a daemon to write to. How can I fix the bug?

Answer 1

You need to call unlink() after closing the file to remove the file from the folder.
Also, you should consider catching the SIGTERM and allowing the signal to also break the loop so the daemon can terminate in a normal way and clean the files when kill <PID> is executed.
So this is the modificaiton I did:
...
...
#include <signal.h>
int stop_loop = 0;
void terminate(int signum)
{
stop_loop = 1;
}
int main()
{
// 1 = keep the current directory (will contain the log and the fifo)
// 0 = close the standard input/output streams for the daemon
int daemonized = daemon(1, 0);
if (daemonized != 0)
err_sys("daemon error");
char* fifo_file = "daemon.fifo";
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_handler = terminate;
sigaction(SIGTERM, &action, NULL);
...
...
and
...
...
} while (stop_loop == 0);
close(fifo_fd);
unlink(fifo_file);
return 0;
}
The file will remain on the system only if the daemon is killed with kill -9 <PID>.