logtee.c

#define _GNU_SOURCE
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>

#define BUFLEN 4096

int
main(int argc, char *argv[])
{
	int fd;
	int len, slen;
	int ret;
	int timeout;
	char *timeout_env;
	struct pollfd fds[] = {{
		.fd = STDIN_FILENO,
		.events = POLLIN | POLLERR,
	}};

	timeout_env = getenv("LOGTEE_TIMEOUT_MS");
	if (timeout_env)
		timeout = atoi(timeout_env);
	else
		timeout = -1;

	if (argc != 2) {
		fprintf(stderr, "Usage: %s <file>\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC | O_NONBLOCK, 0644);
	if (fd == -1) {
		perror("open");
		exit(EXIT_FAILURE);
	}

	fprintf(stderr, "Logging to %s: ", argv[1]);

	slen = 0;

	do {
		ret = poll (fds, sizeof(fds) / sizeof(fds[0]), timeout);
		if (ret == 0) {
			fprintf (stderr, "Timed out after %d milliseconds of no output.\n", timeout);
			exit(EXIT_FAILURE);
		}
		len = splice(STDIN_FILENO, NULL, fd, NULL,
			     BUFLEN, SPLICE_F_MOVE | SPLICE_F_NONBLOCK);

		if (len < 0) {
			if (errno == EAGAIN)
				continue;
			perror("tee");
			exit(EXIT_FAILURE);
		} else
			if (len == 0)
				break;
		slen += len;
		if ((slen/BUFLEN) > 0) {
			fprintf(stderr, ".");
		}
		slen = slen % BUFLEN;

	} while (1);
	close(fd);
	fprintf(stderr, "\n");
	exit(EXIT_SUCCESS);
}