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path: root/tailburst.c
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#include <stdio.h>
#include <fcntl.h>
#include <poll.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>

#define BUFLEN 1024
#define DEBUG 0
#define pr_debug(fmt, args...) if (DEBUG) printf(fmt, ##args)

struct getline_states {
	char *base;
	char *cur;
	size_t size;
	size_t read;
	char *next;
};

ssize_t fdgetline(int fd, struct getline_states *line) {
	char *str;
	ssize_t nread;

	if (line->base == NULL) {
		/* First pass: init state */
		line->size = 120;
		line->base = malloc(line->size);
		if (line->base == NULL)
			return -ENOMEM;
		line->base[0] = '\0';
		line->read = 0;
		line->next = NULL;
	}

	/* Skip after previously returned line */
	if (line->next)
		line->cur = line->next;
	else
		line->cur = line->base;

	/* Do we already have a full line in buffer? */
	if ((str = strchr(line->cur, '\n'))) {
		line->next = str+1;
		str[0] = '\0'; 
		pr_debug("next already buffered, %p %p: %s\n", str, line->cur, line->cur);
		return str - line->cur;
	}

	/* No such luck, move current to base and read what we can */
	if (line->cur != line->base) {
		pr_debug("moving cur: %p, base: %p, read: %zd, moving %zd\n", line->cur, line->base, line->read, line->cur - line->base);
		line->read -= line->cur - line->base;
		memmove(line->base, line->cur, line->read);
		line->cur = line->base;
	}

	/* clear errno before read */
	errno = 0;

	while ((nread = read(fd, line->base + line->read, line->size - line->read)) > 0 ) {
		pr_debug("read %zd\n", nread);
		line->read += nread;

		/* Check if we have a full line now */
		if ((str = strchr(line->base, '\n'))) {
			line->next = str+1;
			str[0] = '\0'; 
			pr_debug("found stuff, %p %p %p: %s\n", str, line->base, line->cur, line->cur);
			return str - line->base;
		}

		/* realloc bigger buffer and try again */
		line->size *= 2;
		line->base = realloc(line->base, line->size);
		if (line->base == NULL)
			return -ENOMEM;
	}
	pr_debug("got here? %zd %d\n", nread, errno);

	line->next = line->cur;
	if (errno)
		return -errno;
	
	return 0; /* no line read */
}


int main(int argc, char **argv)
{
	int flags, fd = 0;
	ssize_t nread;
	struct pollfd pollfd;
	struct getline_states line = { 0 };
	char *cur;

	/* non-buffered output */
	setlinebuf(stdout);

	/* make stream non-block */
	flags = fcntl(fd, F_GETFL);
	flags |= O_NONBLOCK;
	fcntl(fd, F_SETFL, flags);

	pollfd.fd = fd;
	pollfd.events = POLLIN;
	while (poll(&pollfd, 1, -1) > 0) {
		cur = NULL;
		while ((nread = fdgetline(fd, &line)) > 0)
			cur = line.cur;

		if (cur)
			printf("%s\n", cur);

		/* eof */
		if (nread == 0)
			break;
	}

	return 0;
}