#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <limits.h>
#include <err.h>

int main(int argc, char *argv[])
{
	// Just a MB less than LONG_MAX
	size_t size = LONG_MAX - (1024 * 1024);
	int in, pipefd[2], r;

	in = open(argv[1], O_RDONLY);
	if (in < 0)
		err(1, "open");

	r = pipe(pipefd);
	if (r < 0)
		err(1, "pipe");

	r = fork();
	if (r < 0)
		err(1, "fork");

	if (!r) {
		// Discard data from pipe
		char *buffer = malloc(1024 * 1024);

		while (read(pipefd[0], buffer, 1024 * 1024) > 0)
			/* do nothing */ ;

		return 0;
	}

	// splice data from file to pipe
	for (ssize_t copied = 1; copied; ) {
		copied = splice(in, NULL, pipefd[1], NULL, size, 0);
		if (copied < 0) {
			perror("splice");
			// splice() will fail when file pos + size exceeds LONG_MAX
			fprintf(stderr, "Failed to splice %zu bytes at offset %ld\n", size, lseek(in, 0, SEEK_CUR));
			return 1;
		}
	}

	return 0;
}