#define _GNU_SOURCE

#include <stdint.h>

#include <errno.h>
#include <error.h>
#include <fcntl.h>
#include <sysexits.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
	++argv, --argc;
	do {
		const char *filename = "<stdin>";
		if (argc > 0) {
			close(STDIN_FILENO);
			if (open(filename = *argv, O_RDWR) != STDIN_FILENO)
				error(EX_NOINPUT, errno, "%s", filename);
		}
		for (off_t consumed = 0;;) {
			ssize_t n = splice(STDIN_FILENO, NULL, STDOUT_FILENO, NULL, SIZE_MAX, 0);
			if (n <= 0) {
				if (n < 0)
					error(EX_IOERR, errno, "%s: splice", filename);
				break;
			}
			if (fallocate(STDIN_FILENO, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, consumed += n) < 0)
				error(EX_OSERR, errno, "%s: fallocate", filename);
		}
		if (argc > 0 && unlink(filename) < 0)
			error(EX_OSERR, errno, "%s: unlink", filename);
	} while (++argv, --argc > 0);
	return EX_OK;
}