posix-io/truncate.c

/*	A part of the Windows CE C Extra Library (celibc)
	Copyright 2007-2015 PC GO Ld.

	This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

	This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
*/

#include <unistd.h>
#include <windows.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <errno.h>

#define ZERO_BUFFER_SIZE (512)

int ftruncate(int fd, off_t length) {
	off_t current = lseek(fd, 0, SEEK_CUR);
	if(current == -1) return -1;
	off_t current_eof = lseek(fd, 0, SEEK_END);
	if(current_eof == -1) return -1;

	off_t offset = length - current_eof;
	if(offset < 0) {
		if(lseek(fd, length, SEEK_SET) == -1) goto failed;
		if(!SetEndOfFile((void *)fd)) goto failed;
	} else if(offset > 0) {
		void *buffer = malloc(ZERO_BUFFER_SIZE);
		if(!buffer) goto failed;
		memset(buffer, 0, ZERO_BUFFER_SIZE);
		while(offset > 0) {
			int s = write(fd, buffer, ZERO_BUFFER_SIZE < offset ? ZERO_BUFFER_SIZE : offset);
			if(s < 0) {
				free(buffer);
				goto failed;
			}
			offset -= s;
		}
		free(buffer);
	}

	lseek(fd, current, SEEK_SET);
	return 0;

failed:	;
	int e = errno;
	lseek(fd, current, SEEK_SET);
	errno = e;
	return -1;
}

int truncate(const char *path, off_t length) {
	if(!path) {
		errno = EFAULT;
		return -1;
	}
	if(length < 0) {
		errno = EINVAL;
		return -1;
	}
	if(!*path) {
		errno = ENOENT;
		return -1;
	}

	int fd = open(path, O_WRONLY);
	if(fd == -1) return -1;

	int r = ftruncate(fd, length);
	int e = errno;
	if(close(fd) < 0) return -1;
	errno = e;
	return r;
}