/*
 * file_io.c - Helper functions for reading and writing to file descriptors.
 */

/*
 * Copyright (C) 2013 Eric Biggers
 *
 * This file is free software; you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation; either version 3 of the License, or (at your option) any
 * later version.
 *
 * This file 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 Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this file; if not, see http://www.gnu.org/licenses/.
 */

#ifdef HAVE_CONFIG_H
#  include "config.h"
#endif

#include <errno.h>
#include <unistd.h>

#include "wimlib/error.h"
#include "wimlib/file_io.h"
#include "wimlib/util.h"
#include "wimlib/win32.h" /* For pread(), pwrite() replacements */

/*
 * Wrapper around read() that checks for errors and keeps retrying until all
 * requested bytes have been read or until end-of file has occurred.
 *
 * Return values:
 *	WIMLIB_ERR_SUCCESS			(0)
 *	WIMLIB_ERR_READ				(errno set)
 *	WIMLIB_ERR_UNEXPECTED_END_OF_FILE	(errno set to EINVAL)
 */
int
full_read(struct filedes *fd, void *buf, size_t count)
{
	while (count) {
		ssize_t ret = read(fd->fd, buf, count);
		if (unlikely(ret <= 0)) {
			if (ret == 0) {
				errno = EINVAL;
				return WIMLIB_ERR_UNEXPECTED_END_OF_FILE;
			}
			if (errno == EINTR)
				continue;
			return WIMLIB_ERR_READ;
		}
		buf += ret;
		count -= ret;
		fd->offset += ret;
	}
	return 0;
}

static int
pipe_read(struct filedes *fd, void *buf, size_t count, off_t offset)
{
	int ret;

	/* Verify the offset.  */
	if (offset < fd->offset) {
		ERROR("Can't seek backwards in pipe "
		      "(offset %"PRIu64" => %"PRIu64").\n"
		      "        Make sure the WIM was captured as "
		      "pipable.", fd->offset, offset);
		errno = ESPIPE;
		return WIMLIB_ERR_RESOURCE_ORDER;
	}

	/* Manually seek to the requested position.  */
	while (fd->offset != offset) {
		size_t bytes_to_read = min(offset - fd->offset, BUFFER_SIZE);
		u8 dummy[bytes_to_read];

		ret = full_read(fd, dummy, bytes_to_read);
		if (ret)
			return ret;
	}

	/* Do the actual read.  */
	return full_read(fd, buf, count);
}

/*
 * Wrapper around pread() that checks for errors and keeps retrying until all
 * requested bytes have been read or until end-of file has occurred.  This also
 * transparently handle reading from pipe files, but the caller needs to be sure
 * the requested offset is greater than or equal to the current offset, or else
 * WIMLIB_ERR_RESOURCE_ORDER will be returned.
 *
 * Return values:
 *	WIMLIB_ERR_SUCCESS			(0)
 *	WIMLIB_ERR_READ				(errno set)
 *	WIMLIB_ERR_UNEXPECTED_END_OF_FILE	(errno set to EINVAL)
 *	WIMLIB_ERR_RESOURCE_ORDER		(errno set to ESPIPE)
 */
int
full_pread(struct filedes *fd, void *buf, size_t count, off_t offset)
{
	if (fd->is_pipe)
		goto is_pipe;

	while (count) {
		ssize_t ret = pread(fd->fd, buf, count, offset);
		if (unlikely(ret <= 0)) {
			if (ret == 0) {
				errno = EINVAL;
				return WIMLIB_ERR_UNEXPECTED_END_OF_FILE;
			}
			if (errno == EINTR)
				continue;
			if (errno == ESPIPE) {
				fd->is_pipe = 1;
				goto is_pipe;
			}
			return WIMLIB_ERR_READ;
		}
		buf += ret;
		count -= ret;
		offset += ret;
	}
	return 0;

is_pipe:
	return pipe_read(fd, buf, count, offset);
}

/*
 * Wrapper around write() that checks for errors and keeps retrying until all
 * requested bytes have been written.
 *
 * Return values:
 *	WIMLIB_ERR_SUCCESS			(0)
 *	WIMLIB_ERR_WRITE			(errno set)
 */
int
full_write(struct filedes *fd, const void *buf, size_t count)
{
	while (count) {
		ssize_t ret = write(fd->fd, buf, count);
		if (unlikely(ret < 0)) {
			if (errno == EINTR)
				continue;
			return WIMLIB_ERR_WRITE;
		}
		buf += ret;
		count -= ret;
		fd->offset += ret;
	}
	return 0;
}


/*
 * Wrapper around pwrite() that checks for errors and keeps retrying until all
 * requested bytes have been written.
 *
 * Return values:
 *	WIMLIB_ERR_SUCCESS	(0)
 *	WIMLIB_ERR_WRITE	(errno set)
 */
int
full_pwrite(struct filedes *fd, const void *buf, size_t count, off_t offset)
{
	while (count) {
		ssize_t ret = pwrite(fd->fd, buf, count, offset);
		if (unlikely(ret < 0)) {
			if (errno == EINTR)
				continue;
			return WIMLIB_ERR_WRITE;
		}
		buf += ret;
		count -= ret;
		offset += ret;
	}
	return 0;
}

off_t filedes_seek(struct filedes *fd, off_t offset)
{
	if (fd->is_pipe) {
		errno = ESPIPE;
		return -1;
	}
	if (fd->offset != offset) {
		if (lseek(fd->fd, offset, SEEK_SET) == -1)
			return -1;
		fd->offset = offset;
	}
	return offset;
}

bool filedes_is_seekable(struct filedes *fd)
{
	return !fd->is_pipe && lseek(fd->fd, 0, SEEK_CUR) != -1;
}
