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/* SPDX-License-Identifier: LGPL-3.0-or-later */
/*
* data_reader.h - This file is part of libsquashfs
*
* Copyright (C) 2019 David Oberhollenzer <goliath@infraroot.at>
*
* This program 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 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.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#ifndef SQFS_DATA_READER_H
#define SQFS_DATA_READER_H
#include "sqfs/predef.h"
/**
* @file data_reader.h
*
* @brief Contains declarations for the @ref sqfs_data_reader_t.
*/
/**
* @struct sqfs_data_reader_t
*
* @implements sqfs_object_t
*
* @brief Abstracts access to data blocks stored in a SquashFS image.
*
* A SquashFS image can contain a series of file data blocks between the
* super block and the inode table. Blocks may or may not be compressed.
* Data chunks that are smaller than the block size indicated by the super
* block (such as the final chunk of a file or an entire file that is smaller
* than a signle block) can be grouped in a single fragment block.
*
* Regular file inodes referre to the location of the first block and store a
* sequence of block sizes for all consequitve blocks, as well as a fragment
* index and fragment offset which is resolved through a fragment table.
*
* The data reader abstracts all of this away in a simple interface that allows
* reading file data through an inode description and a location in the file.
*/
#ifdef __cplusplus
extern "C" {
#endif
/**
* @brief Create a data reader instance.
*
* @memberof sqfs_data_reader_t
*
* @param file A file interface through which to access the
* underlying filesystem image.
* @param block_size The data block size from the super block.
* @param cmp A compressor to use for uncompressing blocks read from disk.
*
* @return A pointer to a new data reader object. NULL means
* allocation failure.
*/
SQFS_API sqfs_data_reader_t *sqfs_data_reader_create(sqfs_file_t *file,
size_t block_size,
sqfs_compressor_t *cmp);
/**
* @brief Read and decode the fragment table from disk.
*
* @memberof sqfs_data_reader_t
*
* @param data A pointer to a data reader object.
* @param super A pointer to the super block.
*
* @return Zero on succcess, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_data_reader_load_fragment_table(sqfs_data_reader_t *data,
const sqfs_super_t *super);
/**
* @brief Get the tail end of a file.
*
* @memberof sqfs_data_reader_t
*
* @param data A pointer to a data reader object.
* @param inode A pointer to the inode describing the file.
* @param size Returns the size of the data read.
* @param out Returns a pointer to the raw data that must be
* released using free.
*
* @return Zero on succcess, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_data_reader_get_fragment(sqfs_data_reader_t *data,
const sqfs_inode_generic_t *inode,
size_t *size, sqfs_u8 **out);
/**
* @brief Get a full sized data block of a file by block index.
*
* @memberof sqfs_data_reader_t
*
* @param data A pointer to a data reader object.
* @param inode A pointer to the inode describing the file.
* @param index The block index in the inodes block list.
* @param size Returns the size of the data read.
* @param out Returns a pointer to the raw data that must be
* released using free.
*
* @return Zero on succcess, an @ref SQFS_ERROR value on failure.
*/
SQFS_API int sqfs_data_reader_get_block(sqfs_data_reader_t *data,
const sqfs_inode_generic_t *inode,
size_t index, size_t *size,
sqfs_u8 **out);
/**
* @brief A simple UNIX-read-like function to read data from a file.
*
* @memberof sqfs_data_reader_t
*
* This function acts like the read system call in a Unix-like OS. It takes
* care of reading accross data blocks and fragment internally, using a
* data and fragment block cache.
*
* @param data A pointer to a data reader object.
* @param inode A pointer to the inode describing the file.
* @param offset An arbitrary byte offset into the uncompressed file.
* @param buffer Returns the data read from the file.
* @param size The number of uncompressed bytes to read from the given offset.
*
* @return The number of bytes read on succcess, zero if attempting to read
* past the end of the file and a negative @ref SQFS_ERROR value
* on failure.
*/
SQFS_API sqfs_s32 sqfs_data_reader_read(sqfs_data_reader_t *data,
const sqfs_inode_generic_t *inode,
sqfs_u64 offset, void *buffer,
sqfs_u32 size);
#ifdef __cplusplus
}
#endif
#endif /* SQFS_DATA_READER_H */
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