Integrate the data reader into libsquashfs

Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>

2 files changed, 153 insertions, 0 deletions

diff --git a/include/sqfs/data_reader.h b/include/sqfs/data_reader.h
new file mode 100644
index 0000000..7d0f9d7
--- /dev/null
+++ b/include/sqfs/data_reader.h
@@ -0,0 +1,152 @@
+/* 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
+ *
+ * @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 Destroy a data reader instance and free all memory used by it.
+ *
+ * @memberof sqfs_data_reader_t
+ *
+ * @param data A pointer to a data reader object.
+ */
+SQFS_API void sqfs_data_reader_destroy(sqfs_data_reader_t *data);
+
+/**
+ * @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 E_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 out Returns a pointer to the tail block of the file.
+ *
+ * @return Zero on succcess, an @ref E_SQFS_ERROR value on failure.
+ */
+SQFS_API int sqfs_data_reader_get_fragment(sqfs_data_reader_t *data,
+					   const sqfs_inode_generic_t *inode,
+					   sqfs_block_t **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 out Returns a pointer to the data block.
+ *
+ * @return Zero on succcess, an @ref E_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, sqfs_block_t **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 E_SQFS_ERROR value
+ *         on failure.
+ */
+SQFS_API ssize_t sqfs_data_reader_read(sqfs_data_reader_t *data,
+				       const sqfs_inode_generic_t *inode,
+				       uint64_t offset, void *buffer,
+				       size_t size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SQFS_DATA_READER_H */
diff --git a/include/sqfs/predef.h b/include/sqfs/predef.h
index c25a858..aad4eae 100644
--- a/include/sqfs/predef.h
+++ b/include/sqfs/predef.h
@@ -71,6 +71,7 @@ typedef struct sqfs_xattr_reader_t sqfs_xattr_reader_t;
 typedef struct sqfs_file_t sqfs_file_t;
 typedef struct sqfs_sparse_map_t sqfs_sparse_map_t;
 typedef struct sqfs_tree_node_t sqfs_tree_node_t;
+typedef struct sqfs_data_reader_t sqfs_data_reader_t;
 
 typedef struct sqfs_fragment_t sqfs_fragment_t;
 typedef struct sqfs_dir_header_t sqfs_dir_header_t;