Add a helper function to unpack directory index entries

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

3 files changed, 76 insertions, 4 deletions

diff --git a/extras/browse.c b/extras/browse.c
index 1179b33..1d6417f 100644
--- a/extras/browse.c
+++ b/extras/browse.c
@@ -3,6 +3,7 @@
 #include "sqfs/id_table.h"
 #include "sqfs/inode.h"
 #include "sqfs/super.h"
+#include "sqfs/error.h"
 #include "sqfs/dir.h"
 #include "sqfs/io.h"
 
@@ -358,16 +359,22 @@ static void stat_cmd(const char *filename)
 		if (inode->data.dir_ext.size == 0)
 			break;
 
-		idx = (sqfs_dir_index_t *)inode->extra;
+		for (i = 0; ; ++i) {
+			ret = sqfs_inode_unpack_dir_index_entry(inode, &idx, i);
+			if (ret == SQFS_ERROR_OUT_OF_BOUNDS)
+				break;
+			if (ret < 0) {
+				printf("Error reading index, error code %d\n",
+				       ret);
+				break;
+			}
 
-		for (i = 0; i < inode->data.dir_ext.inodex_count; ++i) {
 			printf("\tIndex: %u\n", idx->index);
 			printf("\tStart block: %u\n", idx->start_block);
 			printf("\tSize: %u\n", idx->size + 1);
 			printf("\tEntry: %.*s\n\n", idx->size + 1, idx->name);
 
-			idx = (sqfs_dir_index_t *)
-				((char *)idx + sizeof(*idx) + idx->size + 1);
+			free(idx);
 		}
 		break;
 	}
diff --git a/include/sqfs/inode.h b/include/sqfs/inode.h
index 2b4a550..f2b6ede 100644
--- a/include/sqfs/inode.h
+++ b/include/sqfs/inode.h
@@ -696,6 +696,27 @@ SQFS_API int sqfs_inode_get_frag_location(const sqfs_inode_generic_t *inode,
 SQFS_API int sqfs_inode_get_file_block_start(const sqfs_inode_generic_t *inode,
 					     sqfs_u64 *location);
 
+/**
+ * @brief Unpack the a directory index structure from an inode.
+ *
+ * The generic inode contains in its payload the raw directory index (with
+ * bytes swapped to host enian), but still with single byte alignment. This
+ * function seeks through the blob using an integer index (not offset) and
+ * fiddles the raw data out into a propperly aligned, external structure.
+ *
+ * @param inode A pointer to an inode.
+ * @param out Returns the index entry. Can be freed with a single free call.
+ * @param index An index value between 0 and inodex_count.
+ *
+ * @return Zero on success, @ref SQFS_ERROR_OUT_OF_BOUNDS if the given index
+ *         points outside the directory index. Can return other error codes
+ *         (e.g. if the inode isn't a directory or allocation failed).
+ */
+SQFS_API
+int sqfs_inode_unpack_dir_index_entry(const sqfs_inode_generic_t *inode,
+				      sqfs_dir_index_t **out,
+				      size_t index);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/lib/sqfs/inode.c b/lib/sqfs/inode.c
index bb1ccef..3a4ec09 100644
--- a/lib/sqfs/inode.c
+++ b/lib/sqfs/inode.c
@@ -9,10 +9,13 @@
 
 #include "sqfs/inode.h"
 #include "sqfs/error.h"
+#include "sqfs/dir.h"
 
 #include <string.h>
 #include <stdlib.h>
 
+#include "util.h"
+
 static int inverse_type[] = {
 	[SQFS_INODE_DIR] = SQFS_INODE_EXT_DIR,
 	[SQFS_INODE_FILE] = SQFS_INODE_EXT_FILE,
@@ -386,3 +389,44 @@ int sqfs_inode_get_file_block_start(const sqfs_inode_generic_t *inode,
 
 	return 0;
 }
+
+int sqfs_inode_unpack_dir_index_entry(const sqfs_inode_generic_t *inode,
+				      sqfs_dir_index_t **out,
+				      size_t index)
+{
+	sqfs_dir_index_t ent;
+	size_t offset;
+	char *ptr;
+
+	if (inode->base.type != SQFS_INODE_EXT_DIR) {
+		if (inode->base.type == SQFS_INODE_DIR)
+			return SQFS_ERROR_OUT_OF_BOUNDS;
+
+		return SQFS_ERROR_NOT_DIR;
+	}
+
+	offset = 0;
+	ptr = (char *)inode->extra;
+
+	for (;;) {
+		if (offset >= inode->num_dir_idx_bytes)
+			return SQFS_ERROR_OUT_OF_BOUNDS;
+
+		if (index == 0)
+			break;
+
+		memcpy(&ent, ptr + offset, sizeof(ent));
+		offset += sizeof(ent) + ent.size + 1;
+		index -= 1;
+	}
+
+	memcpy(&ent, ptr + offset, sizeof(ent));
+
+	*out = alloc_flex(sizeof(ent), 1, ent.size + 2);
+	if (*out == NULL)
+		return SQFS_ERROR_ALLOC;
+
+	memcpy(*out, &ent, sizeof(ent));
+	memcpy((*out)->name, ptr + offset + sizeof(ent), ent.size + 1);
+	return 0;
+}