sqfs_dir_tree_destroy/sqfs_destroy: allow NULL input

Many library destructor functions (like free()) allow a NULL
pointer as input, and do nothing in that case.
This allows easier cleanup patterns: initialize pointers to NULL
and then always pass them to the destroyer functions, no need for
verbose goto/if-else patterns.

Signed-off-by: Luca Boccassi <luca.boccassi@microsoft.com>

4 files changed, 23 insertions, 26 deletions

diff --git a/extras/extract_one.c b/extras/extract_one.c
index 4f5b547..fcd8124 100644
--- a/extras/extract_one.c
+++ b/extras/extract_one.c
@@ -52,7 +52,7 @@ int main(int argc, char **argv)
 	ret = sqfs_super_read(&super, file);
 	if (ret) {
 		fprintf(stderr, "%s: error reading super block.\n", argv[1]);
-		goto out_file;
+		goto out;
 	}
 
 	sqfs_compressor_config_init(&cfg, super.compression_id,
@@ -62,62 +62,62 @@ int main(int argc, char **argv)
 	ret = sqfs_compressor_create(&cfg, &cmp);
 	if (ret != 0) {
 		fprintf(stderr, "%s: error creating compressor: %d.\n", argv[1], ret);
-		goto out_file;
+		goto out;
 	}
 
 	if (!(super.flags & SQFS_FLAG_NO_XATTRS)) {
 		xattr = sqfs_xattr_reader_create(0);
 		if (xattr == NULL) {
 			fprintf(stderr, "%s: error creating xattr reader: %d.\n", argv[1], SQFS_ERROR_ALLOC);
-			goto out_cmp;
+			goto out;
 		}
 
 		ret = sqfs_xattr_reader_load(xattr, &super, file, cmp);
 		if (ret) {
 			fprintf(stderr, "%s: error loading xattr reader: %d.\n", argv[1], ret);
-			goto out_xattr;
+			goto out;
 		}
 	}
 
 	idtbl = sqfs_id_table_create(0);
 	if (idtbl == NULL) {
 		fprintf(stderr, "%s: error creating ID table: %d.\n", argv[1], ret);
-		goto out_xattr;
+		goto out;
 	}
 
 	ret = sqfs_id_table_read(idtbl, file, &super, cmp);
 	if (ret) {
 		fprintf(stderr, "%s: error loading ID table: %d.\n", argv[1], ret);
-		goto out_idtbl;
+		goto out;
 	}
 
 	dirrd = sqfs_dir_reader_create(&super, cmp, file, 0);
 	if (dirrd == NULL) {
 		fprintf(stderr, "%s: error creating dir reader: %d.\n", argv[1], SQFS_ERROR_ALLOC);
-		goto out_idtbl;
+		goto out;
 	}
 
 	data = sqfs_data_reader_create(file, super.block_size, cmp, 0);
 	if (data == NULL) {
 		fprintf(stderr, "%s: error creating data reader: %d.\n", argv[1], SQFS_ERROR_ALLOC);
-		goto out_dirrd;
+		goto out;
 	}
 
 	ret = sqfs_data_reader_load_fragment_table(data, &super);
 	if (ret) {
 		fprintf(stderr, "%s: error loading fragment table: %d.\n", argv[1], ret);
-		goto out_data;
+		goto out;
 	}
 
 	ret = sqfs_dir_reader_get_full_hierarchy(dirrd, idtbl, argv[2], 0, &n);
 	if (ret) {
 		fprintf(stderr, "%s: error reading filesystem hierarchy: %d.\n", argv[1], ret);
-		goto out_data;
+		goto out;
 	}
 
 	if (!S_ISREG(n->inode->base.mode)) {
 		fprintf(stderr, "/%s is not a file\n", argv[2]);
-		goto out_tree;
+		goto out;
 	}
 
 	sqfs_inode_get_file_size(n->inode, &file_size);
@@ -125,7 +125,7 @@ int main(int argc, char **argv)
 	output = p = malloc(file_size);
 	if (output == NULL) {
 		fprintf(stderr, "malloc failed: %d\n", errno);
-		goto out_tree;
+		goto out;
 	}
 
 	for (size_t i = 0; i < sqfs_inode_get_file_block_count(n->inode); ++i) {
@@ -135,7 +135,7 @@ int main(int argc, char **argv)
 		ret = sqfs_data_reader_get_block(data, n->inode, i, &chunk_size, &chunk);
 		if (ret) {
 			fprintf(stderr, "reading data block: %d\n", ret);
-			goto out_tree;
+			goto out;
 		}
 
 		memcpy(p, chunk, chunk_size);
@@ -152,7 +152,7 @@ int main(int argc, char **argv)
 		ret = sqfs_data_reader_get_fragment(data, n->inode, &chunk_size, &chunk);
 		if (ret) {
 			fprintf(stderr, "reading fragment block: %d\n", ret);
-			goto out_tree;
+			goto out;
 		}
 
 		memcpy(p, chunk, chunk_size);
@@ -163,20 +163,13 @@ int main(int argc, char **argv)
 	fprintf(stdout, "%s\n", (char *)output);
 
 	status = EXIT_SUCCESS;
-out_tree:
+out:
 	sqfs_dir_tree_destroy(n);
-out_data:
 	sqfs_destroy(data);
-out_dirrd:
 	sqfs_destroy(dirrd);
-out_idtbl:
 	sqfs_destroy(idtbl);
-out_xattr:
-	if (xattr != NULL)
-		sqfs_destroy(xattr);
-out_cmp:
+	sqfs_destroy(xattr);
 	sqfs_destroy(cmp);
-out_file:
 	sqfs_destroy(file);
 	free(output);
 
diff --git a/include/sqfs/dir_reader.h b/include/sqfs/dir_reader.h
index 3bef7e3..2ee7204 100644
--- a/include/sqfs/dir_reader.h
+++ b/include/sqfs/dir_reader.h
@@ -320,7 +320,7 @@ SQFS_API int sqfs_dir_reader_get_full_hierarchy(sqfs_dir_reader_t *rd,
  * This function can be used to clean up after
  * @ref sqfs_dir_reader_get_full_hierarchy.
  *
- * @param root A pointer to the root node.
+ * @param root A pointer to the root node or NULL.
  */
 SQFS_API void sqfs_dir_tree_destroy(sqfs_tree_node_t *root);
 
diff --git a/include/sqfs/predef.h b/include/sqfs/predef.h
index 6296b4b..a976cd4 100644
--- a/include/sqfs/predef.h
+++ b/include/sqfs/predef.h
@@ -133,11 +133,12 @@ typedef struct sqfs_object_t {
  *
  * @memberof sqfs_object_t
  *
- * @param obj A pointer to an object
+ * @param obj A pointer to an object or NULL
  */
 static SQFS_INLINE void sqfs_destroy(void *obj)
 {
-	((sqfs_object_t *)obj)->destroy((sqfs_object_t *)obj);
+	if (obj)
+		((sqfs_object_t *)obj)->destroy((sqfs_object_t *)obj);
 }
 
 /**
diff --git a/lib/sqfs/read_tree.c b/lib/sqfs/read_tree.c
index 802446a..feda691 100644
--- a/lib/sqfs/read_tree.c
+++ b/lib/sqfs/read_tree.c
@@ -179,6 +179,9 @@ void sqfs_dir_tree_destroy(sqfs_tree_node_t *root)
 {
 	sqfs_tree_node_t *it;
 
+	if (!root)
+		return;
+
 	while (root->children != NULL) {
 		it = root->children;
 		root->children = it->next;