From aa549f040e5eb0cd589d720df08970b81beebc1e Mon Sep 17 00:00:00 2001
From: Juraj Budai <jurko.budai@gmail.com>
Date: Thu, 12 Feb 2026 15:22:51 +0100
Subject: [PATCH] tree data UPDATE support applying diff subtrees instead of
 full diff

---
 src/diff.c      | 37 ++++++++++++++++++++++++++++++++++++-
 src/tree_data.h | 18 ++++++++++++++++++
 2 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/src/diff.c b/src/diff.c
index 6fda6962b..0d422c87b 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -1763,7 +1763,7 @@ lyd_diff_apply_metadata(struct lyd_node *node, const struct lyd_node *diff_node)
 /**
  * @brief Apply diff subtree on data tree nodes, recursively.
  *
- * @param[in,out] first_node First sibling of the data tree.
+ * @param[in,out] first_node First sibling of the subtree.
  * @param[in] parent_node Parent of the first sibling.
  * @param[in] diff_node Current diff node.
  * @param[in] diff_cb Optional diff callback.
@@ -1949,6 +1949,41 @@ lyd_diff_apply_all(struct lyd_node **data, const struct lyd_node *diff)
     return lyd_diff_apply_module(data, diff, NULL, NULL, NULL);
 }
 
+LIBYANG_API_DEF LY_ERR
+lyd_diff_apply_node(struct lyd_node *data_parent, struct lyd_node **data_first, const struct lyd_node *diff_node)
+{
+    LY_ERR ret = LY_SUCCESS;
+    struct ly_ht *dup_inst = NULL;
+
+    LY_CHECK_ARG_RET(NULL, data_parent || data_first, diff_node, LY_EINVAL);
+
+    /* diff_node is top level node, data_parent must be NULL */
+    if (!diff_node->parent && data_parent) {
+        LOGERR(LYD_CTX(diff_node), LY_EINVAL, "data_parent must be NULL when applying top-level diff_node.");
+        return LY_EINVAL;
+    }
+
+    if (!data_first) {
+        data_first = lyd_node_child_p(data_parent);
+    }
+
+    /* diff_node is top level node, data_first must be set */
+    if (!diff_node->parent && !data_first) {
+        LOGERR(LYD_CTX(diff_node), LY_EINVAL, "data_first is not set, when working with top-level node.");
+        return LY_EINVAL;
+    }
+
+    if (diff_node->parent && data_parent && (diff_node->parent->schema != data_parent->schema)) {
+        LOGERR(LYD_CTX(diff_node), LY_EINVAL, "Schemas of data_parent and diff_node do not match.");
+        return LY_EINVAL;
+    }
+
+    ret = lyd_diff_apply_r(data_first, data_parent, diff_node, NULL, NULL, &dup_inst);
+
+    lyd_dup_inst_free(dup_inst);
+    return ret;
+}
+
 /**
  * @brief Update operations on a diff node when the new operation is NONE.
  *
diff --git a/src/tree_data.h b/src/tree_data.h
index a35798485..281a1ce3d 100644
--- a/src/tree_data.h
+++ b/src/tree_data.h
@@ -2186,6 +2186,24 @@ LIBYANG_API_DECL LY_ERR lyd_diff_apply_module(struct lyd_node **data, const stru
  */
 LIBYANG_API_DECL LY_ERR lyd_diff_apply_all(struct lyd_node **data, const struct lyd_node *diff);
 
+/**
+ * @brief Apply the diff subtree on a data tree.
+ *
+ * Details are mentioned in ::lyd_diff_apply_module().
+ *
+ * @param[in,out] data_parent Parent of data to apply the diff subtree on.
+ * If @p diff_node is a top-level node, this parameter must be NULL.
+ * If @p diff_node has a parent, its schema must match this parameter schema.
+ * @param[in,out] data_first First sibling of the subtree.
+ * If @p diff_node is a top-level node, this parameter must point to the first top-level sibling.
+ * Optional for nested data.
+ * @param[in] diff_node Diff subtree to apply on data.
+ * @return LY_SUCCESS on success,
+ * @return LY_ERR on error.
+ */
+LIBYANG_API_DECL LY_ERR lyd_diff_apply_node(struct lyd_node *data_parent, struct lyd_node **data_first,
+        const struct lyd_node *diff_node);
+
 /**
  * @ingroup datatree
  * @defgroup diffmergeoptions Data diff merge options.