From 0a2cfd0caa21b7c12a5d4e22241faf787f1d4a5e Mon Sep 17 00:00:00 2001
From: Sylvain Joubert <joubert.sy@gmail.com>
Date: Thu, 20 Jul 2023 17:24:04 +0200
Subject: [PATCH] Fix performance regression from logical combination patch
 discard

A recent fix to discard patch from invalid logical combination
introduced a lot (for large json instance and/or schema) of copies to
make a patch backup. On some case, this introduced up to a 100x slower
validation time.

Resizing the patch object to its previous size avoid unnecessary
temporary allocations from the backup object.
---
 src/json-patch.hpp     | 5 ++++-
 src/json-validator.cpp | 4 ++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/json-patch.hpp b/src/json-patch.hpp
index 80fe1df..39a579b 100644
--- a/src/json-patch.hpp
+++ b/src/json-patch.hpp
@@ -28,10 +28,13 @@ public:
 	json_patch &replace(const json::json_pointer &, json value);
 	json_patch &remove(const json::json_pointer &);
 
+	json &get_json() { return j_; }
+	const json &get_json() const { return j_; }
+
 	operator json() const { return j_; }
 
 private:
-	json j_;
+	json j_ = nlohmann::json::array();
 
 	static void validateJsonPatch(json const &patch);
 };
diff --git a/src/json-validator.cpp b/src/json-validator.cpp
index 77d701f..6ede7c8 100644
--- a/src/json-validator.cpp
+++ b/src/json-validator.cpp
@@ -436,12 +436,12 @@ class logical_combination : public schema
 
 		for (auto &s : subschemata_) {
 			first_error_handler esub;
-			json_patch old_patch(patch);
+			auto oldPatchSize = patch.get_json().size();
 			s->validate(ptr, instance, patch, esub);
 			if (!esub)
 				count++;
 			else
-				patch = old_patch;
+				patch.get_json().get_ref<nlohmann::json::array_t &>().resize(oldPatchSize);
 
 			if (is_validate_complete(instance, ptr, e, esub, count))
 				return;