From 296fe79bfd97442713dab0244c9140996f358070 Mon Sep 17 00:00:00 2001
From: Benoit Blanchon <git@benoitblanchon.fr>
Date: Thu, 1 Feb 2024 10:24:00 +0100
Subject: [PATCH] Stop using `CollectionIterator` in `JsonSerializer`

This reduces stack consumption and code size.
See  #2046
---
 CHANGELOG.md                                  |  1 +
 src/ArduinoJson/Collection/CollectionData.hpp |  4 +++
 src/ArduinoJson/Json/JsonSerializer.hpp       | 32 ++++++++++---------
 3 files changed, 22 insertions(+), 15 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index b28b8301..1d3b5d6a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Improve error messages when using `char` or `char*` (issue #2043)
+* Reduce `serializeJson()`'s size and stack usage (issue #2046)
 
 v7.0.2 (2024-01-19)
 ------
diff --git a/src/ArduinoJson/Collection/CollectionData.hpp b/src/ArduinoJson/Collection/CollectionData.hpp
index 1010795c..07fe7e04 100644
--- a/src/ArduinoJson/Collection/CollectionData.hpp
+++ b/src/ArduinoJson/Collection/CollectionData.hpp
@@ -107,6 +107,10 @@ class CollectionData {
       return collection->remove(it, resources);
   }
 
+  SlotId head() const {
+    return head_;
+  }
+
  protected:
   iterator addSlot(ResourceManager*);
 
diff --git a/src/ArduinoJson/Json/JsonSerializer.hpp b/src/ArduinoJson/Json/JsonSerializer.hpp
index f4751f0c..6c84b3e1 100644
--- a/src/ArduinoJson/Json/JsonSerializer.hpp
+++ b/src/ArduinoJson/Json/JsonSerializer.hpp
@@ -22,16 +22,17 @@ class JsonSerializer : public VariantDataVisitor<size_t> {
   FORCE_INLINE size_t visit(const ArrayData& array) {
     write('[');
 
-    auto it = array.createIterator(resources_);
+    auto slotId = array.head();
 
-    while (!it.done()) {
-      it->accept(*this);
+    while (slotId != NULL_SLOT) {
+      auto slot = resources_->getSlot(slotId);
 
-      it.next(resources_);
-      if (it.done())
-        break;
+      slot->data()->accept(*this);
 
-      write(',');
+      slotId = slot->next();
+
+      if (slotId != NULL_SLOT)
+        write(',');
     }
 
     write(']');
@@ -41,18 +42,19 @@ class JsonSerializer : public VariantDataVisitor<size_t> {
   size_t visit(const ObjectData& object) {
     write('{');
 
-    auto it = object.createIterator(resources_);
+    auto slotId = object.head();
 
-    while (!it.done()) {
-      formatter_.writeString(it.key());
+    while (slotId != NULL_SLOT) {
+      auto slot = resources_->getSlot(slotId);
+
+      formatter_.writeString(slot->key());
       write(':');
-      it->accept(*this);
+      slot->data()->accept(*this);
 
-      it.next(resources_);
-      if (it.done())
-        break;
+      slotId = slot->next();
 
-      write(',');
+      if (slotId != NULL_SLOT)
+        write(',');
     }
 
     write('}');