Store static strings in a dedicated pool

Because a slot id is smaller than a pointer, this change will ultimately allow reducing the slot size.

src/ArduinoJson/Memory/MemoryPool.hpp

@@ -34,6 +34,11 @@ class Slot {
     return ptr_;
   }
 
+  T& operator*() const {
+    ARDUINOJSON_ASSERT(ptr_ != nullptr);
+    return *ptr_;
+  }
+
   T* operator->() const {
     ARDUINOJSON_ASSERT(ptr_ != nullptr);
     return ptr_;
@@ -76,6 +81,14 @@ class MemoryPool {
     return slots_ + id;
   }
 
+  SlotId find(const T& value) const {
+    for (SlotId i = 0; i < usage_; i++) {
+      if (slots_[i] == value)
+        return i;
+    }
+    return NULL_SLOT;
+  }
+
   void clear() {
     usage_ = 0;
   }

src/ArduinoJson/Memory/MemoryPoolList.hpp

@@ -114,6 +114,15 @@ class MemoryPoolList {
     return pools_[poolIndex].getSlot(indexInPool);
   }
 
+  SlotId find(const T& value) const {
+    for (PoolCount i = 0; i < count_; i++) {
+      SlotId id = pools_[i].find(value);
+      if (id != NULL_SLOT)
+        return SlotId(i * ARDUINOJSON_POOL_CAPACITY + id);
+    }
+    return NULL_SLOT;
+  }
+
   void clear(Allocator* allocator) {
     for (PoolCount i = 0; i < count_; i++)
       pools_[i].destroy(allocator);

src/ArduinoJson/Memory/ResourceManager.hpp

@@ -34,6 +34,7 @@ class ResourceManager {
   ~ResourceManager() {
     stringPool_.clear(allocator_);
     variantPools_.clear(allocator_);
+    staticStringsPools_.clear(allocator_);
   }
 
   ResourceManager(const ResourceManager&) = delete;
@@ -42,6 +43,7 @@ class ResourceManager {
   friend void swap(ResourceManager& a, ResourceManager& b) {
     swap(a.stringPool_, b.stringPool_);
     swap(a.variantPools_, b.variantPools_);
+    swap(a.staticStringsPools_, b.staticStringsPools_);
     swap_(a.allocator_, b.allocator_);
     swap_(a.overflowed_, b.overflowed_);
   }
@@ -111,14 +113,34 @@ class ResourceManager {
     stringPool_.dereference(s, allocator_);
   }
 
+  SlotId saveStaticString(const char* s) {
+    auto existingSlotId = staticStringsPools_.find(s);
+    if (existingSlotId != NULL_SLOT)
+      return existingSlotId;
+
+    auto slot = staticStringsPools_.allocSlot(allocator_);
+    if (slot)
+      *slot = s;
+    else
+      overflowed_ = true;
+
+    return slot.id();
+  }
+
+  const char* getStaticString(SlotId id) const {
+    return *staticStringsPools_.getSlot(id);
+  }
+
   void clear() {
-    variantPools_.clear(allocator_);
     overflowed_ = false;
+    variantPools_.clear(allocator_);
     stringPool_.clear(allocator_);
+    staticStringsPools_.clear(allocator_);
   }
 
   void shrinkToFit() {
     variantPools_.shrinkToFit(allocator_);
+    staticStringsPools_.shrinkToFit(allocator_);
   }
 
  private:
@@ -126,6 +148,7 @@ class ResourceManager {
   bool overflowed_;
   StringPool stringPool_;
   MemoryPoolList<SlotData> variantPools_;
+  MemoryPoolList<const char*> staticStringsPools_;
 };
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Object/JsonPair.hpp

@@ -18,7 +18,7 @@ class JsonPair {
   JsonPair(detail::ObjectData::iterator iterator,
            detail::ResourceManager* resources) {
     if (!iterator.done()) {
-      key_ = iterator->asString();
+      key_ = iterator->asString(resources);
       iterator.next(resources);
       value_ = JsonVariant(iterator.data(), resources);
     }
@@ -46,7 +46,7 @@ class JsonPairConst {
   JsonPairConst(detail::ObjectData::iterator iterator,
                 const detail::ResourceManager* resources) {
     if (!iterator.done()) {
-      key_ = iterator->asString();
+      key_ = iterator->asString(resources);
       iterator.next(resources);
       value_ = JsonVariantConst(iterator.data(), resources);
     }

src/ArduinoJson/Object/ObjectImpl.hpp

@@ -36,7 +36,7 @@ inline ObjectData::iterator ObjectData::findKey(
     return iterator();
   bool isKey = true;
   for (auto it = createIterator(resources); !it.done(); it.next(resources)) {
-    if (isKey && stringEquals(key, adaptString(it->asString())))
+    if (isKey && stringEquals(key, adaptString(it->asString(resources))))
       return it;
     isKey = !isKey;
   }

src/ArduinoJson/Strings/Adapters/RamString.hpp

@@ -90,8 +90,9 @@ template <size_t N>
 struct StringAdapter<const char (&)[N]> {
   using AdaptedString = RamString;
 
-  static AdaptedString adapt(const char (&p)[N]) {
-    return RamString(p, N - 1, true);
+  static AdaptedString adapt(const char* p) {
+    ARDUINOJSON_ASSERT(p);
+    return RamString(p, ::strlen(p), true);
   }
 };
 

src/ArduinoJson/Strings/JsonString.hpp

@@ -28,8 +28,7 @@ class JsonString {
             detail::enable_if_t<detail::is_integral<TSize>::value &&
                                     !detail::is_same<TSize, bool>::value,
                                 int> = 0>
-  JsonString(const char* data, TSize sz, bool isStatic = false)
-      : str_(data, size_t(sz), isStatic) {}
+  JsonString(const char* data, TSize sz) : str_(data, size_t(sz), false) {}
 
   // Returns a pointer to the characters.
   const char* c_str() const {

src/ArduinoJson/Variant/ConverterImpl.hpp

@@ -160,7 +160,7 @@ struct Converter<const char*> : private detail::VariantAttorney {
 
   static const char* fromJson(JsonVariantConst src) {
     auto data = getData(src);
-    return data ? data->asString().c_str() : 0;
+    return data ? data->asString(getResourceManager(src)).c_str() : 0;
   }
 
   static bool checkJson(JsonVariantConst src) {
@@ -178,7 +178,7 @@ struct Converter<JsonString> : private detail::VariantAttorney {
 
   static JsonString fromJson(JsonVariantConst src) {
     auto data = getData(src);
-    return data ? data->asString() : JsonString();
+    return data ? data->asString(getResourceManager(src)) : JsonString();
   }
 
   static bool checkJson(JsonVariantConst src) {

src/ArduinoJson/Variant/VariantContent.hpp

@@ -56,13 +56,10 @@ union VariantContent {
   bool asBoolean;
   uint32_t asUint32;
   int32_t asInt32;
-#if ARDUINOJSON_USE_EXTENSIONS
   SlotId asSlotId;
-#endif
   ArrayData asArray;
   ObjectData asObject;
   CollectionData asCollection;
-  const char* asLinkedString;
   struct StringNode* asOwnedString;
   char asTinyString[tinyStringMaxLength + 1];
 };

src/ArduinoJson/Variant/VariantData.hpp

@@ -77,7 +77,7 @@ class VariantData {
         return visit.visit(JsonString(content_.asTinyString));
 
       case VariantType::LinkedString:
-        return visit.visit(JsonString(content_.asLinkedString, true));
+        return visit.visit(JsonString(asLinkedString(resources), true));
 
       case VariantType::OwnedString:
         return visit.visit(JsonString(content_.asOwnedString->data,
@@ -216,7 +216,7 @@ class VariantData {
         str = content_.asTinyString;
         break;
       case VariantType::LinkedString:
-        str = content_.asLinkedString;
+        str = asLinkedString(resources);
         break;
       case VariantType::OwnedString:
         str = content_.asOwnedString->data;
@@ -261,7 +261,7 @@ class VariantData {
         str = content_.asTinyString;
         break;
       case VariantType::LinkedString:
-        str = content_.asLinkedString;
+        str = asLinkedString(resources);
         break;
       case VariantType::OwnedString:
         str = content_.asOwnedString->data;
@@ -298,12 +298,14 @@ class VariantData {
     }
   }
 
-  JsonString asString() const {
+  const char* asLinkedString(const ResourceManager* resources) const;
+
+  JsonString asString(const ResourceManager* resources) const {
     switch (type_) {
       case VariantType::TinyString:
         return JsonString(content_.asTinyString);
       case VariantType::LinkedString:
-        return JsonString(content_.asLinkedString, true);
+        return JsonString(asLinkedString(resources), true);
       case VariantType::OwnedString:
         return JsonString(content_.asOwnedString->data,
                           content_.asOwnedString->length);
@@ -519,12 +521,7 @@ class VariantData {
     var->setString(value, resources);
   }
 
-  void setLinkedString(const char* s) {
-    ARDUINOJSON_ASSERT(type_ == VariantType::Null);  // must call clear() first
-    ARDUINOJSON_ASSERT(s);
-    type_ = VariantType::LinkedString;
-    content_.asLinkedString = s;
-  }
+  bool setLinkedString(const char* s, ResourceManager* resources);
 
   template <typename TAdaptedString>
   void setTinyString(const TAdaptedString& s) {

src/ArduinoJson/Variant/VariantImpl.hpp

@@ -18,6 +18,20 @@ inline void VariantData::setRawString(SerializedValue<T> value,
     setRawString(dup);
 }
 
+inline bool VariantData::setLinkedString(const char* s,
+                                         ResourceManager* resources) {
+  ARDUINOJSON_ASSERT(type_ == VariantType::Null);  // must call clear() first
+  ARDUINOJSON_ASSERT(s);
+
+  auto slotId = resources->saveStaticString(s);
+  if (slotId == NULL_SLOT)
+    return false;
+
+  type_ = VariantType::LinkedString;
+  content_.asSlotId = slotId;
+  return true;
+}
+
 template <typename TAdaptedString>
 inline bool VariantData::setString(TAdaptedString value,
                                    ResourceManager* resources) {
@@ -26,10 +40,8 @@ inline bool VariantData::setString(TAdaptedString value,
   if (value.isNull())
     return false;
 
-  if (value.isStatic()) {
-    setLinkedString(value.data());
-    return true;
-  }
+  if (value.isStatic())
+    return setLinkedString(value.data(), resources);
 
   if (isTinyString(value, value.size())) {
     setTinyString(value);
@@ -70,6 +82,12 @@ inline const VariantExtension* VariantData::getExtension(
 }
 #endif
 
+inline const char* VariantData::asLinkedString(
+    const ResourceManager* resources) const {
+  ARDUINOJSON_ASSERT(type_ == VariantType::LinkedString);
+  return resources->getStaticString(content_.asSlotId);
+}
+
 template <typename T>
 enable_if_t<sizeof(T) == 8, bool> VariantData::setFloat(
     T value, ResourceManager* resources) {