JsonArray::remove() and JsonObject::remove() now release the memory of strings

CHANGELOG.md

@@ -8,7 +8,8 @@ HEAD
 * Removed `JsonObject::is<T>(k)` and `JsonObject::set(k,v)`
 * Replaced `T JsonArray::get<T>(i)` with `JsonVariant JsonArray::get(i)`
 * Replaced `T JsonObject::get<T>(k)` with `JsonVariant JsonObject::get(k)`
-* `JsonArray::remove()` and `JsonObject::remove()` now release the memory of the variant
+* `JsonArray::remove()` and `JsonObject::remove()` now release the memory
+* Added `JSON_STRING_SIZE()`
 
 v6.5.0-beta (2018-10-13)
 -----------

CMakeLists.txt

@@ -11,6 +11,8 @@ if(${COVERAGE})
 	set(CMAKE_CXX_FLAGS "-g -O0 -fprofile-arcs -ftest-coverage")
 endif()
 
+add_definitions(-DARDUINOJSON_DEBUG)
+
 include_directories(${CMAKE_CURRENT_LIST_DIR}/src)
 add_subdirectory(third-party/catch)
 add_subdirectory(test)

fuzzing/Makefile

@@ -1,6 +1,6 @@
 # CAUTION: this file is invoked by https://github.com/google/oss-fuzz
 
-CXXFLAGS += -I../src
+CXXFLAGS += -I../src -DARDUINOJSON_DEBUG
 
 all: \
 	$(OUT)/json_fuzzer \

fuzzing/fuzzer_main.cpp

@@ -5,17 +5,34 @@
 // This file is NOT use by Google's OSS fuzz
 // I only use it to reproduce the bugs found
 
-#include <stdint.h>
-#include <fstream>
+#include <stdint.h>  // size_t
+#include <stdio.h>   // fopen et al.
+#include <stdlib.h>  // exit
 #include <iostream>
-#include <string>
+#include <vector>
 
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size);
 
-std::string read(const char* path) {
-  std::ifstream file(path);
-  return std::string(std::istreambuf_iterator<char>(file),
-                     std::istreambuf_iterator<char>());
+std::vector<uint8_t> read(const char* path) {
+  FILE* f = fopen(path, "rb");
+  if (!f) {
+    std::cerr << "Failed to open " << path << std::endl;
+    exit(1);
+  }
+
+  fseek(f, 0, SEEK_END);
+  size_t size = ftell(f);
+  fseek(f, 0, SEEK_SET);
+
+  std::vector<uint8_t> buffer(size);
+  if (fread(buffer.data(), 1, size, f) != size) {
+    fclose(f);
+    std::cerr << "Failed to read " << path << std::endl;
+    exit(1);
+  }
+
+  fclose(f);
+  return buffer;
 }
 
 int main(int argc, const char* argv[]) {
@@ -26,9 +43,8 @@ int main(int argc, const char* argv[]) {
 
   for (int i = 1; i < argc; i++) {
     std::cout << "Loading " << argv[i] << std::endl;
-    std::string buffer = read(argv[i]);
-    LLVMFuzzerTestOneInput(reinterpret_cast<const uint8_t*>(buffer.data()),
-                           buffer.size());
+    std::vector<uint8_t> buffer = read(argv[i]);
+    LLVMFuzzerTestOneInput(buffer.data(), buffer.size());
   }
   return 0;
 }

src/ArduinoJson/Configuration.hpp

@@ -130,16 +130,6 @@
 #endif
 #endif
 
-#ifndef ARDUINOJSON_ENABLE_ALIGNMENT
-#ifdef ARDUINO_ARCH_AVR
-// alignment isn't needed for 8-bit AVR
-#define ARDUINOJSON_ENABLE_ALIGNMENT 0
-#else
-// but most processors need pointers to be align on word size
-#define ARDUINOJSON_ENABLE_ALIGNMENT 1
-#endif
-#endif
-
 // Control the exponentiation threshold for big numbers
 // CAUTION: cannot be more that 1e9 !!!!
 #ifndef ARDUINOJSON_POSITIVE_EXPONENTIATION_THRESHOLD

src/ArduinoJson/Data/ArrayFunctions.hpp

@@ -5,7 +5,6 @@
 #pragma once
 
 #include "JsonVariantData.hpp"
-#include "Slot.hpp"
 #include "SlotFunctions.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
@@ -13,7 +12,7 @@ namespace ARDUINOJSON_NAMESPACE {
 inline JsonVariantData* arrayAdd(JsonArrayData* arr, MemoryPool* pool) {
   if (!arr) return 0;
 
-  Slot* slot = pool->allocSlot();
+  VariantSlot* slot = pool->allocVariant();
   if (!slot) return 0;
 
   slot->next = 0;
@@ -29,20 +28,22 @@ inline JsonVariantData* arrayAdd(JsonArrayData* arr, MemoryPool* pool) {
     arr->tail = slot;
   }
 
+  slot->value.keyIsOwned = false;
   return &slot->value;
 }
 
-inline Slot* arrayGetSlot(const JsonArrayData* arr, size_t index) {
+inline VariantSlot* arrayGetSlot(const JsonArrayData* arr, size_t index) {
   if (!arr) return 0;
   return slotAdvance(arr->head, index);
 }
 
 inline JsonVariantData* arrayGet(const JsonArrayData* arr, size_t index) {
-  Slot* slot = arrayGetSlot(arr, index);
+  VariantSlot* slot = arrayGetSlot(arr, index);
   return slot ? &slot->value : 0;
 }
 
-inline void arrayRemove(JsonArrayData* arr, Slot* slot, MemoryPool* pool) {
+inline void arrayRemove(JsonArrayData* arr, VariantSlot* slot,
+                        MemoryPool* pool) {
   if (!arr || !slot) return;
 
   if (slot->prev)
@@ -73,7 +74,7 @@ inline bool arrayCopy(JsonArrayData* dst, const JsonArrayData* src,
                       MemoryPool* pool) {
   if (!dst || !src) return false;
   arrayClear(dst);
-  for (Slot* s = src->head; s; s = s->next) {
+  for (VariantSlot* s = src->head; s; s = s->next) {
     if (!variantCopy(arrayAdd(dst, pool), &s->value, pool)) return false;
   }
   return true;
@@ -84,8 +85,8 @@ bool variantEquals(const JsonVariantData*, const JsonVariantData*);
 inline bool arrayEquals(const JsonArrayData* a1, const JsonArrayData* a2) {
   if (a1 == a2) return true;
   if (!a1 || !a2) return false;
-  Slot* s1 = a1->head;
-  Slot* s2 = a2->head;
+  VariantSlot* s1 = a1->head;
+  VariantSlot* s2 = a2->head;
   for (;;) {
     if (s1 == s2) return true;
     if (!s1 || !s2) return false;

src/ArduinoJson/Data/JsonVariantData.hpp

@@ -26,13 +26,13 @@ enum JsonVariantType {
 };
 
 struct JsonObjectData {
-  struct Slot *head;
-  struct Slot *tail;
+  struct VariantSlot *head;
+  struct VariantSlot *tail;
 };
 
 struct JsonArrayData {
-  struct Slot *head;
-  struct Slot *tail;
+  struct VariantSlot *head;
+  struct VariantSlot *tail;
 };
 
 struct RawData {
@@ -48,6 +48,8 @@ union JsonVariantContent {
   JsonArrayData asArray;
   JsonObjectData asObject;
   const char *asString;
+  struct StringSlot *asOwnedString;
+  struct StringSlot *asOwnedRaw;
   struct {
     const char *data;
     size_t size;
@@ -56,7 +58,7 @@ union JsonVariantContent {
 
 // this struct must be a POD type to prevent error calling offsetof on clang
 struct JsonVariantData {
-  bool keyIsStatic : 1;
+  bool keyIsOwned : 1;
   JsonVariantType type : 7;
   JsonVariantContent content;
 };

src/ArduinoJson/Data/ObjectFunctions.hpp

@@ -11,11 +11,11 @@
 namespace ARDUINOJSON_NAMESPACE {
 
 template <typename TKey>
-inline Slot* objectFindSlot(const JsonObjectData* obj, TKey key) {
+inline VariantSlot* objectFindSlot(const JsonObjectData* obj, TKey key) {
   if (!obj) return 0;
-  Slot* slot = obj->head;
+  VariantSlot* slot = obj->head;
   while (slot) {
-    if (key.equals(slot->key)) break;
+    if (key.equals(slotGetKey(slot))) break;
     slot = slot->next;
   }
   return slot;
@@ -29,7 +29,7 @@ inline bool objectContainsKey(const JsonObjectData* obj, const TKey& key) {
 template <typename TKey>
 inline JsonVariantData* objectAdd(JsonObjectData* obj, TKey key,
                                   MemoryPool* pool) {
-  Slot* slot = pool->allocSlot();
+  VariantSlot* slot = pool->allocVariant();
   if (!slot) return 0;
 
   slot->next = 0;
@@ -58,7 +58,7 @@ inline JsonVariantData* objectSet(JsonObjectData* obj, TKey key,
   if (key.isNull()) return 0;
 
   // search a matching key
-  Slot* slot = objectFindSlot(obj, key);
+  VariantSlot* slot = objectFindSlot(obj, key);
   if (slot) return &slot->value;
 
   return objectAdd(obj, key, pool);
@@ -66,7 +66,7 @@ inline JsonVariantData* objectSet(JsonObjectData* obj, TKey key,
 
 template <typename TKey>
 inline JsonVariantData* objectGet(const JsonObjectData* obj, TKey key) {
-  Slot* slot = objectFindSlot(obj, key);
+  VariantSlot* slot = objectFindSlot(obj, key);
   return slot ? &slot->value : 0;
 }
 
@@ -76,7 +76,8 @@ inline void objectClear(JsonObjectData* obj) {
   obj->tail = 0;
 }
 
-inline void objectRemove(JsonObjectData* obj, Slot* slot, MemoryPool* pool) {
+inline void objectRemove(JsonObjectData* obj, VariantSlot* slot,
+                         MemoryPool* pool) {
   if (!obj) return;
   if (!slot) return;
   if (slot->prev)
@@ -102,12 +103,12 @@ inline bool objectCopy(JsonObjectData* dst, const JsonObjectData* src,
                        MemoryPool* pool) {
   if (!dst || !src) return false;
   objectClear(dst);
-  for (Slot* s = src->head; s; s = s->next) {
+  for (VariantSlot* s = src->head; s; s = s->next) {
     JsonVariantData* var;
-    if (s->value.keyIsStatic)
-      var = objectAdd(dst, ZeroTerminatedRamStringConst(s->key), pool);
+    if (s->value.keyIsOwned)
+      var = objectAdd(dst, ZeroTerminatedRamString(s->ownedKey->value), pool);
     else
-      var = objectAdd(dst, ZeroTerminatedRamString(s->key), pool);
+      var = objectAdd(dst, ZeroTerminatedRamStringConst(s->linkedKey), pool);
     if (!variantCopy(var, &s->value, pool)) return false;
   }
   return true;
@@ -117,9 +118,9 @@ inline bool objectEquals(const JsonObjectData* o1, const JsonObjectData* o2) {
   if (o1 == o2) return true;
   if (!o1 || !o2) return false;
 
-  for (Slot* s = o1->head; s; s = s->next) {
+  for (VariantSlot* s = o1->head; s; s = s->next) {
     JsonVariantData* v1 = &s->value;
-    JsonVariantData* v2 = objectGet(o2, makeString(s->key));
+    JsonVariantData* v2 = objectGet(o2, makeString(slotGetKey(s)));
     if (!variantEquals(v1, v2)) return false;
   }
   return true;

src/ArduinoJson/Data/SlotFunctions.hpp

@@ -7,65 +7,80 @@
 #include "../Memory/MemoryPool.hpp"
 #include "../Strings/StringTypes.hpp"
 #include "JsonVariantData.hpp"
-#include "Slot.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
 
 template <typename TKey>
-inline bool slotSetKey(Slot* slot, TKey key, MemoryPool* pool) {
-  const char* dup = key.save(pool);
-  if (!dup) return false;
-  slot->key = dup;
-  slot->value.keyIsStatic = false;
+inline bool slotSetKey(VariantSlot* var, TKey key, MemoryPool* pool) {
+  StringSlot* slot = key.save(pool);
+  if (!slot) return false;
+  var->ownedKey = slot;
+  var->value.keyIsOwned = true;
   return true;
 }
 
-inline bool slotSetKey(Slot* slot, ZeroTerminatedRamStringConst key,
-                       MemoryPool* pool) {
-  slot->key = key.save(pool);
-  slot->value.keyIsStatic = true;
+inline bool slotSetKey(VariantSlot* var, ZeroTerminatedRamStringConst key,
+                       MemoryPool*) {
+  var->linkedKey = key.c_str();
+  var->value.keyIsOwned = false;
   return true;
 }
 
-inline bool slotSetKey(Slot* slot, StringInMemoryPool key, MemoryPool* pool) {
-  slot->key = key.save(pool);
-  slot->value.keyIsStatic = false;
+inline bool slotSetKey(VariantSlot* var, StringInMemoryPool key, MemoryPool*) {
+  var->ownedKey = key.slot();
+  var->value.keyIsOwned = true;
   return true;
 }
 
-inline const Slot* slotAdvance(const Slot* slot, size_t distance) {
-  while (distance && slot) {
-    slot = slot->next;
+inline const char* slotGetKey(const VariantSlot* var) {
+  return var->value.keyIsOwned ? var->ownedKey->value : var->linkedKey;
+}
+
+inline const VariantSlot* slotAdvance(const VariantSlot* var, size_t distance) {
+  while (distance && var) {
+    var = var->next;
     distance--;
   }
-  return slot;
+  return var;
 }
 
-inline Slot* slotAdvance(Slot* slot, size_t distance) {
-  while (distance && slot) {
-    slot = slot->next;
+inline VariantSlot* slotAdvance(VariantSlot* var, size_t distance) {
+  while (distance && var) {
+    var = var->next;
     distance--;
   }
-  return slot;
+  return var;
 }
 
-inline size_t slotSize(const Slot* slot) {
+inline size_t slotSize(const VariantSlot* var) {
   size_t n = 0;
-  while (slot) {
+  while (var) {
     n++;
-    slot = slot->next;
+    var = var->next;
   }
   return n;
 }
 
-inline void slotFree(Slot* slot, MemoryPool* pool) {
-  const JsonVariantData& v = slot->value;
-  if (v.type == JSON_ARRAY || v.type == JSON_OBJECT) {
-    for (Slot* s = v.content.asObject.head; s; s = s->next) {
-      slotFree(s, pool);
-    }
+inline void slotFree(VariantSlot* var, MemoryPool* pool) {
+  const JsonVariantData& v = var->value;
+
+  switch (v.type) {
+    case JSON_ARRAY:
+    case JSON_OBJECT:
+      for (VariantSlot* s = v.content.asObject.head; s; s = s->next) {
+        slotFree(s, pool);
+      }
+      break;
+    case JSON_OWNED_STRING:
+    case JSON_OWNED_RAW:
+      pool->freeString(v.content.asOwnedString);
+      break;
+    default:
+      break;
   }
 
-  pool->freeSlot(slot);
+  if (v.keyIsOwned) pool->freeString(var->ownedKey);
+
+  pool->freeVariant(var);
 }
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Data/VariantFunctions.hpp

@@ -10,7 +10,6 @@
 #include "ArrayFunctions.hpp"
 #include "JsonVariantData.hpp"
 #include "ObjectFunctions.hpp"
-#include "Slot.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -24,8 +23,9 @@ inline T variantAsIntegral(const JsonVariantData* var) {
     case JSON_NEGATIVE_INTEGER:
       return T(~var->content.asInteger + 1);
     case JSON_LINKED_STRING:
-    case JSON_OWNED_STRING:
       return parseInteger<T>(var->content.asString);
+    case JSON_OWNED_STRING:
+      return parseInteger<T>(var->content.asOwnedString->value);
     case JSON_FLOAT:
       return T(var->content.asFloat);
     default:
@@ -48,8 +48,9 @@ inline T variantAsFloat(const JsonVariantData* var) {
     case JSON_NEGATIVE_INTEGER:
       return -static_cast<T>(var->content.asInteger);
     case JSON_LINKED_STRING:
-    case JSON_OWNED_STRING:
       return parseFloat<T>(var->content.asString);
+    case JSON_OWNED_STRING:
+      return parseFloat<T>(var->content.asOwnedString->value);
     case JSON_FLOAT:
       return static_cast<T>(var->content.asFloat);
     default:
@@ -59,11 +60,14 @@ inline T variantAsFloat(const JsonVariantData* var) {
 
 inline const char* variantAsString(const JsonVariantData* var) {
   if (!var) return 0;
-  if (var &&
-      (var->type == JSON_LINKED_STRING || var->type == JSON_OWNED_STRING))
-    return var->content.asString;
-  else
-    return 0;
+  switch (var->type) {
+    case JSON_LINKED_STRING:
+      return var->content.asString;
+    case JSON_OWNED_STRING:
+      return var->content.asOwnedString->value;
+    default:
+      return 0;
+  }
 }
 
 inline JsonArrayData* variantAsArray(JsonVariantData* var) {
@@ -141,11 +145,10 @@ template <typename T>
 inline bool variantSetOwnedRaw(JsonVariantData* var, SerializedValue<T> value,
                                MemoryPool* pool) {
   if (!var) return false;
-  const char* dup = makeString(value.data(), value.size()).save(pool);
-  if (dup) {
+  StringSlot* slot = makeString(value.data(), value.size()).save(pool);
+  if (slot) {
     var->type = JSON_OWNED_RAW;
-    var->content.asRaw.data = dup;
-    var->content.asRaw.size = value.size();
+    var->content.asOwnedRaw = slot;
     return true;
   } else {
     var->type = JSON_NULL;
@@ -156,10 +159,10 @@ inline bool variantSetOwnedRaw(JsonVariantData* var, SerializedValue<T> value,
 template <typename T>
 inline bool variantSetString(JsonVariantData* var, T value, MemoryPool* pool) {
   if (!var) return false;
-  const char* dup = value.save(pool);
-  if (dup) {
+  StringSlot* slot = value.save(pool);
+  if (slot) {
     var->type = JSON_OWNED_STRING;
-    var->content.asString = dup;
+    var->content.asOwnedString = slot;
     return true;
   } else {
     var->type = JSON_NULL;
@@ -167,6 +170,13 @@ inline bool variantSetString(JsonVariantData* var, T value, MemoryPool* pool) {
   }
 }
 
+inline bool variantSetOwnedString(JsonVariantData* var, StringSlot* slot) {
+  if (!var) return false;
+  var->type = JSON_OWNED_STRING;
+  var->content.asOwnedString = slot;
+  return true;
+}
+
 inline bool variantSetString(JsonVariantData* var, const char* value) {
   if (!var) return false;
   var->type = JSON_LINKED_STRING;
@@ -174,11 +184,6 @@ inline bool variantSetString(JsonVariantData* var, const char* value) {
   return true;
 }
 
-inline bool variantSetString(JsonVariantData* var, const char* value,
-                             MemoryPool* pool) {
-  return variantSetString(var, makeString(const_cast<char*>(value)), pool);
-}
-
 inline void variantSetNull(JsonVariantData* var) {
   if (var) var->type = JSON_NULL;
 }
@@ -212,15 +217,17 @@ inline bool variantCopy(JsonVariantData* dst, const JsonVariantData* src,
     case JSON_OBJECT:
       return objectCopy(variantToObject(dst), &src->content.asObject, pool);
     case JSON_OWNED_STRING:
-      return variantSetString(dst, src->content.asString, pool);
+      return variantSetString(
+          dst, makeString(src->content.asOwnedString->value), pool);
     case JSON_OWNED_RAW:
-      return variantSetOwnedRaw(
-          dst,
-          serialized(const_cast<char*>(src->content.asRaw.data),
-                     src->content.asRaw.size),
-          pool);
+      return variantSetOwnedRaw(dst,
+                                serialized(src->content.asOwnedRaw->value,
+                                           src->content.asOwnedRaw->size),
+                                pool);
     default:
-      *dst = *src;
+      // caution: don't override keyIsOwned
+      dst->type = src->type;
+      dst->content = src->content;
       return true;
   }
 }
@@ -260,11 +267,16 @@ inline bool variantEquals(const JsonVariantData* a, const JsonVariantData* b) {
 
   switch (a->type) {
     case JSON_LINKED_RAW:
-    case JSON_OWNED_RAW:
     case JSON_LINKED_STRING:
-    case JSON_OWNED_STRING:
       return !strcmp(a->content.asString, b->content.asString);
 
+    case JSON_OWNED_RAW:
+    case JSON_OWNED_STRING:
+      return a->content.asOwnedString->size == b->content.asOwnedString->size &&
+             !memcmp(a->content.asOwnedString->value,
+                     b->content.asOwnedString->value,
+                     a->content.asOwnedString->size);
+
     case JSON_BOOLEAN:
     case JSON_POSITIVE_INTEGER:
     case JSON_NEGATIVE_INTEGER:

src/ArduinoJson/Json/JsonDeserializer.hpp

@@ -18,6 +18,7 @@ template <typename TReader, typename TStringStorage>
 class JsonDeserializer {
   typedef typename remove_reference<TStringStorage>::type::StringBuilder
       StringBuilder;
+  typedef typename StringBuilder::StringType StringType;
 
  public:
   JsonDeserializer(MemoryPool &memoryPool, TReader reader,
@@ -124,7 +125,7 @@ class JsonDeserializer {
     // Read each key value pair
     for (;;) {
       // Parse key
-      StringInMemoryPool key;
+      StringType key;
       err = parseKey(key);
       if (err) return err;
 
@@ -165,7 +166,7 @@ class JsonDeserializer {
     }
   }
 
-  DeserializationError parseKey(StringInMemoryPool &key) {
+  DeserializationError parseKey(StringType &key) {
     if (isQuote(current())) {
       return parseQuotedString(key);
     } else {
@@ -174,15 +175,15 @@ class JsonDeserializer {
   }
 
   DeserializationError parseStringValue(JsonVariant variant) {
-    StringInMemoryPool value;
+    StringType value;
     DeserializationError err = parseQuotedString(value);
     if (err) return err;
     variant.set(value);
     return DeserializationError::Ok;
   }
 
-  DeserializationError parseQuotedString(StringInMemoryPool &result) {
-    StringBuilder str = _stringStorage.startString();
+  DeserializationError parseQuotedString(StringType &result) {
+    StringBuilder builder = _stringStorage.startString();
     const char stopChar = current();
 
     move();
@@ -203,16 +204,16 @@ class JsonDeserializer {
         move();
       }
 
-      str.append(c);
+      builder.append(c);
     }
 
-    result = str.complete();
+    result = builder.complete();
     if (result.isNull()) return DeserializationError::NoMemory;
     return DeserializationError::Ok;
   }
 
-  DeserializationError parseNonQuotedString(StringInMemoryPool &result) {
-    StringBuilder str = _stringStorage.startString();
+  DeserializationError parseNonQuotedString(StringType &result) {
+    StringBuilder builder = _stringStorage.startString();
 
     char c = current();
     if (c == '\0') return DeserializationError::IncompleteInput;
@@ -220,14 +221,14 @@ class JsonDeserializer {
     if (canBeInNonQuotedString(c)) {  // no quotes
       do {
         move();
-        str.append(c);
+        builder.append(c);
         c = current();
       } while (canBeInNonQuotedString(c));
     } else {
       return DeserializationError::InvalidInput;
     }
 
-    result = str.complete();
+    result = builder.complete();
     if (result.isNull()) return DeserializationError::NoMemory;
     return DeserializationError::Ok;
   }

src/ArduinoJson/JsonArray.hpp

@@ -11,7 +11,7 @@
 // Returns the size (in bytes) of an array with n elements.
 // Can be very handy to determine the size of a StaticMemoryPool.
 #define JSON_ARRAY_SIZE(NUMBER_OF_ELEMENTS) \
-  ((NUMBER_OF_ELEMENTS) * sizeof(ARDUINOJSON_NAMESPACE::Slot))
+  ((NUMBER_OF_ELEMENTS) * sizeof(ARDUINOJSON_NAMESPACE::VariantSlot))
 
 namespace ARDUINOJSON_NAMESPACE {
 

src/ArduinoJson/JsonArrayIterator.hpp

@@ -4,7 +4,6 @@
 
 #pragma once
 
-#include "Data/Slot.hpp"
 #include "Data/SlotFunctions.hpp"
 #include "JsonVariant.hpp"
 
@@ -30,7 +29,7 @@ class JsonVariantPtr {
 class JsonArrayIterator {
  public:
   JsonArrayIterator() : _slot(0) {}
-  explicit JsonArrayIterator(MemoryPool *memoryPool, Slot *slot)
+  explicit JsonArrayIterator(MemoryPool *memoryPool, VariantSlot *slot)
       : _memoryPool(memoryPool), _slot(slot) {}
 
   JsonVariant operator*() const {
@@ -58,13 +57,13 @@ class JsonArrayIterator {
     return *this;
   }
 
-  Slot *internal() {
+  VariantSlot *internal() {
     return _slot;
   }
 
  private:
   MemoryPool *_memoryPool;
-  Slot *_slot;
+  VariantSlot *_slot;
 };
 
 class JsonVariantConstPtr {
@@ -86,7 +85,7 @@ class JsonVariantConstPtr {
 class JsonArrayConstIterator {
  public:
   JsonArrayConstIterator() : _slot(0) {}
-  explicit JsonArrayConstIterator(const Slot *slot) : _slot(slot) {}
+  explicit JsonArrayConstIterator(const VariantSlot *slot) : _slot(slot) {}
 
   JsonVariantConst operator*() const {
     return JsonVariantConst(&_slot->value);
@@ -113,11 +112,11 @@ class JsonArrayConstIterator {
     return *this;
   }
 
-  const Slot *internal() {
+  const VariantSlot *internal() {
     return _slot;
   }
 
  private:
-  const Slot *_slot;
+  const VariantSlot *_slot;
 };
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/JsonKey.hpp

@@ -8,22 +8,18 @@ namespace ARDUINOJSON_NAMESPACE {
 
 class JsonKey {
  public:
-  JsonKey(const Slot* slot) : _slot(slot) {}
+  JsonKey(const VariantSlot* slot) : _slot(slot) {}
 
   operator const char*() const {
     return c_str();
   }
 
   const char* c_str() const {
-    return _slot ? _slot->key : 0;
+    return _slot ? slotGetKey(_slot) : 0;
   }
 
   bool isNull() const {
-    return _slot == 0 || _slot->key == 0;
-  }
-
-  bool isStatic() const {
-    return _slot ? _slot->value.keyIsStatic : true;
+    return _slot == 0 || _slot->linkedKey == 0;
   }
 
   friend bool operator==(JsonKey lhs, const char* rhs) {
@@ -32,6 +28,6 @@ class JsonKey {
   }
 
  private:
-  const Slot* _slot;
+  const VariantSlot* _slot;
 };
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/JsonObject.hpp

@@ -10,7 +10,7 @@
 // Returns the size (in bytes) of an object with n elements.
 // Can be very handy to determine the size of a StaticMemoryPool.
 #define JSON_OBJECT_SIZE(NUMBER_OF_ELEMENTS) \
-  ((NUMBER_OF_ELEMENTS) * sizeof(ARDUINOJSON_NAMESPACE::Slot))
+  ((NUMBER_OF_ELEMENTS) * sizeof(ARDUINOJSON_NAMESPACE::VariantSlot))
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -256,7 +256,11 @@ class JsonObject : public JsonObjectProxy<JsonObjectData>, public Visitable {
     return set_impl(makeString(key));
   }
 
-  FORCE_INLINE JsonVariant set(const StringInMemoryPool& key) const {
+  FORCE_INLINE JsonVariant set(StringInMemoryPool key) const {
+    return set_impl(key);
+  }
+
+  FORCE_INLINE JsonVariant set(ZeroTerminatedRamStringConst key) const {
     return set_impl(key);
   }
 

src/ArduinoJson/JsonObjectIterator.hpp

@@ -11,7 +11,8 @@ namespace ARDUINOJSON_NAMESPACE {
 
 class JsonPairPtr {
  public:
-  JsonPairPtr(MemoryPool *memoryPool, Slot *slot) : _pair(memoryPool, slot) {}
+  JsonPairPtr(MemoryPool *memoryPool, VariantSlot *slot)
+      : _pair(memoryPool, slot) {}
 
   const JsonPair *operator->() const {
     return &_pair;
@@ -29,7 +30,7 @@ class JsonObjectIterator {
  public:
   JsonObjectIterator() : _slot(0) {}
 
-  explicit JsonObjectIterator(MemoryPool *memoryPool, Slot *slot)
+  explicit JsonObjectIterator(MemoryPool *memoryPool, VariantSlot *slot)
       : _memoryPool(memoryPool), _slot(slot) {}
 
   JsonPair operator*() const {
@@ -57,18 +58,18 @@ class JsonObjectIterator {
     return *this;
   }
 
-  Slot *internal() {
+  VariantSlot *internal() {
     return _slot;
   }
 
  private:
   MemoryPool *_memoryPool;
-  Slot *_slot;
+  VariantSlot *_slot;
 };
 
 class JsonPairConstPtr {
  public:
-  JsonPairConstPtr(const Slot *slot) : _pair(slot) {}
+  JsonPairConstPtr(const VariantSlot *slot) : _pair(slot) {}
 
   const JsonPairConst *operator->() const {
     return &_pair;
@@ -86,7 +87,7 @@ class JsonObjectConstIterator {
  public:
   JsonObjectConstIterator() : _slot(0) {}
 
-  explicit JsonObjectConstIterator(const Slot *slot) : _slot(slot) {}
+  explicit JsonObjectConstIterator(const VariantSlot *slot) : _slot(slot) {}
 
   JsonPairConst operator*() const {
     return JsonPairConst(_slot);
@@ -113,11 +114,11 @@ class JsonObjectConstIterator {
     return *this;
   }
 
-  const Slot *internal() {
+  const VariantSlot *internal() {
     return _slot;
   }
 
  private:
-  const Slot *_slot;
+  const VariantSlot *_slot;
 };
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/JsonPair.hpp

@@ -11,7 +11,7 @@ namespace ARDUINOJSON_NAMESPACE {
 // A key value pair for JsonObjectData.
 class JsonPair {
  public:
-  JsonPair(MemoryPool* memoryPool, Slot* slot) : _key(slot) {
+  JsonPair(MemoryPool* memoryPool, VariantSlot* slot) : _key(slot) {
     if (slot) {
       _value = JsonVariant(memoryPool, &slot->value);
     }
@@ -32,7 +32,7 @@ class JsonPair {
 
 class JsonPairConst {
  public:
-  JsonPairConst(const Slot* slot) : _key(slot) {
+  JsonPairConst(const VariantSlot* slot) : _key(slot) {
     if (slot) {
       _value = JsonVariantConst(&slot->value);
     }

src/ArduinoJson/JsonVariant.hpp

@@ -204,9 +204,12 @@ class JsonVariant : public JsonVariantProxy<JsonVariantData>,
     return variantSetString(_data, value);
   }
 
-  // set(const char*);
+  // for internal use only
   FORCE_INLINE bool set(StringInMemoryPool value) const {
-    return variantSetString(_data, value, _memoryPool);
+    return variantSetOwnedString(_data, value.slot());
+  }
+  FORCE_INLINE bool set(ZeroTerminatedRamStringConst value) const {
+    return variantSetString(_data, value.c_str());
   }
 
   bool set(JsonVariantConst value) const;
@@ -323,15 +326,4 @@ class JsonVariantConst : public JsonVariantProxy<const JsonVariantData>,
     return JsonVariantConst(objectGet(variantAsObject(_data), makeString(key)));
   }
 };
-
-class JsonVariantLocal : public JsonVariant {
- public:
-  explicit JsonVariantLocal(MemoryPool *memoryPool)
-      : JsonVariant(memoryPool, &_localData) {
-    _localData.type = JSON_NULL;
-  }
-
- private:
-  JsonVariantData _localData;
-};
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/JsonVariantImpl.hpp

@@ -89,11 +89,16 @@ inline void JsonVariantConst::accept(Visitor& visitor) const {
       return visitor.visitObject(JsonObjectConst(&_data->content.asObject));
 
     case JSON_LINKED_STRING:
-    case JSON_OWNED_STRING:
       return visitor.visitString(_data->content.asString);
 
-    case JSON_LINKED_RAW:
+    case JSON_OWNED_STRING:
+      return visitor.visitString(_data->content.asOwnedString->value);
+
     case JSON_OWNED_RAW:
+      return visitor.visitRawJson(_data->content.asOwnedRaw->value,
+                                  _data->content.asOwnedRaw->size);
+
+    case JSON_LINKED_RAW:
       return visitor.visitRawJson(_data->content.asRaw.data,
                                   _data->content.asRaw.size);
 

src/ArduinoJson/Memory/Alignment.hpp

@@ -0,0 +1,28 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#pragma once
+
+#include <stddef.h>  // size_t
+
+namespace ARDUINOJSON_NAMESPACE {
+
+inline bool isAligned(void *ptr) {
+  const size_t mask = sizeof(void *) - 1;
+  size_t addr = reinterpret_cast<size_t>(ptr);
+  return (addr & mask) == 0;
+}
+
+inline size_t addPadding(size_t bytes) {
+  const size_t mask = sizeof(void *) - 1;
+  return (bytes + mask) & ~mask;
+}
+
+template <size_t bytes>
+struct AddPadding {
+  static const size_t mask = sizeof(void *) - 1;
+  static const size_t value = (bytes + mask) & ~mask;
+};
+
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Memory/DynamicMemoryPool.hpp

@@ -5,8 +5,9 @@
 #pragma once
 
 #include "../Strings/StringInMemoryPool.hpp"
+#include "Alignment.hpp"
 #include "MemoryPool.hpp"
-#include "StringBuilder.hpp"
+#include "StaticMemoryPool.hpp"
 
 #include <stdlib.h>  // malloc, free
 
@@ -33,18 +34,15 @@ class DefaultAllocator {
 
 template <typename TAllocator>
 class DynamicMemoryPoolBase : public MemoryPool {
-  struct Block;
-  struct EmptyBlock {
+  class Block : public StaticMemoryPoolBase {
+   public:
+    Block(char* buf, size_t sz, Block* nxt)
+        : StaticMemoryPoolBase(buf, sz), next(nxt) {}
     Block* next;
-    size_t capacity;
-    size_t size;
-  };
-  struct Block : EmptyBlock {
-    char data[1];
   };
 
  public:
-  enum { EmptyBlockSize = sizeof(EmptyBlock) };
+  enum { EmptyBlockSize = sizeof(Block) };
 
   DynamicMemoryPoolBase(size_t initialSize = ARDUINOJSON_DEFAULT_POOL_SIZE)
       : _head(NULL), _nextBlockCapacity(initialSize) {}
@@ -57,28 +55,82 @@ class DynamicMemoryPoolBase : public MemoryPool {
     _nextBlockCapacity = capacity;
   }
 
-  // Gets the number of bytes occupied in the memoryPool
-  virtual size_t allocated_bytes() const {
-    size_t total = 0;
-    for (const Block* b = _head; b; b = b->next) total += b->size;
-    return total;
+  virtual size_t size() const {
+    size_t sum = 0;
+    for (Block* b = _head; b; b = b->next) {
+      sum += b->size();
+    }
+    return sum;
   }
 
-  // Allocates the specified amount of bytes in the memoryPool
-  virtual char* alloc(size_t bytes) {
-    alignNextAlloc();
-    return canAllocInHead(bytes) ? allocInHead(bytes) : allocInNewBlock(bytes);
+  virtual VariantSlot* allocVariant() {
+    for (Block* b = _head; b; b = b->next) {
+      VariantSlot* s = b->allocVariant();
+      if (s) return s;
+    }
+
+    if (!addNewBlock(sizeof(VariantSlot))) return 0;
+
+    return _head->allocVariant();
   }
 
-  virtual char* realloc(char* oldPtr, size_t oldSize, size_t newSize) {
-    size_t n = newSize - oldSize;
-    if (canAllocInHead(n)) {
-      allocInHead(n);
-      return oldPtr;
-    } else {
-      char* newPtr = allocInNewBlock(newSize);
-      if (oldPtr && newPtr) memcpy(newPtr, oldPtr, oldSize);
-      return newPtr;
+  virtual void freeVariant(VariantSlot* slot) {
+    for (Block* b = _head; b; b = b->next) {
+      if (b->owns(slot)) {
+        b->freeVariant(slot);
+        break;
+      }
+    }
+  }
+
+  virtual void freeString(StringSlot* slot) {
+    for (Block* b = _head; b; b = b->next) {
+      if (b->owns(slot)) {
+        b->freeString(slot);
+        break;
+      }
+    }
+  }
+
+  virtual StringSlot* allocFrozenString(size_t n) {
+    for (Block* b = _head; b; b = b->next) {
+      StringSlot* s = b->allocFrozenString(n);
+      if (s) return s;
+    }
+
+    if (!addNewBlock(sizeof(StringSlot) + n)) return 0;
+
+    return _head->allocFrozenString(n);
+  }
+
+  virtual StringSlot* allocExpandableString() {
+    for (Block* b = _head; b; b = b->next) {
+      StringSlot* s = b->allocExpandableString();
+      if (s) return s;
+    }
+
+    if (!addNewBlock(sizeof(StringSlot))) return 0;
+
+    return _head->allocExpandableString();
+  }
+
+  virtual StringSlot* expandString(StringSlot* oldSlot) {
+    if (!addNewBlock(sizeof(StringSlot) + oldSlot->size)) return 0;
+
+    StringSlot* newSlot = _head->allocExpandableString();
+
+    ARDUINOJSON_ASSERT(newSlot->size > oldSlot->size);
+    memcpy(newSlot->value, oldSlot->value, oldSlot->size);
+    freeString(oldSlot);
+
+    return newSlot;
+  }
+
+  virtual void freezeString(StringSlot* slot, size_t newSize) {
+    for (Block* b = _head; b; b = b->next) {
+      if (b->owns(slot)) {
+        b->freezeString(slot, newSize);
+      }
     }
   }
 
@@ -87,7 +139,7 @@ class DynamicMemoryPoolBase : public MemoryPool {
   void clear() {
     Block* currentBlock = _head;
     while (currentBlock != NULL) {
-      _nextBlockCapacity = currentBlock->capacity;
+      _nextBlockCapacity = currentBlock->capacity();
       Block* nextBlock = currentBlock->next;
       _allocator.deallocate(currentBlock);
       currentBlock = nextBlock;
@@ -95,40 +147,22 @@ class DynamicMemoryPoolBase : public MemoryPool {
     _head = 0;
   }
 
-  StringBuilder startString() {
-    return StringBuilder(this);
+  size_t blockCount() const {
+    size_t sum = 0;
+    for (Block* b = _head; b; b = b->next) sum++;
+    return sum;
   }
 
  private:
-  void alignNextAlloc() {
-    if (_head) _head->size = this->round_size_up(_head->size);
-  }
-
-  bool canAllocInHead(size_t bytes) const {
-    return _head != NULL && _head->size + bytes <= _head->capacity;
-  }
-
-  char* allocInHead(size_t bytes) {
-    char* p = _head->data + _head->size;
-    _head->size += bytes;
-    return p;
-  }
-
-  char* allocInNewBlock(size_t bytes) {
+  bool addNewBlock(size_t minCapacity) {
     size_t capacity = _nextBlockCapacity;
-    if (bytes > capacity) capacity = bytes;
-    if (!addNewBlock(capacity)) return NULL;
-    _nextBlockCapacity *= 2;
-    return allocInHead(bytes);
-  }
-
-  bool addNewBlock(size_t capacity) {
-    size_t bytes = EmptyBlockSize + capacity;
-    Block* block = static_cast<Block*>(_allocator.allocate(bytes));
-    if (block == NULL) return false;
-    block->capacity = capacity;
-    block->size = 0;
-    block->next = _head;
+    if (minCapacity > capacity) capacity = minCapacity;
+    capacity = addPadding(capacity);
+    size_t bytes = sizeof(Block) + capacity;
+    char* p = reinterpret_cast<char*>(_allocator.allocate(bytes));
+    if (!p) return false;
+    Block* block = new (p) Block(p + sizeof(Block), capacity, _head);
+    _nextBlockCapacity = capacity * 2;
     _head = block;
     return true;
   }

src/ArduinoJson/Memory/MemoryPool.hpp

@@ -5,66 +5,30 @@
 #pragma once
 
 #include <stddef.h>  // for size_t
-#include <stdint.h>  // for uint8_t
-#include <string.h>
 
-#include "../Configuration.hpp"
-#include "../Data/Slot.hpp"
 #include "../Polyfills/attributes.hpp"
+#include "StringSlot.hpp"
+#include "VariantSlot.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
-// Handle the memory management (done in derived classes) and calls the parser.
-// This abstract class is implemented by StaticMemoryPool which implements a
-// fixed memory allocation.
+
 class MemoryPool {
  public:
-  // Allocates n bytes in the MemoryPool.
-  // Return a pointer to the allocated memory or NULL if allocation fails.
-  virtual char *alloc(size_t size) = 0;
+  virtual StringSlot *allocExpandableString() = 0;
+  virtual StringSlot *allocFrozenString(size_t) = 0;
+  virtual StringSlot *expandString(StringSlot *) = 0;
+  virtual void freezeString(StringSlot *, size_t) = 0;
+  virtual void freeString(StringSlot *) = 0;
 
-  virtual char *realloc(char *oldPtr, size_t oldSize, size_t newSize) = 0;
+  virtual VariantSlot *allocVariant() = 0;
+  virtual void freeVariant(VariantSlot *) = 0;
 
-  Slot *allocSlot() {
-    if (_freeSlots) {
-      Slot *s = _freeSlots;
-      _freeSlots = s->next;
-      return s;
-    }
-    return reinterpret_cast<Slot *>(alloc(sizeof(Slot)));
-  }
-
-  void freeSlot(Slot *slot) {
-    slot->next = _freeSlots;
-    _freeSlots = slot;
-  }
-
-  size_t size() const {
-    size_t result = allocated_bytes();
-    for (Slot *s = _freeSlots; s; s = s->next) result -= sizeof(Slot);
-    return result;
-  }
+  virtual size_t size() const = 0;
 
  protected:
-  MemoryPool() : _freeSlots(0) {}
-
   // CAUTION: NO VIRTUAL DESTRUCTOR!
   // If we add a virtual constructor the Arduino compiler will add malloc()
   // and free() to the binary, adding 706 useless bytes.
   ~MemoryPool() {}
-
-  virtual size_t allocated_bytes() const = 0;
-
-  // Preserve aligment if necessary
-  static FORCE_INLINE size_t round_size_up(size_t bytes) {
-#if ARDUINOJSON_ENABLE_ALIGNMENT
-    const size_t x = sizeof(void *) - 1;
-    return (bytes + x) & ~x;
-#else
-    return bytes;
-#endif
-  }
-
- private:
-  Slot *_freeSlots;
 };
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Memory/SlotList.hpp

@@ -0,0 +1,67 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#pragma once
+
+#include <stddef.h>  // for size_t
+
+namespace ARDUINOJSON_NAMESPACE {
+
+template <typename TSlot>
+class SlotList {
+ public:
+  SlotList() : _head(0) {}
+
+  TSlot *pop() {
+    TSlot *slot = _head;
+    if (slot) _head = slot->next;
+    return slot;
+  }
+
+  void push(TSlot *slot) {
+    slot->next = _head;
+    _head = slot;
+  }
+
+  bool remove(const TSlot *slot) {
+    if (_head == slot) {
+      _head = slot->next;
+      return true;
+    }
+
+    for (TSlot *s = _head; s; s = s->next) {
+      if (s->next == slot) {
+        s->next = slot->next;
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  bool remove(const void *slot) {
+    return remove(reinterpret_cast<const TSlot *>(slot));
+  }
+
+  template <typename Functor>
+  void forEach(const Functor &f) {
+    for (TSlot *s = _head; s; s = s->next) {
+      f(s);
+    }
+  }
+
+  size_t size() const {
+    size_t sum = 0;
+    for (TSlot *s = _head; s; s = s->next) sum += sizeof(TSlot);
+    return sum;
+  }
+
+  void clear() {
+    _head = 0;
+  }
+
+ private:
+  TSlot *_head;
+};
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Memory/StaticMemoryPool.hpp

@@ -4,74 +4,201 @@
 
 #pragma once
 
+#include "../Polyfills/assert.hpp"
 #include "../Polyfills/mpl/max.hpp"
 #include "../Strings/StringInMemoryPool.hpp"
+#include "Alignment.hpp"
 #include "MemoryPool.hpp"
-#include "StringBuilder.hpp"
+#include "SlotList.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
 
+// _begin                                _end
+// v                                        v
+// +-------------+--------------+-----------+
+// | strings...  |   (free)     |  ...slots |
+// +-------------+--------------+-----------+
+//               ^              ^
+//             _left          _right
+
 class StaticMemoryPoolBase : public MemoryPool {
+  class UpdateStringSlotAddress {
+   public:
+    UpdateStringSlotAddress(const char* address, size_t offset)
+        : _address(address), _offset(offset) {}
+
+    void operator()(StringSlot* slot) const {
+      ARDUINOJSON_ASSERT(slot != NULL);
+      if (slot->value > _address) slot->value -= _offset;
+    }
+
+   private:
+    const char* _address;
+    size_t _offset;
+  };
+
  public:
   // Gets the capacity of the memoryPool in bytes
   size_t capacity() const {
-    return _capacity;
+    return size_t(_end - _begin);
   }
 
-  // Allocates the specified amount of bytes in the memoryPool
-  virtual char* alloc(size_t bytes) {
-    alignNextAlloc();
-    if (!canAlloc(bytes)) return NULL;
-    return doAlloc(bytes);
+  virtual size_t size() const {
+    return allocated_bytes() - _freeVariants.size() - _freeStrings.size();
   }
 
-  virtual char* realloc(char* oldPtr, size_t oldSize, size_t newSize) {
-    size_t n = newSize - oldSize;
-    if (!canAlloc(n)) return NULL;
-    doAlloc(n);
-    return oldPtr;
+  virtual VariantSlot* allocVariant() {
+    VariantSlot* s = _freeVariants.pop();
+    if (s) return s;
+    return s ? s : allocRight<VariantSlot>();
+  }
+
+  virtual void freeVariant(VariantSlot* slot) {
+    freeVariantSlot(slot);
+    compactRightSide();
+  }
+
+  virtual void freeString(StringSlot* slot) {
+    freeStringSlot(slot);
+    compactLeftSide(slot->value, slot->size);
+    compactRightSide();
+  }
+
+  virtual StringSlot* allocFrozenString(size_t n) {
+    StringSlot* s = allocStringSlot();
+    if (!s) return 0;
+    if (!canAlloc(n)) return 0;
+
+    s->value = _left;
+    s->size = n;
+    _left += n;
+    _usedString.push(s);
+    checkInvariants();
+
+    return s;
+  }
+
+  virtual StringSlot* allocExpandableString() {
+    StringSlot* s = allocStringSlot();
+    if (!s) return 0;
+
+    s->value = _left;
+    s->size = size_t(_right - _left);
+    _usedString.push(s);
+    _left = _right;
+
+    checkInvariants();
+    return s;
+  }
+
+  virtual StringSlot* expandString(StringSlot*) {
+    return 0;
+  }
+
+  virtual void freezeString(StringSlot* slot, size_t newSize) {
+    _left -= (slot->size - newSize);
+    slot->size = newSize;
+    checkInvariants();
   }
 
-  // Resets the memoryPool.
-  // USE WITH CAUTION: this invalidates all previously allocated data
   void clear() {
-    _size = 0;
+    _left = _begin;
+    _right = _end;
+    _freeVariants.clear();
+    _freeStrings.clear();
+    _usedString.clear();
   }
 
-  StringBuilder startString() {
-    return StringBuilder(this);
+  bool canAlloc(size_t bytes) const {
+    return _left + bytes <= _right;
+  }
+
+  bool owns(void* p) const {
+    return _begin <= p && p < _end;
+  }
+
+  template <typename T>
+  T* allocRight() {
+    return reinterpret_cast<T*>(allocRight(sizeof(T)));
+  }
+
+  char* allocRight(size_t bytes) {
+    if (!canAlloc(bytes)) return 0;
+    _right -= bytes;
+    return _right;
+  }
+
+  // Workaround for missing placement new
+  void* operator new(size_t, void* p) {
+    return p;
   }
 
  protected:
-  StaticMemoryPoolBase(char* memoryPool, size_t capa)
-      : _buffer(memoryPool), _capacity(capa), _size(0) {}
+  StaticMemoryPoolBase(char* buffer, size_t capa)
+      : _begin(buffer),
+        _left(buffer),
+        _right(buffer + capa),
+        _end(buffer + capa) {}
 
   ~StaticMemoryPoolBase() {}
 
   // Gets the current usage of the memoryPool in bytes
-  virtual size_t allocated_bytes() const {
-    return _size;
+  size_t allocated_bytes() const {
+    return size_t(_left - _begin + _end - _right);
   }
 
  private:
-  void alignNextAlloc() {
-    _size = round_size_up(_size);
+  StringSlot* allocStringSlot() {
+    StringSlot* s = _freeStrings.pop();
+    if (s) return s;
+    return allocRight<StringSlot>();
   }
 
-  bool canAlloc(size_t bytes) const {
-    return _size + bytes <= _capacity;
+  void freeVariantSlot(VariantSlot* slot) {
+    _freeVariants.push(slot);
   }
 
-  char* doAlloc(size_t bytes) {
-    char* p = &_buffer[_size];
-    _size += bytes;
-    return p;
+  void freeStringSlot(StringSlot* slot) {
+    _usedString.remove(slot);
+    _freeStrings.push(slot);
   }
 
-  char* _buffer;
-  size_t _capacity;
-  size_t _size;
-};
+  void compactLeftSide(char* holeAddress, size_t holeSize) {
+    ARDUINOJSON_ASSERT(holeAddress >= _begin);
+    ARDUINOJSON_ASSERT(holeAddress + holeSize <= _left);
+    char* holeEnd = holeAddress + holeSize;
+    memmove(holeAddress,               // where the hole begun
+            holeEnd,                   // where the hole ended
+            size_t(_left - holeEnd));  // everything after the hole
+    _left -= holeSize;
+    _usedString.forEach(UpdateStringSlotAddress(holeAddress, holeSize));
+    checkInvariants();
+  }
+
+  void compactRightSide() {
+  loop:
+    if (_freeStrings.remove(_right)) {
+      _right += sizeof(StringSlot);
+      goto loop;
+    }
+    if (_freeVariants.remove(_right)) {
+      _right += sizeof(VariantSlot);
+      goto loop;
+    }
+    checkInvariants();
+  }
+
+  void checkInvariants() {
+    ARDUINOJSON_ASSERT(_begin <= _left);
+    ARDUINOJSON_ASSERT(_left <= _right);
+    ARDUINOJSON_ASSERT(_right <= _end);
+  }
+
+  char *_begin, *_left, *_right, *_end;
+  SlotList<VariantSlot> _freeVariants;
+  SlotList<StringSlot> _freeStrings;
+  SlotList<StringSlot> _usedString;
+};  // namespace ARDUINOJSON_NAMESPACE
 
 #if defined(__clang__)
 #pragma clang diagnostic push
@@ -88,7 +215,8 @@ class StaticMemoryPoolBase : public MemoryPool {
 // bytes.
 template <size_t CAPACITY>
 class StaticMemoryPool : public StaticMemoryPoolBase {
-  static const size_t ACTUAL_CAPACITY = Max<1, CAPACITY>::value;
+  static const size_t ACTUAL_CAPACITY =
+      AddPadding<Max<1, CAPACITY>::value>::value;
 
  public:
   explicit StaticMemoryPool()

src/ArduinoJson/Memory/StringBuilder.hpp

@@ -11,25 +11,43 @@ namespace ARDUINOJSON_NAMESPACE {
 
 class StringBuilder {
  public:
-  explicit StringBuilder(MemoryPool* parent)
-      : _parent(parent), _start(0), _size(0) {
-    _start = _parent->alloc(1);
+  typedef StringInMemoryPool StringType;
+
+  explicit StringBuilder(MemoryPool* parent) : _parent(parent), _size(0) {
+    _slot = _parent->allocExpandableString();
+  }
+
+  void append(const char* s) {
+    while (*s) append(*s++);
+  }
+
+  void append(const char* s, size_t n) {
+    while (n-- > 0) append(*s++);
   }
 
   void append(char c) {
-    _start = _parent->realloc(_start, _size + 1, _size + 2);
-    if (_start) _start[_size++] = c;
+    if (!_slot) return;
+
+    if (_size >= _slot->size) {
+      _slot = _parent->expandString(_slot);
+      if (!_slot) return;
+    }
+
+    _slot->value[_size++] = c;
   }
 
-  StringInMemoryPool complete() {
-    if (_start) _start[_size] = 0;
-    return _start;
+  StringType complete() {
+    append('\0');
+    if (_slot) {
+      _parent->freezeString(_slot, _size);
+    }
+    return _slot;
   }
 
  private:
   MemoryPool* _parent;
-  char* _start;
   size_t _size;
+  StringSlot* _slot;
 };
 
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Memory/StringSlot.hpp

@@ -0,0 +1,20 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#pragma once
+
+#include <stddef.h>  // for size_t
+#include "../Configuration.hpp"
+
+#define JSON_STRING_SIZE(SIZE) \
+  (sizeof(ARDUINOJSON_NAMESPACE::StringSlot) + (SIZE))
+
+namespace ARDUINOJSON_NAMESPACE {
+
+struct StringSlot {
+  char *value;
+  size_t size;
+  struct StringSlot *next;
+};
+}  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Memory/VariantSlot.hpp

@@ -4,15 +4,18 @@
 
 #pragma once
 
-#include "JsonVariantData.hpp"
+#include "../Data/JsonVariantData.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
 
-struct Slot {
+struct VariantSlot {
   JsonVariantData value;
-  struct Slot* next;
-  struct Slot* prev;
-  const char* key;
+  struct VariantSlot* next;
+  struct VariantSlot* prev;
+  union {
+    const char* linkedKey;
+    StringSlot* ownedKey;
+  };
 };
 
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/MsgPack/MsgPackDeserializer.hpp

@@ -17,6 +17,7 @@ template <typename TReader, typename TStringStorage>
 class MsgPackDeserializer {
   typedef typename remove_reference<TStringStorage>::type::StringBuilder
       StringBuilder;
+  typedef typename StringBuilder::StringType StringType;
 
  public:
   MsgPackDeserializer(MemoryPool &memoryPool, TReader reader,
@@ -220,16 +221,29 @@ class MsgPackDeserializer {
     return readString(variant, size);
   }
 
+  template <typename T>
+  DeserializationError readString(StringType &str) {
+    T size;
+    if (!readInteger(size)) return DeserializationError::IncompleteInput;
+    return readString(str, size);
+  }
+
   DeserializationError readString(JsonVariant variant, size_t n) {
-    StringBuilder str = _stringStorage.startString();
+    StringType s;
+    DeserializationError err = readString(s, n);
+    if (!err) variant.set(s);
+    return err;
+  }
+
+  DeserializationError readString(StringType &s, size_t n) {
+    StringBuilder builder = _stringStorage.startString();
     for (; n; --n) {
       uint8_t c;
       if (!readBytes(c)) return DeserializationError::IncompleteInput;
-      str.append(static_cast<char>(c));
+      builder.append(static_cast<char>(c));
     }
-    StringInMemoryPool s = str.complete();
+    s = builder.complete();
     if (s.isNull()) return DeserializationError::NoMemory;
-    variant.set(s);
     return DeserializationError::Ok;
   }
 
@@ -278,12 +292,11 @@ class MsgPackDeserializer {
     if (_nestingLimit == 0) return DeserializationError::TooDeep;
     --_nestingLimit;
     for (; n; --n) {
-      JsonVariantLocal key(_memoryPool);
-      DeserializationError err = parse(key);
+      StringType key;
+      DeserializationError err = parseKey(key);
       if (err) return err;
-      if (!key.is<char *>()) return DeserializationError::NotSupported;
 
-      JsonVariant value = object.set(StringInMemoryPool(key.as<char *>()));
+      JsonVariant value = object.set(key);
       if (value.isInvalid()) return DeserializationError::NoMemory;
 
       err = parse(value);
@@ -293,6 +306,27 @@ class MsgPackDeserializer {
     return DeserializationError::Ok;
   }
 
+  DeserializationError parseKey(StringType &key) {
+    uint8_t code;
+    if (!readByte(code)) return DeserializationError::IncompleteInput;
+
+    if ((code & 0xe0) == 0xa0) return readString(key, code & 0x1f);
+
+    switch (code) {
+      case 0xd9:
+        return readString<uint8_t>(key);
+
+      case 0xda:
+        return readString<uint16_t>(key);
+
+      case 0xdb:
+        return readString<uint32_t>(key);
+
+      default:
+        return DeserializationError::NotSupported;
+    }
+  }
+
   MemoryPool *_memoryPool;
   TReader _reader;
   TStringStorage _stringStorage;

src/ArduinoJson/Polyfills/assert.hpp

@@ -0,0 +1,12 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#pragma once
+
+#ifdef ARDUINOJSON_DEBUG
+#include <assert.h>
+#define ARDUINOJSON_ASSERT(X) assert(X)
+#else
+#define ARDUINOJSON_ASSERT(X) ((void)0)
+#endif

src/ArduinoJson/StringStorage/StringMover.hpp

@@ -11,13 +11,15 @@ class StringMover {
  public:
   class StringBuilder {
    public:
+    typedef ZeroTerminatedRamStringConst StringType;
+
     StringBuilder(TChar** ptr) : _writePtr(ptr), _startPtr(*ptr) {}
 
     void append(char c) {
       *(*_writePtr)++ = TChar(c);
     }
 
-    StringInMemoryPool complete() const {
+    StringType complete() const {
       *(*_writePtr)++ = 0;
       return reinterpret_cast<const char*>(_startPtr);
     }

src/ArduinoJson/Strings/ArduinoString.hpp

@@ -13,12 +13,12 @@ class ArduinoString {
   ArduinoString(const ::String& str) : _str(&str) {}
 
   template <typename TMemoryPool>
-  const char* save(TMemoryPool* memoryPool) const {
+  StringSlot* save(TMemoryPool* memoryPool) const {
     if (isNull()) return NULL;
     size_t n = _str->length() + 1;
-    void* dup = memoryPool->alloc(n);
-    if (dup != NULL) memcpy(dup, _str->c_str(), n);
-    return static_cast<const char*>(dup);
+    StringSlot* slot = memoryPool->allocFrozenString(n);
+    if (slot) memcpy(slot->value, _str->c_str(), n);
+    return slot;
   }
 
   bool isNull() const {

src/ArduinoJson/Strings/FixedSizeFlashString.hpp

@@ -22,11 +22,11 @@ class FixedSizeFlashString {
   }
 
   template <typename TMemoryPool>
-  const char* save(TMemoryPool* memoryPool) const {
+  StringSlot* save(TMemoryPool* memoryPool) const {
     if (!_str) return NULL;
-    void* dup = memoryPool->alloc(_size);
-    if (dup != NULL) memcpy_P(dup, (const char*)_str, _size);
-    return static_cast<const char*>(dup);
+    StringSlot* slot = memoryPool->allocFrozenString(_size);
+    if (!slot) memcpy_P(slot->value, (const char*)_str, _size);
+    return slot;
   }
 
   size_t size() const {

src/ArduinoJson/Strings/FixedSizeRamString.hpp

@@ -23,12 +23,11 @@ class FixedSizeRamString {
   }
 
   template <typename TMemoryPool>
-  const char* save(TMemoryPool* memoryPool) const {
+  StringSlot* save(TMemoryPool* memoryPool) const {
     if (!_str) return NULL;
-    void* dup = memoryPool->alloc(_size);
-    if (!dup) return NULL;
-    memcpy(dup, _str, _size);
-    return static_cast<const char*>(dup);
+    StringSlot* slot = memoryPool->allocFrozenString(_size);
+    if (slot) memcpy(slot->value, _str, _size);
+    return slot;
   }
 
   size_t size() const {

src/ArduinoJson/Strings/StlString.hpp

@@ -13,11 +13,11 @@ class StlString {
   StlString(const std::string& str) : _str(&str) {}
 
   template <typename TMemoryPool>
-  const char* save(TMemoryPool* memoryPool) const {
+  StringSlot* save(TMemoryPool* memoryPool) const {
     size_t n = _str->length() + 1;
-    void* dup = memoryPool->alloc(n);
-    if (dup != NULL) memcpy(dup, _str->c_str(), n);
-    return static_cast<const char*>(dup);
+    StringSlot* slot = memoryPool->allocFrozenString(n);
+    if (slot) memcpy(slot->value, _str->c_str(), n);
+    return slot;
   }
 
   bool isNull() const {

src/ArduinoJson/Strings/StringInMemoryPool.hpp

@@ -4,13 +4,45 @@
 
 #pragma once
 
-#include "ZeroTerminatedRamStringConst.hpp"
+#include <string.h>
+#include "../Memory/StringSlot.hpp"
 
 namespace ARDUINOJSON_NAMESPACE {
 
-class StringInMemoryPool : public ZeroTerminatedRamStringConst {
+class StringInMemoryPool {
  public:
-  StringInMemoryPool(const char* str = 0) : ZeroTerminatedRamStringConst(str) {}
+  StringInMemoryPool(StringSlot* s = 0) : _slot(s) {}
+
+  bool equals(const char* expected) const {
+    if (!_slot) return expected == 0;
+    const char* actual = _slot->value;
+    if (actual == expected) return true;
+    return strcmp(actual, expected) == 0;
+  }
+
+  bool isNull() const {
+    return !_slot;
+  }
+
+  template <typename TMemoryPool>
+  StringSlot* save(TMemoryPool*) const {
+    return _slot;
+  }
+
+  size_t size() const {
+    return _slot->size;
+  }
+
+  StringSlot* slot() const {
+    return _slot;
+  }
+
+  const char* c_str() const {
+    return _slot->value;
+  }
+
+ protected:
+  StringSlot* _slot;
 };
 
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Strings/ZeroTerminatedFlashString.hpp

@@ -21,12 +21,12 @@ class ZeroTerminatedFlashString {
   }
 
   template <typename TMemoryPool>
-  const char* save(TMemoryPool* memoryPool) const {
+  StringSlot* save(TMemoryPool* memoryPool) const {
     if (!_str) return NULL;
     size_t n = size() + 1;  // copy the terminator
-    void* dup = memoryPool->alloc(n);
-    if (dup != NULL) memcpy_P(dup, (const char*)_str, n);
-    return static_cast<const char*>(dup);
+    StringSlot* slot = memoryPool->allocFrozenString(n);
+    if (slot) memcpy_P(slot->value, reinterpret_cast<const char*>(_str), n);
+    return slot;
   }
 
   size_t size() const {

src/ArduinoJson/Strings/ZeroTerminatedRamString.hpp

@@ -14,13 +14,12 @@ class ZeroTerminatedRamString : public ZeroTerminatedRamStringConst {
       : ZeroTerminatedRamStringConst(str) {}
 
   template <typename TMemoryPool>
-  const char* save(TMemoryPool* memoryPool) const {
+  StringSlot* save(TMemoryPool* memoryPool) const {
     if (!_str) return NULL;
     size_t n = size() + 1;
-    void* dup = memoryPool->alloc(n);
-    if (!dup) return NULL;
-    memcpy(dup, _str, n);
-    return static_cast<const char*>(dup);
+    StringSlot* slot = memoryPool->allocFrozenString(n);
+    if (slot) memcpy(slot->value, _str, n);
+    return slot;
   }
 };
 

src/ArduinoJson/Strings/ZeroTerminatedRamStringConst.hpp

@@ -11,7 +11,7 @@ namespace ARDUINOJSON_NAMESPACE {
 
 class ZeroTerminatedRamStringConst {
  public:
-  ZeroTerminatedRamStringConst(const char* str) : _str(str) {}
+  ZeroTerminatedRamStringConst(const char* str = 0) : _str(str) {}
 
   bool equals(const char* expected) const {
     const char* actual = _str;
@@ -23,15 +23,19 @@ class ZeroTerminatedRamStringConst {
     return !_str;
   }
 
-  template <typename TMemoryPool>
-  const char* save(TMemoryPool*) const {
-    return _str;
-  }
+  // template <typename TMemoryPool>
+  // const char* save(TMemoryPool*) const {
+  //   return _str;
+  // }
 
   size_t size() const {
     return strlen(_str);
   }
 
+  const char* c_str() const {
+    return _str;
+  }
+
  protected:
   const char* _str;
 };

test/DynamicMemoryPool/CMakeLists.txt

@@ -2,12 +2,14 @@
 # Copyright Benoit Blanchon 2014-2018
 # MIT License
 
-add_executable(DynamicMemoryPoolTests 
-	alloc.cpp
-	allocSlot.cpp
+add_executable(DynamicMemoryPoolTests
+	allocString.cpp
+	allocVariant.cpp
+	blocks.cpp
+	clear.cpp
 	no_memory.cpp
 	size.cpp
-	startString.cpp
+	StringBuilder.cpp
 )
 
 target_link_libraries(DynamicMemoryPoolTests catch)

test/DynamicMemoryPool/StringBuilder.cpp

@@ -0,0 +1,41 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
+#include <ArduinoJson/Memory/StringBuilder.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("DynamicMemoryPool::startString()") {
+  SECTION("WorksWhenBufferIsBigEnough") {
+    DynamicMemoryPool memoryPool(JSON_STRING_SIZE(8));
+
+    StringBuilder str(&memoryPool);
+    str.append("abcdefg");
+
+    REQUIRE(memoryPool.blockCount() == 1);
+    REQUIRE(str.complete().equals("abcdefg"));
+  }
+
+  SECTION("GrowsWhenBufferIsTooSmall") {
+    DynamicMemoryPool memoryPool(JSON_STRING_SIZE(8));
+
+    StringBuilder str(&memoryPool);
+    str.append("abcdefghABC");
+
+    REQUIRE(memoryPool.blockCount() == 2);
+    REQUIRE(str.complete().equals("abcdefghABC"));
+  }
+
+  SECTION("SizeIncreases") {
+    DynamicMemoryPool memoryPool(JSON_STRING_SIZE(5));
+
+    StringBuilder str(&memoryPool);
+    str.append('h');
+    str.complete();
+
+    REQUIRE(JSON_STRING_SIZE(2) == memoryPool.size());
+  }
+}

test/DynamicMemoryPool/alloc.cpp

@@ -1,77 +0,0 @@
-// ArduinoJson - arduinojson.org
-// Copyright Benoit Blanchon 2014-2018
-// MIT License
-
-#include <ArduinoJson.h>
-#include <catch.hpp>
-#include <sstream>
-
-using namespace ARDUINOJSON_NAMESPACE;
-
-static bool isAligned(void* ptr) {
-  const size_t mask = sizeof(void*) - 1;
-  size_t addr = reinterpret_cast<size_t>(ptr);
-  return (addr & mask) == 0;
-}
-
-std::stringstream allocatorLog;
-
-struct SpyingAllocator : DefaultAllocator {
-  void* allocate(size_t n) {
-    allocatorLog << "A" << (n - DynamicMemoryPool::EmptyBlockSize);
-    return DefaultAllocator::allocate(n);
-  }
-  void deallocate(void* p) {
-    allocatorLog << "F";
-    return DefaultAllocator::deallocate(p);
-  }
-};
-
-TEST_CASE("DynamicMemoryPool::alloc()") {
-  SECTION("Returns different pointers") {
-    DynamicMemoryPool memoryPool;
-    void* p1 = memoryPool.alloc(1);
-    void* p2 = memoryPool.alloc(2);
-    REQUIRE(p1 != p2);
-  }
-
-  SECTION("Doubles allocation size when full") {
-    allocatorLog.str("");
-    {
-      DynamicMemoryPoolBase<SpyingAllocator> memoryPool(1);
-      memoryPool.alloc(1);
-      memoryPool.alloc(1);
-    }
-    REQUIRE(allocatorLog.str() == "A1A2FF");
-  }
-
-  SECTION("Resets allocation size after clear()") {
-    allocatorLog.str("");
-    {
-      DynamicMemoryPoolBase<SpyingAllocator> memoryPool(1);
-      memoryPool.alloc(1);
-      memoryPool.alloc(1);
-      memoryPool.clear();
-      memoryPool.alloc(1);
-    }
-    REQUIRE(allocatorLog.str() == "A1A2FFA1F");
-  }
-
-  SECTION("Makes a big allocation when needed") {
-    allocatorLog.str("");
-    {
-      DynamicMemoryPoolBase<SpyingAllocator> memoryPool(1);
-      memoryPool.alloc(42);
-    }
-    REQUIRE(allocatorLog.str() == "A42F");
-  }
-
-  SECTION("Alignment") {
-    // make room for two but not three
-    DynamicMemoryPool tinyBuf(2 * sizeof(void*) + 1);
-
-    REQUIRE(isAligned(tinyBuf.alloc(1)));  // this on is aligned by design
-    REQUIRE(isAligned(tinyBuf.alloc(1)));  // this one fits in the first block
-    REQUIRE(isAligned(tinyBuf.alloc(1)));  // this one requires a new block
-  }
-}

test/DynamicMemoryPool/allocSlot.cpp

@@ -1,27 +0,0 @@
-// ArduinoJson - arduinojson.org
-// Copyright Benoit Blanchon 2014-2018
-// MIT License
-
-#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
-#include <catch.hpp>
-
-using namespace ARDUINOJSON_NAMESPACE;
-
-TEST_CASE("DynamicMemoryPool::allocSlot()") {
-  DynamicMemoryPool memoryPool;
-
-  SECTION("Returns different pointer") {
-    Slot* s1 = memoryPool.allocSlot();
-    Slot* s2 = memoryPool.allocSlot();
-
-    REQUIRE(s1 != s2);
-  }
-
-  SECTION("Returns same pointer after freeSlot()") {
-    Slot* s1 = memoryPool.allocSlot();
-    memoryPool.freeSlot(s1);
-    Slot* s2 = memoryPool.allocSlot();
-
-    REQUIRE(s1 == s2);
-  }
-}

test/DynamicMemoryPool/allocString.cpp

@@ -0,0 +1,28 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
+#include <catch.hpp>
+#include <sstream>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("DynamicMemoryPool::allocFrozenString()") {
+  DynamicMemoryPool pool;
+
+  SECTION("Returns different pointers") {
+    StringSlot* a = pool.allocFrozenString(1);
+    StringSlot* b = pool.allocFrozenString(2);
+    REQUIRE(a != b);
+    REQUIRE(a->value != b->value);
+  }
+
+  SECTION("Returns same slot after freeString") {
+    StringSlot* a = pool.allocFrozenString(1);
+    pool.freeString(a);
+    StringSlot* b = pool.allocFrozenString(2);
+    REQUIRE(a == b);
+    REQUIRE(a->value == b->value);
+  }
+}

test/DynamicMemoryPool/allocVariant.cpp

@@ -0,0 +1,41 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("DynamicMemoryPool::allocVariant()") {
+  DynamicMemoryPool memoryPool;
+
+  SECTION("Returns different pointer") {
+    VariantSlot* s1 = memoryPool.allocVariant();
+    VariantSlot* s2 = memoryPool.allocVariant();
+
+    REQUIRE(s1 != s2);
+  }
+
+  SECTION("Returns same pointer after freeSlot()") {
+    VariantSlot* s1 = memoryPool.allocVariant();
+    memoryPool.freeVariant(s1);
+    VariantSlot* s2 = memoryPool.allocVariant();
+
+    REQUIRE(s1 == s2);
+  }
+
+  SECTION("Returns aligned pointers") {
+    // make room for two but not three
+    // pass an uneven capacity
+    DynamicMemoryPool pool(2 * sizeof(VariantSlot) + 1);
+
+    REQUIRE(isAligned(pool.allocVariant()));
+    REQUIRE(isAligned(pool.allocVariant()));
+    REQUIRE(pool.blockCount() == 1);
+
+    REQUIRE(isAligned(pool.allocVariant()));
+    REQUIRE(isAligned(pool.allocVariant()));
+    REQUIRE(pool.blockCount() == 2);
+  }
+}

test/DynamicMemoryPool/blocks.cpp

@@ -0,0 +1,69 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
+#include <catch.hpp>
+#include <sstream>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+std::stringstream allocatorLog;
+
+struct SpyingAllocator : DefaultAllocator {
+  void* allocate(size_t n) {
+    allocatorLog << "A" << (n - DynamicMemoryPool::EmptyBlockSize);
+    return DefaultAllocator::allocate(n);
+  }
+  void deallocate(void* p) {
+    allocatorLog << "F";
+    return DefaultAllocator::deallocate(p);
+  }
+};
+
+TEST_CASE("DynamicMemoryPool blocks") {
+  SECTION("Doubles allocation size when full") {
+    allocatorLog.str("");
+    {
+      DynamicMemoryPoolBase<SpyingAllocator> memoryPool(sizeof(VariantSlot));
+      memoryPool.allocVariant();
+      memoryPool.allocVariant();
+    }
+    std::stringstream expected;
+    expected << "A" << sizeof(VariantSlot)      // block 1
+             << "A" << 2 * sizeof(VariantSlot)  // block 2, twice bigger
+             << "FF";
+
+    REQUIRE(allocatorLog.str() == expected.str());
+  }
+
+  SECTION("Resets allocation size after clear()") {
+    allocatorLog.str("");
+    {
+      DynamicMemoryPoolBase<SpyingAllocator> memoryPool(sizeof(VariantSlot));
+      memoryPool.allocVariant();
+      memoryPool.allocVariant();
+      memoryPool.clear();
+      memoryPool.allocVariant();
+    }
+    std::stringstream expected;
+    expected << "A" << sizeof(VariantSlot)      // block 1
+             << "A" << 2 * sizeof(VariantSlot)  // block 2, twice bigger
+             << "FF"                            // clear
+             << "A" << sizeof(VariantSlot)      // block 1
+             << "F";
+    REQUIRE(allocatorLog.str() == expected.str());
+  }
+
+  /* SECTION("Alloc big block for large string") {
+     allocatorLog.str("");
+     {
+       DynamicMemoryPoolBase<SpyingAllocator> memoryPool(1);
+       memoryPool.allocString(42);
+     }
+     std::stringstream expected;
+     expected << "A" << JSON_STRING_SIZE(42)  // block 1
+              << "F";
+     REQUIRE(allocatorLog.str() == expected.str());
+   }*/
+}

test/DynamicMemoryPool/clear.cpp

@@ -0,0 +1,47 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("StaticMemoryPool::clear()") {
+  DynamicMemoryPool memoryPool;
+
+  SECTION("Discards allocated variants") {
+    memoryPool.allocVariant();
+    REQUIRE(memoryPool.size() > 0);
+
+    memoryPool.clear();
+    CHECK(memoryPool.size() == 0);
+  }
+
+  SECTION("Discards allocated strings") {
+    memoryPool.allocFrozenString(10);
+    REQUIRE(memoryPool.size() > 0);
+
+    memoryPool.clear();
+
+    CHECK(memoryPool.size() == 0);
+  }
+
+  SECTION("Purges variant cache") {
+    memoryPool.freeVariant(memoryPool.allocVariant());
+    REQUIRE(memoryPool.size() == 0);
+
+    memoryPool.clear();
+
+    CHECK(memoryPool.size() == 0);
+  }
+
+  SECTION("Purges string cache") {
+    memoryPool.freeString(memoryPool.allocFrozenString(10));
+    // REQUIRE(memoryPool.size() == 0);
+
+    memoryPool.clear();
+
+    CHECK(memoryPool.size() == 0);
+  }
+}

test/DynamicMemoryPool/no_memory.cpp

@@ -2,7 +2,8 @@
 // Copyright Benoit Blanchon 2014-2018
 // MIT License
 
-#include <ArduinoJson.h>
+#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
+#include <ArduinoJson/Memory/StringBuilder.hpp>
 #include <catch.hpp>
 
 using namespace ARDUINOJSON_NAMESPACE;
@@ -32,8 +33,8 @@ TEST_CASE("DynamicMemoryPool no memory") {
   //   REQUIRE(err != DeserializationError::Ok);
   // }
 
-  SECTION("startString()") {
-    StringBuilder str = _memoryPool.startString();
+  SECTION("StringBuilder returns null") {
+    StringBuilder str(&_memoryPool);
     str.append('!');
     REQUIRE(str.complete().isNull());
   }

test/DynamicMemoryPool/size.cpp

@@ -14,35 +14,43 @@ TEST_CASE("DynamicMemoryPool::size()") {
     REQUIRE(0 == memoryPool.size());
   }
 
-  SECTION("Increases after alloc()") {
-    memoryPool.alloc(1);
-    REQUIRE(1U <= memoryPool.size());
-    memoryPool.alloc(1);
-    REQUIRE(2U <= memoryPool.size());
+  SECTION("Increases after allocExpandableString()") {
+    StringSlot* a = memoryPool.allocExpandableString();
+    memoryPool.freezeString(a, 1);
+    REQUIRE(memoryPool.size() == JSON_STRING_SIZE(1));
+
+    StringSlot* b = memoryPool.allocExpandableString();
+    memoryPool.freezeString(b, 1);
+    REQUIRE(memoryPool.size() == 2 * JSON_STRING_SIZE(1));
   }
 
-  SECTION("Goes back to 0 after clear()") {
-    memoryPool.alloc(1);
-    memoryPool.clear();
+  SECTION("Increases after allocVariant()") {
+    memoryPool.allocVariant();
+    REQUIRE(sizeof(VariantSlot) == memoryPool.size());
+
+    memoryPool.allocVariant();
+    REQUIRE(2 * sizeof(VariantSlot) == memoryPool.size());
+  }
+
+  SECTION("Decreases after freeVariant()") {
+    VariantSlot* a = memoryPool.allocVariant();
+    VariantSlot* b = memoryPool.allocVariant();
+
+    memoryPool.freeVariant(b);
+    REQUIRE(sizeof(VariantSlot) == memoryPool.size());
+
+    memoryPool.freeVariant(a);
     REQUIRE(0 == memoryPool.size());
   }
 
-  SECTION("Increases after allocSlot()") {
-    memoryPool.allocSlot();
-    REQUIRE(sizeof(Slot) == memoryPool.size());
+  SECTION("Decreases after freeString()") {
+    StringSlot* a = memoryPool.allocFrozenString(5);
+    StringSlot* b = memoryPool.allocFrozenString(6);
 
-    memoryPool.allocSlot();
-    REQUIRE(2 * sizeof(Slot) == memoryPool.size());
-  }
+    memoryPool.freeString(b);
+    REQUIRE(memoryPool.size() == JSON_STRING_SIZE(5));
 
-  SECTION("Decreases after freeSlot()") {
-    Slot* s1 = memoryPool.allocSlot();
-    Slot* s2 = memoryPool.allocSlot();
-
-    memoryPool.freeSlot(s1);
-    REQUIRE(sizeof(Slot) == memoryPool.size());
-
-    memoryPool.freeSlot(s2);
-    REQUIRE(0 == memoryPool.size());
+    memoryPool.freeString(a);
+    REQUIRE(memoryPool.size() == 0);
   }
 }

test/DynamicMemoryPool/startString.cpp

@@ -1,46 +0,0 @@
-// ArduinoJson - arduinojson.org
-// Copyright Benoit Blanchon 2014-2018
-// MIT License
-
-#include <ArduinoJson/Memory/DynamicMemoryPool.hpp>
-#include <catch.hpp>
-
-using namespace ARDUINOJSON_NAMESPACE;
-
-TEST_CASE("DynamicMemoryPool::startString()") {
-  SECTION("WorksWhenBufferIsBigEnough") {
-    DynamicMemoryPool memoryPool(6);
-
-    StringBuilder str = memoryPool.startString();
-    str.append('h');
-    str.append('e');
-    str.append('l');
-    str.append('l');
-    str.append('o');
-
-    REQUIRE(str.complete().equals("hello"));
-  }
-
-  SECTION("GrowsWhenBufferIsTooSmall") {
-    DynamicMemoryPool memoryPool(5);
-
-    StringBuilder str = memoryPool.startString();
-    str.append('h');
-    str.append('e');
-    str.append('l');
-    str.append('l');
-    str.append('o');
-
-    REQUIRE(str.complete().equals("hello"));
-  }
-
-  SECTION("SizeIncreases") {
-    DynamicMemoryPool memoryPool(5);
-
-    StringBuilder str = memoryPool.startString();
-    str.append('h');
-    str.complete();
-
-    REQUIRE(2 == memoryPool.size());
-  }
-}

test/JsonArray/add.cpp

@@ -102,13 +102,13 @@ TEST_CASE("JsonArray::add()") {
 
   SECTION("should duplicate char*") {
     array.add(const_cast<char*>("world"));
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 6;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate std::string") {
     array.add(std::string("world"));
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 6;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
@@ -120,19 +120,19 @@ TEST_CASE("JsonArray::add()") {
 
   SECTION("should duplicate serialized(char*)") {
     array.add(serialized(const_cast<char*>("{}")));
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 2;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(2);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate serialized(std::string)") {
     array.add(serialized(std::string("{}")));
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 2;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(2);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate serialized(std::string)") {
     array.add(serialized(std::string("\0XX", 3)));
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 3;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(3);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 }

test/JsonArray/subscript.cpp

@@ -105,13 +105,13 @@ TEST_CASE("JsonArray::operator[]") {
 
   SECTION("should duplicate char*") {
     array[0] = const_cast<char*>("world");
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 6;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate std::string") {
     array[0] = std::string("world");
-    const size_t expectedSize = JSON_ARRAY_SIZE(1) + 6;
+    const size_t expectedSize = JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 

test/JsonDeserializer/deserializeJsonArrayStatic.cpp

@@ -16,7 +16,7 @@ TEST_CASE("deserialize JSON array with a StaticJsonDocument") {
   }
 
   SECTION("TooSmallBufferForArrayWithOneValue") {
-    StaticJsonDocument<JSON_ARRAY_SIZE(1) - 1> doc;
+    StaticJsonDocument<JSON_ARRAY_SIZE(0)> doc;
     char input[] = "[1]";
 
     DeserializationError err = deserializeJson(doc, input);
@@ -34,7 +34,7 @@ TEST_CASE("deserialize JSON array with a StaticJsonDocument") {
   }
 
   SECTION("TooSmallBufferForArrayWithNestedObject") {
-    StaticJsonDocument<JSON_ARRAY_SIZE(1) + JSON_OBJECT_SIZE(0) - 1> doc;
+    StaticJsonDocument<JSON_ARRAY_SIZE(0) + JSON_OBJECT_SIZE(0)> doc;
     char input[] = "[{}]";
 
     DeserializationError err = deserializeJson(doc, input);
@@ -56,7 +56,7 @@ TEST_CASE("deserialize JSON array with a StaticJsonDocument") {
 
     deserializeJson(doc, "  [ \"1234567\" ] ");
 
-    REQUIRE(JSON_ARRAY_SIZE(1) + sizeof("1234567") == doc.memoryUsage());
+    REQUIRE(JSON_ARRAY_SIZE(1) + JSON_STRING_SIZE(8) == doc.memoryUsage());
     // note: we use a string of 8 bytes to be sure that the StaticMemoryPool
     // will not insert bytes to enforce alignement
   }

test/JsonDeserializer/deserializeJsonObjectStatic.cpp

@@ -16,7 +16,7 @@ TEST_CASE("deserialize JSON object with StaticJsonDocument") {
   }
 
   SECTION("TooSmallBufferForObjectWithOneValue") {
-    StaticJsonDocument<JSON_OBJECT_SIZE(1) - 1> doc;
+    StaticJsonDocument<JSON_OBJECT_SIZE(0)> doc;
     char input[] = "{\"a\":1}";
 
     DeserializationError err = deserializeJson(doc, input);
@@ -34,7 +34,7 @@ TEST_CASE("deserialize JSON object with StaticJsonDocument") {
   }
 
   SECTION("TooSmallBufferForObjectWithNestedObject") {
-    StaticJsonDocument<JSON_OBJECT_SIZE(1) + JSON_ARRAY_SIZE(0) - 1> doc;
+    StaticJsonDocument<JSON_OBJECT_SIZE(0) + JSON_ARRAY_SIZE(0)> doc;
     char input[] = "{\"a\":[]}";
 
     DeserializationError err = deserializeJson(doc, input);

test/JsonDocument/DynamicJsonDocument.cpp

@@ -94,35 +94,36 @@ TEST_CASE("DynamicJsonDocument") {
   }
 
   SECTION("memoryUsage()") {
-    typedef ARDUINOJSON_NAMESPACE::Slot Slot;
-
     SECTION("Increases after adding value to array") {
       JsonArray arr = doc.to<JsonArray>();
 
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(0));
       arr.add(42);
-      REQUIRE(sizeof(Slot) == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(1));
       arr.add(43);
-      REQUIRE(2 * sizeof(Slot) == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(2));
     }
 
-    SECTION("Decreases after remove value from array") {
+    SECTION("Decreases after removing value from array") {
       JsonArray arr = doc.to<JsonArray>();
       arr.add(42);
       arr.add(43);
 
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(2));
       arr.remove(1);
-      REQUIRE(sizeof(Slot) == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(1));
       arr.remove(0);
-      REQUIRE(0 == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(0));
     }
 
     SECTION("Increases after adding value to object") {
       JsonObject obj = doc.to<JsonObject>();
 
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(0));
       obj["a"] = 1;
-      REQUIRE(sizeof(Slot) == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(1));
       obj["b"] = 2;
-      REQUIRE(2 * sizeof(Slot) == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
     }
 
     SECTION("Decreases after removing value from object") {
@@ -130,10 +131,11 @@ TEST_CASE("DynamicJsonDocument") {
       obj["a"] = 1;
       obj["b"] = 2;
 
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
       obj.remove("a");
-      REQUIRE(sizeof(Slot) == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(1));
       obj.remove("b");
-      REQUIRE(0 == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(0));
     }
 
     SECTION("Decreases after removing nested object from array") {
@@ -141,8 +143,9 @@ TEST_CASE("DynamicJsonDocument") {
       JsonObject obj = arr.createNestedObject();
       obj["hello"] = "world";
 
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(1) + JSON_OBJECT_SIZE(1));
       arr.remove(0);
-      REQUIRE(0 == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(0));
     }
 
     SECTION("Decreases after removing nested array from object") {
@@ -150,8 +153,9 @@ TEST_CASE("DynamicJsonDocument") {
       JsonArray arr = obj.createNestedArray("hello");
       arr.add("world");
 
+      REQUIRE(doc.memoryUsage() == JSON_ARRAY_SIZE(1) + JSON_OBJECT_SIZE(1));
       obj.remove("hello");
-      REQUIRE(0 == doc.memoryUsage());
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(0));
     }
   }
 }

test/JsonObject/remove.cpp

@@ -19,18 +19,47 @@ TEST_CASE("JsonObject::remove()") {
       obj.remove("a");
       serializeJson(obj, result);
       REQUIRE("{\"b\":1,\"c\":2}" == result);
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
     }
 
     SECTION("Remove middle") {
       obj.remove("b");
       serializeJson(obj, result);
       REQUIRE("{\"a\":0,\"c\":2}" == result);
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
     }
 
     SECTION("Remove last") {
       obj.remove("c");
       serializeJson(obj, result);
       REQUIRE("{\"a\":0,\"b\":1}" == result);
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
+    }
+
+    SECTION("Release value string memory") {
+      obj["c"] = std::string("Copy me!");
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(3) + JSON_STRING_SIZE(9));
+
+      obj.remove("c");
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
+    }
+
+    SECTION("Release key string memory") {
+      obj[std::string("Copy me!")] = 42;
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(4) + JSON_STRING_SIZE(9));
+
+      obj.remove("Copy me!");
+
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(3));
+    }
+
+    SECTION("Release raw string memory") {
+      obj["c"] = serialized(std::string("Copy me!"));
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(3) + JSON_STRING_SIZE(8));
+
+      obj.remove("c");
+
+      REQUIRE(doc.memoryUsage() == JSON_OBJECT_SIZE(2));
     }
   }
 

test/JsonObject/subscript.cpp

@@ -107,37 +107,37 @@ TEST_CASE("JsonObject::operator[]") {
 
   SECTION("should duplicate char* value") {
     obj["hello"] = const_cast<char*>("world");
-    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 6;
+    const size_t expectedSize = JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate char* key") {
     obj[const_cast<char*>("hello")] = "world";
-    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 6;
+    const size_t expectedSize = JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate char* key&value") {
     obj[const_cast<char*>("hello")] = const_cast<char*>("world");
-    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 12;
+    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 2 * JSON_STRING_SIZE(6);
     REQUIRE(expectedSize <= doc.memoryUsage());
   }
 
   SECTION("should duplicate std::string value") {
     obj["hello"] = std::string("world");
-    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 6;
+    const size_t expectedSize = JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate std::string key") {
     obj[std::string("hello")] = "world";
-    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 6;
+    const size_t expectedSize = JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(6);
     REQUIRE(expectedSize == doc.memoryUsage());
   }
 
   SECTION("should duplicate std::string key&value") {
     obj[std::string("hello")] = std::string("world");
-    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 12;
+    const size_t expectedSize = JSON_OBJECT_SIZE(1) + 2 * JSON_STRING_SIZE(6);
     REQUIRE(expectedSize <= doc.memoryUsage());
   }
 

test/JsonVariant/as.cpp

@@ -108,6 +108,16 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<std::string>() == std::string("hello"));
   }
 
+  SECTION("set(std::string(\"4.2\"))") {
+    variant.set(std::string("4.2"));
+
+    REQUIRE(variant.as<bool>() == true);
+    REQUIRE(variant.as<long>() == 4L);
+    REQUIRE(variant.as<double>() == 4.2);
+    REQUIRE(variant.as<char*>() == std::string("4.2"));
+    REQUIRE(variant.as<std::string>() == std::string("4.2"));
+  }
+
   SECTION("set(\"true\")") {
     variant.set("true");
 

test/JsonVariant/compare.cpp

@@ -216,7 +216,7 @@ TEST_CASE("JsonVariant comparisons") {
   JsonVariant variant2 = doc2.to<JsonVariant>();
   JsonVariant variant3 = doc3.to<JsonVariant>();
 
-  SECTION("IntegerInVariant") {
+  SECTION("Variants containing integers") {
     variant1.set(42);
     variant2.set(42);
     variant3.set(666);
@@ -228,7 +228,7 @@ TEST_CASE("JsonVariant comparisons") {
     REQUIRE_FALSE(variant1 == variant3);
   }
 
-  SECTION("StringInVariant") {
+  SECTION("Variants containing linked strings") {
     variant1.set("0hello" + 1);  // make sure they have
     variant2.set("1hello" + 1);  // different addresses
     variant3.set("world");
@@ -240,7 +240,19 @@ TEST_CASE("JsonVariant comparisons") {
     REQUIRE_FALSE(variant1 == variant3);
   }
 
-  SECTION("DoubleInVariant") {
+  SECTION("Variants containing owned strings") {
+    variant1.set(std::string("hello"));
+    variant2.set(std::string("hello"));
+    variant3.set(std::string("world"));
+
+    REQUIRE(variant1 == variant2);
+    REQUIRE_FALSE(variant1 != variant2);
+
+    REQUIRE(variant1 != variant3);
+    REQUIRE_FALSE(variant1 == variant3);
+  }
+
+  SECTION("Variants containing double") {
     variant1.set(42.0);
     variant2.set(42.0);
     variant3.set(666.0);

test/JsonVariant/copy.cpp

@@ -13,22 +13,24 @@ TEST_CASE("JsonVariant::set(JsonVariant)") {
 
   SECTION("stores JsonArray by copy") {
     JsonArray arr = doc2.to<JsonArray>();
-    arr.add(42);
+    JsonObject obj = arr.createNestedObject();
+    obj["hello"] = "world";
 
     var1.set(arr);
 
     arr[0] = 666;
-    REQUIRE(var1.as<std::string>() == "[42]");
+    REQUIRE(var1.as<std::string>() == "[{\"hello\":\"world\"}]");
   }
 
   SECTION("stores JsonObject by copy") {
     JsonObject obj = doc2.to<JsonObject>();
-    obj["value"] = 42;
+    JsonArray arr = obj.createNestedArray("value");
+    arr.add(42);
 
     var1.set(obj);
 
     obj["value"] = 666;
-    REQUIRE(var1.as<std::string>() == "{\"value\":42}");
+    REQUIRE(var1.as<std::string>() == "{\"value\":[42]}");
   }
 
   SECTION("stores const char* by reference") {
@@ -45,20 +47,20 @@ TEST_CASE("JsonVariant::set(JsonVariant)") {
     var1.set(str);
     var2.set(var1);
 
-    REQUIRE(doc1.memoryUsage() == 8);
-    REQUIRE(doc2.memoryUsage() == 8);
+    REQUIRE(doc1.memoryUsage() == JSON_STRING_SIZE(8));
+    REQUIRE(doc2.memoryUsage() == JSON_STRING_SIZE(8));
   }
 
   SECTION("stores std::string by copy") {
     var1.set(std::string("hello!!"));
     var2.set(var1);
 
-    REQUIRE(doc1.memoryUsage() == 8);
-    REQUIRE(doc2.memoryUsage() == 8);
+    REQUIRE(doc1.memoryUsage() == JSON_STRING_SIZE(8));
+    REQUIRE(doc2.memoryUsage() == JSON_STRING_SIZE(8));
   }
 
   SECTION("stores Serialized<const char*> by reference") {
-    var1.set(serialized("hello!!", 8));
+    var1.set(serialized("hello!!", JSON_STRING_SIZE(8)));
     var2.set(var1);
 
     REQUIRE(doc1.memoryUsage() == 0);
@@ -70,15 +72,15 @@ TEST_CASE("JsonVariant::set(JsonVariant)") {
     var1.set(serialized(str, 8));
     var2.set(var1);
 
-    REQUIRE(doc1.memoryUsage() == 8);
-    REQUIRE(doc2.memoryUsage() == 8);
+    REQUIRE(doc1.memoryUsage() == JSON_STRING_SIZE(8));
+    REQUIRE(doc2.memoryUsage() == JSON_STRING_SIZE(8));
   }
 
   SECTION("stores Serialized<std::string> by copy") {
     var1.set(serialized(std::string("hello!!!")));
     var2.set(var1);
 
-    REQUIRE(doc1.memoryUsage() == 8);
-    REQUIRE(doc2.memoryUsage() == 8);
+    REQUIRE(doc1.memoryUsage() == JSON_STRING_SIZE(8));
+    REQUIRE(doc2.memoryUsage() == JSON_STRING_SIZE(8));
   }
 }

test/MsgPackDeserializer/deserializeStaticVariant.cpp

@@ -5,17 +5,21 @@
 #include <ArduinoJson.h>
 #include <catch.hpp>
 
-static const size_t epsilon = sizeof(void*);
-
 template <size_t Capacity>
 static void check(const char* input, DeserializationError expected) {
   StaticJsonDocument<Capacity> variant;
 
   DeserializationError error = deserializeMsgPack(variant, input);
 
+  CAPTURE(input);
   REQUIRE(error == expected);
 }
 
+template <size_t Size>
+static void checkString(const char* input, DeserializationError expected) {
+  check<JSON_STRING_SIZE(Size)>(input, expected);
+}
+
 TEST_CASE("deserializeMsgPack(StaticJsonDocument&)") {
   SECTION("single values always fit") {
     check<0>("\xc0", DeserializationError::Ok);                  // nil
@@ -27,31 +31,39 @@ TEST_CASE("deserializeMsgPack(StaticJsonDocument&)") {
   }
 
   SECTION("fixstr") {
-    check<0>("\xA0", DeserializationError::Ok);
-    check<0>("\xA1H", DeserializationError::NoMemory);
-    check<4>("\xA1H", DeserializationError::Ok);
-    check<4>("\xA5Hello", DeserializationError::NoMemory);
+    checkString<8>("\xA0", DeserializationError::Ok);
+    checkString<8>("\xA7ZZZZZZZ", DeserializationError::Ok);
+    checkString<8>("\xA8ZZZZZZZZ", DeserializationError::NoMemory);
+    checkString<16>("\xAFZZZZZZZZZZZZZZZ", DeserializationError::Ok);
+    checkString<16>("\xB0ZZZZZZZZZZZZZZZZ", DeserializationError::NoMemory);
   }
 
   SECTION("str 8") {
-    check<0>("\xD9\x00", DeserializationError::Ok);
-    check<0>("\xD9\x01H", DeserializationError::NoMemory);
-    check<4>("\xD9\x01H", DeserializationError::Ok);
-    check<4>("\xD9\x05Hello", DeserializationError::NoMemory);
+    checkString<8>("\xD9\x00", DeserializationError::Ok);
+    checkString<8>("\xD9\x07ZZZZZZZ", DeserializationError::Ok);
+    checkString<8>("\xD9\x08ZZZZZZZZ", DeserializationError::NoMemory);
+    checkString<16>("\xD9\x0FZZZZZZZZZZZZZZZ", DeserializationError::Ok);
+    checkString<16>("\xD9\x10ZZZZZZZZZZZZZZZZ", DeserializationError::NoMemory);
   }
 
   SECTION("str 16") {
-    check<0>("\xDA\x00\x00", DeserializationError::Ok);
-    check<0>("\xDA\x00\x01H", DeserializationError::NoMemory);
-    check<4>("\xDA\x00\x01H", DeserializationError::Ok);
-    check<4>("\xDA\x00\x05Hello", DeserializationError::NoMemory);
+    checkString<8>("\xDA\x00\x00", DeserializationError::Ok);
+    checkString<8>("\xDA\x00\x07ZZZZZZZ", DeserializationError::Ok);
+    checkString<8>("\xDA\x00\x08ZZZZZZZZ", DeserializationError::NoMemory);
+    checkString<16>("\xDA\x00\x0FZZZZZZZZZZZZZZZ", DeserializationError::Ok);
+    checkString<16>("\xDA\x00\x10ZZZZZZZZZZZZZZZZ",
+                    DeserializationError::NoMemory);
   }
 
   SECTION("str 32") {
-    check<0>("\xDB\x00\x00\x00\x00", DeserializationError::Ok);
-    check<0>("\xDB\x00\x00\x00\x01H", DeserializationError::NoMemory);
-    check<4>("\xDB\x00\x00\x00\x01H", DeserializationError::Ok);
-    check<4>("\xDB\x00\x00\x00\x05Hello", DeserializationError::NoMemory);
+    checkString<8>("\xDB\x00\x00\x00\x00", DeserializationError::Ok);
+    checkString<8>("\xDB\x00\x00\x00\x07ZZZZZZZ", DeserializationError::Ok);
+    checkString<8>("\xDB\x00\x00\x00\x08ZZZZZZZZ",
+                   DeserializationError::NoMemory);
+    checkString<16>("\xDB\x00\x00\x00\x0FZZZZZZZZZZZZZZZ",
+                    DeserializationError::Ok);
+    checkString<16>("\xDB\x00\x00\x00\x10ZZZZZZZZZZZZZZZZ",
+                    DeserializationError::NoMemory);
   }
 
   SECTION("fixarray") {
@@ -89,14 +101,14 @@ TEST_CASE("deserializeMsgPack(StaticJsonDocument&)") {
     SECTION("{H:1}") {
       check<JSON_OBJECT_SIZE(0)>("\x81\xA1H\x01",
                                  DeserializationError::NoMemory);
-      check<JSON_OBJECT_SIZE(1) + epsilon>("\x81\xA1H\x01",
-                                           DeserializationError::Ok);
+      check<JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(2)>(
+          "\x81\xA1H\x01", DeserializationError::Ok);
     }
     SECTION("{H:1,W:2}") {
-      check<JSON_OBJECT_SIZE(1) + epsilon>("\x82\xA1H\x01\xA1W\x02",
-                                           DeserializationError::NoMemory);
-      check<JSON_OBJECT_SIZE(2) + 2 * epsilon>("\x82\xA1H\x01\xA1W\x02",
-                                               DeserializationError::Ok);
+      check<JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(2)>(
+          "\x82\xA1H\x01\xA1W\x02", DeserializationError::NoMemory);
+      check<JSON_OBJECT_SIZE(2) + 2 * JSON_STRING_SIZE(2)>(
+          "\x82\xA1H\x01\xA1W\x02", DeserializationError::Ok);
     }
   }
 
@@ -107,14 +119,14 @@ TEST_CASE("deserializeMsgPack(StaticJsonDocument&)") {
     SECTION("{H:1}") {
       check<JSON_OBJECT_SIZE(0)>("\xDE\x00\x01\xA1H\x01",
                                  DeserializationError::NoMemory);
-      check<JSON_OBJECT_SIZE(1) + epsilon>("\xDE\x00\x01\xA1H\x01",
-                                           DeserializationError::Ok);
+      check<JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(2)>(
+          "\xDE\x00\x01\xA1H\x01", DeserializationError::Ok);
     }
     SECTION("{H:1,W:2}") {
-      check<JSON_OBJECT_SIZE(1) + epsilon>("\xDE\x00\x02\xA1H\x01\xA1W\x02",
-                                           DeserializationError::NoMemory);
-      check<JSON_OBJECT_SIZE(2) + 2 * epsilon>("\xDE\x00\x02\xA1H\x01\xA1W\x02",
-                                               DeserializationError::Ok);
+      check<JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(2)>(
+          "\xDE\x00\x02\xA1H\x01\xA1W\x02", DeserializationError::NoMemory);
+      check<JSON_OBJECT_SIZE(2) + 2 * JSON_OBJECT_SIZE(1)>(
+          "\xDE\x00\x02\xA1H\x01\xA1W\x02", DeserializationError::Ok);
     }
   }
 
@@ -126,14 +138,14 @@ TEST_CASE("deserializeMsgPack(StaticJsonDocument&)") {
     SECTION("{H:1}") {
       check<JSON_OBJECT_SIZE(0)>("\xDF\x00\x00\x00\x01\xA1H\x01",
                                  DeserializationError::NoMemory);
-      check<JSON_OBJECT_SIZE(1) + epsilon>("\xDF\x00\x00\x00\x01\xA1H\x01",
-                                           DeserializationError::Ok);
+      check<JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(2)>(
+          "\xDF\x00\x00\x00\x01\xA1H\x01", DeserializationError::Ok);
     }
     SECTION("{H:1,W:2}") {
-      check<JSON_OBJECT_SIZE(1) + epsilon>(
+      check<JSON_OBJECT_SIZE(1) + JSON_STRING_SIZE(2)>(
           "\xDF\x00\x00\x00\x02\xA1H\x01\xA1W\x02",
           DeserializationError::NoMemory);
-      check<JSON_OBJECT_SIZE(2) + 2 * epsilon>(
+      check<JSON_OBJECT_SIZE(2) + 2 * JSON_OBJECT_SIZE(1)>(
           "\xDF\x00\x00\x00\x02\xA1H\x01\xA1W\x02", DeserializationError::Ok);
     }
   }

test/StaticMemoryPool/CMakeLists.txt

@@ -3,9 +3,11 @@
 # MIT License
 
 add_executable(StaticMemoryPoolTests 
-	alloc.cpp
+	allocVariant.cpp
+	allocString.cpp
+	clear.cpp
 	size.cpp
-	startString.cpp
+	StringBuilder.cpp
 )
 
 target_link_libraries(StaticMemoryPoolTests catch)

test/StaticMemoryPool/StringBuilder.cpp

@@ -0,0 +1,39 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/StaticMemoryPool.hpp>
+#include <ArduinoJson/Memory/StringBuilder.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("StringBuilder") {
+  SECTION("WorksWhenBufferIsBigEnough") {
+    StaticMemoryPool<JSON_STRING_SIZE(6)> memoryPool;
+
+    StringBuilder str(&memoryPool);
+    str.append("hello");
+
+    REQUIRE(str.complete().equals("hello"));
+  }
+
+  SECTION("ReturnsNullWhenTooSmall") {
+    StaticMemoryPool<1> memoryPool;
+
+    StringBuilder str(&memoryPool);
+    str.append("hello!!!");
+
+    REQUIRE(str.complete().isNull());
+  }
+
+  SECTION("Increases size of memory pool") {
+    StaticMemoryPool<JSON_STRING_SIZE(6)> memoryPool;
+
+    StringBuilder str(&memoryPool);
+    str.append('h');
+    str.complete();
+
+    REQUIRE(JSON_STRING_SIZE(2) == memoryPool.size());
+  }
+}

test/StaticMemoryPool/alloc.cpp

@@ -1,54 +0,0 @@
-// ArduinoJson - arduinojson.org
-// Copyright Benoit Blanchon 2014-2018
-// MIT License
-
-#include <ArduinoJson/Memory/StaticMemoryPool.hpp>
-#include <catch.hpp>
-
-using namespace ARDUINOJSON_NAMESPACE;
-
-static bool isAligned(void *ptr) {
-  const size_t mask = sizeof(void *) - 1;
-  size_t addr = reinterpret_cast<size_t>(ptr);
-  return (addr & mask) == 0;
-}
-
-TEST_CASE("StaticMemoryPool::alloc()") {
-  StaticMemoryPool<64> memoryPool;
-
-  SECTION("Returns different addresses") {
-    void *p1 = memoryPool.alloc(1);
-    void *p2 = memoryPool.alloc(1);
-    REQUIRE(p1 != p2);
-  }
-
-  SECTION("Returns non-NULL when using full capacity") {
-    void *p = memoryPool.alloc(64);
-    REQUIRE(0 != p);
-  }
-
-  SECTION("Returns NULL when full") {
-    memoryPool.alloc(64);
-    void *p = memoryPool.alloc(1);
-    REQUIRE(0 == p);
-  }
-
-  SECTION("Returns NULL when memoryPool is too small") {
-    void *p = memoryPool.alloc(65);
-    REQUIRE(0 == p);
-  }
-
-  SECTION("Returns aligned pointers") {
-    for (size_t size = 1; size <= sizeof(void *); size++) {
-      void *p = memoryPool.alloc(1);
-      REQUIRE(isAligned(p));
-    }
-  }
-
-  SECTION("Returns same address after clear()") {
-    void *p1 = memoryPool.alloc(1);
-    memoryPool.clear();
-    void *p2 = memoryPool.alloc(1);
-    REQUIRE(p1 == p2);
-  }
-}

test/StaticMemoryPool/allocString.cpp

@@ -0,0 +1,131 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/StaticMemoryPool.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("StaticMemoryPool::allocFrozenString()") {
+  const size_t poolCapacity = 64;
+  const size_t longestString = poolCapacity - sizeof(StringSlot);
+  StaticMemoryPool<poolCapacity> pool;
+
+  SECTION("Returns different addresses") {
+    StringSlot *a = pool.allocFrozenString(1);
+    StringSlot *b = pool.allocFrozenString(1);
+    REQUIRE(a != b);
+    REQUIRE(a->value != b->value);
+  }
+
+  SECTION("Returns a StringSlot of the right size") {
+    StringSlot *s = pool.allocFrozenString(12);
+    REQUIRE(s->size == 12);
+  }
+
+  SECTION("Returns NULL when full") {
+    pool.allocFrozenString(longestString);
+    void *p = pool.allocFrozenString(1);
+    REQUIRE(0 == p);
+  }
+
+  SECTION("Returns NULL when pool is too small") {
+    void *p = pool.allocFrozenString(longestString + 1);
+    REQUIRE(0 == p);
+  }
+
+  SECTION("Returns aligned pointers") {
+    REQUIRE(isAligned(pool.allocFrozenString(1)));
+    REQUIRE(isAligned(pool.allocFrozenString(1)));
+  }
+
+  SECTION("Returns same address after clear()") {
+    StringSlot *a = pool.allocFrozenString(1);
+    pool.clear();
+    StringSlot *b = pool.allocFrozenString(1);
+
+    REQUIRE(a == b);
+    REQUIRE(a->value == b->value);
+  }
+
+  SECTION("Returns same address after freeString()") {
+    StringSlot *a = pool.allocFrozenString(1);
+    pool.freeString(a);
+    StringSlot *b = pool.allocFrozenString(1);
+
+    REQUIRE(a == b);
+    REQUIRE(a->value == b->value);
+  }
+
+  SECTION("Can use full capacity when fresh") {
+    StringSlot *a = pool.allocFrozenString(longestString);
+
+    REQUIRE(a != 0);
+  }
+
+  SECTION("Can use full capacity after clear") {
+    pool.allocFrozenString(longestString);
+    pool.clear();
+
+    StringSlot *a = pool.allocFrozenString(longestString);
+
+    REQUIRE(a != 0);
+  }
+}
+
+TEST_CASE("StaticMemoryPool::freeString()") {
+  const size_t poolCapacity = 512;
+  const size_t longestString = poolCapacity - sizeof(StringSlot);
+  StaticMemoryPool<poolCapacity> pool;
+
+  static const size_t testStringSize =
+      (poolCapacity - sizeof(StringSlot) * 4 - sizeof(VariantSlot) * 4) / 4;
+
+  SECTION("Restores full capacity") {
+    StringSlot *strings[4];
+    VariantSlot *variants[4];
+
+    for (int i = 0; i < 4; i++) {
+      strings[i] = pool.allocFrozenString(testStringSize);
+      REQUIRE(strings[i] != 0);
+      variants[i] = pool.allocVariant();
+      REQUIRE(variants[i] != 0);
+    }
+
+    // In random order
+    pool.freeString(strings[2]);
+    pool.freeVariant(variants[3]);
+    pool.freeVariant(variants[0]);
+    pool.freeString(strings[0]);
+    pool.freeVariant(variants[1]);
+    pool.freeString(strings[1]);
+    pool.freeVariant(variants[2]);
+    pool.freeString(strings[3]);
+
+    StringSlot *b = pool.allocFrozenString(longestString);
+
+    REQUIRE(b != 0);
+    REQUIRE(b->size == longestString);
+  }
+
+  SECTION("Move strings") {
+    StringSlot *a = pool.allocFrozenString(6);
+    strcpy(a->value, "hello");
+
+    StringSlot *b = pool.allocFrozenString(7);
+    strcpy(b->value, "world!");
+    pool.freeString(a);
+
+    REQUIRE(b->size == 7);
+    REQUIRE(b->value == std::string("world!"));
+    REQUIRE(a->value == b->value);
+  }
+
+  SECTION("Accepts non-frozen string") {
+    StringSlot *a = pool.allocExpandableString();
+    pool.freeString(a);
+
+    REQUIRE(pool.size() == 0);
+  }
+}

test/StaticMemoryPool/allocVariant.cpp

@@ -0,0 +1,38 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/StaticMemoryPool.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+TEST_CASE("StaticMemoryPool::allocVariant()") {
+  StaticMemoryPool<128> memoryPool;
+
+  SECTION("Returns different pointer") {
+    VariantSlot* s1 = memoryPool.allocVariant();
+    REQUIRE(s1 != 0);
+    VariantSlot* s2 = memoryPool.allocVariant();
+    REQUIRE(s2 != 0);
+
+    REQUIRE(s1 != s2);
+  }
+
+  SECTION("Returns same pointer after freeSlot()") {
+    VariantSlot* s1 = memoryPool.allocVariant();
+    memoryPool.freeVariant(s1);
+    VariantSlot* s2 = memoryPool.allocVariant();
+
+    REQUIRE(s1 == s2);
+  }
+
+  SECTION("Returns aligned pointers") {
+    // make room for two
+    // pass an uneven capacity
+    StaticMemoryPool<2 * sizeof(VariantSlot) + 1> pool;
+
+    REQUIRE(isAligned(pool.allocVariant()));
+    REQUIRE(isAligned(pool.allocVariant()));
+  }
+}

test/StaticMemoryPool/clear.cpp

@@ -0,0 +1,81 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson/Memory/StaticMemoryPool.hpp>
+#include <catch.hpp>
+
+using namespace ARDUINOJSON_NAMESPACE;
+
+static const size_t poolCapacity = 512;
+
+TEST_CASE("StaticMemoryPool::clear()") {
+  StaticMemoryPool<poolCapacity> memoryPool;
+
+  SECTION("Discards allocated variants") {
+    memoryPool.allocVariant();
+
+    memoryPool.clear();
+    REQUIRE(memoryPool.size() == 0);
+  }
+
+  SECTION("Discards allocated strings") {
+    memoryPool.allocFrozenString(10);
+
+    memoryPool.clear();
+
+    REQUIRE(memoryPool.size() == 0);
+  }
+
+  SECTION("Purges variant cache") {
+    VariantSlot* a = memoryPool.allocVariant();
+    REQUIRE(a != 0);
+    VariantSlot* b = memoryPool.allocVariant();
+    REQUIRE(b != 0);
+
+    // place slot a in the pool of free slots
+    memoryPool.freeVariant(a);
+    memoryPool.clear();
+
+    REQUIRE(memoryPool.size() == 0);
+  }
+
+  SECTION("Purges string cache") {
+    StringSlot* a = memoryPool.allocFrozenString(10);
+    REQUIRE(a != 0);
+    StringSlot* b = memoryPool.allocFrozenString(10);
+    REQUIRE(b != 0);
+
+    // place slot a in the pool of free slots
+    memoryPool.freeString(a);
+    memoryPool.clear();
+
+    REQUIRE(memoryPool.size() == 0);
+  }
+
+  SECTION("Purges list of string") {
+    StringSlot* a = memoryPool.allocFrozenString(6);
+    REQUIRE(a != 0);
+    strcpy(a->value, "hello");
+
+    StringSlot* b = memoryPool.allocFrozenString(6);
+    REQUIRE(b != 0);
+    strcpy(b->value, "world");
+
+    memoryPool.clear();  // ACT!
+
+    StringSlot* c = memoryPool.allocFrozenString(2);
+    REQUIRE(c != 0);
+    strcpy(c->value, "H");
+
+    StringSlot* d = memoryPool.allocFrozenString(2);
+    REQUIRE(d != 0);
+    strcpy(d->value, "W");
+
+    // if the memory pool keeps pointer to the old strings
+    // it will try to compact the strings
+    memoryPool.freeString(c);
+
+    REQUIRE(d->value == std::string("W"));
+  }
+}

test/StaticMemoryPool/size.cpp

@@ -8,37 +8,72 @@
 using namespace ARDUINOJSON_NAMESPACE;
 
 TEST_CASE("StaticMemoryPool::size()") {
-  StaticMemoryPool<64> memoryPool;
-
   SECTION("Capacity equals template parameter") {
-    REQUIRE(64 == memoryPool.capacity());
+    const size_t capacity = 64;
+    StaticMemoryPool<capacity> memoryPool;
+    REQUIRE(capacity == memoryPool.capacity());
   }
 
   SECTION("Initial size is 0") {
+    StaticMemoryPool<32> memoryPool;
     REQUIRE(0 == memoryPool.size());
   }
 
-  SECTION("Increases after alloc()") {
-    memoryPool.alloc(1);
-    REQUIRE(1U <= memoryPool.size());
-    memoryPool.alloc(1);
-    REQUIRE(2U <= memoryPool.size());
+  SECTION("Increases after allocFrozenString()") {
+    StaticMemoryPool<128> memoryPool;
+    memoryPool.allocFrozenString(0);
+    REQUIRE(memoryPool.size() == JSON_STRING_SIZE(0));
+    memoryPool.allocFrozenString(0);
+    REQUIRE(memoryPool.size() == 2 * JSON_STRING_SIZE(0));
   }
 
-  SECTION("Doesn't grow when memoryPool is full") {
-    memoryPool.alloc(64);
-    memoryPool.alloc(1);
-    REQUIRE(64 == memoryPool.size());
+  SECTION("Decreases after freeVariant()") {
+    StaticMemoryPool<128> memoryPool;
+    VariantSlot* a = memoryPool.allocVariant();
+    VariantSlot* b = memoryPool.allocVariant();
+
+    memoryPool.freeVariant(b);
+    REQUIRE(memoryPool.size() == sizeof(VariantSlot));
+    memoryPool.freeVariant(a);
+    REQUIRE(memoryPool.size() == 0);
   }
 
-  SECTION("Does't grow when memoryPool is too small for alloc") {
-    memoryPool.alloc(65);
-    REQUIRE(0 == memoryPool.size());
+  SECTION("Decreases after calling freeString() in order") {
+    StaticMemoryPool<128> memoryPool;
+    StringSlot* a = memoryPool.allocFrozenString(5);
+    REQUIRE(a != 0);
+    StringSlot* b = memoryPool.allocFrozenString(6);
+    REQUIRE(b != 0);
+
+    memoryPool.freeString(b);
+    REQUIRE(memoryPool.size() == JSON_STRING_SIZE(5));
+    memoryPool.freeString(a);
+    REQUIRE(memoryPool.size() == 0);
   }
 
-  SECTION("Goes back to zero after clear()") {
-    memoryPool.alloc(1);
-    memoryPool.clear();
-    REQUIRE(0 == memoryPool.size());
+  SECTION("Decreases after calling freeString() in reverse order") {
+    StaticMemoryPool<128> memoryPool;
+    StringSlot* a = memoryPool.allocFrozenString(5);
+    REQUIRE(a != 0);
+    StringSlot* b = memoryPool.allocFrozenString(6);
+    REQUIRE(b != 0);
+
+    memoryPool.freeString(a);
+    REQUIRE(memoryPool.size() == JSON_STRING_SIZE(6));
+    memoryPool.freeString(b);
+    REQUIRE(memoryPool.size() == 0);
+  }
+
+  SECTION("Doesn't grow when memory pool is full") {
+    const size_t variantCount = 4;
+    const size_t capacity = variantCount * sizeof(VariantSlot);
+    StaticMemoryPool<capacity> memoryPool;
+
+    for (size_t i = 0; i < variantCount; i++) memoryPool.allocVariant();
+    REQUIRE(capacity == memoryPool.size());
+
+    memoryPool.allocVariant();
+
+    REQUIRE(capacity == memoryPool.size());
   }
 }

test/StaticMemoryPool/startString.cpp

@@ -1,46 +0,0 @@
-// ArduinoJson - arduinojson.org
-// Copyright Benoit Blanchon 2014-2018
-// MIT License
-
-#include <ArduinoJson.h>
-#include <catch.hpp>
-
-using namespace ARDUINOJSON_NAMESPACE;
-
-TEST_CASE("StaticMemoryPool::startString()") {
-  SECTION("WorksWhenBufferIsBigEnough") {
-    StaticMemoryPool<6> memoryPool;
-
-    StringBuilder str = memoryPool.startString();
-    str.append('h');
-    str.append('e');
-    str.append('l');
-    str.append('l');
-    str.append('o');
-
-    REQUIRE(str.complete().equals("hello"));
-  }
-
-  SECTION("ReturnsNullWhenTooSmall") {
-    StaticMemoryPool<5> memoryPool;
-
-    StringBuilder str = memoryPool.startString();
-    str.append('h');
-    str.append('e');
-    str.append('l');
-    str.append('l');
-    str.append('o');
-
-    REQUIRE(str.complete().isNull());
-  }
-
-  SECTION("SizeIncreases") {
-    StaticMemoryPool<5> memoryPool;
-
-    StringBuilder str = memoryPool.startString();
-    str.append('h');
-    str.complete();
-
-    REQUIRE(2 == memoryPool.size());
-  }
-}