Remove SlotData

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

.github/workflows/ci.yml

@@ -93,44 +93,40 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - clang: "3.9"
-            runner: ubuntu-20.04
-            archive: bionic
-          - clang: "4.0"
-            runner: ubuntu-20.04
-            archive: bionic
-          - clang: "5.0"
-            runner: ubuntu-20.04
-            archive: bionic
-          - clang: "6.0"
-            runner: ubuntu-20.04
-            archive: bionic
           - clang: "7"
-            runner: ubuntu-20.04
+            runner: ubuntu-22.04
+            archive: focal
           - clang: "8"
             cxxflags: -fsanitize=leak -fno-sanitize-recover=all
-            runner: ubuntu-20.04
+            runner: ubuntu-22.04
+            archive: focal
           - clang: "9"
             cxxflags: -fsanitize=undefined -fno-sanitize-recover=all
-            runner: ubuntu-20.04
+            runner: ubuntu-22.04
+            archive: focal
           - clang: "10"
             cxxflags: -fsanitize=address -fno-sanitize-recover=all
-            runner: ubuntu-20.04
+            runner: ubuntu-22.04
+            archive: focal
           - clang: "11"
             runner: ubuntu-22.04
           - clang: "12"
             runner: ubuntu-22.04
           - clang: "13"
             runner: ubuntu-22.04
-          - clang: "14"
-            runner: ubuntu-22.04
-          - clang: "15"
-            runner: ubuntu-22.04
-    runs-on: ${{ matrix.runner }}
+          - clang: 14
+          - clang: 15
+          - clang: 16
+          - clang: 17
+          - clang: 18
+          - clang: 19
+    runs-on: ${{ matrix.runner || 'ubuntu-latest' }}
     steps:
       - name: Add archive repositories
         if: matrix.archive
         run: |
+          sudo gpg --keyserver keyserver.ubuntu.com --recv-keys 3B4FE6ACC0B21F32
+          sudo gpg --export 3B4FE6ACC0B21F32 | sudo tee /etc/apt/trusted.gpg.d/ubuntu-keyring.gpg > /dev/null
           sudo add-apt-repository -yn 'deb http://archive.ubuntu.com/ubuntu/ ${{ matrix.archive }} main'
           sudo add-apt-repository -yn 'deb http://archive.ubuntu.com/ubuntu/ ${{ matrix.archive }} universe'
       - name: Install Clang ${{ matrix.clang }}
@@ -138,10 +134,9 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y clang-${{ matrix.clang }}
       - name: Install libc++ ${{ matrix.clang }}
-        if: matrix.clang >= 11
         run: sudo apt-get install -y libc++-${{ matrix.clang }}-dev libc++abi-${{ matrix.clang }}-dev
       - name: Install libunwind ${{ matrix.clang }}
-        if: matrix.clang == 12  # dependency is missing in Ubuntu 22.04
+        if: matrix.clang == 12 # dependency is missing in Ubuntu 22.04
         run: sudo apt-get install -y libunwind-${{ matrix.clang }}-dev
       - name: Checkout
         uses: actions/checkout@v4
@@ -163,7 +158,7 @@ jobs:
   conf_test:
     name: Test configuration on Linux
     needs: [gcc, clang]
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Install
         run: |
@@ -257,7 +252,7 @@ jobs:
             board: arduino:avr:uno
           - core: arduino:samd
             board: arduino:samd:mkr1000
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -412,7 +407,7 @@ jobs:
   arm:
     name: GCC for ARM processor
     needs: gcc
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Install
         run: |
@@ -431,7 +426,7 @@ jobs:
   coverage:
     needs: gcc
     name: Coverage
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Install
         run: sudo apt-get install -y lcov ninja-build
@@ -463,7 +458,7 @@ jobs:
   valgrind:
     needs: gcc
     name: Valgrind
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Install
         run: |
@@ -485,24 +480,24 @@ jobs:
   clang-tidy:
     needs: clang
     name: Clang-Tidy
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       - name: Install
-        run: sudo apt-get install -y clang-tidy cmake ninja-build
+        run: sudo apt-get install -y clang-tidy libc++-dev libc++abi-dev
       - name: Checkout
         uses: actions/checkout@v4
       - name: Configure
-        run: cmake -G Ninja -DCMAKE_CXX_CLANG_TIDY="clang-tidy-10;--warnings-as-errors=*" -DCMAKE_BUILD_TYPE=Debug .
+        run: cmake -G Ninja -DCMAKE_CXX_CLANG_TIDY="clang-tidy;--warnings-as-errors=*" -DCMAKE_BUILD_TYPE=Debug .
         env:
-          CC: clang-10
-          CXX: clang++-10
+          CC: clang
+          CXX: clang++
       - name: Check
         run: cmake --build . -- -k 0
 
   amalgamate:
     needs: gcc
     name: Amalgamate ArduinoJson.h
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -578,7 +573,7 @@ jobs:
 
   codeql:
     name: CodeQL
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     needs: gcc
 
     permissions:
@@ -587,20 +582,20 @@ jobs:
       security-events: write
 
     steps:
-    - name: Checkout repository
-      uses: actions/checkout@v4
+      - name: Checkout repository
+        uses: actions/checkout@v4
 
-    - name: Initialize CodeQL
-      uses: github/codeql-action/init@v3
-      with:
-        languages: cpp
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@v3
+        with:
+          languages: cpp
 
-    - name: Build
-      run: |
-        cmake -DCMAKE_BUILD_TYPE=Debug .
-        cmake --build .
+      - name: Build
+        run: |
+          cmake -DCMAKE_BUILD_TYPE=Debug .
+          cmake --build .
 
-    - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@v3
-      with:
-        category: "/language:cpp"
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@v3
+        with:
+          category: "/language:cpp"

.github/workflows/release.yml

@@ -8,7 +8,7 @@ on:
 jobs:
   release:
     name: Create release
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
       - name: Set variables
         id: init

CHANGELOG.md

@@ -4,8 +4,6 @@ ArduinoJson: change log
 HEAD
 ----
 
-* Fix conversion from static string to number
-* Slightly reduce code size
 * Optimize storage of static strings
 
 > ### BREAKING CHANGES
@@ -40,6 +38,23 @@ HEAD
 > doc["key"] = str; // same as previous line for supported string classes (`String`, `std::string`, etc.)
 > ```
 
+v7.4.1 (2025-04-11)
+------
+
+* Fix crash with tiny Flash strings (issue #2170)
+
+v7.4.0 (2025-04-09)
+------
+
+* Optimize storage of tiny strings (up to 3 characters)
+* Fix support for `const char[]` (issue #2166)
+
+v7.3.1 (2025-02-27)
+------
+
+* Fix conversion from static string to number
+* Slightly reduce code size
+
 v7.3.0 (2024-12-29)
 ------
 

CMakeLists.txt

@@ -10,7 +10,7 @@ if(ESP_PLATFORM)
 	return()
 endif()
 
-project(ArduinoJson VERSION 7.3.0)
+project(ArduinoJson VERSION 7.4.1)
 
 if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
 	include(CTest)

README.md

@@ -80,7 +80,7 @@ ArduinoJson is a C++ JSON library for Arduino and IoT (Internet Of Things).
     * Continuously tested on
         * [Visual Studio 2017, 2019, 2022](https://ci.appveyor.com/project/bblanchon/arduinojson/branch/7.x)
         * [GCC 4.8, 5, 6, 7, 8, 9, 10, 11, 12](https://github.com/bblanchon/ArduinoJson/actions?query=workflow%3A%22Continuous+Integration%22)
-        * [Clang 3.9, 4.0, 5.0, 6.0, 7, 8, 9, 10, 11, 12, 13, 14, 15](https://github.com/bblanchon/ArduinoJson/actions?query=workflow%3A%22Continuous+Integration%22)
+        * [Clang 7 to 19](https://github.com/bblanchon/ArduinoJson/actions?query=workflow%3A%22Continuous+Integration%22)
     * [Continuously fuzzed with Google OSS Fuzz](https://bugs.chromium.org/p/oss-fuzz/issues/list?sort=-opened&can=1&q=proj:arduinojson)
     * Passes all default checks of [clang-tidy](https://releases.llvm.org/10.0.0/tools/clang/tools/extra/docs/clang-tidy/)
 * Well documented

appveyor.yml

@@ -1,4 +1,4 @@
-version: 7.3.0.{build}
+version: 7.4.1.{build}
 environment:
   matrix:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2022

extras/conf_test/avr.cpp

@@ -12,7 +12,7 @@ static_assert(ARDUINOJSON_LITTLE_ENDIAN == 1, "ARDUINOJSON_LITTLE_ENDIAN");
 
 static_assert(ARDUINOJSON_USE_DOUBLE == 0, "ARDUINOJSON_USE_DOUBLE");
 
-static_assert(ArduinoJson::detail::ResourceManager::slotSize == 6, "slot size");
+static_assert(sizeof(ArduinoJson::detail::VariantData) == 6, "slot size");
 
 void setup() {}
 void loop() {}

extras/conf_test/esp8266.cpp

@@ -10,7 +10,7 @@ static_assert(ARDUINOJSON_LITTLE_ENDIAN == 1, "ARDUINOJSON_LITTLE_ENDIAN");
 
 static_assert(ARDUINOJSON_USE_DOUBLE == 1, "ARDUINOJSON_USE_DOUBLE");
 
-static_assert(ArduinoJson::detail::ResourceManager::slotSize == 8, "slot size");
+static_assert(sizeof(VariantData) == 8, "slot size");
 
 void setup() {}
 void loop() {}

extras/conf_test/x64.cpp

@@ -10,7 +10,6 @@ static_assert(ARDUINOJSON_LITTLE_ENDIAN == 1, "ARDUINOJSON_LITTLE_ENDIAN");
 
 static_assert(ARDUINOJSON_USE_DOUBLE == 1, "ARDUINOJSON_USE_DOUBLE");
 
-static_assert(ArduinoJson::detail::ResourceManager::slotSize == 16,
-              "slot size");
+static_assert(sizeof(ArduinoJson::detail::VariantData) == 16, "slot size");
 
 int main() {}

extras/conf_test/x86.cpp

@@ -10,6 +10,6 @@ static_assert(ARDUINOJSON_LITTLE_ENDIAN == 1, "ARDUINOJSON_LITTLE_ENDIAN");
 
 static_assert(ARDUINOJSON_USE_DOUBLE == 1, "ARDUINOJSON_USE_DOUBLE");
 
-static_assert(ArduinoJson::detail::ResourceManager::slotSize == 8, "slot size");
+static_assert(sizeof(ArduinoJson::detail::VariantData) == 8, "slot size");
 
 int main() {}

extras/tests/Deprecated/BasicJsonDocument.cpp

@@ -46,7 +46,7 @@ TEST_CASE("BasicJsonDocument") {
     deserializeJson(doc, "{\"hello\":\"world\"}");
     REQUIRE(doc.as<std::string>() == "{\"hello\":\"world\"}");
     doc.clear();
-    REQUIRE(allocatorLog == "ARAARDDD");
+    REQUIRE(allocatorLog == "AARARDDD");
   }
 
   SECTION("copy") {

extras/tests/Helpers/Allocators.hpp

@@ -269,10 +269,10 @@ inline size_t sizeofPoolList(size_t n = ARDUINOJSON_INITIAL_POOL_COUNT) {
   return sizeof(MemoryPool<VariantData>) * n;
 }
 
+template <typename T = ArduinoJson::detail::VariantData>
 inline size_t sizeofPool(
     ArduinoJson::detail::SlotCount n = ARDUINOJSON_POOL_CAPACITY) {
-  using namespace ArduinoJson::detail;
-  return MemoryPool<VariantData>::slotsToBytes(n);
+  return ArduinoJson::detail::MemoryPool<T>::slotsToBytes(n);
 }
 
 inline size_t sizeofStaticStringPool(

extras/tests/JsonArray/add.cpp

@@ -8,7 +8,7 @@
 #include "Allocators.hpp"
 #include "Literals.hpp"
 
-using ArduinoJson::detail::sizeofArray;
+using namespace ArduinoJson::detail;
 
 TEST_CASE("JsonArray::add(T)") {
   SpyingAllocator spy;
@@ -33,7 +33,8 @@ TEST_CASE("JsonArray::add(T)") {
     REQUIRE(array[0].is<double>());
     REQUIRE_FALSE(array[0].is<bool>());
     REQUIRE(spy.log() == AllocatorLog{
-                             Allocate(sizeofPool()),
+                             Allocate(sizeofPool<VariantData>()),
+                             Allocate(sizeofPool<EightByteValue>()),
                          });
   }
 

extras/tests/JsonDeserializer/array.cpp

@@ -7,7 +7,7 @@
 
 #include "Allocators.hpp"
 
-using ArduinoJson::detail::sizeofArray;
+using namespace ArduinoJson::detail;
 
 TEST_CASE("deserialize JSON array") {
   SpyingAllocator spy;
@@ -92,8 +92,12 @@ TEST_CASE("deserialize JSON array") {
       REQUIRE(arr[0].as<double>() == Approx(4.2123456));
       REQUIRE(arr[1] == -7E89);
       REQUIRE(spy.log() == AllocatorLog{
-                               Allocate(sizeofPool()),
-                               Reallocate(sizeofPool(), sizeofPool(4)),
+                               Allocate(sizeofPool<VariantData>()),
+                               Allocate(sizeofPool<EightByteValue>()),
+                               Reallocate(sizeofPool<VariantData>(),
+                                          sizeofPool<VariantData>(2)),
+                               Reallocate(sizeofPool<EightByteValue>(),
+                                          sizeofPool<EightByteValue>(2)),
                            });
     }
 

extras/tests/JsonDeserializer/errors.cpp

@@ -121,7 +121,7 @@ TEST_CASE("deserializeJson() returns NoMemory if string length overflows") {
   }
 }
 
-TEST_CASE("deserializeJson() returns NoMemory if extension allocation fails") {
+TEST_CASE("deserializeJson() returns NoMemory if 8-bit slot allocation fails") {
   JsonDocument doc(FailingAllocator::instance());
 
   SECTION("uint32_t should pass") {

extras/tests/JsonDeserializer/input_types.cpp

@@ -26,8 +26,8 @@ TEST_CASE("deserializeJson(char*)") {
   REQUIRE(spy.log() ==
           AllocatorLog{
               Allocate(sizeofStringBuffer()),
-              Reallocate(sizeofStringBuffer(), sizeofString("hello")),
               Allocate(sizeofPool()),
+              Reallocate(sizeofStringBuffer(), sizeofString("hello")),
               Allocate(sizeofStringBuffer()),
               Reallocate(sizeofStringBuffer(), sizeofString("world")),
               Reallocate(sizeofPool(), sizeofObject(1)),

extras/tests/JsonDeserializer/object.cpp

@@ -292,22 +292,23 @@ TEST_CASE("deserialize JSON object") {
     }
 
     SECTION("Repeated key") {
-      DeserializationError err = deserializeJson(doc, "{a:{b:{c:1}},a:2}");
+      DeserializationError err =
+          deserializeJson(doc, "{alfa:{bravo:{charlie:1}},alfa:2}");
 
       REQUIRE(err == DeserializationError::Ok);
-      REQUIRE(doc.as<std::string>() == "{\"a\":2}");
+      REQUIRE(doc.as<std::string>() == "{\"alfa\":2}");
       REQUIRE(spy.log() ==
               AllocatorLog{
                   Allocate(sizeofStringBuffer()),
-                  Reallocate(sizeofStringBuffer(), sizeofString("a")),
                   Allocate(sizeofPool()),
+                  Reallocate(sizeofStringBuffer(), sizeofString("alfa")),
                   Allocate(sizeofStringBuffer()),
-                  Reallocate(sizeofStringBuffer(), sizeofString("b")),
+                  Reallocate(sizeofStringBuffer(), sizeofString("bravo")),
                   Allocate(sizeofStringBuffer()),
-                  Reallocate(sizeofStringBuffer(), sizeofString("c")),
+                  Reallocate(sizeofStringBuffer(), sizeofString("charlie")),
                   Allocate(sizeofStringBuffer()),
-                  Deallocate(sizeofString("b")),
-                  Deallocate(sizeofString("c")),
+                  Deallocate(sizeofString("bravo")),
+                  Deallocate(sizeofString("charlie")),
                   Deallocate(sizeofStringBuffer()),
                   Reallocate(sizeofPool(), sizeofObject(2) + sizeofObject(1)),
               });
@@ -378,7 +379,7 @@ TEST_CASE("deserialize JSON object under memory constraints") {
   }
 
   SECTION("pool allocation fails") {
-    timebomb.setCountdown(2);
+    timebomb.setCountdown(1);
     char input[] = "{\"a\":1}";
 
     DeserializationError err = deserializeJson(doc, input);
@@ -389,11 +390,11 @@ TEST_CASE("deserialize JSON object under memory constraints") {
 
   SECTION("string allocation fails") {
     timebomb.setCountdown(3);
-    char input[] = "{\"a\":\"b\"}";
+    char input[] = "{\"alfa\":\"bravo\"}";
 
     DeserializationError err = deserializeJson(doc, input);
 
     REQUIRE(err == DeserializationError::NoMemory);
-    REQUIRE(doc.as<std::string>() == "{\"a\":null}");
+    REQUIRE(doc.as<std::string>() == "{\"alfa\":null}");
   }
 }

extras/tests/JsonDeserializer/string.cpp

@@ -133,8 +133,8 @@ TEST_CASE("Allocation of the key fails") {
     REQUIRE(spy.log() ==
             AllocatorLog{
                 Allocate(sizeofStringBuffer()),
-                Reallocate(sizeofStringBuffer(), sizeofString("hello")),
                 Allocate(sizeofPool()),
+                Reallocate(sizeofStringBuffer(), sizeofString("hello")),
                 AllocateFail(sizeofStringBuffer()),
                 ReallocateFail(sizeofPool(), sizeofObject(1)),
             });
@@ -155,8 +155,8 @@ TEST_CASE("Allocation of the key fails") {
     REQUIRE(spy.log() ==
             AllocatorLog{
                 Allocate(sizeofStringBuffer()),
-                Reallocate(sizeofStringBuffer(), sizeofString("hello")),
                 Allocate(sizeofPool()),
+                Reallocate(sizeofStringBuffer(), sizeofString("hello")),
                 AllocateFail(sizeofStringBuffer()),
                 ReallocateFail(sizeofPool(), sizeofObject(1)),
             });

extras/tests/JsonDocument/assignment.cpp

@@ -69,6 +69,8 @@ TEST_CASE("JsonDocument assignment") {
       doc2 = std::move(doc1);
 
       REQUIRE(doc2.as<std::string>() == "{\"hello\":\"world\"}");
+
+      // NOLINTNEXTLINE(clang-analyzer-cplusplus.Move)
       REQUIRE(doc1.as<std::string>() == "null");
     }
     REQUIRE(spyingAllocator.log() == AllocatorLog{

extras/tests/JsonDocument/constructor.cpp

@@ -44,6 +44,8 @@ TEST_CASE("JsonDocument constructor") {
       JsonDocument doc2(std::move(doc1));
 
       REQUIRE(doc2.as<std::string>() == "The size of this string is 32!!");
+
+      // NOLINTNEXTLINE(clang-analyzer-cplusplus.Move)
       REQUIRE(doc1.as<std::string>() == "null");
     }
     REQUIRE(spyingAllocator.log() == AllocatorLog{

extras/tests/JsonDocument/set.cpp

@@ -89,6 +89,13 @@ TEST_CASE("JsonDocument::set()") {
                          });
   }
 
+  SECTION("Flash tiny string") {  // issue #2170
+    doc.set(F("abc"));
+
+    REQUIRE(doc.as<const char*>() == "abc"_s);
+    REQUIRE(spy.log() == AllocatorLog{});
+  }
+
 #ifdef HAS_VARIABLE_LENGTH_ARRAY
   SECTION("VLA") {
     size_t i = 16;

extras/tests/JsonDocument/shrinkToFit.cpp

@@ -179,15 +179,15 @@ TEST_CASE("JsonDocument::shrinkToFit()") {
   }
 
   SECTION("owned string in object") {
-    doc["key"_s] = "value"_s;
+    doc["key1"_s] = "value"_s;
 
     doc.shrinkToFit();
 
-    REQUIRE(doc.as<std::string>() == "{\"key\":\"value\"}");
+    REQUIRE(doc.as<std::string>() == "{\"key1\":\"value\"}");
     REQUIRE(spyingAllocator.log() ==
             AllocatorLog{
                 Allocate(sizeofPool()),
-                Allocate(sizeofString("key")),
+                Allocate(sizeofString("key1")),
                 Allocate(sizeofString("value")),
                 Reallocate(sizeofPool(), sizeofPool(2)),
             });

extras/tests/JsonObject/set.cpp

@@ -88,13 +88,13 @@ TEST_CASE("JsonObject::set()") {
     JsonDocument doc3(&timebomb);
     JsonObject obj3 = doc3.to<JsonObject>();
 
-    obj1["a"_s] = 1;
-    obj1["b"_s] = 2;
+    obj1["alpha"_s] = 1;
+    obj1["beta"_s] = 2;
 
     bool success = obj3.set(obj1);
 
     REQUIRE(success == false);
-    REQUIRE(doc3.as<std::string>() == "{\"a\":1}");
+    REQUIRE(doc3.as<std::string>() == "{\"alpha\":1}");
   }
 
   SECTION("copy fails in the middle of an array") {

extras/tests/JsonVariant/as.cpp

@@ -199,7 +199,7 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<JsonString>() == "hello");
   }
 
-  SECTION("set(std::string(\"4.2\"))") {
+  SECTION("set(std::string(\"4.2\")) (tiny string optimization)") {
     variant.set("4.2"_s);
 
     REQUIRE(variant.as<bool>() == true);
@@ -211,6 +211,18 @@ TEST_CASE("JsonVariant::as()") {
     REQUIRE(variant.as<JsonString>().isStatic() == false);
   }
 
+  SECTION("set(std::string(\"123.45\"))") {
+    variant.set("123.45"_s);
+
+    REQUIRE(variant.as<bool>() == true);
+    REQUIRE(variant.as<long>() == 123L);
+    REQUIRE(variant.as<double>() == Approx(123.45));
+    REQUIRE(variant.as<const char*>() == "123.45"_s);
+    REQUIRE(variant.as<std::string>() == "123.45"_s);
+    REQUIRE(variant.as<JsonString>() == "123.45");
+    REQUIRE(variant.as<JsonString>().isStatic() == false);
+  }
+
   SECTION("set(\"true\")") {
     variant.set("true");
 

extras/tests/JsonVariant/set.cpp

@@ -8,7 +8,7 @@
 #include "Allocators.hpp"
 #include "Literals.hpp"
 
-using ArduinoJson::detail::sizeofObject;
+using namespace ArduinoJson::detail;
 
 enum ErrorCode { ERROR_01 = 1, ERROR_10 = 10 };
 
@@ -65,6 +65,18 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
                          });
   }
 
+  SECTION("char* (tiny string optimization)") {
+    char str[16];
+
+    strcpy(str, "abc");
+    bool result = variant.set(str);
+    strcpy(str, "def");
+
+    REQUIRE(result == true);
+    REQUIRE(variant == "abc");  // stores by copy
+    REQUIRE(spy.log() == AllocatorLog{});
+  }
+
   SECTION("(char*)0") {
     bool result = variant.set(static_cast<char*>(0));
 
@@ -185,11 +197,11 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
     REQUIRE(result == true);
     REQUIRE(variant.is<double>() == true);
     REQUIRE(variant.as<double>() == 1.2);
-    REQUIRE(spy.log() ==
-            AllocatorLog{
-                Allocate(sizeofPool()),
-                Reallocate(sizeofPool(), sizeofPool(1)),  // one extension slot
-            });
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool<EightByteValue>()),
+                             Reallocate(sizeofPool<EightByteValue>(),
+                                        sizeofPool<EightByteValue>(1)),
+                         });
   }
 
   SECTION("int32_t") {
@@ -208,11 +220,11 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
     REQUIRE(result == true);
     REQUIRE(variant.is<int64_t>() == true);
     REQUIRE(variant.as<int64_t>() == -2147483649LL);
-    REQUIRE(spy.log() ==
-            AllocatorLog{
-                Allocate(sizeofPool()),
-                Reallocate(sizeofPool(), sizeofPool(1)),  // one extension slot
-            });
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool<EightByteValue>()),
+                             Reallocate(sizeofPool<EightByteValue>(),
+                                        sizeofPool<EightByteValue>(1)),
+                         });
   }
 
   SECTION("uint32_t") {
@@ -231,11 +243,11 @@ TEST_CASE("JsonVariant::set() when there is enough memory") {
     REQUIRE(result == true);
     REQUIRE(variant.is<uint64_t>() == true);
     REQUIRE(variant.as<uint64_t>() == 4294967296);
-    REQUIRE(spy.log() ==
-            AllocatorLog{
-                Allocate(sizeofPool()),
-                Reallocate(sizeofPool(), sizeofPool(1)),  // one extension slot
-            });
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool<EightByteValue>()),
+                             Reallocate(sizeofPool<EightByteValue>(),
+                                        sizeofPool<EightByteValue>(1)),
+                         });
   }
 
   SECTION("JsonDocument") {
@@ -366,7 +378,7 @@ TEST_CASE("JsonVariant::set() releases the previous value") {
   }
 
   SECTION("float") {
-    v.set(1.2);
+    v.set(1.2f);
     REQUIRE(spy.log() == AllocatorLog{
                              Deallocate(sizeofString("world")),
                          });
@@ -381,7 +393,7 @@ TEST_CASE("JsonVariant::set() releases the previous value") {
   }
 }
 
-TEST_CASE("JsonVariant::set() reuses extension slot") {
+TEST_CASE("JsonVariant::set() reuses 8-bit slot") {
   SpyingAllocator spy;
   JsonDocument doc(&spy);
   JsonVariant variant = doc.to<JsonVariant>();

extras/tests/Misc/CMakeLists.txt

@@ -7,6 +7,7 @@ add_executable(MiscTests
 	conflicts.cpp
 	issue1967.cpp
 	issue2129.cpp
+	issue2166.cpp
 	JsonString.cpp
 	NoArduinoHeader.cpp
 	printable.cpp

extras/tests/Misc/StringAdapters.cpp

@@ -128,6 +128,7 @@ TEST_CASE("IsString<T>") {
   CHECK(IsString<const __FlashStringHelper*>::value == true);
   CHECK(IsString<const char*>::value == true);
   CHECK(IsString<const char[8]>::value == true);
+  CHECK(IsString<const char[]>::value == true);
   CHECK(IsString<::String>::value == true);
   CHECK(IsString<::StringSumHelper>::value == true);
   CHECK(IsString<const EmptyStruct*>::value == false);

extras/tests/Misc/issue2166.cpp

@@ -0,0 +1,22 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2025, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+struct CCLASS {
+  static const char mszKey[];
+};
+
+TEST_CASE("Issue #2166") {
+  JsonDocument doc;
+  doc[CCLASS::mszKey] = 12;
+  REQUIRE(doc.as<std::string>() == "{\"test3\":12}");
+
+  JsonObject obj = doc.to<JsonObject>();
+  obj[CCLASS::mszKey] = 12;
+  REQUIRE(doc.as<std::string>() == "{\"test3\":12}");
+}
+
+const char CCLASS::mszKey[] = "test3";

extras/tests/MsgPackDeserializer/deserializeArray.cpp

@@ -5,8 +5,11 @@
 #include <ArduinoJson.h>
 #include <catch.hpp>
 
+#include "Allocators.hpp"
+
 TEST_CASE("deserialize MsgPack array") {
-  JsonDocument doc;
+  SpyingAllocator spy;
+  JsonDocument doc(&spy);
 
   SECTION("fixarray") {
     SECTION("empty") {
@@ -30,6 +33,24 @@ TEST_CASE("deserialize MsgPack array") {
       REQUIRE(array[0] == 1);
       REQUIRE(array[1] == 2);
     }
+
+    SECTION("tiny strings") {
+      DeserializationError error =
+          deserializeMsgPack(doc, "\x92\xA3xxx\xA3yyy");
+
+      REQUIRE(error == DeserializationError::Ok);
+      REQUIRE(doc.is<JsonArray>());
+      REQUIRE(doc.size() == 2);
+      REQUIRE(doc[0] == "xxx");
+      REQUIRE(doc[1] == "yyy");
+      REQUIRE(spy.log() == AllocatorLog{
+                               Allocate(sizeofPool()),
+                               Allocate(sizeofString("xxx")),
+                               // Buffer is reused for the next string
+                               Deallocate(sizeofString("xxx")),
+                               Reallocate(sizeofPool(), sizeofPool(2)),
+                           });
+    }
   }
 
   SECTION("array 16") {

extras/tests/MsgPackDeserializer/deserializeVariant.cpp

@@ -348,13 +348,14 @@ TEST_CASE("deserializeMsgPack() under memory constaints") {
     SECTION("{}") {
       checkError(0, "\x80", DeserializationError::Ok);
     }
-    SECTION("{H:1}") {
-      checkError(1, "\x81\xA1H\x01", DeserializationError::NoMemory);
-      checkError(2, "\x81\xA1H\x01", DeserializationError::Ok);
+    SECTION("{Hello:1}") {
+      checkError(1, "\x81\xA5Hello\x01", DeserializationError::NoMemory);
+      checkError(2, "\x81\xA5Hello\x01", DeserializationError::Ok);
     }
-    SECTION("{H:1,W:2}") {
-      checkError(2, "\x82\xA1H\x01\xA1W\x02", DeserializationError::NoMemory);
-      checkError(3, "\x82\xA1H\x01\xA1W\x02", DeserializationError::Ok);
+    SECTION("{Hello:1,World:2}") {
+      checkError(2, "\x82\xA5Hello\x01\xA5World\x02",
+                 DeserializationError::NoMemory);
+      checkError(3, "\x82\xA5Hello\x01\xA5World\x02", DeserializationError::Ok);
     }
   }
 
@@ -362,14 +363,16 @@ TEST_CASE("deserializeMsgPack() under memory constaints") {
     SECTION("{}") {
       checkError(0, "\xDE\x00\x00", DeserializationError::Ok);
     }
-    SECTION("{H:1}") {
-      checkError(1, "\xDE\x00\x01\xA1H\x01", DeserializationError::NoMemory);
-      checkError(2, "\xDE\x00\x01\xA1H\x01", DeserializationError::Ok);
-    }
-    SECTION("{H:1,W:2}") {
-      checkError(2, "\xDE\x00\x02\xA1H\x01\xA1W\x02",
+    SECTION("{Hello:1}") {
+      checkError(1, "\xDE\x00\x01\xA5Hello\x01",
                  DeserializationError::NoMemory);
-      checkError(3, "\xDE\x00\x02\xA1H\x01\xA1W\x02", DeserializationError::Ok);
+      checkError(2, "\xDE\x00\x01\xA5Hello\x01", DeserializationError::Ok);
+    }
+    SECTION("{Hello:1,World:2}") {
+      checkError(2, "\xDE\x00\x02\xA5Hello\x01\xA5World\x02",
+                 DeserializationError::NoMemory);
+      checkError(3, "\xDE\x00\x02\xA5Hello\x01\xA5World\x02",
+                 DeserializationError::Ok);
     }
   }
 
@@ -382,8 +385,8 @@ TEST_CASE("deserializeMsgPack() under memory constaints") {
                  DeserializationError::NoMemory);
       checkError(2, "\xDF\x00\x00\x00\x01\xA1H\x01", DeserializationError::Ok);
     }
-    SECTION("{H:1,W:2}") {
-      checkError(2, "\xDF\x00\x00\x00\x02\xA1H\x01\xA1W\x02",
+    SECTION("{Hello:1,World:2}") {
+      checkError(2, "\xDF\x00\x00\x00\x02\xA5Hello\x01\xA5World\x02",
                  DeserializationError::NoMemory);
       checkError(3, "\xDF\x00\x00\x00\x02\xA1H\x01\xA1W\x02",
                  DeserializationError::Ok);

extras/tests/ResourceManager/CMakeLists.txt

@@ -9,6 +9,7 @@ add_executable(ResourceManagerTests
 	saveString.cpp
 	shrinkToFit.cpp
 	size.cpp
+	StringBuffer.cpp
 	StringBuilder.cpp
 	swap.cpp
 )

extras/tests/ResourceManager/StringBuffer.cpp

@@ -0,0 +1,50 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2025, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.hpp>
+#include <catch.hpp>
+
+#include "Allocators.hpp"
+#include "Literals.hpp"
+
+using namespace ArduinoJson::detail;
+
+TEST_CASE("StringBuffer") {
+  SpyingAllocator spy;
+  ResourceManager resources(&spy);
+  StringBuffer sb(&resources);
+  VariantData variant;
+
+  SECTION("Tiny string") {
+    auto ptr = sb.reserve(3);
+    strcpy(ptr, "hi!");
+    sb.save(&variant);
+
+    REQUIRE(variant.type() == VariantType::TinyString);
+    REQUIRE(variant.asString(&resources) == "hi!");
+  }
+
+  SECTION("Tiny string can't contain NUL") {
+    auto ptr = sb.reserve(3);
+    memcpy(ptr, "a\0b", 3);
+    sb.save(&variant);
+
+    REQUIRE(variant.type() == VariantType::OwnedString);
+
+    auto str = variant.asString(&resources);
+    REQUIRE(str.size() == 3);
+    REQUIRE(str.c_str()[0] == 'a');
+    REQUIRE(str.c_str()[1] == 0);
+    REQUIRE(str.c_str()[2] == 'b');
+  }
+
+  SECTION("Tiny string can't have 4 characters") {
+    auto ptr = sb.reserve(4);
+    strcpy(ptr, "alfa");
+    sb.save(&variant);
+
+    REQUIRE(variant.type() == VariantType::OwnedString);
+    REQUIRE(variant.asString(&resources) == "alfa");
+  }
+}

extras/tests/ResourceManager/StringBuilder.cpp

@@ -2,11 +2,12 @@
 // Copyright © 2014-2025, Benoit BLANCHON
 // MIT License
 
-#include <ArduinoJson/Memory/StringBuilder.hpp>
+#include <ArduinoJson.hpp>
 #include <catch.hpp>
 
 #include "Allocators.hpp"
 
+using namespace ArduinoJson;
 using namespace ArduinoJson::detail;
 
 TEST_CASE("StringBuilder") {
@@ -16,17 +17,36 @@ TEST_CASE("StringBuilder") {
 
   SECTION("Empty string") {
     StringBuilder str(&resources);
+    VariantData data;
 
     str.startString();
-    str.save();
+    str.save(&data);
 
-    REQUIRE(resources.size() == sizeofString(""));
     REQUIRE(resources.overflowed() == false);
-    REQUIRE(spyingAllocator.log() ==
-            AllocatorLog{
-                Allocate(sizeofStringBuffer()),
-                Reallocate(sizeofStringBuffer(), sizeofString("")),
-            });
+    REQUIRE(spyingAllocator.log() == AllocatorLog{
+                                         Allocate(sizeofStringBuffer()),
+                                     });
+    REQUIRE(data.type() == VariantType::TinyString);
+  }
+
+  SECTION("Tiny string") {
+    StringBuilder str(&resources);
+
+    str.startString();
+    str.append("url");
+
+    REQUIRE(str.isValid() == true);
+    REQUIRE(str.str() == "url");
+    REQUIRE(spyingAllocator.log() == AllocatorLog{
+                                         Allocate(sizeofStringBuffer()),
+                                     });
+
+    VariantData data;
+    str.save(&data);
+
+    REQUIRE(resources.overflowed() == false);
+    REQUIRE(data.type() == VariantType::TinyString);
+    REQUIRE(data.asString(&resources) == "url");
   }
 
   SECTION("Short string fits in first allocation") {
@@ -96,48 +116,72 @@ TEST_CASE("StringBuilder") {
   }
 }
 
-static StringNode* addStringToPool(ResourceManager& resources, const char* s) {
-  StringBuilder str(&resources);
-  str.startString();
-  str.append(s);
-  return str.save();
+static VariantData saveString(StringBuilder& builder, const char* s) {
+  VariantData data;
+  builder.startString();
+  builder.append(s);
+  builder.save(&data);
+  return data;
 }
 
 TEST_CASE("StringBuilder::save() deduplicates strings") {
-  ResourceManager resources;
+  SpyingAllocator spy;
+  ResourceManager resources(&spy);
+  StringBuilder builder(&resources);
 
   SECTION("Basic") {
-    auto s1 = addStringToPool(resources, "hello");
-    auto s2 = addStringToPool(resources, "world");
-    auto s3 = addStringToPool(resources, "hello");
+    auto s1 = saveString(builder, "hello");
+    auto s2 = saveString(builder, "world");
+    auto s3 = saveString(builder, "hello");
 
-    REQUIRE(s1 == s3);
-    REQUIRE(s2 != s3);
-    REQUIRE(s1->references == 2);
-    REQUIRE(s2->references == 1);
-    REQUIRE(s3->references == 2);
-    REQUIRE(resources.size() == sizeofString("hello") + sizeofString("world"));
+    REQUIRE(s1.asString(&resources) == "hello");
+    REQUIRE(s2.asString(&resources) == "world");
+    REQUIRE(+s1.asString(&resources).c_str() ==
+            +s3.asString(&resources).c_str());  // same address
+
+    REQUIRE(spy.log() ==
+            AllocatorLog{
+                Allocate(sizeofStringBuffer()),
+                Reallocate(sizeofStringBuffer(), sizeofString("hello")),
+                Allocate(sizeofStringBuffer()),
+                Reallocate(sizeofStringBuffer(), sizeofString("world")),
+                Allocate(sizeofStringBuffer()),
+            });
   }
 
   SECTION("Requires terminator") {
-    auto s1 = addStringToPool(resources, "hello world");
-    auto s2 = addStringToPool(resources, "hello");
+    auto s1 = saveString(builder, "hello world");
+    auto s2 = saveString(builder, "hello");
 
-    REQUIRE(s2 != s1);
-    REQUIRE(s1->references == 1);
-    REQUIRE(s2->references == 1);
-    REQUIRE(resources.size() ==
-            sizeofString("hello world") + sizeofString("hello"));
+    REQUIRE(s1.asString(&resources) == "hello world");
+    REQUIRE(s2.asString(&resources) == "hello");
+    REQUIRE(+s2.asString(&resources).c_str() !=
+            +s1.asString(&resources).c_str());  // different address
+
+    REQUIRE(spy.log() ==
+            AllocatorLog{
+                Allocate(sizeofStringBuffer()),
+                Reallocate(sizeofStringBuffer(), sizeofString("hello world")),
+                Allocate(sizeofStringBuffer()),
+                Reallocate(sizeofStringBuffer(), sizeofString("hello")),
+            });
   }
 
   SECTION("Don't overrun") {
-    auto s1 = addStringToPool(resources, "hello world");
-    auto s2 = addStringToPool(resources, "wor");
+    auto s1 = saveString(builder, "hello world");
+    auto s2 = saveString(builder, "worl");
 
-    REQUIRE(s2 != s1);
-    REQUIRE(s1->references == 1);
-    REQUIRE(s2->references == 1);
-    REQUIRE(resources.size() ==
-            sizeofString("hello world") + sizeofString("wor"));
+    REQUIRE(s1.asString(&resources) == "hello world");
+    REQUIRE(s2.asString(&resources) == "worl");
+    REQUIRE(s2.asString(&resources).c_str() !=
+            s1.asString(&resources).c_str());  // different address
+
+    REQUIRE(spy.log() ==
+            AllocatorLog{
+                Allocate(sizeofStringBuffer()),
+                Reallocate(sizeofStringBuffer(), sizeofString("hello world")),
+                Allocate(sizeofStringBuffer()),
+                Reallocate(sizeofStringBuffer(), sizeofString("worl")),
+            });
   }
 }

idf_component.yml

@@ -1,7 +1,7 @@
-version: "7.3.0"
+version: "7.4.1"
 description: >-
   A simple and efficient JSON library for embedded C++.
-  ★ 6785 stars on GitHub!
+  ★ 6898 stars on GitHub!
   Supports serialization, deserialization, MessagePack, streams, filtering, and more.
   Fully tested and documented.
 url: https://arduinojson.org/

library.json

@@ -1,13 +1,13 @@
 {
   "name": "ArduinoJson",
   "keywords": "json, rest, http, web",
-  "description": "A simple and efficient JSON library for embedded C++. ⭐ 6785 stars on GitHub! Supports serialization, deserialization, MessagePack, streams, filtering, and more. Fully tested and documented.",
+  "description": "A simple and efficient JSON library for embedded C++. ⭐ 6898 stars on GitHub! Supports serialization, deserialization, MessagePack, streams, filtering, and more. Fully tested and documented.",
   "homepage": "https://arduinojson.org/?utm_source=meta&utm_medium=library.json",
   "repository": {
     "type": "git",
     "url": "https://github.com/bblanchon/ArduinoJson.git"
   },
-  "version": "7.3.0",
+  "version": "7.4.1",
   "authors": {
     "name": "Benoit Blanchon",
     "url": "https://blog.benoitblanchon.fr"

library.properties

@@ -1,9 +1,9 @@
 name=ArduinoJson
-version=7.3.0
+version=7.4.1
 author=Benoit Blanchon <blog.benoitblanchon.fr>
 maintainer=Benoit Blanchon <blog.benoitblanchon.fr>
 sentence=A simple and efficient JSON library for embedded C++.
-paragraph=⭐ 6785 stars on GitHub! Supports serialization, deserialization, MessagePack, streams, filtering, and more. Fully tested and documented.
+paragraph=⭐ 6898 stars on GitHub! Supports serialization, deserialization, MessagePack, streams, filtering, and more. Fully tested and documented.
 category=Data Processing
 url=https://arduinojson.org/?utm_source=meta&utm_medium=library.properties
 architectures=*

src/ArduinoJson/Array/ArrayImpl.hpp

@@ -73,7 +73,7 @@ inline bool ArrayData::addValue(const T& value, ResourceManager* resources) {
 
 // Returns the size (in bytes) of an array with n elements.
 constexpr size_t sizeofArray(size_t n) {
-  return n * ResourceManager::slotSize;
+  return n * sizeof(VariantData);
 }
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Configuration.hpp

@@ -274,9 +274,9 @@
 #endif
 
 #if ARDUINOJSON_USE_LONG_LONG || ARDUINOJSON_USE_DOUBLE
-#  define ARDUINOJSON_USE_EXTENSIONS 1
+#  define ARDUINOJSON_USE_8_BYTE_POOL 1
 #else
-#  define ARDUINOJSON_USE_EXTENSIONS 0
+#  define ARDUINOJSON_USE_8_BYTE_POOL 0
 #endif
 
 #if defined(nullptr)

src/ArduinoJson/Json/JsonDeserializer.hpp

@@ -275,13 +275,11 @@ class JsonDeserializer {
       if (memberFilter.allow()) {
         auto member = object.getMember(adaptString(key), resources_);
         if (!member) {
-          // Save key in memory pool.
-          auto savedKey = stringBuilder_.save();
-
-          // Allocate slot in object
-          member = object.addMember(savedKey, resources_);
-          if (!member)
+          auto keyVariant = object.addPair(&member, resources_);
+          if (!keyVariant)
             return DeserializationError::NoMemory;
+
+          stringBuilder_.save(keyVariant);
         } else {
           member->clear(resources_);
         }
@@ -390,7 +388,7 @@ class JsonDeserializer {
     if (err)
       return err;
 
-    variant.setOwnedString(stringBuilder_.save());
+    stringBuilder_.save(&variant);
 
     return DeserializationError::Ok;
   }

src/ArduinoJson/Memory/ResourceManager.hpp

@@ -18,16 +18,7 @@ class VariantData;
 class VariantWithId;
 
 class ResourceManager {
-  union SlotData {
-    VariantData variant;
-#if ARDUINOJSON_USE_EXTENSIONS
-    VariantExtension extension;
-#endif
-  };
-
  public:
-  constexpr static size_t slotSize = sizeof(SlotData);
-
   ResourceManager(Allocator* allocator = DefaultAllocator::instance())
       : allocator_(allocator), overflowed_(false) {}
 
@@ -35,6 +26,9 @@ class ResourceManager {
     stringPool_.clear(allocator_);
     variantPools_.clear(allocator_);
     staticStringsPools_.clear(allocator_);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    eightBytePools_.clear(allocator_);
+#endif
   }
 
   ResourceManager(const ResourceManager&) = delete;
@@ -44,6 +38,9 @@ class ResourceManager {
     swap(a.stringPool_, b.stringPool_);
     swap(a.variantPools_, b.variantPools_);
     swap(a.staticStringsPools_, b.staticStringsPools_);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    swap(a.eightBytePools_, b.eightBytePools_);
+#endif
     swap_(a.allocator_, b.allocator_);
     swap_(a.overflowed_, b.overflowed_);
   }
@@ -64,10 +61,10 @@ class ResourceManager {
   void freeVariant(Slot<VariantData> slot);
   VariantData* getVariant(SlotId id) const;
 
-#if ARDUINOJSON_USE_EXTENSIONS
-  Slot<VariantExtension> allocExtension();
-  void freeExtension(SlotId slot);
-  VariantExtension* getExtension(SlotId id) const;
+#if ARDUINOJSON_USE_8_BYTE_POOL
+  Slot<EightByteValue> allocEightByte();
+  void freeEightByte(SlotId slot);
+  EightByteValue* getEightByte(SlotId id) const;
 #endif
 
   template <typename TAdaptedString>
@@ -136,19 +133,28 @@ class ResourceManager {
     variantPools_.clear(allocator_);
     stringPool_.clear(allocator_);
     staticStringsPools_.clear(allocator_);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    eightBytePools_.clear(allocator_);
+#endif
   }
 
   void shrinkToFit() {
     variantPools_.shrinkToFit(allocator_);
     staticStringsPools_.shrinkToFit(allocator_);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    eightBytePools_.shrinkToFit(allocator_);
+#endif
   }
 
  private:
   Allocator* allocator_;
   bool overflowed_;
   StringPool stringPool_;
-  MemoryPoolList<SlotData> variantPools_;
+  MemoryPoolList<VariantData> variantPools_;
   MemoryPoolList<const char*> staticStringsPools_;
+#if ARDUINOJSON_USE_8_BYTE_POOL
+  MemoryPoolList<EightByteValue> eightBytePools_;
+#endif
 };
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Memory/ResourceManagerImpl.hpp

@@ -12,40 +12,41 @@
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
 inline Slot<VariantData> ResourceManager::allocVariant() {
-  auto p = variantPools_.allocSlot(allocator_);
-  if (!p) {
+  auto slot = variantPools_.allocSlot(allocator_);
+  if (!slot) {
     overflowed_ = true;
     return {};
   }
-  return {new (&p->variant) VariantData, p.id()};
+  new (slot.ptr()) VariantData();
+  return slot;
 }
 
-inline void ResourceManager::freeVariant(Slot<VariantData> variant) {
-  variant->clear(this);
-  variantPools_.freeSlot({alias_cast<SlotData*>(variant.ptr()), variant.id()});
+inline void ResourceManager::freeVariant(Slot<VariantData> slot) {
+  slot->clear(this);
+  variantPools_.freeSlot(slot);
 }
 
 inline VariantData* ResourceManager::getVariant(SlotId id) const {
   return reinterpret_cast<VariantData*>(variantPools_.getSlot(id));
 }
 
-#if ARDUINOJSON_USE_EXTENSIONS
-inline Slot<VariantExtension> ResourceManager::allocExtension() {
-  auto p = variantPools_.allocSlot(allocator_);
-  if (!p) {
+#if ARDUINOJSON_USE_8_BYTE_POOL
+inline Slot<EightByteValue> ResourceManager::allocEightByte() {
+  auto slot = eightBytePools_.allocSlot(allocator_);
+  if (!slot) {
     overflowed_ = true;
     return {};
   }
-  return {&p->extension, p.id()};
+  return slot;
 }
 
-inline void ResourceManager::freeExtension(SlotId id) {
-  auto p = getExtension(id);
-  variantPools_.freeSlot({reinterpret_cast<SlotData*>(p), id});
+inline void ResourceManager::freeEightByte(SlotId id) {
+  auto p = getEightByte(id);
+  eightBytePools_.freeSlot({p, id});
 }
 
-inline VariantExtension* ResourceManager::getExtension(SlotId id) const {
-  return &variantPools_.getSlot(id)->extension;
+inline EightByteValue* ResourceManager::getEightByte(SlotId id) const {
+  return eightBytePools_.getSlot(id);
 }
 #endif
 

src/ArduinoJson/Memory/StringBuffer.hpp

@@ -32,7 +32,26 @@ class StringBuffer {
     return node_->data;
   }
 
-  StringNode* save() {
+  JsonString str() const {
+    ARDUINOJSON_ASSERT(node_ != nullptr);
+    return JsonString(node_->data, node_->length);
+  }
+
+  void save(VariantData* data) {
+    ARDUINOJSON_ASSERT(node_ != nullptr);
+    const char* s = node_->data;
+    if (isTinyString(s, size_))
+      data->setTinyString(adaptString(s, size_));
+    else
+      data->setOwnedString(commitStringNode());
+  }
+
+  void saveRaw(VariantData* data) {
+    data->setRawString(commitStringNode());
+  }
+
+ private:
+  StringNode* commitStringNode() {
     ARDUINOJSON_ASSERT(node_ != nullptr);
     node_->data[size_] = 0;
     auto node = resources_->getString(adaptString(node_->data, size_));
@@ -52,13 +71,6 @@ class StringBuffer {
     return node;
   }
 
-  JsonString str() const {
-    ARDUINOJSON_ASSERT(node_ != nullptr);
-
-    return JsonString(node_->data, node_->length);
-  }
-
- private:
   ResourceManager* resources_;
   StringNode* node_ = nullptr;
   size_t size_ = 0;

src/ArduinoJson/Memory/StringBuilder.hpp

@@ -25,10 +25,18 @@ class StringBuilder {
       node_ = resources_->createString(initialCapacity);
   }
 
-  StringNode* save() {
+  void save(VariantData* variant) {
+    ARDUINOJSON_ASSERT(variant != nullptr);
     ARDUINOJSON_ASSERT(node_ != nullptr);
-    node_->data[size_] = 0;
-    StringNode* node = resources_->getString(adaptString(node_->data, size_));
+
+    char* p = node_->data;
+    if (isTinyString(p, size_)) {
+      variant->setTinyString(adaptString(p, size_));
+      return;
+    }
+
+    p[size_] = 0;
+    StringNode* node = resources_->getString(adaptString(p, size_));
     if (!node) {
       node = resources_->resizeString(node_, size_);
       ARDUINOJSON_ASSERT(node != nullptr);  // realloc to smaller can't fail
@@ -37,7 +45,7 @@ class StringBuilder {
     } else {
       node->references++;
     }
-    return node;
+    variant->setOwnedString(node);
   }
 
   void append(const char* s) {

src/ArduinoJson/MsgPack/MsgPackDeserializer.hpp

@@ -305,7 +305,7 @@ class MsgPackDeserializer {
     if (err)
       return err;
 
-    variant->setOwnedString(stringBuffer_.save());
+    stringBuffer_.save(variant);
     return DeserializationError::Ok;
   }
 
@@ -334,7 +334,7 @@ class MsgPackDeserializer {
     if (err)
       return err;
 
-    variant->setRawString(stringBuffer_.save());
+    stringBuffer_.saveRaw(variant);
     return DeserializationError::Ok;
   }
 
@@ -403,19 +403,16 @@ class MsgPackDeserializer {
 
       JsonString key = stringBuffer_.str();
       TFilter memberFilter = filter[key.c_str()];
-      VariantData* member;
+      VariantData* member = 0;
 
       if (memberFilter.allow()) {
         ARDUINOJSON_ASSERT(object != 0);
 
-        // Save key in memory pool.
-        auto savedKey = stringBuffer_.save();
-
-        member = object->addMember(savedKey, resources_);
-        if (!member)
+        auto keyVariant = object->addPair(&member, resources_);
+        if (!keyVariant)
           return DeserializationError::NoMemory;
-      } else {
-        member = 0;
+
+        stringBuffer_.save(keyVariant);
       }
 
       err = parseVariant(member, memberFilter, nestingLimit.decrement());

src/ArduinoJson/Object/ObjectData.hpp

@@ -10,9 +10,11 @@ ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
 class ObjectData : public CollectionData {
  public:
-  template <typename TAdaptedString>  // also works with StringNode*
+  template <typename TAdaptedString>
   VariantData* addMember(TAdaptedString key, ResourceManager* resources);
 
+  VariantData* addPair(VariantData** value, ResourceManager* resources);
+
   template <typename TAdaptedString>
   VariantData* getOrAddMember(TAdaptedString key, ResourceManager* resources);
 

src/ArduinoJson/Object/ObjectImpl.hpp

@@ -68,9 +68,25 @@ inline VariantData* ObjectData::addMember(TAdaptedString key,
   return valueSlot.ptr();
 }
 
+inline VariantData* ObjectData::addPair(VariantData** value,
+                                        ResourceManager* resources) {
+  auto keySlot = resources->allocVariant();
+  if (!keySlot)
+    return nullptr;
+
+  auto valueSlot = resources->allocVariant();
+  if (!valueSlot)
+    return nullptr;
+  *value = valueSlot.ptr();
+
+  CollectionData::appendPair(keySlot, valueSlot, resources);
+
+  return keySlot.ptr();
+}
+
 // Returns the size (in bytes) of an object with n members.
 constexpr size_t sizeofObject(size_t n) {
-  return 2 * n * ResourceManager::slotSize;
+  return 2 * n * sizeof(VariantData);
 }
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Strings/Adapters/RamString.hpp

@@ -76,6 +76,16 @@ struct StringAdapter<TChar*, enable_if_t<IsChar<TChar>::value>> {
   }
 };
 
+template <typename TChar>
+struct StringAdapter<TChar[], enable_if_t<IsChar<TChar>::value>> {
+  using AdaptedString = RamString;
+
+  static AdaptedString adapt(const TChar* p) {
+    auto str = reinterpret_cast<const char*>(p);
+    return AdaptedString(str, str ? ::strlen(str) : 0);
+  }
+};
+
 template <size_t N>
 struct StringAdapter<const char (&)[N]> {
   using AdaptedString = RamString;

src/ArduinoJson/Variant/ConverterImpl.hpp

@@ -230,9 +230,9 @@ class StringBuilderPrint : public Print {
     copier_.startString();
   }
 
-  StringNode* save() {
+  void save(VariantData* data) {
     ARDUINOJSON_ASSERT(!overflowed());
-    return copier_.save();
+    copier_.save(data);
   }
 
   size_t write(uint8_t c) {
@@ -268,7 +268,7 @@ inline void convertToJson(const ::Printable& src, JsonVariant dst) {
   src.printTo(print);
   if (print.overflowed())
     return;
-  data->setOwnedString(print.save());
+  print.save(data);
 }
 
 #endif

src/ArduinoJson/Variant/VariantContent.hpp

@@ -16,14 +16,13 @@ ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 enum class VariantTypeBits : uint8_t {
   OwnedStringBit = 0x01,  // 0000 0001
   NumberBit = 0x08,       // 0000 1000
-#if ARDUINOJSON_USE_EXTENSIONS
-  ExtensionBit = 0x10,  // 0001 0000
-#endif
+  EightByteBit = 0x10,    // 0001 0000
   CollectionMask = 0x60,
 };
 
 enum class VariantType : uint8_t {
   Null = 0,             // 0000 0000
+  TinyString = 0x02,    // 0000 0010
   RawString = 0x03,     // 0000 0011
   LinkedString = 0x04,  // 0000 0100
   OwnedString = 0x05,   // 0000 0101
@@ -46,6 +45,8 @@ inline bool operator&(VariantType type, VariantTypeBits bit) {
   return (uint8_t(type) & uint8_t(bit)) != 0;
 }
 
+const size_t tinyStringMaxLength = 3;
+
 union VariantContent {
   VariantContent() {}
 
@@ -58,10 +59,11 @@ union VariantContent {
   ObjectData asObject;
   CollectionData asCollection;
   struct StringNode* asOwnedString;
+  char asTinyString[tinyStringMaxLength + 1];
 };
 
-#if ARDUINOJSON_USE_EXTENSIONS
-union VariantExtension {
+#if ARDUINOJSON_USE_8_BYTE_POOL
+union EightByteValue {
 #  if ARDUINOJSON_USE_LONG_LONG
   uint64_t asUint64;
   int64_t asInt64;
@@ -70,6 +72,9 @@ union VariantExtension {
   double asDouble;
 #  endif
 };
+
+static_assert(sizeof(EightByteValue) == 8,
+              "sizeof(EightByteValue) must be 8 bytes");
 #endif
 
 ARDUINOJSON_END_PRIVATE_NAMESPACE

src/ArduinoJson/Variant/VariantData.hpp

@@ -17,6 +17,16 @@ ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 template <typename T>
 T parseNumber(const char* s);
 
+template <typename T>
+static bool isTinyString(const T& s, size_t n) {
+  if (n > tinyStringMaxLength)
+    return false;
+  bool containsNul = false;
+  for (uint8_t i = 0; i < uint8_t(n); i++)
+    containsNul |= !s[i];
+  return !containsNul;
+}
+
 class VariantData {
   VariantContent content_;  // must be first to allow cast from array to variant
   VariantType type_;
@@ -43,8 +53,8 @@ class VariantData {
   template <typename TVisitor>
   typename TVisitor::result_type accept(
       TVisitor& visit, const ResourceManager* resources) const {
-#if ARDUINOJSON_USE_EXTENSIONS
-    auto extension = getExtension(resources);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    auto eightByteValue = getEightByte(resources);
 #else
     (void)resources;  // silence warning
 #endif
@@ -54,7 +64,7 @@ class VariantData {
 
 #if ARDUINOJSON_USE_DOUBLE
       case VariantType::Double:
-        return visit.visit(extension->asDouble);
+        return visit.visit(eightByteValue->asDouble);
 #endif
 
       case VariantType::Array:
@@ -63,6 +73,9 @@ class VariantData {
       case VariantType::Object:
         return visit.visit(content_.asObject);
 
+      case VariantType::TinyString:
+        return visit.visit(JsonString(content_.asTinyString));
+
       case VariantType::LinkedString:
         return visit.visit(JsonString(asLinkedString(resources), true));
 
@@ -82,10 +95,10 @@ class VariantData {
 
 #if ARDUINOJSON_USE_LONG_LONG
       case VariantType::Int64:
-        return visit.visit(extension->asInt64);
+        return visit.visit(eightByteValue->asInt64);
 
       case VariantType::Uint64:
-        return visit.visit(extension->asUint64);
+        return visit.visit(eightByteValue->asUint64);
 #endif
 
       case VariantType::Boolean:
@@ -132,8 +145,8 @@ class VariantData {
   }
 
   bool asBoolean(const ResourceManager* resources) const {
-#if ARDUINOJSON_USE_EXTENSIONS
-    auto extension = getExtension(resources);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    auto eightByteValue = getEightByte(resources);
 #else
     (void)resources;  // silence warning
 #endif
@@ -147,14 +160,14 @@ class VariantData {
         return content_.asFloat != 0;
 #if ARDUINOJSON_USE_DOUBLE
       case VariantType::Double:
-        return extension->asDouble != 0;
+        return eightByteValue->asDouble != 0;
 #endif
       case VariantType::Null:
         return false;
 #if ARDUINOJSON_USE_LONG_LONG
       case VariantType::Uint64:
       case VariantType::Int64:
-        return extension->asUint64 != 0;
+        return eightByteValue->asUint64 != 0;
 #endif
       default:
         return true;
@@ -180,8 +193,8 @@ class VariantData {
   template <typename T>
   T asFloat(const ResourceManager* resources) const {
     static_assert(is_floating_point<T>::value, "T must be a floating point");
-#if ARDUINOJSON_USE_EXTENSIONS
-    auto extension = getExtension(resources);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    auto eightByteValue = getEightByte(resources);
 #else
     (void)resources;  // silence warning
 #endif
@@ -195,10 +208,13 @@ class VariantData {
         return static_cast<T>(content_.asInt32);
 #if ARDUINOJSON_USE_LONG_LONG
       case VariantType::Uint64:
-        return static_cast<T>(extension->asUint64);
+        return static_cast<T>(eightByteValue->asUint64);
       case VariantType::Int64:
-        return static_cast<T>(extension->asInt64);
+        return static_cast<T>(eightByteValue->asInt64);
 #endif
+      case VariantType::TinyString:
+        str = content_.asTinyString;
+        break;
       case VariantType::LinkedString:
         str = asLinkedString(resources);
         break;
@@ -209,7 +225,7 @@ class VariantData {
         return static_cast<T>(content_.asFloat);
 #if ARDUINOJSON_USE_DOUBLE
       case VariantType::Double:
-        return static_cast<T>(extension->asDouble);
+        return static_cast<T>(eightByteValue->asDouble);
 #endif
       default:
         return 0.0;
@@ -222,8 +238,8 @@ class VariantData {
   template <typename T>
   T asIntegral(const ResourceManager* resources) const {
     static_assert(is_integral<T>::value, "T must be an integral type");
-#if ARDUINOJSON_USE_EXTENSIONS
-    auto extension = getExtension(resources);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+    auto eightByteValue = getEightByte(resources);
 #else
     (void)resources;  // silence warning
 #endif
@@ -237,10 +253,13 @@ class VariantData {
         return convertNumber<T>(content_.asInt32);
 #if ARDUINOJSON_USE_LONG_LONG
       case VariantType::Uint64:
-        return convertNumber<T>(extension->asUint64);
+        return convertNumber<T>(eightByteValue->asUint64);
       case VariantType::Int64:
-        return convertNumber<T>(extension->asInt64);
+        return convertNumber<T>(eightByteValue->asInt64);
 #endif
+      case VariantType::TinyString:
+        str = content_.asTinyString;
+        break;
       case VariantType::LinkedString:
         str = asLinkedString(resources);
         break;
@@ -251,7 +270,7 @@ class VariantData {
         return convertNumber<T>(content_.asFloat);
 #if ARDUINOJSON_USE_DOUBLE
       case VariantType::Double:
-        return convertNumber<T>(extension->asDouble);
+        return convertNumber<T>(eightByteValue->asDouble);
 #endif
       default:
         return 0;
@@ -283,6 +302,8 @@ class VariantData {
 
   JsonString asString(const ResourceManager* resources) const {
     switch (type_) {
+      case VariantType::TinyString:
+        return JsonString(content_.asTinyString);
       case VariantType::LinkedString:
         return JsonString(asLinkedString(resources), true);
       case VariantType::OwnedString:
@@ -293,8 +314,8 @@ class VariantData {
     }
   }
 
-#if ARDUINOJSON_USE_EXTENSIONS
-  const VariantExtension* getExtension(const ResourceManager* resources) const;
+#if ARDUINOJSON_USE_8_BYTE_POOL
+  const EightByteValue* getEightByte(const ResourceManager* resources) const;
 #endif
 
   VariantData* getElement(size_t index,
@@ -357,7 +378,7 @@ class VariantData {
   template <typename T>
   bool isInteger(const ResourceManager* resources) const {
 #if ARDUINOJSON_USE_LONG_LONG
-    auto extension = getExtension(resources);
+    auto eightByteValue = getEightByte(resources);
 #else
     (void)resources;  // silence warning
 #endif
@@ -370,10 +391,10 @@ class VariantData {
 
 #if ARDUINOJSON_USE_LONG_LONG
       case VariantType::Uint64:
-        return canConvertNumber<T>(extension->asUint64);
+        return canConvertNumber<T>(eightByteValue->asUint64);
 
       case VariantType::Int64:
-        return canConvertNumber<T>(extension->asInt64);
+        return canConvertNumber<T>(eightByteValue->asInt64);
 #endif
 
       default:
@@ -397,7 +418,8 @@ class VariantData {
 
   bool isString() const {
     return type_ == VariantType::LinkedString ||
-           type_ == VariantType::OwnedString;
+           type_ == VariantType::OwnedString ||
+           type_ == VariantType::TinyString;
   }
 
   size_t nesting(const ResourceManager* resources) const {
@@ -490,11 +512,6 @@ class VariantData {
   template <typename TAdaptedString>
   bool setString(TAdaptedString value, ResourceManager* resources);
 
-  bool setString(StringNode* s, ResourceManager*) {
-    setOwnedString(s);
-    return true;
-  }
-
   template <typename TAdaptedString>
   static void setString(VariantData* var, TAdaptedString value,
                         ResourceManager* resources) {
@@ -506,6 +523,23 @@ class VariantData {
 
   bool setLinkedString(const char* s, ResourceManager* resources);
 
+  template <typename TAdaptedString>
+  void setTinyString(const TAdaptedString& s) {
+    ARDUINOJSON_ASSERT(type_ == VariantType::Null);  // must call clear() first
+    ARDUINOJSON_ASSERT(s.size() <= tinyStringMaxLength);
+
+    type_ = VariantType::TinyString;
+
+    auto n = uint8_t(s.size());
+    for (uint8_t i = 0; i < n; i++) {
+      char c = s[i];
+      ARDUINOJSON_ASSERT(c != 0);  // no NUL in tiny string
+      content_.asTinyString[i] = c;
+    }
+
+    content_.asTinyString[n] = 0;
+  }
+
   void setOwnedString(StringNode* s) {
     ARDUINOJSON_ASSERT(type_ == VariantType::Null);  // must call clear() first
     ARDUINOJSON_ASSERT(s);

src/ArduinoJson/Variant/VariantImpl.hpp

@@ -43,6 +43,11 @@ inline bool VariantData::setString(TAdaptedString value,
   if (value.isStatic())
     return setLinkedString(value.data(), resources);
 
+  if (isTinyString(value, value.size())) {
+    setTinyString(value);
+    return true;
+  }
+
   auto dup = resources->saveString(value);
   if (dup) {
     setOwnedString(dup);
@@ -56,9 +61,9 @@ inline void VariantData::clear(ResourceManager* resources) {
   if (type_ & VariantTypeBits::OwnedStringBit)
     resources->dereferenceString(content_.asOwnedString->data);
 
-#if ARDUINOJSON_USE_EXTENSIONS
-  if (type_ & VariantTypeBits::ExtensionBit)
-    resources->freeExtension(content_.asSlotId);
+#if ARDUINOJSON_USE_8_BYTE_POOL
+  if (type_ & VariantTypeBits::EightByteBit)
+    resources->freeEightByte(content_.asSlotId);
 #endif
 
   auto collection = asCollection();
@@ -68,12 +73,12 @@ inline void VariantData::clear(ResourceManager* resources) {
   type_ = VariantType::Null;
 }
 
-#if ARDUINOJSON_USE_EXTENSIONS
-inline const VariantExtension* VariantData::getExtension(
+#if ARDUINOJSON_USE_8_BYTE_POOL
+inline const EightByteValue* VariantData::getEightByte(
     const ResourceManager* resources) const {
-  return type_ & VariantTypeBits::ExtensionBit
-             ? resources->getExtension(content_.asSlotId)
-             : nullptr;
+  return type_ & VariantTypeBits::EightByteBit
+             ? resources->getEightByte(content_.asSlotId)
+             : 0;
 }
 #endif
 
@@ -96,12 +101,12 @@ enable_if_t<sizeof(T) == 8, bool> VariantData::setFloat(
     type_ = VariantType::Float;
     content_.asFloat = valueAsFloat;
   } else {
-    auto extension = resources->allocExtension();
-    if (!extension)
+    auto slot = resources->allocEightByte();
+    if (!slot)
       return false;
     type_ = VariantType::Double;
-    content_.asSlotId = extension.id();
-    extension->asDouble = value;
+    content_.asSlotId = slot.id();
+    slot->asDouble = value;
   }
 #else
   type_ = VariantType::Float;
@@ -122,12 +127,12 @@ enable_if_t<is_signed<T>::value, bool> VariantData::setInteger(
   }
 #if ARDUINOJSON_USE_LONG_LONG
   else {
-    auto extension = resources->allocExtension();
-    if (!extension)
+    auto slot = resources->allocEightByte();
+    if (!slot)
       return false;
     type_ = VariantType::Int64;
-    content_.asSlotId = extension.id();
-    extension->asInt64 = value;
+    content_.asSlotId = slot.id();
+    slot->asInt64 = value;
   }
 #endif
   return true;
@@ -145,12 +150,12 @@ enable_if_t<is_unsigned<T>::value, bool> VariantData::setInteger(
   }
 #if ARDUINOJSON_USE_LONG_LONG
   else {
-    auto extension = resources->allocExtension();
-    if (!extension)
+    auto slot = resources->allocEightByte();
+    if (!slot)
       return false;
     type_ = VariantType::Uint64;
-    content_.asSlotId = extension.id();
-    extension->asUint64 = value;
+    content_.asSlotId = slot.id();
+    slot->asUint64 = value;
   }
 #endif
   return true;

src/ArduinoJson/version.hpp

@@ -4,8 +4,8 @@
 
 #pragma once
 
-#define ARDUINOJSON_VERSION "7.3.0"
+#define ARDUINOJSON_VERSION "7.4.1"
 #define ARDUINOJSON_VERSION_MAJOR 7
-#define ARDUINOJSON_VERSION_MINOR 3
-#define ARDUINOJSON_VERSION_REVISION 0
-#define ARDUINOJSON_VERSION_MACRO V730
+#define ARDUINOJSON_VERSION_MINOR 4
+#define ARDUINOJSON_VERSION_REVISION 1
+#define ARDUINOJSON_VERSION_MACRO V741