Set version to 7.4.0

Fixes #2166

CHANGELOG.md

@@ -1,8 +1,14 @@
 ArduinoJson: change log
 =======================
 
-HEAD
-----
+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

CMakeLists.txt

@@ -10,7 +10,7 @@ if(ESP_PLATFORM)
 	return()
 endif()
 
-project(ArduinoJson VERSION 7.3.0)
+project(ArduinoJson VERSION 7.4.0)
 
 if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
 	include(CTest)

appveyor.yml

@@ -1,4 +1,4 @@
-version: 7.3.0.{build}
+version: 7.4.0.{build}
 environment:
   matrix:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2022

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/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/JsonObject/set.cpp

@@ -100,13 +100,13 @@ 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

@@ -63,6 +63,18 @@ 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));
 

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

@@ -8,6 +8,7 @@ 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/Memory/StringBuffer.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() == "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();
+    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() == "alfa");
+  }
+}

extras/tests/ResourceManager/StringBuilder.cpp

@@ -7,6 +7,7 @@
 
 #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() == "url");
   }
 
   SECTION("Short string fits in first allocation") {
@@ -96,48 +116,69 @@ TEST_CASE("StringBuilder") {
   }
 }
 
-static StringNode* addStringToPool(ResourceManager& resources, const char* s) {
-  StringBuilder str(&resources);
-  str.startString();
-  str.append(s);
-  return str.save();
+static JsonString saveString(StringBuilder& builder, const char* s) {
+  VariantData data;
+  builder.startString();
+  builder.append(s);
+  builder.save(&data);
+  return data.asString();
 }
 
 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 == "hello");
+    REQUIRE(s2 == "world");
+    REQUIRE(+s1.c_str() == +s3.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 == "hello world");
+    REQUIRE(s2 == "hello");
+    REQUIRE(+s2.c_str() != +s1.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 == "hello world");
+    REQUIRE(s2 == "worl");
+    REQUIRE(s2.c_str() != s1.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: "7.4.0"
 description: >-
   A simple and efficient JSON library for embedded C++.
-  ★ 6785 stars on GitHub!
+  ★ 6896 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++. ⭐ 6896 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": "7.4.0",
   "authors": {
     "name": "Benoit Blanchon",
     "url": "https://blog.benoitblanchon.fr"

library.properties

@@ -1,9 +1,9 @@
 name=ArduinoJson
-version=7.3.0
+version=7.4.0
 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=⭐ 6896 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/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/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(s, static_cast<uint8_t>(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(p, static_cast<uint8_t>(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

@@ -68,6 +68,22 @@ 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;

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

@@ -24,6 +24,7 @@ enum class VariantTypeBits : uint8_t {
 
 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 +47,8 @@ inline bool operator&(VariantType type, VariantTypeBits bit) {
   return (uint8_t(type) & uint8_t(bit)) != 0;
 }
 
+const size_t tinyStringMaxLength = 3;
+
 union VariantContent {
   VariantContent() {}
 
@@ -61,6 +64,7 @@ union VariantContent {
   CollectionData asCollection;
   const char* asLinkedString;
   struct StringNode* asOwnedString;
+  char asTinyString[tinyStringMaxLength + 1];
 };
 
 #if ARDUINOJSON_USE_EXTENSIONS

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_;
@@ -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(content_.asLinkedString, true));
 
@@ -199,6 +212,9 @@ class VariantData {
       case VariantType::Int64:
         return static_cast<T>(extension->asInt64);
 #endif
+      case VariantType::TinyString:
+        str = content_.asTinyString;
+        break;
       case VariantType::LinkedString:
         str = content_.asLinkedString;
         break;
@@ -241,6 +257,9 @@ class VariantData {
       case VariantType::Int64:
         return convertNumber<T>(extension->asInt64);
 #endif
+      case VariantType::TinyString:
+        str = content_.asTinyString;
+        break;
       case VariantType::LinkedString:
         str = content_.asLinkedString;
         break;
@@ -281,6 +300,8 @@ class VariantData {
 
   JsonString asString() const {
     switch (type_) {
+      case VariantType::TinyString:
+        return JsonString(content_.asTinyString);
       case VariantType::LinkedString:
         return JsonString(content_.asLinkedString, true);
       case VariantType::OwnedString:
@@ -395,7 +416,8 @@ 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 {
@@ -488,11 +510,6 @@ 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) {
@@ -509,6 +526,15 @@ class VariantData {
     content_.asLinkedString = s;
   }
 
+  void setTinyString(const char* s, uint8_t n) {
+    ARDUINOJSON_ASSERT(type_ == VariantType::Null);  // must call clear() first
+    ARDUINOJSON_ASSERT(s);
+    type_ = VariantType::TinyString;
+    for (uint8_t i = 0; i < n; i++)
+      content_.asTinyString[i] = s[i];
+    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

@@ -31,6 +31,11 @@ inline bool VariantData::setString(TAdaptedString value,
     return true;
   }
 
+  if (isTinyString(value, value.size())) {
+    setTinyString(value.data(), uint8_t(value.size()));
+    return true;
+  }
+
   auto dup = resources->saveString(value);
   if (dup) {
     setOwnedString(dup);

src/ArduinoJson/version.hpp

@@ -4,8 +4,8 @@
 
 #pragma once
 
-#define ARDUINOJSON_VERSION "7.3.0"
+#define ARDUINOJSON_VERSION "7.4.0"
 #define ARDUINOJSON_VERSION_MAJOR 7
-#define ARDUINOJSON_VERSION_MINOR 3
+#define ARDUINOJSON_VERSION_MINOR 4
 #define ARDUINOJSON_VERSION_REVISION 0
-#define ARDUINOJSON_VERSION_MACRO V730
+#define ARDUINOJSON_VERSION_MACRO V740