Optimize storage of tiny strings (up to 3 characters)

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");
+  }
+}