Store static strings in a dedicated pool

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

extras/tests/ResourceManager/CMakeLists.txt

@@ -5,6 +5,7 @@
 add_executable(ResourceManagerTests
 	allocVariant.cpp
 	clear.cpp
+	saveStaticString.cpp
 	saveString.cpp
 	shrinkToFit.cpp
 	size.cpp

extras/tests/ResourceManager/StringBuffer.cpp

@@ -2,7 +2,7 @@
 // Copyright © 2014-2025, Benoit BLANCHON
 // MIT License
 
-#include <ArduinoJson/Memory/StringBuffer.hpp>
+#include <ArduinoJson.hpp>
 #include <catch.hpp>
 
 #include "Allocators.hpp"
@@ -22,7 +22,7 @@ TEST_CASE("StringBuffer") {
     sb.save(&variant);
 
     REQUIRE(variant.type() == VariantType::TinyString);
-    REQUIRE(variant.asString() == "hi!");
+    REQUIRE(variant.asString(&resources) == "hi!");
   }
 
   SECTION("Tiny string can't contain NUL") {
@@ -32,7 +32,7 @@ TEST_CASE("StringBuffer") {
 
     REQUIRE(variant.type() == VariantType::OwnedString);
 
-    auto str = variant.asString();
+    auto str = variant.asString(&resources);
     REQUIRE(str.size() == 3);
     REQUIRE(str.c_str()[0] == 'a');
     REQUIRE(str.c_str()[1] == 0);
@@ -45,6 +45,6 @@ TEST_CASE("StringBuffer") {
     sb.save(&variant);
 
     REQUIRE(variant.type() == VariantType::OwnedString);
-    REQUIRE(variant.asString() == "alfa");
+    REQUIRE(variant.asString(&resources) == "alfa");
   }
 }

extras/tests/ResourceManager/StringBuilder.cpp

@@ -2,7 +2,7 @@
 // Copyright © 2014-2025, Benoit BLANCHON
 // MIT License
 
-#include <ArduinoJson/Memory/StringBuilder.hpp>
+#include <ArduinoJson.hpp>
 #include <catch.hpp>
 
 #include "Allocators.hpp"
@@ -46,7 +46,7 @@ TEST_CASE("StringBuilder") {
 
     REQUIRE(resources.overflowed() == false);
     REQUIRE(data.type() == VariantType::TinyString);
-    REQUIRE(data.asString() == "url");
+    REQUIRE(data.asString(&resources) == "url");
   }
 
   SECTION("Short string fits in first allocation") {
@@ -134,9 +134,10 @@ TEST_CASE("StringBuilder::save() deduplicates strings") {
     auto s2 = saveString(builder, "world");
     auto s3 = saveString(builder, "hello");
 
-    REQUIRE(s1.asString() == "hello");
-    REQUIRE(s2.asString() == "world");
-    REQUIRE(+s1.asString().c_str() == +s3.asString().c_str());  // same address
+    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{
@@ -152,10 +153,10 @@ TEST_CASE("StringBuilder::save() deduplicates strings") {
     auto s1 = saveString(builder, "hello world");
     auto s2 = saveString(builder, "hello");
 
-    REQUIRE(s1.asString() == "hello world");
-    REQUIRE(s2.asString() == "hello");
-    REQUIRE(+s2.asString().c_str() !=
-            +s1.asString().c_str());  // different address
+    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{
@@ -170,10 +171,10 @@ TEST_CASE("StringBuilder::save() deduplicates strings") {
     auto s1 = saveString(builder, "hello world");
     auto s2 = saveString(builder, "worl");
 
-    REQUIRE(s1.asString() == "hello world");
-    REQUIRE(s2.asString() == "worl");
-    REQUIRE(s2.asString().c_str() !=
-            s1.asString().c_str());  // different address
+    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{

extras/tests/ResourceManager/saveStaticString.cpp

@@ -0,0 +1,47 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2025, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson/Memory/ResourceManager.hpp>
+#include <ArduinoJson/Strings/StringAdapters.hpp>
+#include <catch.hpp>
+
+#include "Allocators.hpp"
+
+using namespace ArduinoJson::detail;
+
+TEST_CASE("ResourceManager::saveStaticString() deduplicates strings") {
+  SpyingAllocator spy;
+  ResourceManager resources(&spy);
+
+  auto str1 = "hello";
+  auto str2 = "world";
+
+  auto id1 = resources.saveStaticString(str1);
+  auto id2 = resources.saveStaticString(str2);
+  REQUIRE(id1 != id2);
+
+  auto id3 = resources.saveStaticString(str1);
+  REQUIRE(id1 == id3);
+
+  resources.shrinkToFit();
+  REQUIRE(spy.log() ==
+          AllocatorLog{
+              Allocate(sizeofStaticStringPool()),
+              Reallocate(sizeofStaticStringPool(), sizeofStaticStringPool(2)),
+          });
+  REQUIRE(resources.overflowed() == false);
+}
+
+TEST_CASE("ResourceManager::saveStaticString() when allocation fails") {
+  SpyingAllocator spy(FailingAllocator::instance());
+  ResourceManager resources(&spy);
+
+  auto slotId = resources.saveStaticString("hello");
+
+  REQUIRE(slotId == NULL_SLOT);
+  REQUIRE(resources.overflowed() == true);
+  REQUIRE(spy.log() == AllocatorLog{
+                           AllocateFail(sizeofStaticStringPool()),
+                       });
+}