DynamicJsonDocument reallocates memory pool is it's too small

src/ArduinoJson/Document/DynamicJsonDocument.hpp

@@ -13,36 +13,48 @@ namespace ARDUINOJSON_NAMESPACE {
 class DynamicJsonDocument : public JsonDocument {
  public:
   DynamicJsonDocument(size_t capa = ARDUINOJSON_DEFAULT_POOL_SIZE)
-      : JsonDocument(alloc(capa), addPadding(capa)) {}
+      : JsonDocument(allocPool(addPadding(capa))) {}
 
   DynamicJsonDocument(const DynamicJsonDocument& src)
-      : JsonDocument(alloc(src.memoryUsage()), addPadding(src.memoryUsage())) {
+      : JsonDocument(allocPool(src.capacity())) {
     copy(src);
   }
 
   DynamicJsonDocument(const JsonDocument& src)
-      : JsonDocument(alloc(src.memoryUsage()), addPadding(src.memoryUsage())) {
+      : JsonDocument(allocPool(src.capacity())) {
     copy(src);
   }
 
   ~DynamicJsonDocument() {
-    free(memoryPool().buffer());
+    freePool();
   }
 
   DynamicJsonDocument& operator=(const DynamicJsonDocument& src) {
+    reallocPoolIfTooSmall(src.memoryUsage());
     copy(src);
     return *this;
   }
 
   template <typename T>
   DynamicJsonDocument& operator=(const JsonDocument& src) {
+    reallocPoolIfTooSmall(src.memoryUsage());
     copy(src);
     return *this;
   }
 
  private:
-  static char* alloc(size_t capa) {
+  MemoryPool allocPool(size_t capa) {
-    return reinterpret_cast<char*>(malloc(addPadding(capa)));
+    return MemoryPool(reinterpret_cast<char*>(malloc(capa)), capa);
+  }
+
+  void reallocPoolIfTooSmall(size_t requiredSize) {
+    if (requiredSize <= capacity()) return;
+    freePool();
+    replacePool(allocPool(addPadding(requiredSize)));
+  }
+
+  void freePool() {
+    free(memoryPool().buffer());
   }
 };
 

src/ArduinoJson/Document/JsonDocument.hpp

@@ -63,6 +63,9 @@ class JsonDocument : public Visitable {
   }
 
  protected:
+  JsonDocument(MemoryPool pool)
+      : nestingLimit(ARDUINOJSON_DEFAULT_NESTING_LIMIT), _pool(pool) {}
+
   JsonDocument(char* buf, size_t capa)
       : nestingLimit(ARDUINOJSON_DEFAULT_NESTING_LIMIT), _pool(buf, capa) {}
 
@@ -71,6 +74,10 @@ class JsonDocument : public Visitable {
     to<VariantRef>().set(src.as<VariantRef>());
   }
 
+  void replacePool(MemoryPool pool) {
+    _pool = pool;
+  }
+
  private:
   VariantRef getVariant() {
     return VariantRef(&_pool, &_data);

test/JsonDocument/DynamicJsonDocument.cpp

@@ -51,60 +51,6 @@ TEST_CASE("DynamicJsonDocument") {
     }
   }
 
-  SECTION("Copy constructor") {
-    deserializeJson(doc, "{\"hello\":\"world\"}");
-    doc.nestingLimit = 42;
-
-    DynamicJsonDocument doc2 = doc;
-
-    std::string json;
-    serializeJson(doc2, json);
-    REQUIRE(json == "{\"hello\":\"world\"}");
-    REQUIRE(doc2.nestingLimit == 42);
-  }
-
-  SECTION("Copy assignment") {
-    DynamicJsonDocument doc2;
-    deserializeJson(doc2, "{\"hello\":\"world\"}");
-    doc2.nestingLimit = 42;
-
-    doc = doc2;
-
-    std::string json;
-    serializeJson(doc, json);
-    REQUIRE(json == "{\"hello\":\"world\"}");
-    REQUIRE(doc.nestingLimit == 42);
-  }
-
-  SECTION("Construct from StaticJsonDocument") {
-    StaticJsonDocument<200> sdoc;
-    deserializeJson(sdoc, "{\"hello\":\"world\"}");
-    sdoc.nestingLimit = 42;
-
-    DynamicJsonDocument ddoc = sdoc;
-
-    std::string json;
-    serializeJson(ddoc, json);
-    REQUIRE(json == "{\"hello\":\"world\"}");
-    REQUIRE(ddoc.nestingLimit == 42);
-  }
-
-  SECTION("Assign from StaticJsonDocument") {
-    DynamicJsonDocument ddoc;
-    ddoc.to<JsonVariant>().set(666);
-
-    StaticJsonDocument<200> sdoc;
-    deserializeJson(sdoc, "{\"hello\":\"world\"}");
-    sdoc.nestingLimit = 42;
-
-    ddoc = sdoc;
-
-    std::string json;
-    serializeJson(ddoc, json);
-    REQUIRE(json == "{\"hello\":\"world\"}");
-    REQUIRE(ddoc.nestingLimit == 42);
-  }
-
   SECTION("memoryUsage()") {
     SECTION("Increases after adding value to array") {
       JsonArray arr = doc.to<JsonArray>();
@@ -127,3 +73,81 @@ TEST_CASE("DynamicJsonDocument") {
     }
   }
 }
+
+TEST_CASE("DynamicJsonDocument copies") {
+  SECTION("Copy constructor") {
+    DynamicJsonDocument doc1(1234);
+    deserializeJson(doc1, "{\"hello\":\"world\"}");
+    doc1.nestingLimit = 42;
+
+    DynamicJsonDocument doc2 = doc1;
+
+    std::string json;
+    serializeJson(doc2, json);
+    REQUIRE(json == "{\"hello\":\"world\"}");
+
+    REQUIRE(doc2.nestingLimit == 42);
+    REQUIRE(doc2.capacity() == doc1.capacity());
+  }
+
+  SECTION("Copy assignment preserves the buffer when capacity is sufficient") {
+    DynamicJsonDocument doc1(1234);
+    deserializeJson(doc1, "{\"hello\":\"world\"}");
+    doc1.nestingLimit = 42;
+
+    DynamicJsonDocument doc2(doc1.capacity());
+    doc2 = doc1;
+
+    std::string json;
+    serializeJson(doc2, json);
+    REQUIRE(json == "{\"hello\":\"world\"}");
+    REQUIRE(doc2.nestingLimit == 42);
+    REQUIRE(doc2.capacity() == doc1.capacity());
+  }
+
+  SECTION("Copy assignment realloc the buffer when capacity is insufficient") {
+    DynamicJsonDocument doc1(1234);
+    deserializeJson(doc1, "{\"hello\":\"world\"}");
+    doc1.nestingLimit = 42;
+    DynamicJsonDocument doc2(8);
+
+    REQUIRE(doc2.capacity() < doc1.memoryUsage());
+    doc2 = doc1;
+    REQUIRE(doc2.capacity() >= doc1.memoryUsage());
+
+    std::string json;
+    serializeJson(doc2, json);
+    REQUIRE(json == "{\"hello\":\"world\"}");
+    REQUIRE(doc2.nestingLimit == 42);
+  }
+
+  SECTION("Construct from StaticJsonDocument") {
+    StaticJsonDocument<200> sdoc;
+    deserializeJson(sdoc, "{\"hello\":\"world\"}");
+    sdoc.nestingLimit = 42;
+
+    DynamicJsonDocument ddoc = sdoc;
+
+    std::string json;
+    serializeJson(ddoc, json);
+    REQUIRE(json == "{\"hello\":\"world\"}");
+    REQUIRE(ddoc.nestingLimit == 42);
+    REQUIRE(ddoc.capacity() == sdoc.capacity());
+  }
+
+  SECTION("Assign from StaticJsonDocument") {
+    DynamicJsonDocument ddoc;
+    ddoc.to<JsonVariant>().set(666);
+
+    StaticJsonDocument<200> sdoc;
+    deserializeJson(sdoc, "{\"hello\":\"world\"}");
+    sdoc.nestingLimit = 42;
+
+    ddoc = sdoc;
+
+    std::string json;
+    serializeJson(ddoc, json);
+    REQUIRE(json == "{\"hello\":\"world\"}");
+    REQUIRE(ddoc.nestingLimit == 42);
+  }
+}