Fixed dangling reference in MemberProxy and ElementProxy (fixes #1120)

CHANGELOG.md

@@ -10,6 +10,7 @@ HEAD
 * Improved `deserializeMsgPack()` speed by reading several bytes at once
 * Added detection of Atmel AVR8/GNU C Compiler (issue #1112)
 * Fixed deserializer that stopped reading at the first `0xFF` (PR #1118 by @mikee47)
+* Fixed dangling reference in copies of `MemberProxy` and `ElementProxy` (issue #1120)
 
 v6.12.0 (2019-09-05)
 -------

extras/tests/MixedConfiguration/cpp11.cpp

@@ -28,4 +28,59 @@ TEST_CASE("nullptr") {
   }
 }
 
+TEST_CASE("Issue #1120") {
+  StaticJsonDocument<500> doc;
+  constexpr char str[] =
+      "{\"contents\":[{\"module\":\"Packet\"},{\"module\":\"Analog\"}]}";
+  deserializeJson(doc, str);
+
+  SECTION("MemberProxy<std::string>::isNull()") {
+    SECTION("returns false") {
+      auto value = doc[std::string("contents")];
+      CHECK(value.isNull() == false);
+    }
+
+    SECTION("returns true") {
+      auto value = doc[std::string("zontents")];
+      CHECK(value.isNull() == true);
+    }
+  }
+
+  SECTION("ElementProxy<MemberProxy<const char*> >::isNull()") {
+    SECTION("returns false") {  // Issue #1120
+      auto value = doc["contents"][1];
+      CHECK(value.isNull() == false);
+    }
+
+    SECTION("returns true") {
+      auto value = doc["contents"][2];
+      CHECK(value.isNull() == true);
+    }
+  }
+
+  SECTION("MemberProxy<ElementProxy<MemberProxy>, const char*>::isNull()") {
+    SECTION("returns false") {
+      auto value = doc["contents"][1]["module"];
+      CHECK(value.isNull() == false);
+    }
+
+    SECTION("returns true") {
+      auto value = doc["contents"][1]["zodule"];
+      CHECK(value.isNull() == true);
+    }
+  }
+
+  SECTION("MemberProxy<ElementProxy<MemberProxy>, std::string>::isNull()") {
+    SECTION("returns false") {
+      auto value = doc["contents"][1][std::string("module")];
+      CHECK(value.isNull() == false);
+    }
+
+    SECTION("returns true") {
+      auto value = doc["contents"][1][std::string("zodule")];
+      CHECK(value.isNull() == true);
+    }
+  }
+}
+
 #endif

src/ArduinoJson/Array/ArrayImpl.hpp

@@ -19,4 +19,10 @@ inline ObjectRef ArrayShortcuts<TArray>::createNestedObject() const {
   return impl()->addElement().template to<ObjectRef>();
 }
 
+template <typename TArray>
+inline ElementProxy<TArray> ArrayShortcuts<TArray>::operator[](
+    size_t index) const {
+  return ElementProxy<TArray>(*impl(), index);
+}
+
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Array/ArrayShortcuts.hpp

@@ -16,7 +16,7 @@ template <typename TArray>
 class ArrayShortcuts {
  public:
   // Returns the element at specified index if the variant is an array.
-  FORCE_INLINE ElementProxy<const TArray &> operator[](size_t index) const;
+  FORCE_INLINE ElementProxy<TArray> operator[](size_t index) const;
 
   FORCE_INLINE ObjectRef createNestedObject() const;
 

src/ArduinoJson/Array/ElementProxy.hpp

@@ -161,12 +161,6 @@ class ElementProxy : public VariantOperators<ElementProxy<TArray> >,
   const size_t _index;
 };
 
-template <typename TArray>
-inline ElementProxy<const TArray&> ArrayShortcuts<TArray>::operator[](
-    size_t index) const {
-  return ElementProxy<const TArray&>(*impl(), index);
-}
-
 }  // namespace ARDUINOJSON_NAMESPACE
 
 #ifdef _MSC_VER

src/ArduinoJson/Document/JsonDocument.hpp

@@ -141,11 +141,10 @@ class JsonDocument : public Visitable {
   // operator[](const std::string&)
   // operator[](const String&)
   template <typename TString>
-  FORCE_INLINE
-      typename enable_if<IsString<TString>::value,
-                         MemberProxy<JsonDocument&, const TString&> >::type
+  FORCE_INLINE typename enable_if<IsString<TString>::value,
+                                  MemberProxy<JsonDocument&, TString> >::type
   operator[](const TString& key) {
-    return MemberProxy<JsonDocument&, const TString&>(*this, key);
+    return MemberProxy<JsonDocument&, TString>(*this, key);
   }
 
   // operator[](char*)

src/ArduinoJson/Object/MemberProxy.hpp

@@ -174,22 +174,6 @@ class MemberProxy : public VariantOperators<MemberProxy<TObject, TStringRef> >,
   TStringRef _key;
 };
 
-template <typename TObject>
-template <typename TString>
-inline typename enable_if<IsString<TString>::value,
-                          MemberProxy<const TObject &, const TString &> >::type
-    ObjectShortcuts<TObject>::operator[](const TString &key) const {
-  return MemberProxy<const TObject &, const TString &>(*impl(), key);
-}
-
-template <typename TObject>
-template <typename TString>
-inline typename enable_if<IsString<TString *>::value,
-                          MemberProxy<const TObject &, TString *> >::type
-    ObjectShortcuts<TObject>::operator[](TString *key) const {
-  return MemberProxy<const TObject &, TString *>(*impl(), key);
-}
-
 }  // namespace ARDUINOJSON_NAMESPACE
 
 #ifdef _MSC_VER

src/ArduinoJson/Object/ObjectImpl.hpp

@@ -49,4 +49,21 @@ inline typename enable_if<IsString<TChar*>::value, bool>::type
 ObjectShortcuts<TObject>::containsKey(TChar* key) const {
   return !impl()->getMember(key).isUndefined();
 }
+
+template <typename TObject>
+template <typename TString>
+inline typename enable_if<IsString<TString*>::value,
+                          MemberProxy<TObject, TString*> >::type
+    ObjectShortcuts<TObject>::operator[](TString* key) const {
+  return MemberProxy<TObject, TString*>(*impl(), key);
+}
+
+template <typename TObject>
+template <typename TString>
+inline typename enable_if<IsString<TString>::value,
+                          MemberProxy<TObject, TString> >::type
+    ObjectShortcuts<TObject>::operator[](const TString& key) const {
+  return MemberProxy<TObject, TString>(*impl(), key);
+}
+
 }  // namespace ARDUINOJSON_NAMESPACE

src/ArduinoJson/Object/ObjectShortcuts.hpp

@@ -31,9 +31,8 @@ class ObjectShortcuts {
   // operator[](const std::string&) const
   // operator[](const String&) const
   template <typename TString>
-  FORCE_INLINE
-      typename enable_if<IsString<TString>::value,
-                         MemberProxy<const TObject &, const TString &> >::type
+  FORCE_INLINE typename enable_if<IsString<TString>::value,
+                                  MemberProxy<TObject, TString> >::type
   operator[](const TString &key) const;
 
   // operator[](char*) const
@@ -41,7 +40,7 @@ class ObjectShortcuts {
   // operator[](const __FlashStringHelper*) const
   template <typename TChar>
   FORCE_INLINE typename enable_if<IsString<TChar *>::value,
-                                  MemberProxy<const TObject &, TChar *> >::type
+                                  MemberProxy<TObject, TChar *> >::type
   operator[](TChar *key) const;
 
   // createNestedArray(const std::string&) const