C++: Make proxies safer

If a user happens to store an ElementProxy or a PropertyProxy
instance, we need to take a reference to the JSON value they point to.
With PropertyProxy, the key needs to be copied as well.

2 files changed, 40 insertions, 5 deletions

diff --git a/src/jansson.hpp b/src/jansson.hpp
index bf723bd..ad6d177 100644
--- a/src/jansson.hpp
+++ b/src/jansson.hpp
@@ -166,8 +166,9 @@ namespace json {
         // proxies an array element
         class ElementProxy {
         public:
-            // constructor
-            ElementProxy(json_t* array, unsigned int index) : _array(array), _index(index) {}
+            ElementProxy(json_t* array, unsigned int index);
+            ElementProxy(const ElementProxy& other);
+            ~ElementProxy();
 
             // assign to the proxied element
             inline ElementProxy& operator=(const Value& value);
@@ -186,8 +187,9 @@ namespace json {
         // proxies an object property
         class PropertyProxy {
         public:
-            // constructor
-            PropertyProxy(json_t* array, const char* key) : _object(array), _key(key) {}
+            PropertyProxy(json_t* object, const char *key);
+            PropertyProxy(const PropertyProxy& other);
+            ~PropertyProxy();
 
             // assign to the proxied element
             inline PropertyProxy& operator=(const Value& value);
@@ -200,7 +202,7 @@ namespace json {
             json_t* _object;
 
             // key of property
-            const char* _key;
+            char* _key;
         };
 
     } // namespace json::detail
diff --git a/src/jansson.ipp b/src/jansson.ipp
index 5938f0f..fd3a1bf 100644
--- a/src/jansson.ipp
+++ b/src/jansson.ipp
@@ -8,6 +8,8 @@
 #error "jansson.ipp may only be included from jansson.hpp"
 #endif
 
+#include <string.h>
+
 namespace json {
     namespace detail {
         // assignment operator
@@ -310,6 +312,20 @@ namespace json {
             return v;
         }
 
+        ElementProxy::ElementProxy(json_t* array, unsigned int index)
+            : _array(array), _index(index) {
+            json_incref(_array);
+        }
+
+        ElementProxy::ElementProxy(const ElementProxy& other) 
+            : _array(other._array), _index(other._index) {
+            json_incref(_array);
+        }
+
+        ElementProxy::~ElementProxy() {
+            json_decref(_array);
+        }
+
         // assign value to proxied array element
         ElementProxy& ElementProxy::operator=(const Value& value) {
             json_array_set(_array, _index, value.as_json());
@@ -321,6 +337,23 @@ namespace json {
             return json_array_get(_array, _index);
         }
 
+        PropertyProxy::PropertyProxy(json_t* object, const char* key)
+            : _object(object) {
+            _key = strdup(key);
+            json_incref(_object);
+        }
+
+        PropertyProxy::PropertyProxy(const PropertyProxy& other)
+            : _object(other._object) {
+            _key = strdup(other._key);
+            json_incref(_object);
+        }
+
+        PropertyProxy::~PropertyProxy() {
+            free(_key);
+            json_decref(_object);
+        }
+
         // assign value to proxied object property
         PropertyProxy& PropertyProxy::operator=(const Value& value) {
             json_object_set(_object, _key, value.as_json());