cocos2d::Data: prevent use after free.

cocos/base/CCData.cpp

@@ -82,7 +82,7 @@ Data& Data::operator= (Data&& other)
 
 void Data::move(Data& other)
 {
-    clear();
+    if(_bytes != other._bytes) clear();
 
     _bytes = other._bytes;
     _size = other._size;
@@ -106,27 +106,35 @@ ssize_t Data::getSize() const
     return _size;
 }
 
-void Data::copy(const unsigned char* bytes, const ssize_t size)
+ssize_t Data::copy(const unsigned char* bytes, const ssize_t size)
 {
-    clear();
+    CCASSERT(size >= 0, "copy size should be non-negative");
+    CCASSERT(bytes, "bytes should not be nullptr");
+
+    if (size <= 0) return 0;
 
-    if (size > 0)
+    if (bytes != _bytes)
     {
-        _size = size;
+        clear();
         _bytes = (unsigned char*)malloc(sizeof(unsigned char) * _size);
         memcpy(_bytes, bytes, _size);
     }
+
+    _size = size;
+    return _size;
 }
 
 void Data::fastSet(unsigned char* bytes, const ssize_t size)
 {
+    CCASSERT(size >= 0, "fastSet size should be non-negative");
+    CCASSERT(bytes, "bytes should not be nullptr");
     _bytes = bytes;
     _size = size;
 }
 
 void Data::clear()
 {
-    free(_bytes);
+    if(_bytes) free(_bytes);
     _bytes = nullptr;
     _size = 0;
 }

cocos/base/CCData.h

@@ -97,8 +97,9 @@ class CC_DLL Data
      *  @note This method will copy the whole buffer.
      *        Developer should free the pointer after invoking this method.
      *  @see Data::fastSet
+     * @return The size of bytes copied, return 0 if size <= 0
      */
-    void copy(const unsigned char* bytes, const ssize_t size);
+    ssize_t copy(const unsigned char* bytes, const ssize_t size);
 
     /** Fast set the buffer pointer and its size. Please use it carefully.
      *  @param bytes The buffer pointer, note that it have to be allocated by 'malloc' or 'calloc',