fix: memory leak from string cstring disposal (#40)

* fix: memory leak from string cstring disposal

* undo test case

Author: bgiori

src/amplitude_experiment/local/evaluation/evaluation.py

@@ -1,4 +1,5 @@
 from .libevaluation_interop import libevaluation_interop_symbols
+from ctypes import cast, c_char_p
 
 def evaluate(rules: str, user: str) -> str:
     """
@@ -11,4 +12,6 @@ def evaluate(rules: str, user: str) -> str:
             Evaluation results with variants in JSON
     """
     result = libevaluation_interop_symbols().contents.kotlin.root.evaluate(rules, user)
-    return str(result, 'utf-8')
+    py_result = cast(result, c_char_p).value
+    libevaluation_interop_symbols().contents.DisposeString(result)
+    return str(py_result, 'utf-8')

src/amplitude_experiment/local/evaluation/libevaluation_interop.py

@@ -1086,7 +1086,11 @@ class struct_anon_14(Structure):
     'evaluate',
 ]
 struct_anon_14._fields_ = [
-    ('evaluate', CFUNCTYPE(UNCHECKED(c_char_p), String, String)),
+    # NOTE(bgiori): Changed this line from `UNCHECKED(c_char_p)` to `UNCHECKED(c_void_p)`
+    #               to help fix a memory leak. Strings returned from kotlin/native must
+    #               be freed using the DisposeString function, but c_char_p converts the
+    #               c value making it incompatible with the dispose function.
+    ('evaluate', CFUNCTYPE(UNCHECKED(c_void_p), String, String)),
 ]
 
 # src/amplitude_experiment/local/evaluation/lib/macosX64/libevaluation_interop_api.h: 100