Fix segfault issue

I think we need to keep a reference to the ctypes voidp object that we
pass as userdata alive

weaseljson.py

@@ -33,52 +33,7 @@ class WeaselJsonStatus(enum.Enum):
     OVERFLOW = 3
 
 
-class WeaselJsonParserBase:
+class WeaselJsonCallbacksBase:
-    def __init__(
-        self,
-        build_dir: Optional[str] = None,
-        stackSize: int = 1024,
-    ) -> None:
-        self._lib = None
-        if build_dir is None:
-            build_dir = os.path.dirname(__file__) + "/build"
-        for f in (build_dir + "/" + "libweaseljson.so",):
-            try:
-                self._lib = ctypes.cdll.LoadLibrary(f)
-            except OSError:
-                print("Could not load " + f)
-                pass
-
-        if self._lib is None:
-            import sys
-
-            print(
-                "Could not find libweaseljson implementation",
-                file=sys.stderr,
-            )
-            sys.exit(1)
-
-        self._lib.WeaselJsonParser_create.argtypes = (
-            ctypes.c_int,
-            ctypes.POINTER(WeaselJsonCallbacks),
-            ctypes.c_void_p,
-        )
-        self._lib.WeaselJsonParser_create.restype = ctypes.c_void_p
-        self._lib.WeaselJsonParser_reset.argtypes = (ctypes.c_void_p,)
-        self._lib.WeaselJsonParser_destroy.argtypes = (ctypes.c_void_p,)
-        self._lib.WeaselJsonParser_parse.argtypes = (
-            ctypes.c_void_p,
-            ctypes.c_void_p,
-            ctypes.c_int,
-        )
-        self._lib.WeaselJsonParser_parse.restype = WeaselJsonStatus
-
-        self.p = self._lib.WeaselJsonParser_create(
-            stackSize,
-            callbacks,
-            ctypes.cast(ctypes.pointer(ctypes.py_object(self)), ctypes.c_void_p),
-        )
-
     def on_begin_object(self):
         pass
 
@@ -118,6 +73,57 @@ class WeaselJsonParserBase:
     def on_null_literal(self):
         pass
 
+
+class WeaselJsonParser:
+    def __init__(
+        self,
+        callbacks: WeaselJsonCallbacksBase,
+        build_dir: Optional[str] = None,
+        stackSize: int = 1024,
+    ) -> None:
+        self._lib = None
+        if build_dir is None:
+            build_dir = os.path.dirname(__file__) + "/build"
+        for f in (build_dir + "/" + "libweaseljson.so",):
+            try:
+                self._lib = ctypes.cdll.LoadLibrary(f)
+            except OSError:
+                print("Could not load " + f)
+                pass
+
+        if self._lib is None:
+            import sys
+
+            print(
+                "Could not find libweaseljson implementation",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+
+        self._lib.WeaselJsonParser_create.argtypes = (
+            ctypes.c_int,
+            ctypes.POINTER(WeaselJsonCallbacks),
+            ctypes.c_void_p,
+        )
+        self._lib.WeaselJsonParser_create.restype = ctypes.c_void_p
+        self._lib.WeaselJsonParser_reset.argtypes = (ctypes.c_void_p,)
+        self._lib.WeaselJsonParser_destroy.argtypes = (ctypes.c_void_p,)
+        self._lib.WeaselJsonParser_parse.argtypes = (
+            ctypes.c_void_p,
+            ctypes.c_void_p,
+            ctypes.c_int,
+        )
+        self._lib.WeaselJsonParser_parse.restype = WeaselJsonStatus
+        self.voidp_callbacks = ctypes.cast(
+            ctypes.pointer(ctypes.py_object(callbacks)), ctypes.c_void_p
+        )
+
+        self.p = self._lib.WeaselJsonParser_create(
+            stackSize,
+            c_callbacks,
+            self.voidp_callbacks,
+        )
+
     def parse(self, data: bytes) -> WeaselJsonStatus:
         buf = (ctypes.c_ubyte * len(data)).from_buffer(bytearray(data))
         return self._lib.WeaselJsonParser_parse(self.p, buf, len(data))
@@ -215,7 +221,7 @@ def on_null_literal(p):
     self.on_null_literal()
 
 
-callbacks = WeaselJsonCallbacks(
+c_callbacks = WeaselJsonCallbacks(
     on_begin_object,
     on_end_object,
     on_begin_string,
@@ -232,13 +238,13 @@ callbacks = WeaselJsonCallbacks(
 )
 
 
-class JsonParser(WeaselJsonParserBase):
+class MyCallbacks(WeaselJsonCallbacksBase):
     # override callbacks
     def on_string_data(self, data):
         print(data)
 
 
-with JsonParser() as parser:
+with WeaselJsonParser(MyCallbacks()) as parser:
     raw = json.dumps({"hello": "world", "foo": 42}).encode()
     i = 0
     stride = 1