fix: Safer context handling in streams (#170)

* fix: 1

* fix: Update c2pa.py code

* fix: Renamings

* fix: Format

Author: tmathern

src/c2pa/c2pa.py

@@ -1107,9 +1107,14 @@ def flush_callback(ctx):
         self._write_cb = WriteCallback(write_callback)
         self._flush_cb = FlushCallback(flush_callback)
 
+        # Create a placeholder context as we don't actually use the context,
+        # but we need having a valid context pointer. Therefore, we create
+        # a small buffer and cast it to a StreamContext pointer
+        self._context = ctypes.create_string_buffer(1)
+
         # Create the stream
         self._stream = _lib.c2pa_create_stream(
-            None,  # context
+            ctypes.cast(self._context, ctypes.POINTER(StreamContext)),
             self._read_cb,
             self._seek_cb,
             self._write_cb,