Really fix python.

src/python/grpcio/grpc/_cython/_cygrpc/grpc.pxi

@@ -279,12 +279,21 @@ cdef extern from "grpc/grpc.h":
   ctypedef struct grpc_op_data_recv_close_on_server:
     int *cancelled
 
+  ctypedef struct grpc_op_data_send_message:
+    grpc_byte_buffer *send_message
+
+  ctypedef struct grpc_op_data_receive_message:
+    grpc_byte_buffer **receive_message "recv_message"
+
+  ctypedef struct grpc_op_data_receive_initial_metadata:
+    grpc_metadata_array *receive_initial_metadata "recv_initial_metadata"
+
   union grpc_op_data:
     grpc_op_data_send_initial_metadata send_initial_metadata
-    grpc_byte_buffer *send_message
+    grpc_op_data_send_message send_message
     grpc_op_data_send_status_from_server send_status_from_server
-    grpc_metadata_array *receive_initial_metadata "recv_initial_metadata"
-    grpc_byte_buffer **receive_message "recv_message"
+    grpc_op_data_receive_initial_metadata receive_initial_metadata "recv_initial_metadata"
+    grpc_op_data_receive_message receive_message "recv_message"
     grpc_op_data_recv_status_on_client receive_status_on_client "recv_status_on_client"
     grpc_op_data_recv_close_on_server receive_close_on_server "recv_close_on_server"
 

src/python/grpcio/grpc/_cython/_cygrpc/records.pyx.pxi

@@ -639,7 +639,7 @@ def operation_receive_initial_metadata(int flags):
   op.c_op.type = GRPC_OP_RECV_INITIAL_METADATA
   op.c_op.flags = flags
   op._received_metadata = Metadata([])
-  op.c_op.data.recv_initial_metadata.receive_initial_metadata = (
+  op.c_op.data.receive_initial_metadata.receive_initial_metadata = (
       &op._received_metadata.c_metadata_array)
   op.is_valid = True
   return op
@@ -652,7 +652,7 @@ def operation_receive_message(int flags):
   # n.b. the c_op.data.receive_message field needs to be deleted by us,
   # anyway, so we just let that be handled by the ByteBuffer() we allocated
   # the line before.
-  op.c_op.data.recv_message.receive_message = (
+  op.c_op.data.receive_message.receive_message = (
       &op._received_message.c_byte_buffer)
   op.is_valid = True
   return op