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include/grpc/impl/codegen/grpc_types.h

@@ -511,6 +511,11 @@ typedef struct grpc_op {
       } maybe_stream_compression_level;
     } send_initial_metadata;
     struct grpc_op_send_message {
+      /** This op takes ownership of the slices in send_message.  After
+       * a call completes, the contents of send_message are not guaranteed
+       * and likely empty.  The original owner should still call
+       * grpc_byte_buffer_destroy() on this object however.
+       */
       struct grpc_byte_buffer *send_message;
     } send_message;
     struct grpc_op_send_status_from_server {