| MessagingHandler | A general purpose handler that makes the proton-c events somewhat simpler to deal with and/or avoids repetitive tasks for common use cases. |
| TransactionHandler | The interface for transaction handlers - ie objects that want to be notified of state changes related to a transaction. |
| TransactionalClientHandler | An extension to the MessagingHandler for applications using transactions. |
| Reject | An exception that indicates a message should be rejected. |
| Release | An exception that indicates a message should be released. |