As we develop support for message streaming in Qpid Dispatch Router (i.e. frames for large multi-frame messages are forwarded to destinations as they arrive, before the complete message is received), there is a need to handle the case where a received message is never completed.
The AMQP protocol has a provision for this in the "aborted" flag in the transfer performative. If the router is in the process of streaming a large message from sender to receiver and the sender drops before completing the delivery, the router can send a transfer to the downstream receivers with the "aborted" flag set. This would indicate that the message should not be processed and would not cause any framing errors on the link.
Proton does not currently expose this capability in its API (There is a pn_link_abort in the C header file, but it is commented out and not implemented).
In order to properly handle the failure cases for message streaming, this feature must be usable in Proton.