ReceivedOrdersElement

The received_orders header tells other parties how the sender has experienced the unfolding interaction so far. This allows gaps to be detected, possibly triggering a resend. The value of this header is an array of gap detector objects in the format {"id": , "last": , "gaps": []}. In our running auction example, if the auctioneer sees bids 1 and 2 from Bob, and bid 1 and 4 from Alice, the auctioneer might send a message to all the bidders that includes the following received_orders header:

"received_orders": [
 {"id": "did:ex:bob", "last": 2, "gaps": []},
 {"id": "did:ex:alice", "last": 4, "gaps": [2,3]}
 ]

This lets Alice (or Bob) notice that the auctioneer hasn't seen the messages that Alice numbered 2 and 3. Gaps can then be plugged or ignored, depending on protocol rules.