Ordered / unordered channels

[cwgoes]

Split off from #126. Would be superseded by #131 if we implement that. Otherwise,

• Add unordered channels, with timeout semantics as they currently are
• Alter ordered channels so that timeouts (of any packet) immediately close ordered channels

[cwgoes]

Unordered channels will need an accumulator to track received packets. It can just store a hash though.

[cwgoes]

We could still keep the maximum index before which all packets have been received.

[mossid]

We could still keep the maximum index before which all packets have been received

func receivePacketUnordered(packet Packet) {
  allpacketmax := getMaximuimIndexAllPacketReceived()
  if allpacketmax + 1 != packet.Index {
    setPacketReceived(packet.Index)
    return
  }
  allpacketmax += 1
  for rpacket := range iteratePacketReceived() {
    if rpacket.Index != allpacketmax + 1 {
      break
    }
    allpacketmax += 1
    deletePacketReceived(rpacket.Index)
  }
  setMaximumIndexAllPacketReceived(allpacketmax)
}

The relayers can still relay ordered

func relayOrdered() {
  allpacketmax := chainDest.QueryMaximimIndexAllPacketReceived()
  packet := chainSrc.QueryPacketSent(allpacketmax)
  chainDest.TxRelayPacket(packet)
} 

or unordered

func relayUnordered(index uint64) {
  chainSrc.QueryPacketSent(index)
  chainDest.TxRelayPacket(packet) 
  // unlike ordered channel, it does not fail even if 
  // the packet is not the successor of the latest packet sent
}

in this way any packet sent unordered are marked as sent(setPacketReceived) individually onchain and pruned once the maximum index catches it

[cwgoes]

in this way any packet sent unordered are marked as sent(setPacketReceived) individually onchain and pruned once the maximum index catches it

Yes, that would be the idea. I am a bit concerned about the iteration on-chain however.

Better to have the relayer provide start / end indices of packets to be cleaned up and the chain just verifies that they have all been received (and cleanupReceived should be separate from recvPacket).