Complex Relay
Both Source Chain and Target Chains have Bridge Messages pallets deployed. They also have required
finality pallets deployed - we don't care about finality type here - they can be either Bridge GRANDPA,
or Bridge Parachains finality pallets, or any combination of those.
There are 4-6 relayer subprocesses inside the Complex Relayer. They include two message relayers,
serving the lane in both directions and 2-4 Complex Relayers (depending on the finality type of Source
and Target Chains).
The following diagram shows the way the complex relayer serves the lane in single direction. Everything
below may be applied to the opposite direction if you'll swap the Source and Target Chains.
sequenceDiagram
participant Source Chain
participant Complex Relayer
participant Target Chain
Note right of Source Chain: Finalized: 480, Target Finalized: 50, Sent Messages: 42, Confirmed Messages: 42
Note left of Target Chain: Finalized: 60, Source Finalized: 420, Received Messages: 42
Source Chain ->> Source Chain: someone Sends Message 43
Source Chain ->> Source Chain: Import and Finalize Block 481
Source Chain ->> Complex Relayer: notes new outbound message 43 at Source Chain Block 481
Note right of Complex Relayer: can't deliver message 43, Source Chain Block 481 is not relayed
Complex Relayer ->> Complex Relayer: asks on-demand Finality Relayer to relay Source Chain Block 481
Source Chain ->> Complex Relayer: Read Finality Proof of Block 481
Complex Relayer ->> Target Chain: Submit Finality Proof of Block 481
Target Chain ->> Target Chain: Import and Finalize Block 61
Note left of Target Chain: Finalized: 61, Source Finalized: 481, Received Messages: 42
Source Chain ->> Complex Relayer: Read Proof of Message 43 at Block 481
Complex Relayer ->> Target Chain: Submit Proof of Message 43 at Block 481
Target Chain ->> Target Chain: Import and Finalize Block 62
Note left of Target Chain: Finalized: 62, Source Finalized: 481, Received Messages: { rewarded: 42, messages-relayer-account: [43] }
Target Chain ->> Complex Relayer: notes new unrewarded relayer at Target Chain Block 62
Note right of Complex Relayer: can't relay delivery confirmations because Target Chain Block 62 is not relayed
Complex Relayer ->> Complex Relayer: asks on-demand Finality Relayer to relay Target Chain Block 62
Target Chain ->> Complex Relayer: Read Finality Proof of Block 62
Complex Relayer ->> Source Chain: Submit Finality Proof of Block 62
Source Chain ->> Source Chain: Import and Finalize Block 482
Note right of Source Chain: Finalized: 482, Target Finalized: 62, Confirmed Messages: 42
Target Chain ->> Complex Relayer: Read Proof of Message 43 Delivery at Block 62
Complex Relayer ->> Source Chain: Submit Proof of Message 43 Delivery at Block 612
Source Chain ->> Source Chain: rewards messages-relayer-account for delivering message [43]
Source Chain ->> Source Chain: prune delivered message 43 from runtime storage
Note right of Source Chain: Finalized: 482, Target Finalized: 61, Confirmed Messages: 43
Source Chain ->> Source Chain: someone Sends Message 44
Source Chain ->> Source Chain: Import and Finalize Block 483
Source Chain ->> Complex Relayer: notes new outbound message 44 at Source Chain Block 483 and new confirmed message 43
Note right of Complex Relayer: can't deliver message 44, Source Chain Block 483 is not relayed
Complex Relayer ->> Complex Relayer: asks on-demand Finality Relayer to relay Source Chain Block 483
Source Chain ->> Complex Relayer: Read Finality Proof of Block 483
Complex Relayer ->> Target Chain: Submit Finality Proof of Block 483
Target Chain ->> Target Chain: Import and Finalize Block 63
Note left of Target Chain: Finalized: 63, Source Finalized: 483, Received Messages: { rewarded: 42, messages-relayer-account: [43] }
Source Chain ->> Complex Relayer: Read Proof of Message 44 and Proof of Message 43 reward at Block 483
Complex Relayer ->> Target Chain: Submit Proof of Message 44 and Proof of Message 43 reward at Block 483
Target Chain ->> Target Chain: Import and Finalize Block 64
Note left of Target Chain: Finalized: 64, Source Finalized: 483, Received Messages: { rewarded: 43, messages-relayer-account: [44] }-->