# Messages 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.

Finality Relayer represents two actual relayers - one relays Source Chain Finality to Target Chain. And another one relays Target Chain Finality to Source Chain.

sequenceDiagram participant Source Chain participant Finality Relayer participant Messages 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 ->> Messages Relayer: notes new outbound message 43 at Source Chain Block 481 Note right of Messages Relayer: can't deliver message 43, Source Chain Block 481 is not relayed Source Chain ->> Finality Relayer: Read Finality Proof of Block 481 Finality 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 ->> Messages Relayer: Read Proof of Message 43 at Block 481 Messages 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 ->> Messages Relayer: notes new unrewarded relayer at Target Chain Block 62 Note right of Messages Relayer: can't relay delivery confirmations because Target Chain Block 62 is not relayed Target Chain ->> Finality Relayer: Read Finality Proof of Block 62 Finality 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 ->> Messages Relayer: Read Proof of Message 43 Delivery at Block 62 Messages 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 ->> Messages Relayer: notes new outbound message 44 at Source Chain Block 483 and new confirmed message 43 Note right of Messages Relayer: can't deliver message 44, Source Chain Block 483 is not relayed Source Chain ->> Finality Relayer: Read Finality Proof of Block 483 Finality 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 ->> Messages Relayer: Read Proof of Message 44 and Proof of Message 43 reward at Block 483 Messages 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] }