Relayer Service

The relayer is probably the simplest component of the bridge. It receives blocks from a source chain and sends those blocks to a light client contract on the destination chain, establishing a bidirectional bridge between the chains. In order to accomplish this, light client contracts must exist on both chains.

The NEAR to Calimero relayer reads latest blocks on the NEAR blockchain and sends (relays) those blocks to the light client contract on Calimero shard.

Similarly, the Calimero to NEAR relayer reads latest blocks on the Calimero shards and relays those blocks to the light client contract on the NEAR blockchain.

Here is the light client block structure that is being relayed with its substructs:

pub struct LightClientBlock {
    pub prev_block_hash: Hash,
    pub next_block_inner_hash: Hash,
    pub inner_lite: BlockHeaderInnerLite,
    pub inner_rest_hash: Hash,
    pub next_bps: Option<Vec<Validator>>,
    pub approvals_after_next: Vec<Option<Signature>>,
}

pub struct BlockHeaderInnerLite {
    pub height: u64, // Height of this block since the genesis block (height 0).
    pub epoch_id: Hash, // Epoch start hash of this block's epoch. Used for retrieving validator information
    pub next_epoch_id: Hash,
    pub prev_state_root: Hash, // Root hash of the state at the previous block.
    pub outcome_root: Hash, // Root of the outcomes of transactions and receipts.
    pub timestamp: u64, // Timestamp at which the block was built.
    pub next_bp_hash: Hash, // Hash of the next epoch block producers set
    pub block_merkle_root: Hash,
}

pub enum Validator {
    V1(ValidatorV1),
    V2(ValidatorV2),
}

pub struct ValidatorV1 {
    pub account_id: String,
    pub public_key: PublicKey,
    pub stake: u128,
}

pub struct ValidatorV2 {
    pub account_id: String,
    pub public_key: PublicKey,
    pub stake: u128,
    pub is_chunk_only: bool,
}

pub enum Signature {
    ED25519(ed25519_dalek::Signature),
    SECP256K1(Secp256K1Signature),
}