Light client module interface for ICS

[majecty]

This issue is a work-in-progress version of the interface for a light client module.

Serialization format

Module programmers will use two types of serialization format.

Let's assume that chain A has light clients of chain B, and chain C. Chain B is using MessagePack to serialize data. Chain C is using ProtoBuf to serialize data. Let's think of verifyChannelState in the light client. The handler module passes the expected ChannelEnd value to the function. So we need a serialization method of how to serialize the ChannelEnd (this is the serialization type 1). To verify the ChannelEnd struct, each light client serializes the ChannelEnd data to each chain's serialization format (MessagePack and ProtoBuf). This is the serialization type 2.

Serialization type 1

We will use JSON.

The handler module will send several types of data to the light client modules. If we use "RLP" for this serialization format, each module's developer should implement decoder of RLP. To reduce the light client developer's work, we (Junha and I) concluded to use JSON format in this case.

If the module system supports a default serialization method of simple struct types, we can use it instead.

Serialization type 2

Each light client must implement each chain's serialize code.

Interface functions

Query

fn query_client_state(client_id: String, block_number: Option<u64>) -> Bytes

fn query_consensus_state(
        client_id: String,
        counterparty_block_number: u64,
        block_number: Option<u64>,
    ) -> Bytes

Transaction

fn create(id: IdentifierSlice, _consensus_state: Bytes, header: Bytes)

fn update(id: IdentifierSlice, header: Bytes)

Functions can be called from other modules

pub fn query_latest_height(id: IdentifierSlice) -> u64

pub fn verify_connection_state(
        client_identifier: IdentifierSlice,
        proof_height: BlockNumber,
        proof: Bytes,
        counterparty_connection_identifier: IdentifierSlice,
        connection_end: &ConnectionEnd,
    )

fn verify_channel_state(
        id: IdentifierSlice,
        proof_height: BlockNumber,
        proof: Bytes,
        port_identifier: IdentifierSlice,
        counterparty_channel_identifier: IdentifierSlice,
        channel_end: &ChannelEnd,
    )

fn verify_packet_data(
        id: IdentifierSlice,
        proof_height: BlockNumber,
        proof: Bytes,
        counterparty_port_identifier: IdentifierSlice,
        counterparty_channel_identifier: IdentifierSlice,
        sequence: &Sequence,
        packet_commitment: &PacketCommitment,
    )

fn verify_packet_acknowledgment(
        id: IdentifierSlice,
        proof_height: BlockNumber,
        proof: Bytes,
        port_identifier: IdentifierSlice,
        channel_identifier: IdentifierSlice,
        sequence: &Sequence,
        acknowledgment: &Acknowledgement,
    )

fn verify_packet_acknowledgment_absence(
        id: IdentifierSlice,
        proof_height: BlockNumber,
        proof: Bytes,
        port_identifier: IdentifierSlice,
        channel_identifier: IdentifierSlice,
        sequence: &Sequence,
    )

fn verify_next_sequence_recv(
        id: IdentifierSlice,
        proof_height: BlockNumber,
        proof: Bytes,
        port_identifier: IdentifierSlice,
        channel_identifier: IdentifierSlice,
        next_sequence_recv: &Sequence,
    )

[majecty]

This issue will be used in the final version of ICS implementation (not ICS version). I'll remove the "experiment" tag.

[junha1]

Good