Contracts

Learn about the expected behaviour of Wasm light client contracts and the between with 08-wasm.

API

The 08-wasm light client proxy performs calls to the Wasm light client via the Wasm VM. The calls require as input JSON-encoded payload messages that fall in the three categories described in the next sections.

InstantiateMessage

This is the message sent to the contract's instantiate entry point. It contains the bytes of the protobuf-encoded client and consensus states of the underlying light client, both provided in MsgCreateClient. Please note that the bytes contained within the JSON message are represented as base64-encoded strings.

type InstantiateMessage struct {
	ClientState    []byte `json:"client_state"`
	ConsensusState []byte `json:"consensus_state"`
	Checksum       []byte `json:"checksum"
}

The Wasm light client contract is expected to store the client and consensus state in the corresponding keys of the client-prefixed store.

QueryMsg

QueryMsg acts as a discriminated union type that is used to encode the messages that are sent to the contract's query entry point. Only one of the fields of the type should be set at a time, so that the other fields are omitted in the encoded JSON and the payload can be correctly translated to the corresponding element of the enumeration in Rust.

type QueryMsg struct {
  Status               *StatusMsg               `json:"status,omitempty"`
  TimestampAtHeight    *TimestampAtHeightMsg    `json:"timestamp_at_height,omitempty"`
  VerifyClientMessage  *VerifyClientMessageMsg  `json:"verify_client_message,omitempty"`
  CheckForMisbehaviour *CheckForMisbehaviourMsg `json:"check_for_misbehaviour,omitempty"`
}

#[cw_serde]
pub enum QueryMsg {
  Status(StatusMsg),
  TimestampAtHeight(TimestampAtHeightMsg),
  VerifyClientMessage(VerifyClientMessageRaw),
  CheckForMisbehaviour(CheckForMisbehaviourMsgRaw),
}

To learn what it is expected from the Wasm light client contract when processing each message, please read the corresponding section of the Light client developer guide:

• For StatusMsg, see the section Status method.
• For TimestampAtHeightMsg, see the section GetTimestampAtHeight method.
• For VerifyClientMessageMsg, see the section VerifyClientMessage.
• For CheckForMisbehaviourMsg, see the section CheckForMisbehaviour method.

SudoMsg

SudoMsg acts as a discriminated union type that is used to encode the messages that are sent to the contract's sudo entry point. Only one of the fields of the type should be set at a time, so that the other fields are omitted in the encoded JSON and the payload can be correctly translated to the corresponding element of the enumeration in Rust.

The sudo entry point is able to perform state-changing writes in the client-prefixed store.

type SudoMsg struct {
  UpdateState                 *UpdateStateMsg                 `json:"update_state,omitempty"`
  UpdateStateOnMisbehaviour   *UpdateStateOnMisbehaviourMsg   `json:"update_state_on_misbehaviour,omitempty"`
  VerifyUpgradeAndUpdateState *VerifyUpgradeAndUpdateStateMsg `json:"verify_upgrade_and_update_state,omitempty"`
  VerifyMembership            *VerifyMembershipMsg            `json:"verify_membership,omitempty"`
  VerifyNonMembership         *VerifyNonMembershipMsg         `json:"verify_non_membership,omitempty"`
  MigrateClientStore          *MigrateClientStoreMsg          `json:"migrate_client_store,omitempty"`
}

#[cw_serde]
pub enum SudoMsg {
  UpdateState(UpdateStateMsgRaw),
  UpdateStateOnMisbehaviour(UpdateStateOnMisbehaviourMsgRaw),
  VerifyUpgradeAndUpdateState(VerifyUpgradeAndUpdateStateMsgRaw),
  VerifyMembership(VerifyMembershipMsgRaw),
  VerifyNonMembership(VerifyNonMembershipMsgRaw),
  MigrateClientStore(MigrateClientStoreMsgRaw),
}

To learn what it is expected from the Wasm light client contract when processing each message, please read the corresponding section of the Light client developer guide:

• For UpdateStateMsg, see the section UpdateState.
• For UpdateStateOnMisbehaviourMsg, see the section UpdateStateOnMisbehaviour.
• For VerifyUpgradeAndUpdateStateMsg, see the section GetTimestampAtHeight method.
• For VerifyMembershipMsg, see the section VerifyMembership method.
• For VerifyNonMembershipMsg, see the section VerifyNonMembership method.
• For MigrateClientStoreMsg, see the section Implementing CheckSubstituteAndUpdateState.

Migration

The 08-wasm proxy light client exposes the MigrateContract RPC endpoint that can be used to migrate a given Wasm light client contract (specified by the client identifier) to a new Wasm byte code (specified by the hash of the byte code). The expected use case for this RPC endpoint is to enable contracts to migrate to new byte code in case the current byte code is found to have a bug or vulnerability. The Wasm byte code that contracts are migrated have to be uploaded beforehand using MsgStoreCode and must implement the migrate entry point. See sectionMsgMigrateContract for information about the request message for this RPC endpoint.

Expected behaviour

The 08-wasm proxy light client modules expects the following behaviour from the Wasm light client contracts when executing messages that perform state-changing writes:

• The contract must not delete the client state from the store.
• The contract must not change the client state to a client state of another type.
• The contract must not change the checksum in the client state.

Any violation of these rules will result in an error returned from 08-wasm that will abort the transaction.