SignalService
SignalService is a cross-chain signaling contract that enables secure message passing Taiko Alethia. It allows applications to send signals, synchronize chain data, and verify signals using Merkle proofs. The contract ensures that cross-chain messages are securely persisted and verifiable without introducing additional trust assumptions.
Features
- Cross-chain message synchronization: Facilitates Merkle-proof-based message verification.
- State root and signal caching: Stores and verifies state roots and signal roots for cross-layer communication.
- Efficient storage: Uses slot-based storage for optimized signal retrieval.
- Authorization mechanism: Controls who can sync chain data to prevent unauthorized updates.
Contract Methods
sendSignal
Stores a signal in contract storage for cross-chain message passing.
| Parameter | Type | Description |
|---|---|---|
_signal | bytes32 | The signal (message) to store. |
Returns:
| Return Value | Type | Description |
|---|---|---|
slot_ | bytes32 | The storage slot where the signal is stored. |
syncChainData
Synchronizes state roots and signal roots from other chains.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Identifier of the source chain. |
_kind | bytes32 | Type of data being synced (e.g., state root, signal root). |
_blockId | uint64 | Block ID from which the data is sourced. |
_chainData | bytes32 | Data to be stored as the signal. |
Returns:
| Return Value | Type | Description |
|---|---|---|
signal_ | bytes32 | The signal corresponding to the stored chain data. |
proveSignalReceived
Verifies that a signal has been received on the target chain using Merkle proofs.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Source chain identifier. |
_app | address | Address that sent the signal. |
_signal | bytes32 | The signal being verified. |
_proof | bytes | Merkle proof that the signal was persisted on the source chain. |
Returns:
| Return Value | Type | Description |
|---|---|---|
numCacheOps_ | uint256 | The number of newly cached items. |
Mechanism:
- Uses
_verifySignalReceived()to validate the proof. - Caches state roots and signal roots for future verification.
verifySignalReceived
Read-only version of proveSignalReceived, verifying without modifying state.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Source chain identifier. |
_app | address | Address that sent the signal. |
_signal | bytes32 | The signal being verified. |
_proof | bytes | Merkle proof that the signal was persisted on the source chain. |
Technical Note:
- Uses
_verifySignalReceived()for validation. - Does not cache or modify contract state.
isSignalSent
Checks whether a given signal has been sent.
| Parameter | Type | Description |
|---|---|---|
_app | address | Address that sent the signal. |
_signal | bytes32 | The signal to check. |
Returns:
| Return Value | Type | Description |
|---|---|---|
bool | bool | Returns true if the signal has been sent, otherwise false. |
isChainDataSynced
Checks if a given chain data has been successfully synced.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Source chain identifier. |
_kind | bytes32 | Data type identifier. |
_blockId | uint64 | Block ID from which the data is sourced. |
_chainData | bytes32 | Data to check for synchronization. |
Returns:
| Return Value | Type | Description |
|---|---|---|
bool | bool | Returns true if the data is synced, otherwise false. |
getSyncedChainData
Fetches the latest synchronized chain data.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Source chain identifier. |
_kind | bytes32 | Data type identifier. |
_blockId | uint64 | Block ID (if 0, retrieves the most recent). |
Returns:
| Return Value | Type | Description |
|---|---|---|
blockId_ | uint64 | Block ID of the synced data. |
chainData_ | bytes32 | Synchronized data from the source chain. |
signalForChainData
Derives a unique signal for given chain data.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Source chain identifier. |
_kind | bytes32 | Data type identifier. |
_blockId | uint64 | Block ID from which the data is sourced. |
Returns:
| Return Value | Type | Description |
|---|---|---|
signal_ | bytes32 | Unique signal hash representing the chain data. |
getSignalSlot
Computes the storage slot where a signal is stored.
| Parameter | Type | Description |
|---|---|---|
_chainId | uint64 | Chain ID of the signal. |
_app | address | Address that initiated the signal. |
_signal | bytes32 | Signal message to retrieve. |
Returns:
| Return Value | Type | Description |
|---|---|---|
slot_ | bytes32 | Storage slot where the signal is stored. |
Events
SignalSent
Emitted when a signal is sent.
| Parameter | Type | Description |
|---|---|---|
app | address | Address that initiated the signal. |
signal | bytes32 | The signal (message) that was sent. |
slot | bytes32 | Storage slot of the signal. |
value | bytes32 | The signal’s value. |
ChainDataSynced
Emitted when state or signal roots are synced from another chain.
| Parameter | Type | Description |
|---|---|---|
chainId | uint64 | Source chain identifier. |
blockId | uint64 | Block ID associated with the data. |
kind | bytes32 | Data type identifier (state root or signal root). |
data | bytes32 | The synchronized chain data. |
signal | bytes32 | Signal associated with the chain data. |
Authorized
Emitted when an address is authorized or deauthorized for syncing chain data.
| Parameter | Type | Description |
|---|---|---|
addr | address | The address being authorized or deauthorized. |
authorized | bool | true if authorized, false otherwise. |
State Variables
| Variable | Type | Description |
|---|---|---|
topBlockId | mapping(uint64 => mapping(bytes32 => uint64)) | Tracks the highest synced block ID for each chain and data type. |
isAuthorized | mapping(address => bool) | Stores addresses authorized to sync chain data. |