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import { Contract, BigNumber } from 'ethers'
export interface OutputOracle<TSubmissionEventArgs> {
contract: Contract
filter: any
getTotalElements: () => Promise<BigNumber>
getEventIndex: (args: TSubmissionEventArgs) => BigNumber
}
/**
* Partial event interface, meant to reduce the size of the event cache to avoid
* running out of memory.
*/
export interface PartialEvent {
blockNumber: number
transactionHash: string
args: any
}
// Event caching is necessary for the fault detector to work properly with Geth.
const caches: {
[contractAddress: string]: {
highestBlock: number
eventCache: Map<string, PartialEvent>
}
} = {}
/**
* Retrieves the cache for a given address.
*
* @param address Address to get cache for.
* @returns Address cache.
*/
const getCache = (
address: string
): {
highestBlock: number
eventCache: Map<string, PartialEvent>
} => {
if (!caches[address]) {
caches[address] = {
highestBlock: 0,
eventCache: new Map(),
}
}
return caches[address]
}
/**
* Updates the event cache for a contract and event.
*
* @param contract Contract to update cache for.
* @param filter Event filter to use.
*/
export const updateOracleCache = async <TSubmissionEventArgs>(
oracle: OutputOracle<TSubmissionEventArgs>
): Promise<void> => {
const cache = getCache(oracle.contract.address)
let currentBlock = cache.highestBlock
const endingBlock = await oracle.contract.provider.getBlockNumber()
let step = endingBlock - currentBlock
let failures = 0
while (currentBlock < endingBlock) {
try {
const events = await oracle.contract.queryFilter(
oracle.filter,
currentBlock,
currentBlock + step
)
// Throw the events into the cache.
for (const event of events) {
cache.eventCache[
oracle.getEventIndex(event.args as TSubmissionEventArgs).toNumber()
] = {
blockNumber: event.blockNumber,
transactionHash: event.transactionHash,
args: event.args,
}
}
// Update the current block and increase the step size for the next iteration.
currentBlock += step
step = Math.ceil(step * 2)
} catch {
// Might happen if we're querying too large an event range.
step = Math.floor(step / 2)
// When the step gets down to zero, we're pretty much guaranteed that range size isn't the
// problem. If we get three failures like this in a row then we should just give up.
if (step === 0) {
failures++
} else {
failures = 0
}
// We've failed 3 times in a row, we're probably stuck.
if (failures >= 3) {
throw new Error('failed to update event cache')
}
}
}
// Update the highest block.
cache.highestBlock = endingBlock
}
/**
* Finds the Event that corresponds to a given state batch by index.
*
* @param oracle Output oracle contract
* @param index State batch index to search for.
* @returns Event corresponding to the batch.
*/
export const findEventForStateBatch = async <TSubmissionEventArgs>(
oracle: OutputOracle<TSubmissionEventArgs>,
index: number
): Promise<PartialEvent> => {
const cache = getCache(oracle.contract.address)
// Try to find the event in cache first.
if (cache.eventCache[index]) {
return cache.eventCache[index]
}
// Update the event cache if we don't have the event.
await updateOracleCache(oracle)
// Event better be in cache now!
if (cache.eventCache[index] === undefined) {
throw new Error(`unable to find event for batch ${index}`)
}
return cache.eventCache[index]
}
/**
* Finds the first state batch index that has not yet passed the fault proof window.
*
* @param oracle Output oracle contract.
* @returns Starting state root batch index.
*/
export const findFirstUnfinalizedStateBatchIndex = async <TSubmissionEventArgs>(
oracle: OutputOracle<TSubmissionEventArgs>,
fpw: number
): Promise<number> => {
const latestBlock = await oracle.contract.provider.getBlock('latest')
const totalBatches = (await oracle.getTotalElements()).toNumber()
// Perform a binary search to find the next batch that will pass the challenge period.
let lo = 0
let hi = totalBatches
while (lo !== hi) {
const mid = Math.floor((lo + hi) / 2)
const event = await findEventForStateBatch(oracle, mid)
const block = await oracle.contract.provider.getBlock(event.blockNumber)
if (block.timestamp + fpw < latestBlock.timestamp) {
lo = mid + 1
} else {
hi = mid
}
}
// Result will be zero if the chain is less than FPW seconds old. Only returns undefined in the
// case that no batches have been submitted for an entire challenge period.
if (lo === totalBatches) {
return undefined
} else {
return lo
}
}