import { AbiDefinition, AbiType, DecodedLogArgs, EventAbi, EventParameter, LogEntry, LogWithDecodedArgs, RawLog, SolidityTypes, } from 'ethereum-types'; import * as ethers from 'ethers'; import * as _ from 'lodash'; import { addressUtils } from './address_utils'; import { BigNumber } from './configured_bignumber'; /** * AbiDecoder allows you to decode event logs given a set of supplied contract ABI's. It takes the contract's event * signature from the ABI and attempts to decode the logs using it. */ export class AbiDecoder { private readonly _methodIds: { [signatureHash: string]: { [numIndexedArgs: number]: EventAbi } } = {}; /** * Instantiate an AbiDecoder * @param abiArrays An array of contract ABI's * @return AbiDecoder instance */ constructor(abiArrays: AbiDefinition[][]) { _.forEach(abiArrays, this.addABI.bind(this)); } /** * Attempt to decode a log given the ABI's the AbiDecoder knows about. * @param log The log to attempt to decode * @return The decoded log if the requisite ABI was available. Otherwise the log unaltered. */ public tryToDecodeLogOrNoop(log: LogEntry): LogWithDecodedArgs | RawLog { const methodId = log.topics[0]; const numIndexedArgs = log.topics.length - 1; if (_.isUndefined(this._methodIds[methodId]) || _.isUndefined(this._methodIds[methodId][numIndexedArgs])) { return log; } const event = this._methodIds[methodId][numIndexedArgs]; const ethersInterface = new ethers.Interface([event]); const decodedParams: DecodedLogArgs = {}; let topicsIndex = 1; let decodedData: any[]; try { decodedData = ethersInterface.events[event.name].parse(log.data); } catch (error) { if (error.code === ethers.errors.INVALID_ARGUMENT) { // Because we index events by Method ID, and Method IDs are derived from the method // name and the input parameters, it's possible that the return value of the event // does not match our ABI. If that's the case, then ethers will throw an error // when we try to parse the event. We handle that case here by returning the log rather // than throwing an error. return log; } throw error; } let didFailToDecode = false; _.forEach(event.inputs, (param: EventParameter, i: number) => { // Indexed parameters are stored in topics. Non-indexed ones in decodedData let value: BigNumber | string | number = param.indexed ? log.topics[topicsIndex++] : decodedData[i]; if (_.isUndefined(value)) { didFailToDecode = true; return; } if (param.type === SolidityTypes.Address) { const baseHex = 16; value = addressUtils.padZeros(new BigNumber(value).toString(baseHex)); } else if (param.type === SolidityTypes.Uint256 || param.type === SolidityTypes.Uint) { value = new BigNumber(value); } else if (param.type === SolidityTypes.Uint8) { value = new BigNumber(value).toNumber(); } decodedParams[param.name] = value; }); if (didFailToDecode) { return log; } else { return { ...log, event: event.name, args: decodedParams, }; } } /** * Add additional ABI definitions to the AbiDecoder * @param abiArray An array of ABI definitions to add to the AbiDecoder */ public addABI(abiArray: AbiDefinition[]): void { if (_.isUndefined(abiArray)) { return; } const ethersInterface = new ethers.Interface(abiArray); _.map(abiArray, (abi: AbiDefinition) => { if (abi.type === AbiType.Event) { const topic = ethersInterface.events[abi.name].topics[0]; const numIndexedArgs = _.reduce(abi.inputs, (sum, input) => (input.indexed ? sum + 1 : sum), 0); this._methodIds[topic] = { ...this._methodIds[topic], [numIndexedArgs]: abi, }; } }); } }