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import { AbiDefinition, MethodAbi } from 'ethereum-types';
import * as _ from 'lodash';
import { AbiEncoder } from '.';
import { DeployedContractInfo, FunctionInfoBySelector, TransactionData, TransactionProperties } from './types';
export class TransactionDecoder {
private readonly _functionInfoBySelector: FunctionInfoBySelector = {};
/**
* Retrieves the function selector from tranasction data.
* @param txData hex-encoded transaction data.
* @return hex-encoded function selector.
*/
private static _getFunctionSelector(txData: string): string {
const functionSelectorLength = 10;
if (!txData.startsWith('0x') || txData.length < functionSelectorLength) {
throw new Error(
`Malformed transaction data. Must include a hex prefix '0x' and 4-byte function selector. Got '${txData}'`,
);
}
const functionSelector = txData.substr(0, functionSelectorLength);
return functionSelector;
}
/**
* Adds a set of ABI definitions, after which transaction data targeting these ABI's can be decoded.
* Additional properties can be included to disambiguate similar ABI's. For example, if two functions
* have the same signature but different parameter names, then their ABI definitions can be disambiguated
* by specifying a contract name.
* @param abiDefinitions ABI definitions for a given contract.
* @param contractName Name of contract that encapsulates the ABI definitions (optional).
* @param deploymentInfos A collection of network/address pairs where this contract is deployed (optional).
*/
public addABI(
abiDefinitions: AbiDefinition[],
contractName?: string,
deploymentInfos?: DeployedContractInfo[],
): void {
// Disregard definitions that are not functions
const functionAbis = _.filter(abiDefinitions, abiEntry => {
return abiEntry.type === 'function';
}) as MethodAbi[];
// Record function ABI's
_.each(functionAbis, functionAbi => {
const abiEncoder = new AbiEncoder.Method(functionAbi);
const functionSelector = abiEncoder.getSelector();
if (!(functionSelector in this._functionInfoBySelector)) {
this._functionInfoBySelector[functionSelector] = [];
}
// Recored a copy of this ABI for each deployment
const functionSignature = abiEncoder.getSignature();
_.each(deploymentInfos, deploymentInfo => {
this._functionInfoBySelector[functionSelector].push({
functionSignature,
abiEncoder,
contractName,
contractAddress: deploymentInfo.contractAddress,
networkId: deploymentInfo.networkId,
});
});
// There is no deployment info for this contract; record it without an address/network id
if (_.isEmpty(deploymentInfos)) {
this._functionInfoBySelector[functionSelector].push({
functionSignature,
abiEncoder,
contractName,
});
}
});
}
/**
* Decodes transaction data for a known ABI.
* @param txData hex-encoded transaction data.
* @param txProperties Properties about the transaction used to disambiguate similar ABI's (optional).
* @return Decoded transaction data. Includes: function name and signature, along with the decoded arguments.
*/
public decode(txData: string, txProperties_?: TransactionProperties): TransactionData {
// Lookup
const functionSelector = TransactionDecoder._getFunctionSelector(txData);
const txProperties = _.isUndefined(txProperties_) ? {} : txProperties_;
const candidateFunctionInfos = this._functionInfoBySelector[functionSelector];
if (_.isUndefined(candidateFunctionInfos)) {
throw new Error(`No functions registered for selector '${functionSelector}'`);
}
const functionInfo = _.find(candidateFunctionInfos, txDecoder => {
return (
(_.isUndefined(txProperties.contractName) ||
_.toLower(txDecoder.contractName) === _.toLower(txProperties.contractName)) &&
(_.isUndefined(txProperties.contractAddress) ||
txDecoder.contractAddress === txProperties.contractAddress) &&
(_.isUndefined(txProperties.networkId) || txDecoder.networkId === txProperties.networkId)
);
});
if (_.isUndefined(functionInfo)) {
throw new Error(`No function registered with properties: ${JSON.stringify(txProperties)}.`);
} else if (_.isUndefined(functionInfo.abiEncoder)) {
throw new Error(
`Function ABI Encoder is not defined, for function with properties: ${JSON.stringify(txProperties)}.`,
);
}
const functionName = functionInfo.abiEncoder.getDataItem().name;
const functionSignature = functionInfo.abiEncoder.getSignatureType();
const functionArguments = functionInfo.abiEncoder.decode(txData);
const decodedCalldata = {
functionName,
functionSignature,
functionArguments,
};
return decodedCalldata;
}
}
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