90 lines
2.1 KiB
JavaScript
90 lines
2.1 KiB
JavaScript
// @flow
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// TODO support events, constructors, fallbacks, array slots, types
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import { sha3, setLengthLeft, toBuffer } from 'ethereumjs-util';
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import Big from 'bignumber.js';
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type ABIType = 'address' | 'uint256' | 'bool';
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type ABITypedSlot = {
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name: string,
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type: ABIType
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};
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type ABIMethod = {
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name: string,
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type: 'function',
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constant: boolean,
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inputs: ABITypedSlot[],
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outputs: ABITypedSlot[],
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// default - false
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payable?: boolean
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};
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export type ABI = ABIMethod[];
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function assertString(arg: any) {
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if (typeof arg !== 'string') {
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throw new Error('Expected string');
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}
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}
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// Contract helper, returns data for given call
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export default class Contract {
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abi: ABI;
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constructor(abi: ABI) {
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this.abi = abi;
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}
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getMethodAbi(name: string): ABIMethod {
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const method = this.abi.find(x => x.name === name);
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if (!method) {
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throw new Error('Unknown method');
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}
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if (method.type !== 'function') {
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throw new Error('Not a function');
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}
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return method;
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}
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call(name: string, args: any[]): string {
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const method = this.getMethodAbi(name);
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const selector = sha3(
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`${name}(${method.inputs.map(i => i.type).join(',')})`
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);
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// TODO: Add explanation, why slice the first 8?
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return (
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'0x' +
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selector.toString('hex').slice(0, 8) +
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this.encodeArgs(method, args)
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);
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}
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encodeArgs(method: ABIMethod, args: any[]): string {
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if (method.inputs.length !== args.length) {
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throw new Error('Invalid number of arguments');
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}
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return method.inputs
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.map((input, idx) => this.encodeArg(input, args[idx]))
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.join('');
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}
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encodeArg(input: ABITypedSlot, arg: any): string {
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switch (input.type) {
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case 'address':
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case 'uint160':
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assertString(arg);
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return setLengthLeft(toBuffer(arg), 32).toString('hex');
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case 'uint256':
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if (arg instanceof Big) {
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arg = '0x' + arg.toString(16);
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}
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assertString(arg);
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return setLengthLeft(toBuffer(arg), 32).toString('hex');
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default:
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throw new Error(`Dont know how to handle abi type ${input.type}`);
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}
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}
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}
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