677 lines
22 KiB
TypeScript
677 lines
22 KiB
TypeScript
/**
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* Explain all the nitty-gritty about the **FallbackProvider**.
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*
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* @_section: api/providers/fallback-provider:Fallback Provider [about-fallback-provider]
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*/
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import {
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getBigInt, getNumber, assert, assertArgument
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} from "../utils/index.js";
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import { AbstractProvider } from "./abstract-provider.js";
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import { Network } from "./network.js"
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import type { PerformActionRequest } from "./abstract-provider.js";
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import type { Networkish } from "./network.js"
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const BN_1 = BigInt("1");
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const BN_2 = BigInt("2");
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function shuffle<T = any>(array: Array<T>): void {
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for (let i = array.length - 1; i > 0; i--) {
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const j = Math.floor(Math.random() * (i + 1));
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const tmp = array[i];
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array[i] = array[j];
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array[j] = tmp;
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}
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}
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function stall(duration: number): Promise<void> {
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return new Promise((resolve) => { setTimeout(resolve, duration); });
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}
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function getTime(): number { return (new Date()).getTime(); }
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function stringify(value: any): string {
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return JSON.stringify(value, (key, value) => {
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if (typeof(value) === "bigint") {
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return { type: "bigint", value: value.toString() };
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}
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return value;
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});
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}
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/**
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* A configuration entry for how to use a [[Provider]].
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*/
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export interface FallbackProviderConfig {
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// The provider
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provider: AbstractProvider;
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// How long to wait for a response before getting impatient
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// and ispatching the next provider
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stallTimeout?: number;
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// Lower values are dispatched first
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priority?: number;
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// How much this provider contributes to the quorum
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weight?: number;
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};
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const defaultConfig = { stallTimeout: 400, priority: 1, weight: 1 };
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// We track a bunch of extra stuff that might help debug problems or
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// optimize infrastructure later on.
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/**
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* The statistics and state maintained for a [[Provider]].
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*/
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export interface FallbackProviderState extends Required<FallbackProviderConfig> {
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// The most recent blockNumber this provider has reported (-2 if none)
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blockNumber: number;
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// The number of total requests ever sent to this provider
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requests: number;
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// The number of responses that errored
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errorResponses: number;
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// The number of responses that occured after the result resolved
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lateResponses: number;
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// How many times syncing was required to catch up the expected block
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outOfSync: number;
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// The number of requests which reported unsupported operation
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unsupportedEvents: number;
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// A rolling average (5% current duration) for response time
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rollingDuration: number;
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// The ratio of quorum-agreed results to total
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score: number;
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}
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interface Config extends FallbackProviderState {
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_updateNumber: null | Promise<any>;
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_network: null | Network;
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_totalTime: number;
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}
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const defaultState = {
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blockNumber: -2, requests: 0, lateResponses: 0, errorResponses: 0,
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outOfSync: -1, unsupportedEvents: 0, rollingDuration: 0, score: 0,
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_network: null, _updateNumber: null, _totalTime: 0
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};
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async function waitForSync(config: Config, blockNumber: number): Promise<void> {
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while (config.blockNumber < 0 || config.blockNumber < blockNumber) {
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if (!config._updateNumber) {
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config._updateNumber = (async () => {
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const blockNumber = await config.provider.getBlockNumber();
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if (blockNumber > config.blockNumber) {
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config.blockNumber = blockNumber;
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}
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config._updateNumber = null;
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})();
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}
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await config._updateNumber;
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config.outOfSync++;
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}
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}
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/**
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* Additional options to configure a [[FallbackProvider]].
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*/
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export type FallbackProviderOptions = {
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// How many providers must agree on a value before reporting
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// back the response
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quorum: number;
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// How many providers must have reported the same event
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// for it to be emitted
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eventQuorum: number;
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// How many providers to dispatch each event to simultaneously.
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// Set this to 0 to use getLog polling, which implies eventQuorum
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// is equal to quorum.
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eventWorkers: number;
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};
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type RunnerResult = { result: any } | { error: Error };
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type RunnerState = {
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config: Config;
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staller: null | Promise<void>;
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didBump: boolean;
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perform: null | Promise<any>;
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result: null | RunnerResult;
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}
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function _normalize(value: any): string {
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if (value == null) { return "null"; }
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if (Array.isArray(value)) {
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return "[" + (value.map(_normalize)).join(",") + "]";
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}
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if (typeof(value) === "object" && typeof(value.toJSON) === "function") {
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return _normalize(value.toJSON());
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}
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switch (typeof(value)) {
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case "boolean": case "symbol":
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return value.toString();
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case "bigint": case "number":
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return BigInt(value).toString();
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case "string":
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return JSON.stringify(value);
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case "object": {
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const keys = Object.keys(value);
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keys.sort();
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return "{" + keys.map((k) => `${ JSON.stringify(k) }:${ _normalize(value[k]) }`).join(",") + "}";
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}
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}
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console.log("Could not serialize", value);
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throw new Error("Hmm...");
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}
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function normalizeResult(value: RunnerResult): { tag: string, value: any } {
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if ("error" in value) {
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const error = value.error;
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return { tag: _normalize(error), value: error };
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}
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const result = value.result;
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return { tag: _normalize(result), value: result };
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}
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type TallyResult = {
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tag: string;
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value: any;
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weight: number;
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};
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// This strategy picks the highest weight result, as long as the weight is
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// equal to or greater than quorum
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function checkQuorum(quorum: number, results: Array<TallyResult>): any | Error {
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const tally: Map<string, { value: any, weight: number }> = new Map();
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for (const { value, tag, weight } of results) {
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const t = tally.get(tag) || { value, weight: 0 };
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t.weight += weight;
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tally.set(tag, t);
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}
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let best: null | { value: any, weight: number } = null;
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for (const r of tally.values()) {
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if (r.weight >= quorum && (!best || r.weight > best.weight)) {
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best = r;
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}
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}
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if (best) { return best.value; }
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return undefined;
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}
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function getMedian(quorum: number, results: Array<TallyResult>): undefined | bigint | Error {
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let resultWeight = 0;
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const errorMap: Map<string, { weight: number, value: Error }> = new Map();
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let bestError: null | { weight: number, value: Error } = null;
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const values: Array<bigint> = [ ];
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for (const { value, tag, weight } of results) {
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if (value instanceof Error) {
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const e = errorMap.get(tag) || { value, weight: 0 };
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e.weight += weight;
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errorMap.set(tag, e);
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if (bestError == null || e.weight > bestError.weight) { bestError = e; }
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} else {
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values.push(BigInt(value));
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resultWeight += weight;
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}
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}
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if (resultWeight < quorum) {
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// We have quorum for an error
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if (bestError && bestError.weight >= quorum) { return bestError.value; }
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// We do not have quorum for a result
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return undefined;
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}
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// Get the sorted values
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values.sort((a, b) => ((a < b) ? -1: (b > a) ? 1: 0));
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const mid = Math.floor(values.length / 2);
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// Odd-length; take the middle value
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if (values.length % 2) { return values[mid]; }
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// Even length; take the ceiling of the mean of the center two values
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return (values[mid - 1] + values[mid] + BN_1) / BN_2;
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}
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function getAnyResult(quorum: number, results: Array<TallyResult>): undefined | any | Error {
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// If any value or error meets quorum, that is our preferred result
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const result = checkQuorum(quorum, results);
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if (result !== undefined) { return result; }
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// Otherwise, do we have any result?
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for (const r of results) {
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if (r.value) { return r.value; }
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}
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// Nope!
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return undefined;
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}
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function getFuzzyMode(quorum: number, results: Array<TallyResult>): undefined | number {
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if (quorum === 1) { return getNumber(<bigint>getMedian(quorum, results), "%internal"); }
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const tally: Map<number, { result: number, weight: number }> = new Map();
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const add = (result: number, weight: number) => {
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const t = tally.get(result) || { result, weight: 0 };
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t.weight += weight;
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tally.set(result, t);
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};
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for (const { weight, value } of results) {
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const r = getNumber(value);
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add(r - 1, weight);
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add(r, weight);
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add(r + 1, weight);
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}
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let bestWeight = 0;
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let bestResult = undefined;
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for (const { weight, result } of tally.values()) {
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// Use this result, if this result meets quorum and has either:
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// - a better weight
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// - or equal weight, but the result is larger
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if (weight >= quorum && (weight > bestWeight || (bestResult != null && weight === bestWeight && result > bestResult))) {
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bestWeight = weight;
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bestResult = result;
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}
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}
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return bestResult;
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}
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/**
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* A Fallback Provider.
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*
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*/
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export class FallbackProvider extends AbstractProvider {
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readonly quorum: number;
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readonly eventQuorum: number;
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readonly eventWorkers: number;
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readonly #configs: Array<Config>;
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#height: number;
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#initialSyncPromise: null | Promise<void>;
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constructor(providers: Array<AbstractProvider | FallbackProviderConfig>, network?: Networkish) {
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super(network);
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this.#configs = providers.map((p) => {
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if (p instanceof AbstractProvider) {
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return Object.assign({ provider: p }, defaultConfig, defaultState );
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} else {
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return Object.assign({ }, defaultConfig, p, defaultState );
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}
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});
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this.#height = -2;
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this.#initialSyncPromise = null;
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this.quorum = 2; //Math.ceil(providers.length / 2);
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this.eventQuorum = 1;
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this.eventWorkers = 1;
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assertArgument(this.quorum <= this.#configs.reduce((a, c) => (a + c.weight), 0),
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"quorum exceed provider wieght", "quorum", this.quorum);
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}
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get providerConfigs(): Array<FallbackProviderState> {
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return this.#configs.map((c) => {
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const result: any = Object.assign({ }, c);
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for (const key in result) {
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if (key[0] === "_") { delete result[key]; }
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}
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return result;
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});
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}
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async _detectNetwork(): Promise<Network> {
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return Network.from(getBigInt(await this._perform({ method: "chainId" })));
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}
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// @TODO: Add support to select providers to be the event subscriber
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//_getSubscriber(sub: Subscription): Subscriber {
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// throw new Error("@TODO");
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//}
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async _translatePerform(provider: AbstractProvider, req: PerformActionRequest): Promise<any> {
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switch (req.method) {
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case "broadcastTransaction":
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return await provider.broadcastTransaction(req.signedTransaction);
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case "call":
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return await provider.call(Object.assign({ }, req.transaction, { blockTag: req.blockTag }));
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case "chainId":
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return (await provider.getNetwork()).chainId;
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case "estimateGas":
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return await provider.estimateGas(req.transaction);
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case "getBalance":
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return await provider.getBalance(req.address, req.blockTag);
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case "getBlock": {
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const block = ("blockHash" in req) ? req.blockHash: req.blockTag;
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return await provider.getBlock(block, req.includeTransactions);
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}
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case "getBlockNumber":
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return await provider.getBlockNumber();
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case "getCode":
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return await provider.getCode(req.address, req.blockTag);
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case "getGasPrice":
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return (await provider.getFeeData()).gasPrice;
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case "getLogs":
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return await provider.getLogs(req.filter);
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case "getStorage":
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return await provider.getStorage(req.address, req.position, req.blockTag);
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case "getTransaction":
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return await provider.getTransaction(req.hash);
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case "getTransactionCount":
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return await provider.getTransactionCount(req.address, req.blockTag);
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case "getTransactionReceipt":
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return await provider.getTransactionReceipt(req.hash);
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case "getTransactionResult":
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return await provider.getTransactionResult(req.hash);
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}
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}
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// Grab the next (random) config that is not already part of
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// the running set
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#getNextConfig(running: Set<RunnerState>): null | Config {
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// @TODO: Maybe do a check here to favour (heavily) providers that
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// do not require waitForSync and disfavour providers that
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// seem down-ish or are behaving slowly
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const configs = Array.from(running).map((r) => r.config)
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// Shuffle the states, sorted by priority
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const allConfigs = this.#configs.slice();
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shuffle(allConfigs);
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allConfigs.sort((a, b) => (b.priority - a.priority));
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for (const config of allConfigs) {
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if (configs.indexOf(config) === -1) { return config; }
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}
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return null;
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}
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// Adds a new runner (if available) to running.
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#addRunner(running: Set<RunnerState>, req: PerformActionRequest): null | RunnerState {
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const config = this.#getNextConfig(running);
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// No runners available
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if (config == null) { return null; }
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// Create a new runner
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const runner: RunnerState = {
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config, result: null, didBump: false,
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perform: null, staller: null
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};
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const now = getTime();
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// Start performing this operation
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runner.perform = (async () => {
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try {
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config.requests++;
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const result = await this._translatePerform(config.provider, req);
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runner.result = { result };
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} catch (error: any) {
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config.errorResponses++;
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runner.result = { error };
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}
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const dt = (getTime() - now);
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config._totalTime += dt;
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config.rollingDuration = 0.95 * config.rollingDuration + 0.05 * dt;
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runner.perform = null;
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})();
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// Start a staller; when this times out, it's time to force
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// kicking off another runner because we are taking too long
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runner.staller = (async () => {
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await stall(config.stallTimeout);
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runner.staller = null;
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})();
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running.add(runner);
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return runner;
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}
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// Initializes the blockNumber and network for each runner and
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// blocks until initialized
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async #initialSync(): Promise<void> {
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let initialSync = this.#initialSyncPromise;
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if (!initialSync) {
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const promises: Array<Promise<any>> = [ ];
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this.#configs.forEach((config) => {
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promises.push(waitForSync(config, 0));
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promises.push((async () => {
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config._network = await config.provider.getNetwork();
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})());
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});
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this.#initialSyncPromise = initialSync = (async () => {
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// Wait for all providers to have a block number and network
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await Promise.all(promises);
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// Check all the networks match
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let chainId: null | bigint = null;
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for (const config of this.#configs) {
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const network = <Network>(config._network);
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if (chainId == null) {
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chainId = network.chainId;
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} else if (network.chainId !== chainId) {
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assert(false, "cannot mix providers on different networks", "UNSUPPORTED_OPERATION", {
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operation: "new FallbackProvider"
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});
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}
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}
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})();
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}
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await initialSync
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}
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async #checkQuorum(running: Set<RunnerState>, req: PerformActionRequest): Promise<any> {
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// Get all the result objects
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const results: Array<TallyResult> = [ ];
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for (const runner of running) {
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if (runner.result != null) {
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const { tag, value } = normalizeResult(runner.result);
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results.push({ tag, value, weight: runner.config.weight });
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}
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}
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// Are there enough results to event meet quorum?
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if (results.reduce((a, r) => (a + r.weight), 0) < this.quorum) {
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return undefined;
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}
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switch (req.method) {
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case "getBlockNumber": {
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// We need to get the bootstrap block height
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if (this.#height === -2) {
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this.#height = Math.ceil(getNumber(<bigint>getMedian(this.quorum, this.#configs.map((c) => ({
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value: c.blockNumber,
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tag: getNumber(c.blockNumber).toString(),
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weight: c.weight
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})))));
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}
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// Find the mode across all the providers, allowing for
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// a little drift between block heights
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const mode = getFuzzyMode(this.quorum, results);
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if (mode === undefined) { return undefined; }
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if (mode > this.#height) { this.#height = mode; }
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return this.#height;
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}
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case "getGasPrice":
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case "estimateGas":
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return getMedian(this.quorum, results);
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case "getBlock":
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// Pending blocks are in the mempool and already
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// quite untrustworthy; just grab anything
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if ("blockTag" in req && req.blockTag === "pending") {
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return getAnyResult(this.quorum, results);
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}
|
|
return checkQuorum(this.quorum, results);
|
|
|
|
case "call":
|
|
case "chainId":
|
|
case "getBalance":
|
|
case "getTransactionCount":
|
|
case "getCode":
|
|
case "getStorage":
|
|
case "getTransaction":
|
|
case "getTransactionReceipt":
|
|
case "getLogs":
|
|
return checkQuorum(this.quorum, results);
|
|
|
|
case "broadcastTransaction":
|
|
return getAnyResult(this.quorum, results);
|
|
}
|
|
|
|
assert(false, "unsupported method", "UNSUPPORTED_OPERATION", {
|
|
operation: `_perform(${ stringify((<any>req).method) })`
|
|
});
|
|
}
|
|
|
|
async #waitForQuorum(running: Set<RunnerState>, req: PerformActionRequest): Promise<any> {
|
|
if (running.size === 0) { throw new Error("no runners?!"); }
|
|
|
|
// Any promises that are interesting to watch for; an expired stall
|
|
// or a successful perform
|
|
const interesting: Array<Promise<void>> = [ ];
|
|
|
|
let newRunners = 0;
|
|
for (const runner of running) {
|
|
|
|
// No responses, yet; keep an eye on it
|
|
if (runner.perform) {
|
|
interesting.push(runner.perform);
|
|
}
|
|
|
|
// Still stalling...
|
|
if (runner.staller) {
|
|
interesting.push(runner.staller);
|
|
continue;
|
|
}
|
|
|
|
// This runner has already triggered another runner
|
|
if (runner.didBump) { continue; }
|
|
|
|
// Got a response (result or error) or stalled; kick off another runner
|
|
runner.didBump = true;
|
|
newRunners++;
|
|
}
|
|
|
|
// Check if we have reached quorum on a result (or error)
|
|
const value = await this.#checkQuorum(running, req);
|
|
if (value !== undefined) {
|
|
if (value instanceof Error) { throw value; }
|
|
return value;
|
|
}
|
|
|
|
// Add any new runners, because a staller timed out or a result
|
|
// or error response came in.
|
|
for (let i = 0; i < newRunners; i++) {
|
|
this.#addRunner(running, req)
|
|
}
|
|
|
|
// All providers have returned, and we have no result
|
|
|
|
assert(interesting.length > 0, "quorum not met", "SERVER_ERROR", {
|
|
request: "%sub-requests",
|
|
info: { request: req, results: Array.from(running).map((r) => stringify(r.result)) }
|
|
});
|
|
|
|
// Wait for someone to either complete its perform or stall out
|
|
await Promise.race(interesting);
|
|
|
|
// This is recursive, but at worst case the depth is 2x the
|
|
// number of providers (each has a perform and a staller)
|
|
return await this.#waitForQuorum(running, req);
|
|
}
|
|
|
|
async _perform<T = any>(req: PerformActionRequest): Promise<T> {
|
|
// Broadcasting a transaction is rare (ish) and already incurs
|
|
// a cost on the user, so spamming is safe-ish. Just send it to
|
|
// every backend.
|
|
if (req.method === "broadcastTransaction") {
|
|
const results = await Promise.all(this.#configs.map(async ({ provider, weight }) => {
|
|
try {
|
|
const result = await provider._perform(req);
|
|
return Object.assign(normalizeResult({ result }), { weight });
|
|
} catch (error: any) {
|
|
return Object.assign(normalizeResult({ error }), { weight });
|
|
}
|
|
}));
|
|
|
|
const result = getAnyResult(this.quorum, results);
|
|
assert(result !== undefined, "problem multi-broadcasting", "SERVER_ERROR", {
|
|
request: "%sub-requests",
|
|
info: { request: req, results: results.map(stringify) }
|
|
})
|
|
if (result instanceof Error) { throw result; }
|
|
return result;
|
|
}
|
|
|
|
await this.#initialSync();
|
|
|
|
// Bootstrap enough runners to meet quorum
|
|
const running: Set<RunnerState> = new Set();
|
|
for (let i = 0; i < this.quorum; i++) {
|
|
this.#addRunner(running, req);
|
|
}
|
|
|
|
const result = await this.#waitForQuorum(running, req);
|
|
|
|
// Track requests sent to a provider that are still
|
|
// outstanding after quorum has been otherwise found
|
|
for (const runner of running) {
|
|
if (runner.perform && runner.result == null) {
|
|
runner.config.lateResponses++;
|
|
}
|
|
}
|
|
|
|
return result;
|
|
}
|
|
|
|
async destroy(): Promise<void> {
|
|
for (const { provider } of this.#configs) {
|
|
provider.destroy();
|
|
}
|
|
super.destroy();
|
|
}
|
|
}
|