feat: retrieve epoch start and length from contract on startup PE-5240

Defaults to the values in the constants when unable to retrieve from the
contract. Right now this results in nonsense values that don't match the
contract but at least keeps reports and interactions posting
periodically. When the contract is finalized we can sync the constants
in the observer and the contract.

src/system.ts

@@ -22,6 +22,7 @@ import {
 } from '@ardrive/turbo-sdk/node';
 import { ArweaveSigner } from 'arbundles/node';
 import Arweave from 'arweave';
+import got from 'got';
 import { default as NodeCache } from 'node-cache';
 import * as fs from 'node:fs';
 import {
@@ -47,7 +48,11 @@ import { RemoteCacheArnsNameList } from './names/remote-cache-arns-name-list.js'
 import { StaticArnsNameList } from './names/static-arns-name-list.js';
 import { Observer } from './observer.js';
 import { ContractObserversSource } from './observers/contract-observers-source.js';
-import { EPOCH_BLOCK_LENGTH, EpochHeightSource } from './protocol.js';
+import {
+  EPOCH_BLOCK_LENGTH,
+  EpochHeightSource,
+  START_HEIGHT,
+} from './protocol.js';
 import { ContractReportSink } from './store/contract-report-sink.js';
 import { FsReportStore } from './store/fs-report-store.js';
 import {
@@ -75,8 +80,41 @@ const chainSource = new ChainSource({
   arweaveBaseUrl: config.ARWEAVE_URL,
 });
 
+// Attempt to read the start height and epoch block length from the contract
+let epochZeroStartHeigth = START_HEIGHT;
+let epochBlockLength = EPOCH_BLOCK_LENGTH;
+try {
+  const resp = await got
+    .get(
+      `${config.CONTRACT_CACHE_URL}/v1/contract/${config.CONTRACT_ID}/read/epoch`,
+    )
+    .json<any>();
+  epochZeroStartHeigth = +(resp?.result?.epochZeroStartHeight ?? START_HEIGHT);
+  log.info(
+    `Got epoch zero start height from contract: ${epochZeroStartHeigth}`,
+    {
+      epochZeroStartHeigth,
+    },
+  );
+  epochBlockLength = +(resp?.result?.epochBlockLength ?? EPOCH_BLOCK_LENGTH);
+  log.info(`Got epoch block length from contract: ${epochBlockLength}`, {
+    epochBlockLength,
+  });
+} catch (error: any) {
+  log.error(
+    `Unable to get start height from contract cache: ${error.message}; defaulting to ${START_HEIGHT}`,
+  );
+  log.error(
+    `Unable to get epoch block length from contract cache: ${error.message}; defaulting to ${EPOCH_BLOCK_LENGTH}`,
+  );
+}
+
 export const epochHeightSelector = new EpochHeightSource({
   heightSource: chainSource,
+  epochParams: {
+    startHeight: epochZeroStartHeigth,
+    epochBlockLength,
+  },
 });
 
 const remoteCacheArnsNameList =
@@ -301,7 +339,7 @@ export async function updateAndSaveCurrentReport() {
       report.epochStartHeight +
       START_HEIGHT_START_OFFSET +
       (entropy.readUInt32BE(0) %
-        (EPOCH_BLOCK_LENGTH -
+        (epochBlockLength -
           START_HEIGHT_START_OFFSET -
           START_HEIGHT_END_OFFSET));