feat: add syncFromCheckpoint method

src/baseClient.ts

@@ -56,7 +56,7 @@ export default abstract class BaseClient extends EventEmitter {
     return this._latestOptimisticUpdate as Uint8Array;
   }
 
-  private _latestPeriod: number = -1;
+  protected _latestPeriod: number = -1;
 
   get latestPeriod(): number {
     return this._latestPeriod;

src/client/client.ts

@@ -1,6 +1,8 @@
 import BaseClient, { BaseClientOptions } from "#baseClient.js";
 import { IProver, IVerifyingProviderConstructor } from "#interfaces.js";
 import { IClientVerifyingProvider } from "#client/verifyingProvider.js";
+import { LightClientUpdate } from "#types.js";
+import { computeSyncPeriodAtSlot } from "@lodestar/light-client/utils/index.js";
 
 interface Config extends BaseClientOptions {
   prover: IProver;
@@ -19,7 +21,10 @@ export default class Client extends BaseClient {
 
   async sync(): Promise<void> {
     await super.sync();
+    await this.boot();
+  }
 
+  private async boot() {
     if (!this.provider) {
       const { blockHash, blockNumber } = await this.getNextValidExecutionInfo();
       const factory = this.options.provider;
@@ -40,6 +45,16 @@ export default class Client extends BaseClient {
     }
   }
 
+  public async syncFromCheckpoint(checkpoint: LightClientUpdate) {
+    this._latestPeriod = computeSyncPeriodAtSlot(
+      checkpoint.attestedHeader.beacon.slot,
+    );
+    this.latestCommittee = checkpoint.nextSyncCommittee.pubkeys;
+    this.booted = true;
+
+    await super.sync();
+  }
+
   public async rpcCall(method: string, params: any) {
     return this.provider?.rpcMethod(method, params);
   }