From 96bcd9dde2a836a90ae9c6c050f0edf053404097 Mon Sep 17 00:00:00 2001
From: PhilWindle <60546371+PhilWindle@users.noreply.github.com>
Date: Mon, 13 Mar 2023 17:20:13 +0000
Subject: [PATCH] Pw/block download fix (#27)

* Fixed the block download calculation

* Comment fix

* More fixes
---
 .../sdk/src/core_sdk/block_downloader.ts      | 22 ++++++++++++-------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/yarn-project/sdk/src/core_sdk/block_downloader.ts b/yarn-project/sdk/src/core_sdk/block_downloader.ts
index 015dcb108..b7fe24e72 100644
--- a/yarn-project/sdk/src/core_sdk/block_downloader.ts
+++ b/yarn-project/sdk/src/core_sdk/block_downloader.ts
@@ -11,10 +11,17 @@ export class BlockDownloader {
   private interruptableSleep = new InterruptableSleep();
   private semaphore: Semaphore;
   private queue = new MemoryFifo<Block[]>();
+  private genesisTake;
   private debug = createDebugLogger('bb:block_downloader');
 
-  constructor(private rollupProvider: RollupProvider, maxQueueSize: number, private initialTreeSize: number) {
+  constructor(private rollupProvider: RollupProvider, maxQueueSize: number, initialTreeSize: number) {
     this.semaphore = new Semaphore(maxQueueSize);
+    // Choosing 55 as an initial chunk to insert if starting from 0, is an aztec-connect optimisation.
+    // The aztec-connect genesis data consists of 73 rollups.
+    // Initially inserting 55 brings us to 128, after which we work with chunks of 128 rollups.
+    // If not synching from zero, the chunk size is whatever takes us up to the next 128 alignment.
+    // This allows for optimal subtree insertions in the client side merkle tree for better sync performance.
+    this.genesisTake = 128 - (initialTreeSize % 128);
   }
 
   public start(from = 0) {
@@ -31,13 +38,12 @@ export class BlockDownloader {
     const fn = async () => {
       while (this.running) {
         try {
-          // Choosing 55 as an initial chunk to insert if starting from 0, is an aztec-connect optimisation.
-          // The aztec-connect genesis data consists of 73 rollups.
-          // Initially inserting 55 brings us to 128, after which we work with chunks of 128 rollups.
-          // If not synching from zero, the chunk size is whatever takes us up to the next 128 alignment.
-          // This allows for optimal subtree insertions in the client side merkle tree for better sync performance.
-          const initialTake = 128 - ((this.from === 0 ? this.initialTreeSize : this.from) % 128);
-          const blocks = await this.rollupProvider.getBlocks(this.from, this.from === from ? initialTake : 128);
+          // If requesting from block 0, then take the fixed number of blocks to take us to 128 (genesisTake)
+          // Otherwise, take blocks as required to get us to a 128 aligned boundary starting from block (128 - initialTreeSize).
+          // e.g. we are trying to get to blocks 183, 311, 439 etc....
+          const takeValue =
+            this.from < this.genesisTake ? this.genesisTake - this.from : 128 - ((this.from - this.genesisTake) % 128);
+          const blocks = await this.rollupProvider.getBlocks(this.from, takeValue);
 
           if (!blocks.length) {
             await this.interruptableSleep.sleep(10000);