From 5148de8f171dbe0e81da6526acf9bdea5d1fc5b9 Mon Sep 17 00:00:00 2001
From: softsimon <softsimon@users.noreply.github.com>
Date: Fri, 19 Mar 2021 13:47:37 +0700
Subject: [PATCH] Shuffle mempool transactions before saving disk cache. (#398)

fixes #397
---
 backend/src/api/common.ts     | 8 +++++++-
 backend/src/api/disk-cache.ts | 3 +++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/backend/src/api/common.ts b/backend/src/api/common.ts
index 021990418..130e0205d 100644
--- a/backend/src/api/common.ts
+++ b/backend/src/api/common.ts
@@ -71,6 +71,13 @@ export class Common {
        }, ms);
     });
   }
+  
+  static shuffleArray(array: any[]) {
+    for (let i = array.length - 1; i > 0; i--) {
+        const j = Math.floor(Math.random() * (i + 1));
+        [array[i], array[j]] = [array[j], array[i]];
+    }
+  }
 
   static setRelativesAndGetCpfpInfo(tx: TransactionExtended, memPool: { [txid: string]: TransactionExtended }): CpfpInfo {
     const parents = this.findAllParents(tx, memPool);
@@ -129,5 +136,4 @@ export class Common {
     });
     return parents;
   }
-
 }
diff --git a/backend/src/api/disk-cache.ts b/backend/src/api/disk-cache.ts
index cbdff49f0..909f12681 100644
--- a/backend/src/api/disk-cache.ts
+++ b/backend/src/api/disk-cache.ts
@@ -6,6 +6,7 @@ import blocks from './blocks';
 import logger from '../logger';
 import config from '../config';
 import { TransactionExtended } from '../mempool.interfaces';
+import { Common } from './common';
 
 class DiskCache {
   private static FILE_NAME = config.MEMPOOL.CACHE_DIR + '/cache.json';
@@ -27,6 +28,8 @@ class DiskCache {
         mempoolArray.push(mempool[tx]);
       }
 
+      Common.shuffleArray(mempoolArray);
+
       const chunkSize = Math.floor(mempoolArray.length / DiskCache.CHUNK_FILES);
 
       await fsPromises.writeFile(DiskCache.FILE_NAME, JSON.stringify({