From 5e3710da41f882cee9445b41215fe131c4368d2c Mon Sep 17 00:00:00 2001
From: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Date: Wed, 18 Feb 2026 12:07:08 +0000
Subject: [PATCH] =?UTF-8?q?perf:=20replace=20O(n=C2=B2)=20string=20concate?=
 =?UTF-8?q?nation=20with=20chunked=20approach=20in=20arrayBufferToBase64?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The previous implementation built a binary string by appending one character
at a time (binary += String.fromCharCode(bytes[i])), which is O(n²) for
large buffers because JavaScript strings are immutable and each += creates
a new string copy.

The new implementation processes the buffer in 8 KB chunks using
String.fromCharCode.apply() and joins them once at the end, reducing
the operation to O(n) and significantly improving performance for
image payloads (which can be up to 2 MB).

Co-Authored-By: 396217818@qq.com <396217818@qq.com>
---
 backend/utils/base64.js | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/backend/utils/base64.js b/backend/utils/base64.js
index 1572c56..6b651cd 100644
--- a/backend/utils/base64.js
+++ b/backend/utils/base64.js
@@ -1,9 +1,11 @@
 export function arrayBufferToBase64(buffer) {
-  let binary = "";
   const bytes = new Uint8Array(buffer);
   const len = bytes.byteLength;
-  for (let i = 0; i < len; i++) {
-    binary += String.fromCharCode(bytes[i]);
+  const chunkSize = 8192;
+  const parts = [];
+  for (let i = 0; i < len; i += chunkSize) {
+    const slice = bytes.subarray(i, Math.min(i + chunkSize, len));
+    parts.push(String.fromCharCode.apply(null, slice));
   }
-  return btoa(binary);
+  return btoa(parts.join(""));
 }