From 22f194241195f105751f88b7b981313fac24c240 Mon Sep 17 00:00:00 2001
From: Meghan Denny <meghan@bun.sh>
Date: Thu, 26 Sep 2024 19:00:40 -0700
Subject: [PATCH] fix Buffer.fill with a non-null empty fill including
 uninitialized bytes

---
 src/bun.js/bindings/JSBuffer.cpp | 5 +++++
 test/js/node/buffer.test.js      | 4 ++++
 2 files changed, 9 insertions(+)

diff --git a/src/bun.js/bindings/JSBuffer.cpp b/src/bun.js/bindings/JSBuffer.cpp
index 8a0aea2c36c00..c88626f780e05 100644
--- a/src/bun.js/bindings/JSBuffer.cpp
+++ b/src/bun.js/bindings/JSBuffer.cpp
@@ -601,6 +601,11 @@ static inline JSC::EncodedJSValue jsBufferConstructorFunction_allocBody(JSC::JSG
             }
             auto startPtr = uint8Array->typedVector() + start;
             auto str_ = value.toWTFString(lexicalGlobalObject);
+            if (str_.isEmpty()) {
+                memset(startPtr, 0, length);
+                RELEASE_AND_RETURN(scope, JSC::JSValue::encode(uint8Array));
+            }
+
             ZigString str = Zig::toZigString(str_);
 
             if (UNLIKELY(!Bun__Buffer_fill(&str, startPtr, end - start, encoding))) {
diff --git a/test/js/node/buffer.test.js b/test/js/node/buffer.test.js
index 17f25ec067a9b..9b3c6459fbad6 100644
--- a/test/js/node/buffer.test.js
+++ b/test/js/node/buffer.test.js
@@ -964,6 +964,10 @@ for (let withOverridenBufferWrite of [false, true]) {
         expect(buf[4]).toBe(128);
       });
 
+      it("fill(N, empty string) should be the same as fill(N) and not include any uninitialized bytes", () => {
+        expect(Buffer.alloc(100, "")).toEqual(Buffer.alloc(100));
+      });
+
       // https://github.com/joyent/node/issues/1758
       it("check for fractional length args, junk length args, etc.", () => {
         // Call .fill() first, stops valgrind warning about uninitialized memory reads.