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buffer: optimize buffer.concat performance #61721

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Merged
nodejs-github-bot merged 7 commits into from
Feb 27, 2026
+50 −9
Merged

buffer: optimize buffer.concat performance #61721

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7ded458
buffer: optimize buffer.concat performance
mertcanaltin Feb 7, 2026
a7fd75d
revert comment lines
mertcanaltin Feb 7, 2026
885c7a3
revert comment lines
mertcanaltin Feb 7, 2026
ba806ae
revert listLen caching
mertcanaltin Feb 7, 2026
559f5e9
move type validation before allocation
mertcanaltin Feb 7, 2026
1898304
use TypedArrayPrototypeGetByteLength
mertcanaltin Feb 8, 2026
4848305
add test for spoofed length getter in concat
mertcanaltin Feb 10, 2026
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48 changes: 39 additions & 9 deletions lib/buffer.js
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Original file line number Diff line number Diff line change
Expand Up @@ -614,25 +614,55 @@ Buffer.concat = function concat(list, length) {
if (length === undefined) {
length = 0;
for (let i = 0; i < list.length; i++) {
if (list[i].length) {
length += list[i].length;
const buf = list[i];
if (!isUint8Array(buf)) {
// TODO(BridgeAR): This should not be of type ERR_INVALID_ARG_TYPE.
// Instead, find the proper error code for this.
throw new ERR_INVALID_ARG_TYPE(
`list[${i}]`, ['Buffer', 'Uint8Array'], buf);
}
length += TypedArrayPrototypeGetByteLength(buf);
}
} else {
validateOffset(length, 'length');

const buffer = allocate(length);
let pos = 0;
for (let i = 0; i < list.length; i++) {
const buf = list[i];
const bufLength = TypedArrayPrototypeGetByteLength(buf);
TypedArrayPrototypeSet(buffer, buf, pos);
pos += bufLength;
}

if (pos < length) {
TypedArrayPrototypeFill(buffer, 0, pos, length);
}
return buffer;
}

const buffer = Buffer.allocUnsafe(length);
let pos = 0;
validateOffset(length, 'length');
for (let i = 0; i < list.length; i++) {
const buf = list[i];
if (!isUint8Array(buf)) {
if (!isUint8Array(list[i])) {
// TODO(BridgeAR): This should not be of type ERR_INVALID_ARG_TYPE.
// Instead, find the proper error code for this.
throw new ERR_INVALID_ARG_TYPE(
`list[${i}]`, ['Buffer', 'Uint8Array'], list[i]);
}
pos += _copyActual(buf, buffer, pos, 0, buf.length, true);
}

const buffer = allocate(length);
let pos = 0;
for (let i = 0; i < list.length; i++) {
const buf = list[i];
const bufLength = TypedArrayPrototypeGetByteLength(buf);
if (pos + bufLength > length) {
TypedArrayPrototypeSet(buffer,
TypedArrayPrototypeSlice(buf, 0, length - pos),
pos);
pos = length;
break;
}
TypedArrayPrototypeSet(buffer, buf, pos);
pos += bufLength;
}

// Note: `length` is always equal to `buffer.length` at this point
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