Bug in fileHandle.readableWebStream implementation

[pdaehne]

Version

v24.2.0

Platform

Darwin mac.igd.fraunhofer.de 24.5.0 Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:25 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T6020 arm64

Subsystem

No response

What steps will reproduce the bug?

Start the attached script.

bug.zip

#!/usr/bin/env node

import * as fsPromises from 'node:fs/promises';

const scriptURL = new URL(import.meta.url);
const fileHandle = await fsPromises.open(scriptURL);
const readableStream = fileHandle.readableWebStream();
const reader = readableStream.getReader({ mode: "byob" });
const arrayBuffer = new ArrayBuffer(3);
const view = new Uint8Array(arrayBuffer, 2, 1);
const result = await reader.read(view);

How often does it reproduce? Is there a required condition?

Always.

What is the expected behavior? Why is that the expected behavior?

I do not expect to get an exception.

What do you see instead?

I do get the following exception:

node:internal/fs/promises:689
  validateOffsetLengthRead(offset, length, buffer.byteLength);
  ^

RangeError [ERR_OUT_OF_RANGE]: The value of "length" is out of range. It must be <= -1. Received 1
    at read (node:internal/fs/promises:689:3)
    at fsCall (node:internal/fs/promises:467:18)
    at FileHandle.read (node:internal/fs/promises:199:12)
    at Object.pull (node:internal/fs/promises:322:37)
    at invokePromiseCallback (node:internal/webstreams/util:172:10)
    at Object.<anonymous> (node:internal/webstreams/util:177:23)
    at readableByteStreamControllerCallPullIfNeeded (node:internal/webstreams/readablestream:3145:24)
    at node:internal/webstreams/readablestream:3295:7 {
  code: 'ERR_OUT_OF_RANGE'
}

Node.js v24.2.0

Additional information

There seems to be a bug in line 321 of "node/lib/internal/fs/promises.js". The line currently looks like this:

const { bytesRead } = await readFn(view, view.byteOffset, view.byteLength);

It probably should look like this:

const { bytesRead } = await readFn(view, 0, view.byteLength);

You want to read to offset 0 of the Uint8Array "view", not to the byteOffset of its underlying ArrayBuffer.

I'm not able to test this fix (I cannot build node.js myself).

[juanarbol]

Are you going to fix it?

[mertcanaltin]

@pdaehne hello would you like to open Pr for this place:

In BYOB reader, the view with offset already comes, and
is automatically offset.

Return only the base pointer from Buffer::Data() and let the
view handle its own offset:

char* Data(Local<Value> val) {
 CHECK(val->IsArrayBufferView());
 Local<ArrayBufferView> ui = val.As<ArrayBufferView>();
 return static_cast<char*>(ui->Buffer()->Data()); // only base pointer
 }

[pdaehne]

I do not understand what you want me to do, please clarify.

As I already wrote above, in my opinion the bug is located in line 321 of "node/lib/internal/fs/promises.js". I did fix this in my local fork of node, added a test, and the test passes:

pdaehne@f6dfeb4

I'm perfectly ok with creating a pull request with that fix.

I also tried your change in line 253 of "node/src/node_buffer.cc". It does not fix my problem, and it does not pass the test.

pdaehne@6b9d3ef

Obviously I will not create a pull request with a fix that does not work.

[mertcanaltin]

Yes, you are right, I thought wrong for a moment, I thought that this problem was in return ByteOffset and that we should not solve it on the cpp side, but what you said seems healthy to me.

[pdaehne]

Ok, I did create a PR for my fix.