Stream created by Writable.toWeb() hangs when highWaterMark is set to 0 #61145

Version

v24.12.0

Platform

Darwin [REDACTED] 25.1.0 Darwin Kernel Version 25.1.0: Mon Oct 20 19:33:36 PDT 2025; root:xnu-12377.41.6~2/RELEASE_ARM64_T6030 arm64 arm Darwin

Subsystem

No response

What steps will reproduce the bug?

Run the following code:

const writable = new Writable({
  highWaterMark: 0,
  write(chunk) {
    console.log(chunk);
  },
});

const stream = Writable.toWeb(writable);
const writer = stream.getWriter();
await writer.write(new Uint8Array([1, 2, 3]));
await writer.write(new Uint8Array([4, 5, 6]));

After <Buffer 01 02 03> is emitted, the stream hangs and remaining chunks will never be written.

In contrast, the following code runs correctly:

const stream = new WritableStream(
  {
    write(chunk) {
      console.log(chunk);
    },
  },
  {
    highWaterMark: 0,
  },
);

const writer = stream.getWriter();
await writer.write(new Uint8Array([1, 2, 3]));
await writer.write(new Uint8Array([4, 5, 6]));

This shows that this is not a bug of the implementation of Web Stream API itself, but the conversion using Writable.toWeb().

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

Always

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

The stream keeps running and consumes the remaining chunks.

What do you see instead?

The stream hangs and the remaining chunks will never be consumed.

Additional information

No response