Readable stream internal buffer grows unbounded under backpressure (regression vs Node 10) #62558
Description
Version
v24.13.1, v25.8.1
Platform
Linux KContainer 5.10.0-12-amd64 #1 SMP Debian 5.10.103-1 (2022-03-07) x86_64 x86_64 x86_64 GNU/Linux
Subsystem
No response
What steps will reproduce the bug?
Hi,
The bug can be reproduced using the below PoC:
const stream = require('stream');
const rs = stream.Readable({
read: function () {
// Fast readable: push a large chunk and then many smaller ones
this.push(Buffer.alloc(65500));
for (let i = 0; i < 40; i++) {
this.push(Buffer.alloc(1024));
}
}
});
const ws = stream.Writable({
write: function (data, enc, cb) {
// Slow writable: simulate slow consumer
setTimeout(cb, 10);
}
});
setInterval(function () {
const state = rs._readableState;
console.log('state.length %d, state.buffer.length %d, state.highWaterMark %d',
state.length,
state.buffer.length,
state.highWaterMark
);
}, 1000);
rs.pipe(ws);How often does it reproduce? Is there a required condition?
No specific condition required
What is the expected behavior? Why is that the expected behavior?
This was previously reported as an issue (#19601) and later fixed in Node v10.0.0
root@KContainer:~/19601# nvm use 10.0.0
Now using node v10.0.0 (npm v5.6.0)
root@KContainer:~/19601# node repro.cjs
state.length 24576, state.buffer.length 24, state.highWaterMark 16384
state.length 40960, state.buffer.length 40, state.highWaterMark 16384
state.length 24576, state.buffer.length 24, state.highWaterMark 16384
state.length 114652, state.buffer.length 49, state.highWaterMark 16384
state.length 24576, state.buffer.length 24, state.highWaterMark 16384
^C
Notice that buffer length does not increase in an unbounded manner
What do you see instead?
Buffer length keeps increasing in Node v24.13.1 and 25.8.1
root@KContainer:~/19601# node repro.cjs
state.length 147420, state.buffer.length 205, state.highWaterMark 65536
state.length 147420, state.buffer.length 287, state.highWaterMark 65536
state.length 147420, state.buffer.length 410, state.highWaterMark 65536
state.length 147420, state.buffer.length 492, state.highWaterMark 65536
state.length 147420, state.buffer.length 574, state.highWaterMark 65536
state.length 147420, state.buffer.length 697, state.highWaterMark 65536
state.length 147420, state.buffer.length 779, state.highWaterMark 65536
^C
Additional information
No response
