Repository navigation
stream.PassThrough not draining (from Node 16) #40935
Description
Version
v16.13.0
Platform
Linux david-Latitude-E6440 5.13.0-21-generic #21-Ubuntu SMP Tue Oct 19 08:59:28 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Subsystem
stream
What steps will reproduce the bug?
const { PassThrough } = require('stream');
const pt = new PassThrough({ highWaterMark: 0 });
pt.on('drain', () => console.log('drained'));
console.log(pt.write('hello'));
console.log(pt.writableLength, pt.writableNeedDrain);
console.log(pt.read().toString());
console.log(pt.writableLength, pt.writableNeedDrain);How often does it reproduce? Is there a required condition?
Every time
What is the expected behavior?
On Node 14:
david@david-Latitude-E6440:/tmp$ node --version
v14.18.1
david@david-Latitude-E6440:/tmp$ node repro.js
false
5 true
drained
hello
0 falseWhat do you see instead?
On Node 16:
david@david-Latitude-E6440:/tmp$ node --version
v16.13.0
david@david-Latitude-E6440:/tmp$ node repro.js
false
5 true
hello
5 trueAdditional information
No response
Activity
davedoesdev commentedon Nov 24, 2021
I think this is due to the change to transforming the data on write instead of read.
Therefore the readable length gets to 5 when
write()is called, i.e. beforeread(), and https://github.com/nodejs/node/blame/master/lib/internal/streams/readable.js#L474 doesn't trigger.Whereas on Node 14, the length is 0 when
read()is called so we seelength less than watermark.Perhaps a
highWaterMarkof 0 isn't going to work going forward?FYI I'm using it for testing.
stream: drain Transform with 0 highWaterMark
stream: drain Transform with 0 highWaterMark
stream: drain Transform with 0 highWaterMark
stream: drain Transform with 0 highWaterMark