`Duplex.allowHalfOpen` not behaving according to the docs?

[mrkishi]

It seems like Duplex's allowHalfOpen option is not following the documentation behavior:

If set to false, then the stream will automatically end the readable side when the writable side ends and vice versa.

'use strict';

var stream = require('stream');

class RangeSource extends stream.Readable {

 constructor(min, max, options) {

 super(options);

 this.min = min|0;
 this.max = max|0;
 this.next = this.min;

 }

 _read() {

 for (let data = this.next; data <= this.max; ++data) {
 if (!this.push(data.toString())) {
 this.next = data + 1;
 return;
 }
 }

 this.push(null);

 }

}

class Sink extends stream.Writable {
 _write(data, encoding, next) { next() }
}

class PushDuplex extends stream.Duplex {

 constructor(options) {

 super(options);

 // uncomment for the correct (?) behavior:
 /*

 this.on('finish', () => {
 if (!this.allowHalfOpen) {
 this.push(null);
 }
 });

 //*/

 }

 _read() {}

 _write(data, enc, next) {
 this.push(data);
 next();
 }

}

var source = new RangeSource(1, 3);
var allow = new PushDuplex({ allowHalfOpen: true });
var disallow = new PushDuplex({ allowHalfOpen: false });
var sink = new Sink();

source
 .on('data', (data) => console.log('source data:', data.toString()))
 .on('end', () => console.log('source ended'));

source.pipe(allow, { end: true })
 .on('data', (data) => console.log('allow data:', data.toString()))
 .on('end', () => console.log('allow ended'))
 .pipe(sink);

source.pipe(disallow, { end: true })
 .on('data', (data) => console.log('disallow data:', data.toString()))
 .on('end', () => console.log('disallow ended'))
 .pipe(sink);

You can see the readable side isn't closed when the writable side ends. Are the docs, Duplex or am I wrong?

[mscdex]

/cc @nodejs/streams

[mrkishi]

I'm still seeing this behavior on v5.9.0. Did I misunderstand the docs?

[calvinmetcalf]

from what I can tell looking at the code the docs are wrong in that it only closes the writable side if the readable side ends.

[Trott]

Doc update PR: #14127