stream: use lazy registration for drain for fast destinations

PR-URL: https://github.com/nodejs/node/pull/29095
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/test/parallel/test-stream-pipe-flow.js b/test/parallel/test-stream-pipe-flow.js
index b696821c0d..1f2e8f54ce 100644
--- a/test/parallel/test-stream-pipe-flow.js
+++ b/test/parallel/test-stream-pipe-flow.js
@@ -1,5 +1,6 @@
 'use strict';
 const common = require('../common');
+const assert = require('assert');
 const { Readable, Writable, PassThrough } = require('stream');
 
 {
@@ -65,3 +66,25 @@ const { Readable, Writable, PassThrough } = require('stream');
   wrapper.resume();
   wrapper.on('end', common.mustCall());
 }
+
+{
+  // Only register drain if there is backpressure.
+  const rs = new Readable({ read() {} });
+
+  const pt = rs
+    .pipe(new PassThrough({ objectMode: true, highWaterMark: 2 }));
+  assert.strictEqual(pt.listenerCount('drain'), 0);
+  pt.on('finish', () => {
+    assert.strictEqual(pt.listenerCount('drain'), 0);
+  });
+
+  rs.push('asd');
+  assert.strictEqual(pt.listenerCount('drain'), 0);
+
+  process.nextTick(() => {
+    rs.push('asd');
+    assert.strictEqual(pt.listenerCount('drain'), 0);
+    rs.push(null);
+    assert.strictEqual(pt.listenerCount('drain'), 0);
+  });
+}