stream: fix readable behavior for highWaterMark === 0

Avoid trying to emit 'readable' due to the fact that
state.length is always >= state.highWaterMark if highWaterMark is 0.
Therefore upon .read(0) call (through .on('readable')) stream assumed
that it has enough data to emit 'readable' even though
state.length === 0 instead of issuing _read(). Which led to the TTY
not recognizing that someone is waiting for the input.

Fixes: https://github.com/nodejs/node/issues/20503
Refs: https://github.com/nodejs/node/pull/18372

PR-URL: https://github.com/nodejs/node/pull/21690
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/test/parallel/test-readable-single-end.js b/test/parallel/test-readable-single-end.js
new file mode 100644
index 0000000000..0969d49aa4
--- /dev/null
+++ b/test/parallel/test-readable-single-end.js
@@ -0,0 +1,16 @@
+'use strict';
+
+const common = require('../common');
+const { Readable } = require('stream');
+
+// This test ensures that there will not be an additional empty 'readable'
+// event when stream has ended (only 1 event signalling about end)
+
+const r = new Readable({
+  read: () => {},
+});
+
+r.push(null);
+
+r.on('readable', common.mustCall());
+r.on('end', common.mustCall());