stream: Fixes missing 'unpipe' event

Currently when the destination emits an 'error', 'finish' or 'close'
event the pipe calls unpipe to emit 'unpipe' and trigger the clean up
of all it's listeners.
When the source emits an 'end' event without {end: false} it calls
end() on the destination leading it to emit a 'close', this will again
lead to the pipe calling unpipe. However the source emitting an 'end'
event along side {end: false} is the only time the cleanup gets ran
directly without unpipe being called. This fixes that so the 'unpipe'
event does get emitted and cleanup in turn gets ran by that event.

Fixes: https://github.com/nodejs/node/issues/11837
PR-URL: https://github.com/nodejs/node/pull/11876
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/_stream_readable.js

@@ -494,7 +494,7 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
               dest !== process.stdout &&
               dest !== process.stderr;
 
-  var endFn = doEnd ? onend : cleanup;
+  var endFn = doEnd ? onend : unpipe;
   if (state.endEmitted)
     process.nextTick(endFn);
   else
@@ -530,7 +530,7 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
     dest.removeListener('error', onerror);
     dest.removeListener('unpipe', onunpipe);
     src.removeListener('end', onend);
-    src.removeListener('end', cleanup);
+    src.removeListener('end', unpipe);
     src.removeListener('data', ondata);
 
     cleanedUp = true;

test/parallel/test-stream-unpipe-event.js

@@ -0,0 +1,87 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const {Writable, Readable} = require('stream');
+class NullWriteable extends Writable {
+  _write(chunk, encoding, callback) {
+    return callback();
+  }
+}
+class QuickEndReadable extends Readable {
+  _read() {
+    this.push(null);
+  }
+}
+class NeverEndReadable extends Readable {
+  _read() {}
+}
+
+function noop() {}
+
+{
+  const dest = new NullWriteable();
+  const src = new QuickEndReadable();
+  dest.on('pipe', common.mustCall(noop));
+  dest.on('unpipe', common.mustCall(noop));
+  src.pipe(dest);
+  setImmediate(() => {
+    assert.strictEqual(src._readableState.pipesCount, 0);
+  });
+}
+
+{
+  const dest = new NullWriteable();
+  const src = new NeverEndReadable();
+  dest.on('pipe', common.mustCall(noop));
+  dest.on('unpipe', common.mustNotCall('unpipe should not have been emitted'));
+  src.pipe(dest);
+  setImmediate(() => {
+    assert.strictEqual(src._readableState.pipesCount, 1);
+  });
+}
+
+{
+  const dest = new NullWriteable();
+  const src = new NeverEndReadable();
+  dest.on('pipe', common.mustCall(noop));
+  dest.on('unpipe', common.mustCall(noop));
+  src.pipe(dest);
+  src.unpipe(dest);
+  setImmediate(() => {
+    assert.strictEqual(src._readableState.pipesCount, 0);
+  });
+}
+
+{
+  const dest = new NullWriteable();
+  const src = new QuickEndReadable();
+  dest.on('pipe', common.mustCall(noop));
+  dest.on('unpipe', common.mustCall(noop));
+  src.pipe(dest, {end: false});
+  setImmediate(() => {
+    assert.strictEqual(src._readableState.pipesCount, 0);
+  });
+}
+
+{
+  const dest = new NullWriteable();
+  const src = new NeverEndReadable();
+  dest.on('pipe', common.mustCall(noop));
+  dest.on('unpipe', common.mustNotCall('unpipe should not have been emitted'));
+  src.pipe(dest, {end: false});
+  setImmediate(() => {
+    assert.strictEqual(src._readableState.pipesCount, 1);
+  });
+}
+
+{
+  const dest = new NullWriteable();
+  const src = new NeverEndReadable();
+  dest.on('pipe', common.mustCall(noop));
+  dest.on('unpipe', common.mustCall(noop));
+  src.pipe(dest, {end: false});
+  src.unpipe(dest);
+  setImmediate(() => {
+    assert.strictEqual(src._readableState.pipesCount, 0);
+  });
+}