stream: simplify .pipe() and .unpipe() in Readable

Now we are using `pipes` and `pipesCount` in Readable state and the
`pipes` value can be a stream or an array of streams. This change
reducing them into one `pipes` value, which is an array of streams.
It also adds a deprecation warning of `_readableState.pipesCount`.

doc/api/deprecations.md

@@ -2498,6 +2498,20 @@ Type: Runtime
 Passing a callback to [`worker.terminate()`][] is deprecated. Use the returned
 `Promise` instead, or a listener to the worker’s `'exit'` event.
 
+<a id="DEP0133"></a>
+### DEP0133: _readableState.pipesCount
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/28583
+    description: Documentation-only.
+-->
+
+Type: Documentation-only
+
+`_readableState.pipesCount` is deprecated. Please use
+`_readableState.pipes.length` instead.
+
 [`--http-parser=legacy`]: cli.html#cli_http_parser_library
 [`--pending-deprecation`]: cli.html#cli_pending_deprecation
 [`Buffer.allocUnsafeSlow(size)`]: buffer.html#buffer_class_method_buffer_allocunsafeslow_size

lib/_stream_readable.js

@@ -30,6 +30,7 @@ const EE = require('events');
 const Stream = require('stream');
 const { Buffer } = require('buffer');
 
+const internalUtil = require('internal/util');
 const debug = require('internal/util/debuglog').debuglog('stream');
 const BufferList = require('internal/streams/buffer_list');
 const destroyImpl = require('internal/streams/destroy');
@@ -97,8 +98,7 @@ function ReadableState(options, stream, isDuplex) {
   // array.shift()
   this.buffer = new BufferList();
   this.length = 0;
-  this.pipes = null;
-  this.pipesCount = 0;
+  this.pipes = [];
   this.flowing = null;
   this.ended = false;
   this.endEmitted = false;
@@ -148,6 +148,13 @@ function ReadableState(options, stream, isDuplex) {
   }
 }
 
+Object.defineProperty(ReadableState.prototype, 'pipesCount', {
+  get: internalUtil.deprecate(function() {
+    return this.pipes.length;
+  }, '_readableState.pipesCount is deprecated. ' +
+  'Use _readableState.pipes.length instead.', 'DEP0133'),
+});
+
 function Readable(options) {
   if (!(this instanceof Readable))
     return new Readable(options);
@@ -635,19 +642,8 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
   const src = this;
   const state = this._readableState;
 
-  switch (state.pipesCount) {
-    case 0:
-      state.pipes = dest;
-      break;
-    case 1:
-      state.pipes = [state.pipes, dest];
-      break;
-    default:
-      state.pipes.push(dest);
-      break;
-  }
-  state.pipesCount += 1;
-  debug('pipe count=%d opts=%j', state.pipesCount, pipeOpts);
+  state.pipes.push(dest);
+  debug('pipe count=%d opts=%j', state.pipes.length, pipeOpts);
 
   const doEnd = (!pipeOpts || pipeOpts.end !== false) &&
               dest !== process.stdout &&
@@ -717,9 +713,7 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
       // to get stuck in a permanently paused state if that write
       // also returned false.
       // => Check whether `dest` is still a piping destination.
-      if (((state.pipesCount === 1 && state.pipes === dest) ||
-           (state.pipesCount > 1 && state.pipes.includes(dest))) &&
-          !cleanedUp) {
+      if (state.pipes.length > 0 && state.pipes.includes(dest) && !cleanedUp) {
         debug('false write response, pause', state.awaitDrain);
         state.awaitDrain++;
       }
@@ -789,38 +783,16 @@ Readable.prototype.unpipe = function(dest) {
   const unpipeInfo = { hasUnpiped: false };
 
   // If we're not piping anywhere, then do nothing.
-  if (state.pipesCount === 0)
-    return this;
-
-  // Just one destination.  most common case.
-  if (state.pipesCount === 1) {
-    // Passed in one, but it's not the right one.
-    if (dest && dest !== state.pipes)
-      return this;
-
-    if (!dest)
-      dest = state.pipes;
-
-    // got a match.
-    state.pipes = null;
-    state.pipesCount = 0;
-    state.flowing = false;
-    if (dest)
-      dest.emit('unpipe', this, unpipeInfo);
+  if (state.pipes.length === 0)
     return this;
-  }
-
-  // Slow case with multiple pipe destinations.
 
   if (!dest) {
     // remove all.
     var dests = state.pipes;
-    var len = state.pipesCount;
-    state.pipes = null;
-    state.pipesCount = 0;
+    state.pipes = [];
     state.flowing = false;
 
-    for (var i = 0; i < len; i++)
+    for (var i = 0; i < dests.length; i++)
       dests[i].emit('unpipe', this, { hasUnpiped: false });
     return this;
   }
@@ -831,9 +803,8 @@ Readable.prototype.unpipe = function(dest) {
     return this;
 
   state.pipes.splice(index, 1);
-  state.pipesCount -= 1;
-  if (state.pipesCount === 1)
-    state.pipes = state.pipes[0];
+  if (state.pipes.length === 0)
+    state.flowing = false;
 
   dest.emit('unpipe', this, unpipeInfo);
 

test/parallel/test-stream-pipe-same-destination-twice.js

@@ -20,15 +20,15 @@ const { PassThrough, Writable } = require('stream');
   passThrough.pipe(dest);
 
   assert.strictEqual(passThrough._events.data.length, 2);
-  assert.strictEqual(passThrough._readableState.pipesCount, 2);
+  assert.strictEqual(passThrough._readableState.pipes.length, 2);
   assert.strictEqual(passThrough._readableState.pipes[0], dest);
   assert.strictEqual(passThrough._readableState.pipes[1], dest);
 
   passThrough.unpipe(dest);
 
   assert.strictEqual(passThrough._events.data.length, 1);
-  assert.strictEqual(passThrough._readableState.pipesCount, 1);
-  assert.strictEqual(passThrough._readableState.pipes, dest);
+  assert.strictEqual(passThrough._readableState.pipes.length, 1);
+  assert.deepStrictEqual(passThrough._readableState.pipes, [dest]);
 
   passThrough.write('foobar');
   passThrough.pipe(dest);
@@ -47,7 +47,7 @@ const { PassThrough, Writable } = require('stream');
   passThrough.pipe(dest);
 
   assert.strictEqual(passThrough._events.data.length, 2);
-  assert.strictEqual(passThrough._readableState.pipesCount, 2);
+  assert.strictEqual(passThrough._readableState.pipes.length, 2);
   assert.strictEqual(passThrough._readableState.pipes[0], dest);
   assert.strictEqual(passThrough._readableState.pipes[1], dest);
 
@@ -64,15 +64,15 @@ const { PassThrough, Writable } = require('stream');
   passThrough.pipe(dest);
 
   assert.strictEqual(passThrough._events.data.length, 2);
-  assert.strictEqual(passThrough._readableState.pipesCount, 2);
+  assert.strictEqual(passThrough._readableState.pipes.length, 2);
   assert.strictEqual(passThrough._readableState.pipes[0], dest);
   assert.strictEqual(passThrough._readableState.pipes[1], dest);
 
   passThrough.unpipe(dest);
   passThrough.unpipe(dest);
 
   assert.strictEqual(passThrough._events.data, undefined);
-  assert.strictEqual(passThrough._readableState.pipesCount, 0);
+  assert.strictEqual(passThrough._readableState.pipes.length, 0);
 
   passThrough.write('foobar');
 }

test/parallel/test-stream-pipe-unpipe-streams.js

@@ -22,15 +22,15 @@ assert.strictEqual(source._readableState.pipes.length, 2);
 
 source.unpipe(dest2);
 
-assert.strictEqual(source._readableState.pipes, dest1);
+assert.deepStrictEqual(source._readableState.pipes, [dest1]);
 assert.notStrictEqual(source._readableState.pipes, dest2);
 
 dest2.on('unpipe', common.mustNotCall());
 source.unpipe(dest2);
 
 source.unpipe(dest1);
 
-assert.strictEqual(source._readableState.pipes, null);
+assert.strictEqual(source._readableState.pipes.length, 0);
 
 {
   // Test `cleanup()` if we unpipe all streams.
@@ -43,8 +43,7 @@ assert.strictEqual(source._readableState.pipes, null);
   const destCheckEventNames = ['close', 'finish', 'drain', 'error', 'unpipe'];
 
   const checkSrcCleanup = common.mustCall(() => {
-    assert.strictEqual(source._readableState.pipes, null);
-    assert.strictEqual(source._readableState.pipesCount, 0);
+    assert.strictEqual(source._readableState.pipes.length, 0);
     assert.strictEqual(source._readableState.flowing, false);
 
     srcCheckEventNames.forEach((eventName) => {

test/parallel/test-stream-pipescount-deprecation-warning.js

@@ -0,0 +1,12 @@
+'use strict';
+
+const common = require('../common');
+const { Readable } = require('stream');
+
+const warning = '_readableState.pipesCount is deprecated. ' +
+                'Use _readableState.pipes.length instead.';
+
+common.expectWarning('DeprecationWarning', warning, 'DEP0133');
+
+const readable = new Readable();
+readable._readableState.pipesCount;

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

@@ -23,7 +23,7 @@ class NeverEndReadable extends Readable {
   dest.on('unpipe', common.mustCall());
   src.pipe(dest);
   setImmediate(() => {
-    assert.strictEqual(src._readableState.pipesCount, 0);
+    assert.strictEqual(src._readableState.pipes.length, 0);
   });
 }
 
@@ -34,7 +34,7 @@ class NeverEndReadable extends Readable {
   dest.on('unpipe', common.mustNotCall('unpipe should not have been emitted'));
   src.pipe(dest);
   setImmediate(() => {
-    assert.strictEqual(src._readableState.pipesCount, 1);
+    assert.strictEqual(src._readableState.pipes.length, 1);
   });
 }
 
@@ -46,7 +46,7 @@ class NeverEndReadable extends Readable {
   src.pipe(dest);
   src.unpipe(dest);
   setImmediate(() => {
-    assert.strictEqual(src._readableState.pipesCount, 0);
+    assert.strictEqual(src._readableState.pipes.length, 0);
   });
 }
 
@@ -57,7 +57,7 @@ class NeverEndReadable extends Readable {
   dest.on('unpipe', common.mustCall());
   src.pipe(dest, { end: false });
   setImmediate(() => {
-    assert.strictEqual(src._readableState.pipesCount, 0);
+    assert.strictEqual(src._readableState.pipes.length, 0);
   });
 }
 
@@ -68,7 +68,7 @@ class NeverEndReadable extends Readable {
   dest.on('unpipe', common.mustNotCall('unpipe should not have been emitted'));
   src.pipe(dest, { end: false });
   setImmediate(() => {
-    assert.strictEqual(src._readableState.pipesCount, 1);
+    assert.strictEqual(src._readableState.pipes.length, 1);
   });
 }
 
@@ -80,6 +80,6 @@ class NeverEndReadable extends Readable {
   src.pipe(dest, { end: false });
   src.unpipe(dest);
   setImmediate(() => {
-    assert.strictEqual(src._readableState.pipesCount, 0);
+    assert.strictEqual(src._readableState.pipes.length, 0);
   });
 }

test/parallel/test-stream2-basic.js

@@ -171,10 +171,10 @@ class TestWriter extends EE {
   w[0].on('write', function() {
     if (--writes === 0) {
       r.unpipe();
-      assert.strictEqual(r._readableState.pipes, null);
+      assert.deepStrictEqual(r._readableState.pipes, []);
       w[0].end();
       r.pipe(w[1]);
-      assert.strictEqual(r._readableState.pipes, w[1]);
+      assert.deepStrictEqual(r._readableState.pipes, [w[1]]);
     }
   });