stream: lazy allocate back pressure buffer

PR-URL: #50013
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

lib/internal/streams/writable.js

@@ -77,6 +77,7 @@ const kErroredValue = Symbol('kErroredValue');
 const kDefaultEncodingValue = Symbol('kDefaultEncodingValue');
 const kWriteCbValue = Symbol('kWriteCbValue');
 const kAfterWriteTickInfoValue = Symbol('kAfterWriteTickInfoValue');
+const kBufferedValue = Symbol('kBufferedValue');
 
 const kObjectMode = 1 << 0;
 const kEnded = 1 << 1;
@@ -108,7 +109,7 @@ const kWriteCb = 1 << 26;
 const kExpectWriteCb = 1 << 27;
 const kAfterWriteTickInfo = 1 << 28;
 const kAfterWritePending = 1 << 29;
-const kHasBuffer = 1 << 30;
+const kBuffered = 1 << 30;
 
 // TODO(benjamingr) it is likely slower to do it this way than with free functions
 function makeBitMapDescriptor(bit) {
@@ -270,6 +271,21 @@ ObjectDefineProperties(WritableState.prototype, {
       }
     },
   },
+
+  buffered: {
+    __proto__: null,
+    enumerable: false,
+    get() { return (this.state & kBuffered) !== 0 ? this[kBufferedValue] : []; },
+    set(value) {
+      this[kBufferedValue] = value;
+      if (value) {
+        this.state |= kBuffered;
+      } else {
+        this.state &= ~kBuffered;
+      }
+    },
+  },
+
 });
 
 function WritableState(options, stream, isDuplex) {
@@ -338,20 +354,20 @@ function WritableState(options, stream, isDuplex) {
 }
 
 function resetBuffer(state) {
-  state.buffered = [];
+  state[kBufferedValue] = null;
   state.bufferedIndex = 0;
   state.state |= kAllBuffers | kAllNoop;
-  state.state &= ~kHasBuffer;
+  state.state &= ~kBuffered;
 }
 
 WritableState.prototype.getBuffer = function getBuffer() {
-  return ArrayPrototypeSlice(this.buffered, this.bufferedIndex);
+  return (this.state & kBuffered) === 0 ? [] : ArrayPrototypeSlice(this.buffered, this.bufferedIndex);
 };
 
 ObjectDefineProperty(WritableState.prototype, 'bufferedRequestCount', {
   __proto__: null,
   get() {
-    return this.buffered.length - this.bufferedIndex;
+    return (this.state & kBuffered) === 0 ? 0 : this[kBufferedValue].length - this.bufferedIndex;
   },
 });
 
@@ -518,8 +534,12 @@ function writeOrBuffer(stream, state, chunk, encoding, callback) {
   state.length += len;
 
   if ((state.state & (kWriting | kErrored | kCorked | kConstructed)) !== kConstructed) {
-    state.buffered.push({ chunk, encoding, callback });
-    state.state |= kHasBuffer;
+    if ((state.state & kBuffered) === 0) {
+      state.state |= kBuffered;
+      state[kBufferedValue] = [];
+    }
+
+    state[kBufferedValue].push({ chunk, encoding, callback });
     if ((state.state & kAllBuffers) !== 0 && encoding !== 'buffer') {
       state.state &= ~kAllBuffers;
     }
@@ -611,7 +631,7 @@ function onwrite(stream, er) {
       onwriteError(stream, state, er, cb);
     }
   } else {
-    if ((state.state & kHasBuffer) !== 0) {
+    if ((state.state & kBuffered) !== 0) {
       clearBuffer(stream, state);
     }
 
@@ -687,11 +707,13 @@ function errorBuffer(state) {
     return;
   }
 
-  for (let n = state.bufferedIndex; n < state.buffered.length; ++n) {
-    const { chunk, callback } = state.buffered[n];
-    const len = (state.state & kObjectMode) !== 0 ? 1 : chunk.length;
-    state.length -= len;
-    callback(state.errored ?? new ERR_STREAM_DESTROYED('write'));
+  if ((state.state & kBuffered) !== 0) {
+    for (let n = state.bufferedIndex; n < state.buffered.length; ++n) {
+      const { chunk, callback } = state[kBufferedValue][n];
+      const len = (state.state & kObjectMode) !== 0 ? 1 : chunk.length;
+      state.length -= len;
+      callback(state.errored ?? new ERR_STREAM_DESTROYED('write'));
+    }
   }
 
 
@@ -702,13 +724,12 @@ function errorBuffer(state) {
 
 // If there's something in the buffer waiting, then process it.
 function clearBuffer(stream, state) {
-  if ((state.state & (kDestroyed | kBufferProcessing | kCorked | kHasBuffer)) !== kHasBuffer ||
-    (state.state & kConstructed) === 0) {
+  if ((state.state & (kDestroyed | kBufferProcessing | kCorked | kBuffered)) !== kBuffered) {
     return;
   }
 
   const objectMode = (state.state & kObjectMode) !== 0;
-  const { buffered, bufferedIndex } = state;
+  const { [kBufferedValue]: buffered, bufferedIndex } = state;
   const bufferedLength = buffered.length - bufferedIndex;
 
   if (!bufferedLength) {
@@ -838,10 +859,9 @@ function needFinish(state) {
           kWriting |
           kErrorEmitted |
           kCloseEmitted |
-          kErrored
-    )) === (kEnding | kConstructed) &&
-          state.length === 0 &&
-          state.buffered.length === 0);
+          kErrored |
+          kBuffered
+    )) === (kEnding | kConstructed) && state.length === 0);
 }
 
 function callFinal(stream, state) {
@@ -1083,9 +1103,7 @@ Writable.prototype.destroy = function(err, cb) {
   const state = this._writableState;
 
   // Invoke pending callbacks.
-  if ((state.state & kDestroyed) === 0 &&
-    (state.bufferedIndex < state.buffered.length ||
-      (state.state & kOnFinished) !== 0)) {
+  if ((state.state & (kBuffered | kOnFinished | kDestroyed)) !== kDestroyed) {
     process.nextTick(errorBuffer, state);
   }