stream: writableNeedDrain

Don't write to a stream which already has a full buffer.

Fixes: #35341

Author: ronag

doc/api/stream.md

@@ -573,6 +573,15 @@ This property contains the number of bytes (or objects) in the queue
 ready to be written. The value provides introspection data regarding
 the status of the `highWaterMark`.
 
+##### `writable.writableNeedDrain`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {boolean}
+
+Is `true` if buffer is full.
+
 ##### `writable.writableObjectMode`
 <!-- YAML
 added: v12.3.0

lib/_http_outgoing.js

@@ -649,6 +649,11 @@ ObjectDefineProperty(OutgoingMessage.prototype, 'writableEnded', {
   get: function() { return this.finished; }
 });
 
+ObjectDefineProperty(OutgoingMessage.prototype, 'writableNeedDrain', {
+  get: function() {
+    return !this.destroyed && !this.finished && this[kNeedDrain];
+  }
+});
 
 const crlf_buf = Buffer.from('\r\n');
 OutgoingMessage.prototype.write = function write(chunk, encoding, callback) {

lib/internal/streams/duplex.js

@@ -87,6 +87,8 @@ ObjectDefineProperties(Duplex.prototype, {
     ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableCorked'),
   writableEnded:
     ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableEnded'),
+  writableNeedDrain:
+    ObjectGetOwnPropertyDescriptor(Writable.prototype, 'writableNeedDrain'),
 
   destroyed: {
     get() {

lib/internal/streams/pipeline.js

@@ -126,6 +126,10 @@ async function pump(iterable, writable, finish) {
   }
   let error;
   try {
+    if (writable.writableNeedDrain === true) {
+      await EE.once(writable, 'drain');
+    }
+
     for await (const chunk of iterable) {
       if (!writable.write(chunk)) {
         if (writable.destroyed) return;

lib/internal/streams/readable.js

@@ -727,35 +727,44 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
       ondrain();
   }
 
+  function pause() {
+    // If the user unpiped during `dest.write()`, it is possible
+    // to get stuck in a permanently paused state if that write
+    // also returned false.
+    // => Check whether `dest` is still a piping destination.
+    if (!cleanedUp) {
+      if (state.pipes.length === 1 && state.pipes[0] === dest) {
+        debug('false write response, pause', 0);
+        state.awaitDrainWriters = dest;
+        state.multiAwaitDrain = false;
+      } else if (state.pipes.length > 1 && state.pipes.includes(dest)) {
+        debug('false write response, pause', state.awaitDrainWriters.size);
+        state.awaitDrainWriters.add(dest);
+      }
+      src.pause();
+    }
+    if (!ondrain) {
+      // When the dest drains, it reduces the awaitDrain counter
+      // on the source.  This would be more elegant with a .once()
+      // handler in flow(), but adding and removing repeatedly is
+      // too slow.
+      ondrain = pipeOnDrain(src, dest);
+      dest.on('drain', ondrain);
+    }
+  }
+
   src.on('data', ondata);
+
+  if (dest.writableNeedDrain === true) {
+    pause();
+  }
+
   function ondata(chunk) {
     debug('ondata');
     const ret = dest.write(chunk);
     debug('dest.write', ret);
     if (ret === false) {
-      // If the user unpiped during `dest.write()`, it is possible
-      // to get stuck in a permanently paused state if that write
-      // also returned false.
-      // => Check whether `dest` is still a piping destination.
-      if (!cleanedUp) {
-        if (state.pipes.length === 1 && state.pipes[0] === dest) {
-          debug('false write response, pause', 0);
-          state.awaitDrainWriters = dest;
-          state.multiAwaitDrain = false;
-        } else if (state.pipes.length > 1 && state.pipes.includes(dest)) {
-          debug('false write response, pause', state.awaitDrainWriters.size);
-          state.awaitDrainWriters.add(dest);
-        }
-        src.pause();
-      }
-      if (!ondrain) {
-        // When the dest drains, it reduces the awaitDrain counter
-        // on the source.  This would be more elegant with a .once()
-        // handler in flow(), but adding and removing repeatedly is
-        // too slow.
-        ondrain = pipeOnDrain(src, dest);
-        dest.on('drain', ondrain);
-      }
+      pause();
     }
   }
 

lib/internal/streams/writable.js

@@ -805,6 +805,14 @@ ObjectDefineProperties(Writable.prototype, {
     }
   },
 
+  writableNeedDrain: {
+    get() {
+      const wState = this._writableState;
+      if (!wState) return false;
+      return !this._writable.destroyed && !wState.ending && wState.needDrain;
+    }
+  },
+
   writableHighWaterMark: {
     get() {
       return this._writableState && this._writableState.highWaterMark;