stream: support readable/writableHWM for Duplex

This commits adds support for readableHighWaterMark and
writableHighWaterMark in Duplex stream, so that they can be set without
accessing the internal state.

Fixes: https://github.com/nodejs/node/issues/14555
PR-URL: https://github.com/nodejs/node/pull/14636
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/lib/_stream_writable.js b/lib/_stream_writable.js
index 334f492ba6..6e0eaf45b5 100644
--- a/lib/_stream_writable.js
+++ b/lib/_stream_writable.js
@@ -41,19 +41,33 @@ function nop() {}
 function WritableState(options, stream) {
   options = options || {};
 
+  // Duplex streams are both readable and writable, but share
+  // the same options object.
+  // However, some cases require setting options to different
+  // values for the readable and the writable sides of the duplex stream.
+  // These options can be provided separately as readableXXX and writableXXX.
+  var isDuplex = stream instanceof Stream.Duplex;
+
   // object stream flag to indicate whether or not this stream
   // contains buffers or objects.
   this.objectMode = !!options.objectMode;
 
-  if (stream instanceof Stream.Duplex)
+  if (isDuplex)
     this.objectMode = this.objectMode || !!options.writableObjectMode;
 
   // the point at which write() starts returning false
   // Note: 0 is a valid value, means that we always return false if
   // the entire buffer is not flushed immediately on write()
   var hwm = options.highWaterMark;
+  var writableHwm = options.writableHighWaterMark;
   var defaultHwm = this.objectMode ? 16 : 16 * 1024;
-  this.highWaterMark = (hwm || hwm === 0) ? hwm : defaultHwm;
+
+  if (hwm || hwm === 0)
+    this.highWaterMark = hwm;
+  else if (isDuplex && (writableHwm || writableHwm === 0))
+    this.highWaterMark = writableHwm;
+  else
+    this.highWaterMark = defaultHwm;
 
   // cast to ints.
   this.highWaterMark = Math.floor(this.highWaterMark);