stream: change default hwm for objectMode to 16

doc/api/stream.markdown

@@ -871,7 +871,7 @@ SimpleProtocol.prototype._read = function(n) {
 * `options` {Object}
   * `highWaterMark` {Number} The maximum number of bytes to store in
     the internal buffer before ceasing to read from the underlying
-    resource.  Default=16kb
+    resource.  Default=16kb, or 16 for `objectMode` streams
   * `encoding` {String} If specified, then buffers will be decoded to
     strings using the specified encoding.  Default=null
   * `objectMode` {Boolean} Whether this stream should behave
@@ -987,7 +987,7 @@ how to implement Writable streams in your programs.
 
 * `options` {Object}
   * `highWaterMark` {Number} Buffer level when [`write()`][] starts
-    returning false. Default=16kb
+    returning false. Default=16kb, or 16 for `objectMode` streams
   * `decodeStrings` {Boolean} Whether or not to decode strings into
     Buffers before passing them to [`_write()`][].  Default=true
 

lib/_stream_readable.js

@@ -36,7 +36,8 @@ function ReadableState(options, stream) {
   // the point at which it stops calling _read() to fill the buffer
   // Note: 0 is a valid value, means "don't call _read preemptively ever"
   var hwm = options.highWaterMark;
-  this.highWaterMark = (hwm || hwm === 0) ? hwm : 16 * 1024;
+  var defaultHwm = options.objectMode ? 16 : 16 * 1024;
+  this.highWaterMark = (hwm || hwm === 0) ? hwm : defaultHwm;
 
   // cast to ints.
   this.highWaterMark = ~~this.highWaterMark;

lib/_stream_writable.js

@@ -44,7 +44,8 @@ function WritableState(options, stream) {
   // 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;
-  this.highWaterMark = (hwm || hwm === 0) ? hwm : 16 * 1024;
+  var defaultHwm = options.objectMode ? 16 : 16 * 1024;
+  this.highWaterMark = (hwm || hwm === 0) ? hwm : defaultHwm;
 
   // object stream flag to indicate whether or not this stream
   // contains buffers or objects.