stream: Fix double pipe error emit

If an error listener is added to a stream using once() before it is
piped, it is invoked and removed during pipe() but before pipe() sees it
which causes it to be emitted again.

Fixes #4155 #4978

lib/_stream_readable.js

@@ -511,9 +511,11 @@ Readable.prototype.pipe = function(dest, pipeOpts) {
 
   // if the dest has an error, then stop piping into it.
   // however, don't suppress the throwing behavior for this.
+  // check for listeners before emit removes one-time listeners.
+  var errListeners = EE.listenerCount(dest, 'error');
   function onerror(er) {
     unpipe();
-    if (EE.listenerCount(dest, 'error') === 0)
+    if (errListeners === 0 && EE.listenerCount(dest, 'error') === 0)
       dest.emit('error', er);
   }
   dest.once('error', onerror);

test/simple/test-stream2-pipe-error-once-listener.js

@@ -0,0 +1,64 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+
+var common = require('../common.js');
+var assert = require('assert');
+
+var util = require('util');
+var stream = require('stream');
+
+
+var Read = function() {
+  stream.Readable.call(this);
+};
+util.inherits(Read, stream.Readable);
+
+Read.prototype._read = function(size) {
+  this.push('x');
+  this.push(null);
+};
+
+
+var Write = function() {
+  stream.Writable.call(this);
+};
+util.inherits(Write, stream.Writable);
+
+Write.prototype._write = function(buffer, encoding, cb) {
+  this.emit('error', new Error('boom'));
+  this.emit('alldone');
+};
+
+var read = new Read();
+var write = new Write();
+
+write.once('error', function(err) {});
+write.once('alldone', function(err) {
+  console.log('ok');
+});
+
+process.on('exit', function(c) {
+  console.error('error thrown even with listener');
+});
+
+read.pipe(write);
+