zlib: do not emit event on *Sync() methods

Asynchronous functions in `zlib` should not emit the close event.

This fixes an issue where asynchronous calls in a for loop could exhaust
memory because the pending event prevents the objects from being garbage
collected.

Fixes: https://github.com/nodejs/node/issues/1668
PR-URL: https://github.com/nodejs/node/pull/5707
Reviewed-By: jasnell - James M Snell <jasnell@gmail.com>
Reviewed-By: trevnorris - Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

lib/zlib.js

@@ -454,18 +454,21 @@ Zlib.prototype.flush = function(kind, callback) {
 };
 
 Zlib.prototype.close = function(callback) {
+  _close(this, callback);
+  process.nextTick(emitCloseNT, this);
+};
+
+function _close(engine, callback) {
   if (callback)
     process.nextTick(callback);
 
-  if (this._closed)
+  if (engine._closed)
     return;
 
-  this._closed = true;
+  engine._closed = true;
 
-  this._handle.close();
+  engine._handle.close();
-
+}
-  process.nextTick(emitCloseNT, this);
-};
 
 function emitCloseNT(self) {
   self.emit('close');
@@ -535,12 +538,12 @@ Zlib.prototype._processChunk = function(chunk, flushFlag, cb) {
     }
 
     if (nread >= kMaxLength) {
-      this.close();
+      _close(this);
       throw new RangeError(kRangeErrorMessage);
     }
 
     var buf = Buffer.concat(buffers, nread);
-    this.close();
+    _close(this);
 
     return buf;
   }

test/parallel/test-zlib-sync-no-event.js

@@ -0,0 +1,21 @@
+'use strict';
+require('../common');
+const zlib = require('zlib');
+const assert = require('assert');
+
+const shouldNotBeCalled = () => { throw new Error('unexpected event'); };
+
+const message = 'Come on, Fhqwhgads.';
+
+const zipper = new zlib.Gzip();
+zipper.on('close', shouldNotBeCalled);
+
+const buffer = new Buffer(message);
+const zipped = zipper._processChunk(buffer, zlib.Z_FINISH);
+
+const unzipper = new zlib.Gunzip();
+unzipper.on('close', shouldNotBeCalled);
+
+const unzipped = unzipper._processChunk(zipped, zlib.Z_FINISH);
+assert.notEqual(zipped.toString(), message);
+assert.strictEqual(unzipped.toString(), message);