fs.WriteStream: Handle modifications to fs.open

If the fs.open method is modified via AOP-style extension, in between
the creation of an fs.WriteStream and the processing of its action
queue, then the test of whether or not the method === fs.open will fail,
because fs.open has been replaced.

The solution is to save a reference to fs.open on the stream itself when
the action is placed in the queue.

This fixes isaacs/node-graceful-fs#6.

lib/fs.js

@@ -1253,7 +1253,8 @@ var WriteStream = fs.WriteStream = function(path, options) {
   this._queue = [];
 
   if (this.fd === null) {
-    this._queue.push([fs.open, this.path, this.flags, this.mode, undefined]);
+    this._open = fs.open;
+    this._queue.push([this._open, this.path, this.flags, this.mode, undefined]);
     this.flush();
   }
 };
@@ -1295,7 +1296,7 @@ WriteStream.prototype.flush = function() {
         cb(null, arguments[1]);
       }
 
-    } else if (method === fs.open) {
+    } else if (method === self._open) {
       // save reference for file pointer
       self.fd = arguments[1];
       self.emit('open', self.fd);
@@ -1313,7 +1314,7 @@ WriteStream.prototype.flush = function() {
   });
 
   // Inject the file pointer
-  if (method !== fs.open) {
+  if (method !== self._open) {
     args.unshift(this.fd);
   }
 

test/simple/test-fs-write-stream-change-open.js

@@ -0,0 +1,52 @@
+// 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');
+var assert = require('assert');
+
+var path = require('path'),
+    fs = require('fs');
+
+var file = path.join(common.tmpDir, 'write.txt');
+
+var stream = fs.WriteStream(file),
+    _fs_close = fs.close,
+    _fs_open = fs.open;
+
+// change the fs.open with an identical function after the WriteStream
+// has pushed it onto its internal action queue, but before it's
+// returned.  This simulates AOP-style extension of the fs lib.
+fs.open = function() {
+  return _fs_open.apply(fs, arguments);
+};
+
+fs.close = function(fd) {
+  assert.ok(fd, 'fs.close must not be called with an undefined fd.');
+  fs.close = _fs_close;
+  fs.open = _fs_open;
+}
+
+stream.write('foo');
+stream.end();
+
+process.on('exit', function() {
+  assert.equal(fs.open, _fs_open);
+});