Fix: Don't rely on undocumented Stream.fd property (#175)

lib/dest/write-contents/write-stream.js

@@ -12,17 +12,24 @@ function writeStream(file, written) {
   };
 
   var outStream = fs.createWriteStream(file.path, opt);
+  var fd = null;
 
   file.contents.once('error', complete);
   file.contents.once('end', readStreamEnd);
   outStream.once('error', complete);
   outStream.once('finish', complete);
+  outStream.once('open', onOpen);
 
   // Streams are piped with end disabled, this prevents the
   // WriteStream from closing the file descriptor after all
   // data is written.
   file.contents.pipe(outStream, { end: false });
 
+  // Obtain the file descriptor from the "open" event.
+  function onOpen(openFd) {
+    fd = openFd;
+  }
+
   function readStreamEnd() {
     readStream(file, complete);
   }
@@ -41,16 +48,17 @@ function writeStream(file, written) {
     file.contents.removeListener('end', readStreamEnd);
     outStream.removeListener('error', complete);
     outStream.removeListener('finish', complete);
+    outStream.removeListener('open', onOpen);
 
     if (streamErr) {
       return end(streamErr);
     }
 
-    if (typeof outStream.fd !== 'number') {
+    if (typeof fd !== 'number') {
       return end();
     }
 
-    fo.updateMetadata(outStream.fd, file, end);
+    fo.updateMetadata(fd, file, end);
   }
 }