build res.download() on top of res.sendfile()

like it should have always been

lib/response.js

@@ -200,6 +200,30 @@ res.sendfile = function(path, options, fn){
   send(this.req, this, next, options);
 };
 
+/**
+ * Transfer the file at the given `path` as an attachment.
+ *
+ * Optionally providing an alternate attachment `filename`,
+ * and optional callback `fn(err)`. The callback is invoked
+ * when the data transfer is complete, or when an error has
+ * ocurred. Be sure to check `res.sendHeader` if you plan to respond.
+ *
+ * @param {String} path
+ * @param {String|Function} filename or fn
+ * @param {Function} fn
+ * @api public
+ */
+
+res.download = function(path, filename, fn){
+  // support function as second arg
+  if ('function' == typeof filename) {
+    fn = filename;
+    filename = null;
+  }
+
+  return this.attachment(filename || path).sendfile(path, fn);
+};
+
 /**
  * Set _Content-Type_ response header passed through `mime.lookup()`.
  *
@@ -239,47 +263,6 @@ res.attachment = function(filename){
   return this;
 };
 
-/**
- * Transfer the file at the given `path`, with optional 
- * `filename` as an attachment and optional callback `fn(err)`,
- * and optional `fn2(err)` which is invoked when an error has
- * occurred after header has been sent.
- *
- * @param {String} path
- * @param {String|Function} filename or fn
- * @param {Function} fn
- * @param {Function} fn2
- * @api public
- */
-
-res.download = function(path, filename, fn, fn2){
-  var self = this;
-
-  // support callback as second arg
-  if ('function' == typeof filename) {
-    fn2 = fn;
-    fn = filename;
-    filename = null;
-  }
-
-  // transfer the file
-  this.attachment(filename || path).sendfile(path, function(err){
-    var sentHeader = self._header;
-    if (err) {
-      if (!sentHeader) self.removeHeader('Content-Disposition');
-      if (sentHeader) {
-        fn2 && fn2(err);
-      } else if (fn) {
-        fn(err);
-      } else {
-        self.req.next(err);
-      }
-    } else if (fn) {
-      fn();
-    }
-  });
-};
-
 /**
  * Set header `field` to `val`.
  *