feat(index): add getFileReadStreamById method

lib/index.js

@@ -220,15 +220,20 @@ MongoStorage = (function() {
     }, callback);
   };
 
+  MongoStorage.prototype.getFileReadStreamById = function(id) {
+    var gfs;
+    gfs = Grid(this.db, mongodb);
+    return gfs.createReadStream({
+      _id: id
+    });
+  };
+
   MongoStorage.prototype.__download = function(file, res, callback) {
-    var gfs, read;
+    var read;
     if (callback == null) {
       callback = (function() {});
     }
-    gfs = Grid(this.db, mongodb);
-    read = gfs.createReadStream({
-      _id: file._id
-    });
+    read = this.getFileReadStreamById(file._id);
     res.set('Content-Disposition', "attachment; filename=\"" + file.filename + "\"");
     res.set('Content-Type', file.metadata.mimetype);
     res.set('Content-Length', file.length);

source/index.coffee

@@ -155,10 +155,13 @@ class MongoStorage
   getFileById: (id, callback) ->
     @__getFile _id: id, callback
 
-  __download: (file, res, callback = (-> return)) ->
+  getFileReadStreamById: (id) ->
     gfs = Grid @db, mongodb
-    read = gfs.createReadStream
-      _id: file._id
+    gfs.createReadStream
+      _id: id
+
+  __download: (file, res, callback = (-> return)) ->
+    read = @getFileReadStreamById file._id
     res.set 'Content-Disposition', "attachment; filename=\"#{file.filename}\""
     res.set 'Content-Type', file.metadata.mimetype
     res.set 'Content-Length', file.length