Add method readAsStream on fs model

lib/models/fs.js

@@ -1,5 +1,6 @@
 var path = require('path');
 var Immutable = require('immutable');
+var stream = require('stream');
 
 var File = require('./file');
 var Promise = require('../utils/promise');
@@ -13,7 +14,9 @@ var FS = Immutable.Record({
     fsReadFile:       Function(),
     fsStatFile:       Function(),
     fsReadDir:        Function(),
-    fsLoadObject:     null
+
+    fsLoadObject:     null,
+    fsReadAsStream:   null
 });
 
 /**
@@ -111,6 +114,30 @@ FS.prototype.readAsString = function(filename, encoding) {
     });
 };
 
+/**
+    Read file as a stream
+
+    @param {String} filename
+    @return {Promise<Stream>}
+*/
+FS.prototype.readAsStream = function(filename) {
+    var that = this;
+    var filepath = that.resolve(filename);
+    var fsReadAsStream = this.get('fsReadAsStream');
+
+    if (fsReadAsStream) {
+        return Promise(fsReadAsStream(filepath));
+    }
+
+    return this.read(filename)
+    .then(function(buf) {
+        var bufferStream = new stream.PassThrough();
+        bufferStream.end(buf);
+
+        return bufferStream;
+    });
+};
+
 /**
     Read stat infos about a file