Allowing File#read to chunk IO

lib/fakefs/file.rb

@@ -125,7 +125,7 @@ module FakeFS
     def self.readlines(path)
       read(path).split("\n")
     end
-    
+
     def self.link(source, dest)
       if directory?(source)
         raise Errno::EPERM, "Operation not permitted - #{source} or #{dest}"
@@ -134,11 +134,11 @@ module FakeFS
       if !exists?(source)
         raise Errno::ENOENT, "No such file or directory - #{source} or #{dest}"
       end
-      
+
       if exists?(dest)
         raise Errno::EEXIST, "File exists - #{source} or #{dest}"
       end
-      
+
       source = FileSystem.find(source)
       dest = FileSystem.add(dest, source.entry.clone)
       source.link(dest)
@@ -201,6 +201,7 @@ module FakeFS
       @mode = mode
       @file = FileSystem.find(path)
       @open = true
+      @stream = StringIO.new(@file.content) if @file
 
       check_valid_mode
       file_creation_mode? ? create_missing_file : check_file_existence!
@@ -211,11 +212,14 @@ module FakeFS
       @open = false
     end
 
-    def read
+    def read(chunk = nil)
       raise IOError, 'closed stream' unless @open
       raise IOError, 'not opened for reading' if write_only?
+      @stream.read(chunk)
+    end
 
-      @file.content
+    def rewind
+      @stream.rewind
     end
 
     def exists?

test/fakefs_test.rb

@@ -200,6 +200,19 @@ class FakeFSTest < Test::Unit::TestCase
     assert_equal 'Yada Yada', File.read(path)
   end
 
+  def test_can_chunk_io_when_reading
+    path = '/path/to/file.txt'
+    File.open(path, 'w') do |f|
+      f << 'Yada Yada'
+    end
+    file = File.new(path, 'r')
+    assert_equal 'Yada', file.read(4)
+    assert_equal ' Yada', file.read(5)
+    assert_equal '', file.read
+    file.rewind
+    assert_equal 'Yada Yada', file.read
+  end
+
   def test_can_get_size_of_files
     path = '/path/to/file.txt'
     File.open(path, 'w') do |f|