Add #rewind method to File operation

This is another method an IO-like object should provide. It resets the
beginning state of the file.

Author: jstuckey

lib/net/sftp/operations/file.rb

@@ -127,6 +127,14 @@ def readline(sep_or_limit=$/, limit=Float::INFINITY)
       return line
     end
 
+    # Resets position to beginning of file
+    def rewind
+      @pos      = 0
+      @real_pos = 0
+      @real_eof = false
+      @buffer   = ""
+    end
+
     # Writes the given data to the stream, incrementing the file position and
     # returning the number of bytes written.
     def write(data)

test/test_file.rb

@@ -133,6 +133,15 @@ def test_readline_should_raise_exception_on_EOF
     assert_raises(EOFError) { @file.readline }
   end
 
+  def test_rewind_should_reset_to_beginning_of_file
+    @sftp.expects(:read!).times(2).returns("hello world", nil)
+    @file.read
+    assert @file.eof?
+    @file.rewind
+    assert !@file.eof?
+    assert_equal 0, @file.pos
+  end
+
   def test_write_should_write_data_and_increment_pos_and_return_data_length
     @sftp.expects(:write!).with("handle", 0, "hello world")
     assert_equal 11, @file.write("hello world")