Handle nil separator passed to #gets

Ruby's IO documentation says that if nil is passed as the separator
argument, the IO object should read to the end of the file or until the
limit argument is reached.

Author: jstuckey

lib/net/sftp/operations/file.rb

@@ -93,14 +93,14 @@ def gets(sep_or_limit=$/, limit=Float::INFINITY)
         lim = limit
       end
 
-      delim = if sep_string.length == 0
+      delim = if sep_string && sep_string.length == 0
         "#{$/}#{$/}"
       else
         sep_string
       end
 
       loop do
-        at = @buffer.index(delim)
+        at = @buffer.index(delim) if delim
         if at
           offset = [at + delim.length, lim].min
           @pos += offset

test/test_file.rb

@@ -91,6 +91,12 @@ def test_gets_when_no_such_delimiter_exists_in_stream_should_read_to_EOF
     assert @file.eof?
   end
 
+  def test_gets_when_nil_delimiter_should_fread_to_EOF
+    @sftp.expects(:read!).times(2).returns("hello world\ngoodbye world\n\nfarewell!\n", nil)
+    assert_equal "hello world\ngoodbye world\n\nfarewell!\n", @file.gets(nil)
+    assert @file.eof?
+  end
+
   def test_gets_with_integer_argument_should_read_number_of_bytes
     @sftp.expects(:read!).returns("hello world\ngoodbye world\n\nfarewell!\n")
     assert_equal "hello w", @file.gets(7)
@@ -111,6 +117,11 @@ def test_gets_when_no_such_delimiter_exists_in_stream_but_limit_provided_should_
     assert_equal "hello w", @file.gets("z", 7)
   end
 
+  def test_gets_when_nil_delimiter_and_limit_provided_should_read_to_limit
+    @sftp.expects(:read!).returns("hello world\ngoodbye world\n\nfarewell!\n")
+    assert_equal "hello w", @file.gets(nil, 7)
+  end
+
   def test_gets_at_EOF_should_return_nil
     @sftp.expects(:read!).returns(nil)
     assert_nil @file.gets