merge revision(s) 61639: [Backport #14323]

	net/ftp: fix FrozenError in BufferedSocket

	I noticed this bug while working on something else with
	RUBYOPT=-d on, existing test cases all passed with it.

	Note: I use String.new because it is the local style, here,
	I prefer +'' (or ''.b, for a future commit)

	* lib/net/ftp.rb (BufferedSocket#read): use String.new
	* test/net/ftp/test_buffered_socket.rb (test_read_nil): new test
	  [ruby-core:84675] [Bug #14323]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_4@62867 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 8 insertions, 2 deletions

diff --git a/lib/net/ftp.rb b/lib/net/ftp.rb
index bd74323987..31f93b8b34 100644
--- a/lib/net/ftp.rb
+++ b/lib/net/ftp.rb
@@ -1434,7 +1434,7 @@ module Net
           s = super(len, String.new, true)
           return s.empty? ? nil : s
         else
-          result = ""
+          result = String.new
           while s = super(DEFAULT_BLOCKSIZE, String.new, true)
             break if s.empty?
             result << s
diff --git a/test/net/ftp/test_buffered_socket.rb b/test/net/ftp/test_buffered_socket.rb
index 3cc46fa555..875c53f4e0 100644
--- a/test/net/ftp/test_buffered_socket.rb
+++ b/test/net/ftp/test_buffered_socket.rb
@@ -33,6 +33,12 @@ class BufferedSocketTest < Test::Unit::TestCase
     assert_equal("bar", sock.gets)
   end
 
+  def test_read_nil
+    sock = create_buffered_socket("foo\nbar")
+    assert_equal("foo\nbar", sock.read)
+    assert_equal("", sock.read)
+  end
+
   private
 
   def create_buffered_socket(s)
diff --git a/version.h b/version.h
index f2122d1ee4..9888d024e8 100644
--- a/version.h
+++ b/version.h
@@ -1,6 +1,6 @@
 #define RUBY_VERSION "2.4.4"
 #define RUBY_RELEASE_DATE "2018-03-21"
-#define RUBY_PATCHLEVEL 275
+#define RUBY_PATCHLEVEL 276
 
 #define RUBY_RELEASE_YEAR 2018
 #define RUBY_RELEASE_MONTH 3