io.c: buffer must be modifiable

* io.c (io_setstrbuf): always check if the buffer is modifiable.
  [ruby-core:62643] [Bug #9847]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45979 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 11 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index 91d14526a1..1845e5abc2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun May 18 08:22:25 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (io_setstrbuf): always check if the buffer is modifiable.
+	  [ruby-core:62643] [Bug #9847]
+
 Sun May 18 01:21:23 2014  Tanaka Akira  <akr@fsij.org>
 
 	* include/ruby/ruby.h: Hide Rational internal.
diff --git a/io.c b/io.c
index 533989cb62..5499086448 100644
--- a/io.c
+++ b/io.c
@@ -2370,8 +2370,8 @@ io_setstrbuf(VALUE *str, long len)
 	VALUE s = StringValue(*str);
 	long clen = RSTRING_LEN(s);
 	if (clen >= len) {
+	    rb_str_modify(s);
 	    if (clen != len) {
-		rb_str_modify(s);
 		rb_str_set_len(s, len);
 	    }
 	    return;
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index 5ed2ddd13b..9d89772d99 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -2839,25 +2839,24 @@ End
 
   def assert_buffer_not_raise_shared_string_error
     bug6764 = '[ruby-core:46586]'
+    bug9847 = '[ruby-core:62643] [Bug #9847]'
     size = 28
     data = [*"a".."z", *"A".."Z"].shuffle.join("")
     t = Tempfile.new("test_io")
     t.write(data)
     t.close
-    w = Tempfile.new("test_io")
+    w = []
     assert_nothing_raised(RuntimeError, bug6764) do
+      buf = ''
       File.open(t.path, "r") do |r|
-        buf = ''
         while yield(r, size, buf)
-          w << buf
+          w << buf.dup
         end
       end
     end
-    w.close
-    assert_equal(data, w.open.read, bug6764)
+    assert_equal(data, w.join(""), bug9847)
   ensure
     t.close!
-    w.close!
   end
 
   def test_read_buffer_not_raise_shared_string_error