io.c: not shorten buffer unless succeeded

* io.c (io_setstrbuf, io_read): should not shorten the given buffer until
  read succeeds.  [ruby-core:55951] [Bug #8625]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46360 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 17 insertions, 4 deletions

diff --git a/ChangeLog b/ChangeLog
index 569db972c0..9d1cea85dd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jun  6 13:39:32 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (io_setstrbuf, io_read): should not shorten the given buffer until
+	  read succeeds.  [ruby-core:55951] [Bug #8625]
+
 Fri Jun  6 07:41:41 2014  Aaron Patterson <aaron@tenderlovemaking.com>
 
 	* ext/psych/lib/psych/visitors/yaml_tree.rb: dump empty symbols with a
diff --git a/io.c b/io.c
index 6926316569..653034dd58 100644
--- a/io.c
+++ b/io.c
@@ -2372,9 +2372,6 @@ io_setstrbuf(VALUE *str, long len)
 	long clen = RSTRING_LEN(s);
 	if (clen >= len) {
 	    rb_str_modify(s);
-	    if (clen != len) {
-		rb_str_set_len(s, len);
-	    }
 	    return;
 	}
 	len -= clen;
@@ -2902,7 +2899,10 @@ io_read(int argc, VALUE *argv, VALUE io)
 
     GetOpenFile(io, fptr);
     rb_io_check_byte_readable(fptr);
-    if (len == 0) return str;
+    if (len == 0) {
+	io_set_read_length(str, 0);
+	return str;
+    }
 
     READ_CHECK(fptr);
 #if defined(RUBY_TEST_CRLF_ENVIRONMENT) || defined(_WIN32)
diff --git a/test/ruby/test_io.rb b/test/ruby/test_io.rb
index dca78603c7..fab142a5ee 100644
--- a/test/ruby/test_io.rb
+++ b/test/ruby/test_io.rb
@@ -1230,6 +1230,14 @@ class TestIO < Test::Unit::TestCase
       t.value
       assert_equal("", s)
     end
+    with_pipe do |r, w|
+      s = "xxx"
+      t = Thread.new {r.read(2, s)}
+      Thread.pass until t.stop?
+      t.kill
+      t.value
+      assert_equal("xxx", s)
+    end
   end
 
   def test_write_nonblock