merge revision(s) 56416: [Backport #12836]

	* io.c (copy_stream_body): use IO to write to copy to duplex IO.
	  http://twitter.com/knu/status/786505317974585344


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@56569 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 1 deletions

diff --git a/io.c b/io.c
index 6f9896462e..3707a69344 100644
--- a/io.c
+++ b/io.c
@@ -10619,7 +10619,7 @@ copy_stream_body(VALUE arg)
     else {
 	VALUE tmp_io = rb_io_check_io(dst_io);
 	if (!NIL_P(tmp_io)) {
-	    dst_io = tmp_io;
+	    dst_io = GetWriteIO(tmp_io);
 	}
 	else if (!RB_TYPE_P(dst_io, T_FILE)) {
 	    VALUE args[3];