From 6776e0bc99abfbdb9e4c406c447942e971af37ff Mon Sep 17 00:00:00 2001
From: normal <normal@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date: Fri, 5 Jan 2018 21:14:19 +0000
Subject: io.c: clear Strings we create for IO.copy_stream

While we can't recycle strings after giving them rb_funcall*,
we can reduce their malloc overhead by resizing them to zero.
This only affects cases where either `src' or `dst' is a non-IO
object and either `copy_length' is passed or there is
pre-existing data in the read buffer.

* io.c (copy_stream_fallback_body): clear when done with `copy_length'
  (copy_stream_body): clear when done with pre-existing read buffer

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61632 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

diff --git a/io.c b/io.c
index f14e144..1986d3e 100644
--- a/io.c
+++ b/io.c
@@ -11163,8 +11163,10 @@ copy_stream_fallback_body(VALUE arg)
             l = buflen;
         }
         else {
-            if (rest == 0)
-                break;
+	    if (rest == 0) {
+		rb_str_resize(buf, 0);
+		break;
+	    }
             l = buflen < rest ? buflen : (long)rest;
         }
         if (stp->src_fd == -1) {
@@ -11305,6 +11307,7 @@ copy_stream_body(VALUE arg)
         }
         else /* others such as StringIO */
 	    rb_io_write(dst_io, str);
+        rb_str_resize(str, 0);
         stp->total += len;
         if (stp->copy_length != (off_t)-1)
             stp->copy_length -= len;
-- 
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