io.c: shrink read buffer

* io.c (io_setstrbuf): return true if the buffer is newly created.

* io.c (io_set_read_length): shrink the read buffer if it is a new
  object and is too large.  [ruby-core:81370] [Bug #13597]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59701 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 8 insertions, 0 deletions

diff --git a/test/-ext-/string/test_capacity.rb b/test/-ext-/string/test_capacity.rb
index 48d2deadee..6ef5a8c4da 100644
--- a/test/-ext-/string/test_capacity.rb
+++ b/test/-ext-/string/test_capacity.rb
@@ -29,4 +29,12 @@ class Test_StringCapacity < Test::Unit::TestCase
     assert_equal("", String.new(capacity: -1000))
     assert_equal(capa(String.new(capacity: -10000)), capa(String.new(capacity: -1000)))
   end
+
+  def test_io_read
+    s = String.new(capacity: 1000)
+    open(__FILE__) {|f|f.read(1024*1024, s)}
+    assert_equal(1024*1024, capa(s))
+    open(__FILE__) {|f|s = f.read(1024*1024)}
+    assert_operator(capa(s), :<=, s.bytesize+4096)
+  end
 end