zlib (gzfile_write_raw): do not resize string after .write call

Apparently, a component of Rails implements a buffering .write
method which keeps the String buffer around and makes it unsafe
for us to clear it after calling .write.

This caused Rack::Deflater to give empty results when enabled.

Fortunately, per r61631 / a55abcc0ca6f628fc05304f81e5a044d65ab4a68,
this misguided optimization was only worth a small (0.5MB) savings
and we still benefit from the majority of the memory savings in
that change.

Thanks to zunda for the bug report.

[ruby-core:90133] [Bug #15356]

Fixes: r61631 (commit a55abcc0ca6f628fc05304f81e5a044d65ab4a68)
       ("zlib: reduce garbage on gzip writes (deflate)")

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66268 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 17 insertions, 0 deletions

diff --git a/test/zlib/test_zlib.rb b/test/zlib/test_zlib.rb
index 6a90c6782c..fc2ab5073f 100644
--- a/test/zlib/test_zlib.rb
+++ b/test/zlib/test_zlib.rb
@@ -1081,6 +1081,23 @@ if defined? Zlib
         assert_nothing_raised { w.close }
       }
     end
+
+    def test_zlib_writer_buffered_write
+      bug15356 = '[ruby-core:90346] [Bug #15356]'.freeze
+      fixes = 'r61631 (commit a55abcc0ca6f628fc05304f81e5a044d65ab4a68)'.freeze
+      ary = []
+      def ary.write(*args)
+        self.concat(args)
+      end
+      gz = Zlib::GzipWriter.new(ary)
+      gz.write(bug15356)
+      gz.write("\n")
+      gz.write(fixes)
+      gz.close
+      assert_not_predicate ary, :empty?
+      exp = [ bug15356, fixes ]
+      assert_equal exp, Zlib.gunzip(ary.join('')).split("\n")
+    end
   end
 
   class TestZlib < Test::Unit::TestCase