openssl: avoid undefined behavior on empty SSL_write

SSL_write(3ssl) manpage has this in the WARNINGS section:

       When calling SSL_write() with num=0 bytes to be sent the
       behaviour is undefined.

And indeed, the new test case demonstrates failures when
empty strings are used.  So, match the behavior of IO#write,
IO#write_nonblock, and IO#syswrite by returning zero, as the
OpenSSL::SSL::SSLSocket API already closely mimics the IO one.

* ext/openssl/ossl_ssl.c (ossl_ssl_write_internal):
  avoid undefined behavior
* test/openssl/test_pair.rb (test_write_zero): new test
  [ruby-core:76751] [Bug #12660]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@55822 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 11 insertions, 0 deletions

diff --git a/test/openssl/test_pair.rb b/test/openssl/test_pair.rb
index 5750f3b7df..d611d0f965 100644
--- a/test/openssl/test_pair.rb
+++ b/test/openssl/test_pair.rb
@@ -311,6 +311,17 @@ module OpenSSL::TestPairM
     }
   end
 
+  def test_write_zero
+    ssl_pair {|s1, s2|
+      assert_equal 0, s2.write_nonblock('', exception: false)
+      assert_kind_of Symbol, s1.read_nonblock(1, exception: false)
+      assert_equal 0, s2.syswrite('')
+      assert_kind_of Symbol, s1.read_nonblock(1, exception: false)
+      assert_equal 0, s2.write('')
+      assert_kind_of Symbol, s1.read_nonblock(1, exception: false)
+    }
+  end
+
   def tcp_pair
     host = "127.0.0.1"
     serv = TCPServer.new(host, 0)