handle RubyString#setByteListShared with backwards compatibility

Author: kares

src/main/java/org/jruby/ext/openssl/Cipher.java

@@ -1267,8 +1267,7 @@ public IRubyObject set_auth_tag(final ThreadContext context, final IRubyObject t
             throw newCipherError(context.runtime, "authentication tag not supported by this cipher");
         }
         final RubyString auth_tag = tag.asString();
-        this.auth_tag = auth_tag.getByteList();
-        auth_tag.setByteListShared();
+        this.auth_tag = StringHelper.setByteListShared(auth_tag);
         return auth_tag;
     }
 
@@ -1290,8 +1289,7 @@ public IRubyObject set_auth_data(final ThreadContext context, final IRubyObject
             throw newCipherError(context.runtime, "authentication data not supported by this cipher");
         }
         final RubyString auth_data = data.asString();
-        this.auth_data = auth_data.getByteList();
-        auth_data.setByteListShared();
+        this.auth_data = StringHelper.setByteListShared(auth_data);
         return auth_data;
     }
 

src/main/java/org/jruby/ext/openssl/StringHelper.java

@@ -61,6 +61,17 @@ static RubyString newString(final Ruby runtime, final byte[] bytes, final int co
         return RubyString.newString(runtime, byteList);
     }
 
+    static ByteList setByteListShared(final RubyString str) {
+        try {
+            str.setByteListShared();
+            return str.getByteList();
+        }
+        catch (NoSuchMethodError err) { // JRuby 1.6
+            RubyString dup = (RubyString) str.dup();
+            return dup.getByteList();
+        }
+    }
+
     static RubyString newUTF8String(final Ruby runtime, final ByteList bytes) {
         ByteList byteList = new ByteList(RubyEncoding.encodeUTF8(bytes), UTF8Encoding.INSTANCE, false);
         return new RubyString(runtime, runtime.getString(), byteList);