zlib: make constants keep readonly

In zlib module, a dozen constants were exported to user land,
If user change the constant, maybe lead unexcepted error.

Make them readonly and freezon.

PR-URL: https://github.com/iojs/io.js/pull/1361
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Shigeki Ohtsu <ohtsu@iij.ad.jp>

1 files changed, 16 insertions, 0 deletions

diff --git a/test/parallel/test-zlib-const.js b/test/parallel/test-zlib-const.js
new file mode 100644
index 0000000000..df9ca3d500
--- /dev/null
+++ b/test/parallel/test-zlib-const.js
@@ -0,0 +1,16 @@
+var common = require('../common');
+var assert = require('assert');
+
+var zlib = require('zlib');
+
+assert.equal(zlib.Z_OK, 0, 'Z_OK should be 0');
+zlib.Z_OK = 1;
+assert.equal(zlib.Z_OK, 0, 'Z_OK should be 0');
+
+assert.equal(zlib.codes.Z_OK, 0, 'Z_OK should be 0');
+zlib.codes.Z_OK = 1;
+assert.equal(zlib.codes.Z_OK, 0, 'zlib.codes.Z_OK should be 0');
+zlib.codes = {Z_OK: 1};
+assert.equal(zlib.codes.Z_OK, 0, 'zlib.codes.Z_OK should be 0');
+
+assert.ok(Object.isFrozen(zlib.codes), 'zlib.codes should be frozen');