net: move isLegalPort to internal/net

isLegalPort can be used in more places than just net.js. This change
moves it to a new internal net module in preparation for using it in
the dns module.

PR-URL: https://github.com/nodejs/node/pull/4882
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/lib/internal/net.js b/lib/internal/net.js
new file mode 100644
index 0000000000..effc6485d2
--- /dev/null
+++ b/lib/internal/net.js
@@ -0,0 +1,11 @@
+'use strict';
+
+module.exports = { isLegalPort };
+
+// Check that the port number is not NaN when coerced to a number,
+// is an integer and that it falls within the legal range of port numbers.
+function isLegalPort(port) {
+  if (typeof port === 'string' && port.trim() === '')
+    return false;
+  return +port === (port >>> 0) && port >= 0 && port <= 0xFFFF;
+}