facebook auth code becomes invalidate after hours?

I've a simple application in facebook. To change user's facebook status, I need to get code via

https://www.facebook.com/dialog/oauth?
 client_id=YOUR_APP_ID&redirect_uri=YOUR_URL

The开发者_开发知识库n I use that code to generate a auth token. With the token I can update user's stauts. It works for one or two days. After that, when trying to generate auth token with code, I got an error like:

{
  "error":{
     "type":"OAuthException",
     "message":"Code was invalid or expired."
  }
} 

So how long can a code be validate?

There is a way to get an infinite token from facebook. Use the offline_access parameter in requesting permissions, and you will never lose the token.

You just need to grant the publish_stream the first time and get the user id, after that no need to go through this process again and you can just use:

curl -F 'message=Hello World.' \
     https://graph.facebook.com/USERID/feed

or in PHP-SDK:

$facebook->api("/USER_ID/feed", "post", array("message"=>"Hello World!"));