Duplicated "set-cookie: ci-session" fields in header by codeigniter

check https://github.com/EllisLab/CodeIgniter/pull/1780

By default when using the cookie session handler (encrypted or unencrypted), CI sends the entire "Set-Cookie" header each time a new value is written to the session. This results in multiple headers being sent to the client.

This is a problem because if too many values are written to the session, the HTTP headers can grow quite large, and some web servers will reject the response. (see http://wiki.nginx.org/HttpProxyModule#proxy_buffer_size)

The solution is to only run 'sess_save()' one time right after all other headers are sent before outputting the page contents.

I believe you can pass an array to $this->session->set_userdata(); I haven't tested this code so it is merely a suggestion to try something along these lines:

$data = array(    'whatever' => 'somevalue',    'youget' => 'theidea');$this->session->set_userdata($data);

NB: When I say I haven't tested the code.. I have used this code and I know it works, I mean I havent tested if it will reduce the amount of headers sent.

In my case, the error is in the browser (Chrome). It stored 2 cookie and send both to server, this make server create new session all the time.I fixed it by clear the cookies in browser.Hope it help someone. :)