I think you're suffering AJAX session race condition. I had the same problem, and I solved it overriding the CI session class. You have the article here:
http://www.hiretheworld.com/blog/tech-blog/codeigniter-session-race-conditions
The cleanest thing would be use a MY_Session class, in your libraries folder, and then override the methods written in the link above. Sorry for the lack of indentation, :P
class MY_Session extends CI_Session
{
public function __construct()
{
parent::__construct();
}
/*********************************************************************
* overrides to codeigniter session library
*
* Handle race condition during session_id updates.
* - Keep the old session id around in case we have to handle race
* conditions.
* - Changes are marked with the string "old_session_id_changes".
*
* session table changes:
* ALTER TABLE `sessions` ADD COLUMN `old_session_id` VARCHAR(40) DEFAULT NULL COMMENT 'old session id' AFTER `user_data`,
* ADD INDEX `old_session_id`(`old_session_id`);
* DELETE FROM `sessions`;
*********************************************************************/
/**
* Fetch the current session data if it exists
*
* @return bool
*/
public function sess_read()
{
// Fetch the cookie
$session = $this->CI->input->cookie($this->sess_cookie_name);
// No cookie? Goodbye cruel world!...
if ($session === NULL)
{
log_message('debug', 'A session cookie was not found.');
return FALSE;
}
// Decrypt the cookie data
if ($this->sess_encrypt_cookie === TRUE)
{
$session = $this->CI->encrypt->decode($session);
}
else
{
// encryption was not used, so we need to check the md5 hash
$hash = substr($session, strlen($session)-32); // get last 32 chars
$session = substr($session, 0, strlen($session)-32);
// Does the md5 hash match? This is to prevent manipulation of session data in userspace
if ($hash !== md5($session.$this->encryption_key))
{
log_message('error', 'The session cookie data did not match what was expected. This could be a possible hacking attempt.');
$this->sess_destroy();
return FALSE;
}
}
// Unserialize the session array
$session = $this->_unserialize($session);
// Is the session data we unserialized an array with the correct format?
if ( ! is_array($session) OR ! isset($session['session_id'], $session['ip_address'], $session['user_agent'], $session['last_activity']))
{
$this->sess_destroy();
return FALSE;
}
// Is the session current?
if (($session['last_activity'] + $this->sess_expiration) < $this->now)
{
$this->sess_destroy();
return FALSE;
}
// Does the IP match?
if ($this->sess_match_ip === TRUE && $session['ip_address'] !== $this->CI->input->ip_address())
{
$this->sess_destroy();
return FALSE;
}
// Does the User Agent Match?
if ($this->sess_match_useragent === TRUE && trim($session['user_agent']) !== trim(substr($this->CI->input->user_agent(), 0, 120)))
{
$this->sess_destroy();
return FALSE;
}
// Is there a corresponding session in the DB?
if ($this->sess_use_database === TRUE)
{
/*
* begin old_session_id_changes
*
* Search both session_id and old_session_id fields for the
* incoming session id.
*
* used to be:
* $this->CI->db->where('session_id', $session['session_id']);
*
* Manually create the OR condition because it causes the least
* disturbance to existing code.
*
* Store the session id from the cookie so that we can see if we
* came in through the old session id later.
*/
$this->CI->db->where( '(session_id = ' . $this->CI->db->escape($session['session_id']) . ' OR old_session_id = ' . $this->CI->db->escape($session['session_id']) . ')' );
$this->cookie_session_id = $session['session_id'];
/*
* end old_session_id_changes
*/
if ($this->sess_match_ip === TRUE)
{
$this->CI->db->where('ip_address', $session['ip_address']);
}
if ($this->sess_match_useragent === TRUE)
{
$this->CI->db->where('user_agent', $session['user_agent']);
}
$query = $this->CI->db->limit(1)->get($this->sess_table_name);
// No result? Kill it!
if ($query->num_rows() === 0)
{
$this->sess_destroy();
return FALSE;
}
// Is there custom data? If so, add it to the main session array
$row = $query->row();
if ( ! empty($row->user_data))
{
$custom_data = $this->_unserialize($row->user_data);
if (is_array($custom_data))
{
foreach ($custom_data as $key => $val)
{
$session[$key] = $val;
}
}
}
/*
* begin old_session_id_changes
*
* Pull the session_id from the database to populate the curent
* session id because the old one is stale.
*
* Pull the old_session_id from the database so that we can
* compare the current (cookie) session id against it later.
*/
$session['session_id'] = $row->session_id;
$session['old_session_id'] = $row->old_session_id;
/*
* end old_session_id_changes
*/
}
// Session is valid!
$this->userdata = $session;
unset($session);
return TRUE;
}
// --------------------------------------------------------------------
/**
* Write the session data
*
* @return void
*/
public function sess_write()
{
// Are we saving custom data to the DB? If not, all we do is update the cookie
if ($this->sess_use_database === FALSE)
{
$this->_set_cookie();
return;
}
// set the custom userdata, the session data we will set in a second
$custom_userdata = $this->userdata;
$cookie_userdata = array();
// Before continuing, we need to determine if there is any custom data to deal with.
// Let's determine this by removing the default indexes to see if there's anything left in the array
// and set the session data while we're at it
foreach (array('session_id','ip_address','user_agent','last_activity') as $val)
{
unset($custom_userdata[$val]);
$cookie_userdata[$val] = $this->userdata[$val];
}
/*
* begin old_session_id_changes
*
* old_session_id has its own field, but it doesn't need to go into
* a cookie because we'll always retrieve it from the database.
*/
unset($custom_userdata['old_session_id']);
/*
* end old_session_id_changes
*/
// Did we find any custom data? If not, we turn the empty array into a string
// since there's no reason to serialize and store an empty array in the DB
if (count($custom_userdata) === 0)
{
$custom_userdata = '';
}
else
{
// Serialize the custom data array so we can store it
$custom_userdata = $this->_serialize($custom_userdata);
}
// Run the update query
$this->CI->db->where('session_id', $this->userdata['session_id']);
$this->CI->db->update($this->sess_table_name, array('last_activity' => $this->userdata['last_activity'], 'user_data' => $custom_userdata));
// Write the cookie. Notice that we manually pass the cookie data array to the
// _set_cookie() function. Normally that function will store $this->userdata, but
// in this case that array contains custom data, which we do not want in the cookie.
$this->_set_cookie($cookie_userdata);
}
// --------------------------------------------------------------------
/**
* Update an existing session
*
* @return void
*/
public function sess_update()
{
// We only update the session every five minutes by default
if (($this->userdata['last_activity'] + $this->sess_time_to_update) >= $this->now)
{
return;
}
// _set_cookie() will handle this for us if we aren't using database sessions
// by pushing all userdata to the cookie.
$cookie_data = NULL;
/*
* begin old_session_id_changes
*
* Don't need to regenerate the session if we came in by indexing to
* the old_session_id), but send out the cookie anyway to make sure
* that the client has a copy of the new cookie.
*
* Do an isset check first in case we're not using the database to
* store extra data. The old_session_id field only exists in the
* database.
*/
if ((isset($this->userdata['old_session_id'])) &&
($this->cookie_session_id === $this->userdata['old_session_id']))
{
// set cookie explicitly to only have our session data
$cookie_data = array();
foreach (array('session_id','ip_address','user_agent','last_activity') as $val)
{
$cookie_data[$val] = $this->userdata[$val];
}
$this->_set_cookie($cookie_data);
return;
}
/*
* end old_session_id_changes
*/
// Save the old session id so we know which record to
// update in the database if we need it
$old_sessid = $this->userdata['session_id'];
$new_sessid = '';
do
{
$new_sessid .= mt_rand(0, mt_getrandmax());
}
while (strlen($new_sessid) < 32);
// To make the session ID even more secure we'll combine it with the user's IP
$new_sessid .= $this->CI->input->ip_address();
// Turn it into a hash and update the session data array
$this->userdata['session_id'] = $new_sessid = md5(uniqid($new_sessid, TRUE));
$this->userdata['last_activity'] = $this->now;
// Update the session ID and last_activity field in the DB if needed
if ($this->sess_use_database === TRUE)
{
// set cookie explicitly to only have our session data
$cookie_data = array();
foreach (array('session_id','ip_address','user_agent','last_activity') as $val)
{
$cookie_data[$val] = $this->userdata[$val];
}
/*
* begin old_session_id_changes
*
* Save the old session id into the old_session_id field so that
* we can reference it later.
*
* Rewrite the cookie's session id if there are zero affected rows
* because that means that another request changed the database
* under the current request. In this case, we want to return a
* value consistent with the previous request. Reread immediately
* after the update call here to minimize timing problems. This
* should be in a transaction for databases that support them.
*
* Also rewrite the userdata so that future calls to sess_write
* will output the correct cookie data.
*
* used to be:
* $this->CI->db->query($this->CI->db->update_string($this->sess_table_name, array('last_activity' => $this->now, 'session_id' => $new_sessid), array('session_id' => $old_sessid)));
*/
$this->CI->db->query($this->CI->db->update_string($this->sess_table_name, array('last_activity' => $this->now, 'session_id' => $new_sessid, 'old_session_id' => $old_sessid), array('session_id' => $old_sessid)));
if ($this->CI->db->affected_rows() === 0)
{
$this->CI->db->where('old_session_id', $this->cookie_session_id);
$query = $this->CI->db->get($this->sess_table_name);
// We've lost track of the session if there are no results, so
// don't set a cookie and just return.
if ($query->num_rows() == 0)
{
return;
}
$row = $query->row();
foreach (array('session_id','ip_address','user_agent','last_activity') as $val)
{
$this->userdata[$val] = $row->$val;
$cookie_data[$val] = $this->userdata[$val];
}
// Set the request session id to the old session id so that we
// won't try to regenerate the cookie again on this request --
// just in case sess_update is ever called again (which it
// shouldn't be).
$this->cookie_session_id = $this->userdata['old_session_id'];
}
/*
* end old_session_id_changes
*/
}
// Write the cookie
$this->_set_cookie($cookie_data);
}
/*********************************************************************
* end overrides to codeigniter session library
*********************************************************************/
