CodeIgniter Session类 源代码 分析

一、Session类的参数：可以在application/config/config.php 文件中找到以下的 Session
相关的参数:

参数	默认	选项	描述
sess_cookie_name	ci_session	无	你想要保存 Session Cookie 的名字。
sess_expiration	7200	无	session 持续的秒数。默认是2个小时(7200秒)。如果将这个数值设为: 0，就可以得到 永久 session。
sess_expire_on_close	FALSE	TRUE/FALSE (boolean)	这个选项决定当浏览器窗口关闭时是否自动使session过期。
sess_encrypt_cookie	FALSE	TRUE/FALSE (布尔值boolean)	是否对 session 数据加密.
sess_use_database	FALSE	TRUE/FALSE (布尔值boolean)	是否将 session 数据存放入数据库中。在开启这个选项前，你要先创建一个数据库表。
sess_table_name	ci_sessions	任何有效的 SQL 表名	session 数据库表的名字。
sess_time_to_update	300	时间以秒计算	这个选项控制 session 类多久会产生一个新的session 和 session id。
sess_match_ip	FALSE	TRUE/FALSE (布尔值boolean)	是否通过用户的IP地址来读取 session 的数据。 注意 ，有些网络运行商 ISPs 会动态的改变IP, 所以将这个选项设为 FALSE， 才有可能得到永久的 session。
sess_match_useragent	TRUE	TRUE/FALSE (布尔值boolean)	是否要按照对应的 User Agent 来读取 session 数据。

二、Session类的构造函数：构造函数做的事情有：

①初始化Session参数

②判断加密密钥是否为空，则返回错误

③加载字符串辅助函数使用strip_slashes()函数

④判断是否加密Session，如果加密Session则加载加密类

⑤判断Session是否写入数据库，则加载数据库类

⑥初始化当前时间

⑦初始化过期时间

⑧初始化$this->sess_cookie_name

⑨判断Session是否存在，如不存在创建Session，若存在更新Session

⑩垃圾回收

public function __construct($params = array())
{
log_message('debug', "Session Class Initialized");

// Set the super object to a local variable for use throughout the class
$this->CI =& get_instance();

// Set all the session preferences, which can either be set
// manually via the $params array above or via the config file
// 设置session参数，首先判断是否设置$params，如果没有则从config文件中设置
foreach (array('sess_encrypt_cookie', 'sess_use_database', 'sess_table_name', 'sess_expiration', 'sess_expire_on_close', 'sess_match_ip', 'sess_match_useragent', 'sess_cookie_name', 'cookie_path', 'cookie_domain', 'cookie_secure', 'sess_time_to_update', 'time_reference', 'cookie_prefix', 'encryption_key') as $key)
{
$this->$key = (isset($params[$key])) ? $params[$key] : $this->CI->config->item($key);
}

// 判断加密密钥是否为空，为空则返回错误
if ($this->encryption_key == '')
{
show_error('In order to use the Session class you are required to set an encryption key in your config file.');
}

// Load the string helper so we can use the strip_slashes() function
// 加载字符串辅助函数以使用strip_slashes()函数
$this->CI->load->helper('string');

// Do we need encryption? If so, load the encryption class
// 判断是否加密Session,如果加密session则加载类库encrypt
if ($this->sess_encrypt_cookie == TRUE)
{
$this->CI->load->library('encrypt');
}

// Are we using a database?  If so, load it
// 判断是否将Session存入数据库，如果存入则加载数据库类
if ($this->sess_use_database === TRUE AND $this->sess_table_name != '')
{
$this->CI->load->database();
}

// Set the "now" time.  Can either be GMT or server time, based on the
// config prefs.  We use this to set the "last activity" time
// 获取当前时间
$this->now = $this->_get_time();

// Set the session length. If the session expiration is
// set to zero we'll set the expiration two years from now.
// 如果sess_expiration设置为0，则把过期时间设置为两年后
if ($this->sess_expiration == 0)
{
$this->sess_expiration = (60*60*24*365*2);
}

// Set the cookie name
// 设置Session名称，为$this->cookie_prefix.$this->sess_cookie_name，$this->cookie_prefix在config文件中设置
$this->sess_cookie_name = $this->cookie_prefix.$this->sess_cookie_name;

// Run the Session routine. If a session doesn't exist we'll
// create a new one.  If it does, we'll update it.
// 如果Session不存在，则创建Session，否则更新它
if ( ! $this->sess_read())
{
$this->sess_create();
}
else
{
$this->sess_update();
}

// Delete 'old' flashdata (from last request)
$this->_flashdata_sweep();

// Mark all new flashdata as old (data will be deleted before next request)
$this->_flashdata_mark();

// Delete expired sessions if necessary
$this->_sess_gc();

log_message('debug', "Session routines successfully run");
}

三、构造函数中调用的sess_read()方法：获取当前的Session

function sess_read()
{
// Fetch the cookie
// 获取cookie的值
$session = $this->CI->input->cookie($this->sess_cookie_name);

// No cookie?  Goodbye cruel world!...
// 如果没有cookie，返回错误
if ($session === FALSE)
{
log_message('debug', 'A session cookie was not found.');
return FALSE;
}

// Decrypt the cookie data
// 判断是否加密session，如果为真则加密session
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)-3
d3b2
2); // 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?
// 判断被unserialized的数组是否有正确的session格式，若没有执行sess_destroy
if ( ! is_array($session) OR ! isset($session['session_id']) OR ! isset($session['ip_address']) OR ! isset($session['user_agent']) OR ! isset($session['last_activity']))
{
$this->sess_destroy();
return FALSE;
}

// Is the session current?
// 判断最新的一个活跃时间戳+Session有效期是否小于现在时间，若小于sess_destroy
if (($session['last_activity'] + $this->sess_expiration) < $this->now)
{
$this->sess_destroy();
return FALSE;
}

// Does the IP Match?
// 判断IP是否匹配
if ($this->sess_match_ip == TRUE AND $session['ip_address'] != $this->CI->input->ip_address())
{
$this->sess_destroy();
return FALSE;
}

// Does the User Agent Match?
// 判断user_agent是否匹配
if ($this->sess_match_useragent == TRUE AND trim($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?
// 判断数据库中的Session是否正确
if ($this->sess_use_database === TRUE)
{
$this->CI->db->where('session_id', $session['session_id']);

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 = $this->CI->db->get($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 = $query->row();
if (isset($row->user_data) AND $row->user_data != '')
{
$custom_data = $this->_unserialize($row->user_data);

if (is_array($custom_data))
{
foreach ($custom_data as $key => $val)
{
$session[$key] = $val;
}
}
}
}

// Session is valid!
$this->userdata = $session;
unset($session);

return TRUE;
}

四：创建Session的方法sess_create()

function sess_create()
{
// 初始化sessid，并将它用mt_rand(0, mt_getrandmax())循环生成随机值，直到sessid的长度大于32
$sessid = '';
while (strlen($sessid) < 32)
{
$sessid .= mt_rand(0, mt_getrandmax());
}

// To make the session ID even more secure we'll combine it with the user's IP
// 为了更安全，将IP地址结合，加到$sessid的末尾
$sessid .= $this->CI->input->ip_address();

$this->userdata = array(
'session_id'	=> md5(uniqid($sessid, TRUE)),
'ip_address'	=> $this->CI->input->ip_address(),
'user_agent'	=> substr($this->CI->input->user_agent(), 0, 120),
'last_activity'	=> $this->now,
'user_data'		=> ''
);

// Save the data to the DB if needed
// 如果启用了Session存入数据库，则将数据存入数据库中
if ($this->sess_use_database === TRUE)
{
$this->CI->db->query($this->CI->db->insert_string($this->sess_table_name, $this->userdata));
}

// Write the cookie
// 设置cookie
$this->_set_cookie();
}

该方法调用私有成员方法_set_cookie()

function _set_cookie($cookie_data = NULL)
{
if (is_null($cookie_data))
{
$cookie_data = $this->userdata;
}

// Serialize the userdata for the cookie
// 序列化userdata
$cookie_data = $this->_serialize($cookie_data);

// 判断是否加密Session
if ($this->sess_encrypt_cookie == TRUE)
{
$cookie_data = $this->CI->encrypt->encode($cookie_data);
}
else
{
// if encryption is not used, we provide an md5 hash to prevent userside tampering
// 如果加密没有启用，则提供一个md5 hash
$cookie_data = $cookie_data.md5($cookie_data.$this->encryption_key);
}

$expire = ($this->sess_expire_on_close === TRUE) ? 0 : $this->sess_expiration + time();

// Set the cookie
setcookie(
$this->sess_cookie_name,
$cookie_data,
$expire,
$this->cookie_path,
$this->cookie_domain,
$this->cookie_secure
);
}

五、Session更新方法sess_update()

function sess_update()
{
// We only update the session every five minutes by default
// 默认每五分钟更新一次Session
if (($this->userdata['last_activity'] + $this->sess_time_to_update) >= $this->now)
{
return;
}

// Save the old session id so we know which record to
// update in the database if we need it
// 记住旧的Session id所以我们能从数据库中知道哪个记录要更新
$old_sessid = $this->userdata['session_id'];
$new_sessid = '';
while (strlen($new_sessid) < 32)
{
$new_sessid .= mt_rand(0, mt_getrandmax());
}

// 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
$new_sessid = md5(uniqid($new_sessid, TRUE));

// Update the session data in the session data array
$this->userdata['session_id'] = $new_sessid;
$this->userdata['last_activity'] = $this->now;

// _set_cookie() will handle this for us if we aren't using database sessions
// by pushing all userdata to the cookie.
$cookie_data = NULL;

// Update the session ID and last_activity field in the DB if needed
// 如果是Session保存在数据库，则更新相应的记录
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];
}

$this->CI->db->query($this->CI->db->update_string($this->sess_table_name, array('last_activity' => $this->now, 'session_id' => $new_sessid), array('session_id' => $old_sessid)));
}

// Write the cookie
$this->_set_cookie($cookie_data);
}

六、Session销毁方法sess_destroy()

function sess_destroy()
{
// Kill the session DB row
// 如果Session是存在数据库中，则删除数据库中的指定行
if ($this->sess_use_database === TRUE && isset($this->userdata['session_id']))
{
$this->CI->db->where('session_id', $this->userdata['session_id']);
$this->CI->db->delete($this->sess_table_name);
}

// Kill the cookie
// 将过期时间设置为一个过去的时间
setcookie(
$this->sess_cookie_name,
addslashes(serialize(array())),
($this->now - 31500000),
$this->cookie_path,
$this->cookie_domain,
0
);

// Kill session data
// 将$this->userdata设定为空数组
$this->userdata = array();
}

七、设置自定义Session数据方法set_userdata($newdata = array(), $newval = '')

function set_userdata($newdata = array(), $newval = '')
{
// 如果$newdata是字符串，则说明是只添加一个用户数据
if (is_string($newdata))
{
$newdata = array($newdata => $newval);
}

// 添加一个数组
if (count($newdata) > 0)
{
foreach ($newdata as $key => $val)
{
$this->userdata[$key] = $val;
}
}

$this->sess_write();
}

该方法调用成员方法sess_write()

function sess_write()
{
// Are we saving custom data to the DB?  If not, all we do is update the cookie
// 如果不是将Sessin存入数据库，只要更新当前cookie就行了
if ($this->sess_use_database === FALSE)
{
$this->_set_cookie();
return;
}

// set the custom userdata, the session data we will set in a second
// 自定义的Session数据
$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
// 将$custom_userdata中不是用户自定义数据的销毁
foreach (array('session_id','ip_address','user_agent','last_activity') as $val)
{
unset($custom_userdata[$val]);
$cookie_userdata[$val] = $this->userdata[$val];
}

// 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
// 如果没有自定义Session数据，我们将空数组转换为空字符串
if (count($custom_userdata) === 0)
{
$custom_userdata = '';
}
else
{
// Serialize the custom data array so we can store it
// 如果设置了自定义Session数据，则将其序列化
$custom_userdata = $this->_serialize($custom_userdata);
}

// Run the update query
// 更新数据库中的last_activity和user_data
$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.
// 设置不是自定义Session数据
$this->_set_cookie($cookie_userdata);
}

八、垃圾回收方法_sess_gc()

function _sess_gc()
{
if ($this->sess_use_database != TRUE)
{
return;
}

srand(time());
if ((rand() % 100) < $this->gc_probability)
{
$expire = $this->now - $this->sess_expiration;

$this->CI->db->where("last_activity < {$expire}");
$this->CI->db->delete($this->sess_table_name);

log_message('debug', 'Session garbage collection performed.');
}
}