CI框架源码翻阅-Output.php

<?php  if ( ! defined('BASEPATH')) exit('No direct script access allowed');
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP 5.1.6 or newer
 *
 * @package		CodeIgniter
 * @author		ExpressionEngine Dev Team
 * @copyright	Copyright (c) 2008 - 2011, EllisLab, Inc.
 * @license		http://codeigniter.com/user_guide/license.html
 * @link		http://codeigniter.com
 * @since		Version 1.0
 * @filesource
 */

// ------------------------------------

/**
 * Output Class
 *
 * Responsible 负责 for sending final output to browser
 * 负责把最终的输出发送到浏览器
 * @package		CodeIgniter
 * @subpackage	Libraries
 * @category	Output
 * @author		ExpressionEngine Dev Team
 * @link		http://codeigniter.com/user_guide/libraries/output.html
 */
class CI_Output {

	/**
	 * Current output string
	 * 当前输出的字符串
	 *
	 * @var string
	 * @access 	protected
	 */
	protected $final_output;
	/**
	 * Cache expiration time
	 * 缓存终结的时间
	 * @var int
	 * @access 	protected
	 */
	protected $cache_expiration	= 0;
	/**
	 * List of server headers
	 * 服务器头列表
	 * @var array
	 * @access 	protected
	 */
	protected $headers			= array();
	/**
	 * List of mime types
	 * 
	 * @var array
	 * @access 	protected
	 */
	protected $mime_types		= array();
	/**
	 * Determines wether profiler is enabled
	 * 是否启用分析器
	 * @var book
	 * @access 	protected
	 */
	protected $enable_profiler	= FALSE;
	/**
	 * Determines if output compression is enabled
	 * 是否开启输出压缩
	 * @var bool
	 * @access 	protected
	 */
	protected $_zlib_oc			= FALSE;
	/**
	 * List of profiler sections
	 * 分析器列表
	 *
	 * @var array
	 * @access 	protected
	 */
	protected $_profiler_sections = array();
	/**
	 * Whether or not to parse variables like {elapsed_time} and {memory_usage}
	 * 是否解析变量{elapsed_time} and {memory_usage}
	 * 注意文档说这里有错误详见http://codeigniter.org.cn/user_guide/libraries/output.html
	 * 最下方
	 * @var bool
	 * @access 	protected
	 */
	protected $parse_exec_vars	= TRUE;

	/**
	 * Constructor
	 *
	 */
	function __construct()
	{
		// 返回配置项zlib.output_compression的值并赋给$this->_zlib_oc 
		// 如果配置项中开启了输出压缩功能则	$this->_zlib_oc 的值为on
		$this->_zlib_oc = @ini_get('zlib.output_compression');

		// Get mime types for later
		// 获取mimetype
		if (defined('ENVIRONMENT') AND file_exists(APPPATH.'config/'.ENVIRONMENT.'/mimes.php'))
		{
		    include APPPATH.'config/'.ENVIRONMENT.'/mimes.php';
		}
		else
		{
			include APPPATH.'config/mimes.php';
		}
		
		// $mimes 是mimes.php中定义的一个数组
		$this->mime_types = $mimes;

		log_message('debug', "Output Class Initialized");
	}

	// --------------------------------

	/**
	 * Get Output
	 * 使用这个方法，你可以得到将要输出的数据，并把它保存起来
	 * Returns the current output string
	 * 返回当前输出的字符串
	 * @access	public
	 * @return	string
	 */
	function get_output()
	{
		return $this->final_output;
	}

	// --------------------------------

	/**
	 * Set Output
	 *
	 * Sets the output string
	 * 设置输出的字符串
	 * @access	public
	 * @param	string
	 * @return	void
	 */
	function set_output($output)
	{
		$this->final_output = $output;

		return $this;
	}

	// --------------------------------

	/**
	 * Append Output
	 * 在最终输出字符串后，追加数据
	 * Appends data onto the output string
	 * 
	 * @access	public
	 * @param	string
	 * @return	void
	 */
	function append_output($output)
	{
		if ($this->final_output == '')
		{
			$this->final_output = $output;
		}
		else
		{
			$this->final_output .= $output;
		}

		return $this;
	}

	// --------------------------------

	/**
	 * Set Header
	 * 使用此方法，允许你设置将会被发送到浏览器的HTTP协议的标头，作用相当于php的标准函数: header()。
	 * Lets you set a server header which will be outputted with the final display.
	 * 允许您设置一个服务器头用于最终的显示输出。
	 * Note:  If a file is cached, headers will not be sent.  We need to figure 计算 out
	 * how to permit header data to be saved with the cache data...
	 *
	 * @access	public
	 * @param	string
	 * @param 	bool
	 * @return	void
	 */
	function set_header($header, $replace = TRUE)
	{
		// If zlib.output_compression is enabled it will compress the output,
		// but it will not modify the content-length header to compensate 补偿 for
		// the reduction减少 还原, causing the browser to hang waiting for more data.
		// We'll just skip content-length in those cases.

		if ($this->_zlib_oc && strncasecmp($header, 'content-length', 14) == 0)
		{
			return;
		}

		$this->headers[] = array($header, $replace);

		return $this;
	}

	// --------------------------------

	/**
	 * Set Content Type Header
	 * 设置Content-Type
	 * @access	public
	 * @param	string	extension of the file we're outputting
	 * @return	void
	 */
	function set_content_type($mime_type)
	{
		if (strpos($mime_type, '/') === FALSE)
		{
			$extension = ltrim($mime_type, '.');

			// Is this extension supported?
			if (isset($this->mime_types[$extension]))
			{
				$mime_type =& $this->mime_types[$extension];

				if (is_array($mime_type))
				{
					$mime_type = current($mime_type);
				}
			}
		}

		$header = 'Content-Type: '.$mime_type;

		$this->headers[] = array($header, TRUE);

		return $this;
	}

	// --------------------------------

	/**
	 * Set HTTP Status Header
	 * moved to Common procedural functions in 1.7.2
	 * 允许你手动设置服务器状态头(header)
	 * @access	public
	 * @param	int		the status code
	 * @param	string
	 * @return	void
	 */
	function set_status_header($code = 200, $text = '')
	{
		set_status_header($code, $text);

		return $this;
	}

	// --------------------------------

	/**
	 * Enable/disable Profiler
	 * 允许你开启或禁用分析器
	 * @access	public
	 * @param	bool
	 * @return	void
	 */
	function enable_profiler($val = TRUE)
	{
		$this->enable_profiler = (is_bool($val)) ? $val : TRUE;

		return $this;
	}

	// --------------------------------

	/**
	 * Set Profiler Sections
	 * 设置$this->_profiler_sections
	 * Allows override of default / config settings for Profiler section display
	 * 允许你在评测器启用时，控制(开/关)其特定部分
	 * 
	 * @access	public
	 * @param	array
	 * @return	void
	 */
	function set_profiler_sections($sections)
	{
		foreach ($sections as $section => $enable)
		{
			$this->_profiler_sections[$section] = ($enable !== FALSE) ? TRUE : FALSE;
		}

		return $this;
	}

	// --------------------------------

	/**
	 * Set Cache
	 * 设置缓存以及缓存时间 
	 * @access	public
	 * @param	integer 其中 $time 是你希望缓存更新的 分钟 数
	 * @return	void
	 */
	function cache($time)
	{
		$this->cache_expiration = ( ! is_numeric($time)) ? 0 : $time;

		return $this;
	}

	// --------------------------------

	/**
	 * Display Output
	 * 显示输出
	 * All "view" data is automatically put into this variable by the controller class:
	 *
	 * $this->final_output
	 *
	 * This function sends the finalized output data to the browser along
	 * with any server headers and profile data.  It also stops the
	 * benchmark timer so the page rendering speed and memory usage can be shown.
	 *
	 * @access	public
	 * @param 	string
	 * @return	mixed
	 */
	function _display($output = '')
	{
		// Note:  We use globals because we can't use $CI =& get_instance()
		// since this function is sometimes called by the caching mechanism,
		// which happens before the CI super object is available.
		// 注意：我们使用global 是因为我们不能使用$CI =& get_instance() 
		global $BM, $CFG;

		// Grab the super object if we can.
		// //当然如果可以拿到超级控制器，我们先拿过来。
		if (class_exists('CI_Controller'))
		{
			$CI =& get_instance();
		}

		// --------------------------------

		// Set the output data
		// 设置输出数据
		if ($output == '')
		{
			$output =& $this->final_output;
		}

		// --------------------------------

		// Do we need to write a cache file?  Only if the controller does not have its
		// own _output() method and we are not dealing with a cache file, which we
		// can determine by the existence of the $CI object above
		// 如果缓存时间>0 ，$CI 超级对象存在并且超级对象下面存在_output 方法
		// 调用_write_cache 方法，写一个缓存文件
		if ($this->cache_expiration > 0 && isset($CI) && ! method_exists($CI, '_output'))
		{
			$this->_write_cache($output);
		}

		// --------------------------------

		// Parse out the elapsed time and memory usage,
		// then swap the pseudo-variables with the data
		// 计算代码执行时间和内存使用时间
		$elapsed = $BM->elapsed_time('total_execution_time_start', 'total_execution_time_end');

		// 如果$this->parse_exec_vars为true，将输出中的{elapsed_time}，{memory_usage}
		// 替换为计算出的时间。
		if ($this->parse_exec_vars === TRUE)
		{
			$memory	 = ( ! function_exists('memory_get_usage')) ? '0' : round(memory_get_usage()/1024/1024, 2).'MB';

			$output = str_replace('{elapsed_time}', $elapsed, $output);
			$output = str_replace('{memory_usage}', $memory, $output);
		}

		// --------------------------------

		// Is compression requested?压缩传输的处理。
		if ($CFG->item('compress_output') === TRUE && $this->_zlib_oc == FALSE)
		{
			if (extension_loaded('zlib'))
			{
				if (isset($_SERVER['HTTP_ACCEPT_ENCODING']) AND strpos($_SERVER['HTTP_ACCEPT_ENCODING'], 'gzip') !== FALSE)
				{
					ob_start('ob_gzhandler');
				}
			}
		}

		// --------------------------------

		// Are there any server headers to send?
		// 有没有服务器头发送？
		if (count($this->headers) > 0)
		{
			foreach ($this->headers as $header)
			{
				@header($header[0], $header[1]);
			}
		}

		// --------------------------------

		// Does the $CI object exist?
		// If not we know we are dealing with a cache file so we'll
		// simply echo out the data and exit.
		// 如果没有$CI就证明当前是一个缓存的输出，我们只简单的发送数据并退出
		if ( ! isset($CI))
		{
			echo $output;
			log_message('debug', "Final output sent to browser");
			log_message('debug', "Total execution time: ".$elapsed);
			return TRUE;
		}

		// --------------------------------

		// Do we need to generate profile data?
		// If so, load the Profile class and run it.
		// 如果开启了性能分析我们就调用，
		// 会生成一些报告到页面尾部用于辅助我们调试。
		if ($this->enable_profiler == TRUE)
		{
			$CI->load->library('profiler');

			if ( ! empty($this->_profiler_sections))
			{
				$CI->profiler->set_sections($this->_profiler_sections);
			}

			// If the output data contains closing </body> and </html> tags
			// we will remove them and add them back after we insert the profile data
			// 如果存在</body></html>标签，我们将删除，插入我们的性能分析代码后再添加回去
			if (preg_match("|</body>.*?</html>|is", $output))
			{
				$output  = preg_replace("|</body>.*?</html>|is", '', $output);
				$output .= $CI->profiler->run();
				$output .= '</body></html>';
			}
			else
			{
				$output .= $CI->profiler->run();
			}
		}

		// --------------------------------

		// Does the controller contain a function named _output()?
		// If so send the output there.  Otherwise, echo it.
		// 如果控制器中有_output 这个方法我们直接调用
		// 如果没有直接发送数据到浏览器
		if (method_exists($CI, '_output'))
		{
			$CI->_output($output);
		}
		else
		{
			echo $output;  // Send it to the browser!
		}

		log_message('debug', "Final output sent to browser");
		log_message('debug', "Total execution time: ".$elapsed);
	}

	// --------------------------------

	/**
	 * Write a Cache File
	 * 生成一个缓存文件
	 * @access	public
	 * @param 	string
	 * @return	void
	 */
	function _write_cache($output)
	{
		// 调用超级对象
		$CI =& get_instance();
		// 找到缓存路径
		$path = $CI->config->item('cache_path');

		$cache_path = ($path == '') ? APPPATH.'cache/' : $path;

		// 如果缓存路径不是一个文件夹或者不可写 ，报错返回。
		if ( ! is_dir($cache_path) OR ! is_really_writable($cache_path))
		{
			log_message('error', "Unable to write cache file: ".$cache_path);
			return;
		}

		// 获取$uri
		$uri =	$CI->config->item('base_url').
				$CI->config->item('index_page').
				$CI->uri->uri_string();

		// 生成缓存文件。
		$cache_path .= md5($uri);

		if ( ! $fp = @fopen($cache_path, FOPEN_WRITE_CREATE_DESTRUCTIVE))
		{
			log_message('error', "Unable to write cache file: ".$cache_path);
			return;
		}

		// 计算缓存文件过期时间。
		$expire = time() + ($this->cache_expiration * 60);

		if (flock($fp, LOCK_EX))
		{
			fwrite($fp, $expire.'TS--->'.$output);
			flock($fp, LOCK_UN);
		}
		else
		{
			log_message('error', "Unable to secure a file lock for file at: ".$cache_path);
			return;
		}
		fclose($fp);
		@chmod($cache_path, FILE_WRITE_MODE);

		log_message('debug', "Cache file written: ".$cache_path);
	}

	// --------------------------------

	/**
	 * Update/serve a cached file
	 * 在CodeIgniter.php里面有调用此方法，此方法是负责缓存的输出，
	 * 如果在CodeIgniter.php中调用此方法有输出，则
	 * 本次请求的运行将直接结束，直接以缓存输出作为响应。
	 * 
	 * @access	public
	 * @param 	object	config class
	 * @param 	object	uri class
	 * @return	void
	 */
	function _display_cache(&$CFG, &$URI)
	{
		// 取得保存缓存的路径
		$cache_path = ($CFG->item('cache_path') == '') ? APPPATH.'cache/' : $CFG->item('cache_path');

		// Build the file path.  The file name is an MD5 hash of the full URI
		// 一条准确的路由都会对应一个缓存文件，缓存文件是对应路由字符串的md5密文。
		$uri =	$CFG->item('base_url').
				$CFG->item('index_page').
				$URI->uri_string;

		$filepath = $cache_path.md5($uri);

		// 如果没有此缓存文件，获取缓存内容失败，则可以返回FALSE。
		if ( ! @file_exists($filepath))
		{
			return FALSE;
		}
		// 如果有此缓存文件，但是无法读，获取缓存内容失败，同样返回FALSE。
		if ( ! $fp = @fopen($filepath, FOPEN_READ))
		{
			return FALSE;
		}

		// 打开到缓存文件，并以$fp作为句柄。下一步先取得共享锁（读取）。
		flock($fp, LOCK_SH);

		$cache = '';
		if (filesize($filepath) > 0)
		{
			$cache = fread($fp, filesize($filepath));
		}
		// 解锁
		flock($fp, LOCK_UN);
		// 关闭文件连接。
		fclose($fp);

		// 下面这个TS--->字样，只是因为CI的缓存文件里面的内容
		// 是规定以数字＋TS--->开头而已。这个数字是代表创建时间。
		// 如果不符合此结构，可视为非CI的缓存文件，或者文件已损坏，
		// 获取缓存内容失败，返回FALSE。
		// Strip out the embedded timestamp
		if ( ! preg_match("/(\d+TS--->)/", $cache, $match))
		{
			return FALSE;
		}

		// Has the file expired? If so we'll delete it.
		// 判断缓存是否过期，如果过期我们将删除它
		if (time() >= trim(str_replace('TS--->', '', $match['1'])))
		{
			if (is_really_writable($cache_path))
			{
				@unlink($filepath);
				log_message('debug', "Cache file has expired. File deleted");
				return FALSE;
			}
		}
		
		// Display the cache
		$this->_display(str_replace($match['0'], '', $cache));
		log_message('debug', "Cache file is current. Sending it to browser.");
		return TRUE;
	}


}
// END Output Class

/* End of file Output.php */
/* Location: ./system/core/Output.php */