php 实现文件下载 断点续传 原理

class downLoad{
	var $file_name;
	var $file_dir;
	var $buffer_size = 1024;
	var $err = "";
	public static $MIME_type = array(
								"pdf"  =>"application/pdf",
								"exe"  =>"application/octet-stream",
								"zip"  =>"application/zip",
								"doc"  =>"application/msword",
								"xls"  =>"application/vnd.ms-excel",
								"ppt"  =>"application/vnd.ms-powerpoint",
								"gif"  =>"image/gif",
								"png"  =>"image/png",
								"jpeg" =>"jpg",
								"mp3"  =>"audio/mpeg",
								"wav"  =>"audio/x-wav",
								"mpeg" =>"mpg",
								"mpe"  =>"video/mpeg",
								"mov"  =>"video/quicktime",
								"avi"  =>"video/x-msvideo",				
							);
	public function __construct($file_dir="",$file_name=""){
		$this->file_dir  = $file_dir;
		$this->file_name = $file_name;
		$this->path = $file_dir."/".$file_name;
		$this->suffix = pathinfo($file_name,PATHINFO_EXTENSION);
	}
	
	public function down(){
		if(!file_exists($this->path)){
			$this->err = "该文件被移除了";
			return false;
		}

		$content_type = $this->getMIME($this->suffix);
		$file_size = filesize($this->path);
		
		header("Content-type: ".$content_type);
		header('Content-Disposition: attachment; filename="'.$this->file_name.'"');
		
		@header("Cache-control: public");
		@header("Pragma: public"); 
		header("Content-Length: ".$file_size);
		ob_end_clean(); 
		//readfile($this->path); 一次性读出来

		$fp= fopen($this->path,"r");
		$buffer_size = $this->buffer_size;
		$cur_pos = 0; //记录读了多少了
		
		while(!feof($fp) && $file_size>$buffer_size+$cur_pos){
			$buffer = fread($fp,$buffer_size); //每次读1024字节
			echo $buffer;
			$cur_pos += $buffer_size;
		}
		//把剩下的读出来 因为文件的带下很有很能不是1024 的整数倍
		$buffer = fread($fp,$file_size-$cur_pos);
  		echo $buffer;
  		fclose($fp);
  		return true;		
	}
	
	public function getMIME($key=""){
		if($key == "" || !isset(self::$MIME_type[$key])){
			return "application/octet-stream";
		}
		return self::$MIME_type[$key];
	}
}
//	$x = new downLoad($file_dir,$file_name);  $file_dir路径 比如 all     $file_name文件名 比如 a.exe  合起来就是全部的路径了all/a.exe
//	$x->down();

	class downLoad
	{
		var $file_path;
		var $file_name;
		var $file_suffix;
		var $speed = 1024; //表示下载速度1m
		var $err = "";
		var $range_start=0;
		var $range_end;
		var $http_range;
		var $file_size;
		public static $MIME_type = array(
									"pdf"  =>"application/pdf",
									"exe"  =>"application/octet-stream",
									"zip"  =>"application/zip",
									"doc"  =>"application/msword",
									"xls"  =>"application/vnd.ms-excel",
									"ppt"  =>"application/vnd.ms-powerpoint",
									"gif"  =>"image/gif",
									"png"  =>"image/png",
									"jpeg" =>"jpg",
									"mp3"  =>"audio/mpeg",
									"wav"  =>"audio/x-wav",
									"mpeg" =>"mpg",
									"mpe"  =>"video/mpeg",
									"mov"  =>"video/quicktime",
									"avi"  =>"video/x-msvideo",				
								);
		public function __construct($file_path="",$http_ranges="",$speed=""){
			$this->file_path = $file_path;
			$this->file_name = basename($file_path);
			$this->file_suffix = substr(strrchr($this->file_name, '.'),1);
			$this->file_size= filesize($file_path);
			$this->http_range = (isset($http_ranges) && !empty($http_ranges)!="")?$http_ranges:false;
			!empty($speed)&&($this->speed = $speed);  
		}
		public function down(){
			if(!file_exists($this->file_path)){
				$this->err = "该文件被移除";
				return false;
			}
			$file_path = $this->file_path;
			$content_type = $this->getMIME($this->file_suffix);
			$http_range = $this->http_range;
			if($http_range){
				//$http_range 的形式为 bytes=3145728-  差不多就是这个样子的
				$http_range = preg_replace('/[\s|,]*/', '', $http_range);
				$arr = explode('-',substr($http_range,6));
				$this->range_start = ( isset($arr[0]) && !empty($arr[0]) ) ? $arr[0] : 0;
				$this->range_end   = ( isset($arr[1]) && !empty($arr[1]) && $arr[1]!=0 ) ? $arr[1] : $this->file_size-1;
			}

			$this->setHeader();
			
			$fh =  fopen($file_path, "rb");			
			fseek($fh, $this->range_start);
			
			$speed = $this->speed;
			while(!feof($fh))
			{
				echo fread($fh, 1024*$speed);
				ob_flush();
				sleep(1);
			}
			fclose($fh);
		}
		public function getMIME($key=""){
			if($key=="" || !isset(self::$MIME_type[$key])){
				return "application/octet-stream";
			}
			return self::$MIME_type[$key];
		}
		public function setHeader(){
			header('Cache-control: public');
			header('Content-Type: application/octet-stream');
			header('Content-Disposition: attachment; filename='.$this->file_name);						
			if($this->http_range){
				$range_start = $this->range_start;
				$range_end = $this->range_end;
				header('HTTP/1.1 206 Partial Content');
				header('Accept-Ranges: bytes');
				header( sprintf('Content-Length: %u',$range_end - $range_start) );
				header( sprintf('Content-Range: bytes %s-%s/%s', $range_start, $range_end, $this->file_size) );
			}else{
				header("HTTP/1.1 200 OK");
				header(sprintf('Content-Length: %s',$this->file_size));
			}
		}
	}
	//$http_range = isset($_SERVER['HTTP_RANGE'])?$_SERVER['HTTP_RANGE']:false;
	//$x = new downLoad("all/1.exe",$http_range);
	//$x->down();