PHP基于闭包思想实现的BT(torrent)文件解析工具实例详解

function count_down($count)
{
  return $func = function()
    use($count,$func)
  {
    if(--$count > 0)
      $func();
    echo "wow\n";
  };
}
$foo = count_down(3);
$foo();

function count_down($count)
{
  return $foo = function()
    use(&$count,&$foo)
  {
    echo $count."\n";
    if(--$count > 0)
      $foo();
  };
}
$foo = count_down(4);
$foo();

function count_down_again($count)
{
  return function()use($count)
  {
    printf("wow %d\n",$count);
    return --$count;
  };
}
$foo = count_down_again(5);
while($foo() >0);

function count_down_again($count)
{
  return function()use(&$count)
  {
    printf("wow %d\n",$count);
    return --$count;
  };
}
$foo = count_down_again(5);
while($foo() >0);

class Foo
{
  public function __invoke($count)
  {
    if($count > 0)
      $this($count - 1);
    echo "wow\n";
  }
}
$foo = new Foo();
$foo(4);

function yet_another_count_down($func,$count)
{
  $func($count);
  if($count > 0)
    yet_another_count_down($func,$count - 1);
}
yet_another_count_down(function($var){echo $var."\n";},6);

<?php
$file_name = '1.torrent';
$file = fopen($file_name,'r');
$nil = new Parser($file);//构造解析器
$nil = $nil();//进行解析
$pos = ftell($file);
echo '读取到文件位置'.sprintf('0x%08X',$pos)."\r\n";
fseek($file,0,SEEK_END);
echo '还剩下'.(ftell($file) - $pos).'字节未读取'."\r\n";
if(!feof($file))
{
  echo '文件还未结束，再读一个字符:';
  $ch = fgetc($file);
  if(is_string($ch) && ereg('\w',$ch))
  {
    echo $ch."\r\n";
  }
  else
  {
    printf('0x%02X',$ch);
    echo "\r\n";
  }
  echo '现在的文件位置是'.sprintf('0x%08X',ftell($file))."\r\n";
  echo '文件'.(feof($file)?'已结束':'还未结束')."\r\n";
}
fclose($file);//解析器后面不再工作了，此时可以释放文件指针了。
$info = @$nil['value'][0]['info'];
if(!$info)
{
  echo '这是一个有效的B-Encoding文件，但它不是一个有效的种子文件';
  exit();
}
$name = $info['name.utf-8'] ?$info['name.utf-8']:$info['name'];
if(!$name)
{
  echo '这是一个有效的B-Encoding文件，但它不是一个有效的种子文件';
  exit();
}
echo $name."\r\n";
if($info['files'])
{
  $index = 0;
  foreach($info['files'] as $f)
  {
    $index += 1;
    $path = $f['path.utf8'] ?$f['path.utf8'] :$f['path'];
    if(!$path)
    {
      echo '文件列表中的第'.$index."个文件不含目录\r\n";
      continue;
    }
    if(0 === strpos($path[0],"_____padding_file_"))continue;
    $under_folder = false;
    foreach($path as $item)
    {
      if($under_folder)
      {
        echo '/';
      }else{
        $under_folder = true;
      }
      echo $item;
    }
    echo "\r\n";
  }
}
else
{
  echo "仅有一个文件\r\n";
}
class Parser
{
  private $_file;
  public function __construct($file)
  {
    $this ->_file = $file;
  }
  public function __invoke($parent = array())
  {
    $ch = $this ->read();
    switch($ch)
    {
    case 'i':
      {
        $n = $ch;
        while(($ch = $this ->read()) != 'e')
        {
          if(!is_numeric($ch))
          {
            echo '在';
            echo sprintf(
                '0x%08X',ftell($this ->_file));
            echo '解析数字时遇到错误',"\r\n";
            echo '在i和e之间不应该出现非数字字符'."\r\n";
            echo '意外的字符'.sprintf('0x%02X',$ch);
            exit();
          }
          else
          {
            $n .= $ch;
          }
        }
        $n += 0;
        $offset = count($parent['value']);
        $parent['value'][$offset] = $n;
        return $parent;
      }
      break;
    case 'd':
      {
        $node = array();
        //这个$node变量作为字典对象准备加入到$parent的孩子节点中去
        //$node['type'] = 'd';
        while('e' != ($tmp = $this($node)))
        {//每次给$node带来一个新孩子
          $node = $tmp;
        }
        $child_count = count($node['value']);
        if($child_count % 2 != 0)
        {
          echo '解析结尾于';
          echo sprintf('0x%08X',ftell($this ->_file));
          echo '的字典时遇到错误:'."\r\n";
          echo '字典的对象映射不匹配';
          exit();
        }
        $product = array();
        for($i = 0; $i < $child_count; $i += 2)
        {
          $key = $node['value'][$i];
          $value = $node['value'][$i + 1];
          if(!is_string($key))
          {
            echo '无效的字典结尾于';
            echo sprintf('0x%08X',ftell($this ->_file));
            echo ":\r\n";
            echo '解析[k => v]配对时遇到错误，k应为字符串';
            exit();
          }
          $product[$key] = $value;
        }
        /*
         * 思想是这样的：子节点想要加入父节点时，
         * 往父节点的value数组添加。
         * 当父节点收集好所需的信息后，
         * 父节点自身再从它的value节点整合内容
         * 对于字典和列表统一这样处理会大大降低代码量
         */
        $offset = count($parent['value']);
        $parent['value'][$offset] = $product;
        return $parent;
      }
      break;
    case 'l';
      {
        $node = array();
        while('e' != ($tmp = $this($node)))
        {
          $node = $tmp;
        }
        $offset = count($parent['value']);
        $parent['value'][$offset] = $node['value'];
        return $parent;
      }
      break;
    case 'e':
        return 'e';
      break;
    default:
      {
        if(!is_numeric($ch))
        {
          $this ->unexpected_character(
            ftell($this ->_file) - 1,$ch);
        }
        $n = $ch;
        while(($ch = $this ->read()) != ':')
        {
          $n .= $ch;
          if(!is_numeric($n))
          {
            unexpected_character(
              ftell($this ->_file) - 1,$ch);
          }
        }
        $n += 0;
        $str = '';
        for(; $n > 0; --$n)
        {
          $str .= $this ->read();
        }
        $offset = count($parent['value']);
        $parent['value'][$offset] = $str;
        return $parent;
      }
      break;
    }
  }
  /*
   * read函数包裹了$this ->_file变量
   */
  function read()
  {
    if(!feof($this ->_file))
    {
      return fgetc($this ->_file);
    }else{
      echo '意外的文件结束';
      exit();
    }
  }
  /*
   * unexpected_character函数接收2个参数
   * 它用于指明脚本在何处遇到了哪个不合法的字符，
   * 并在返回前终止脚本的运行。
   */
  function unexpected_character($pos,$val)
  {
    $hex_pos = sprintf("0x%08X",$pos);
    $hex_val = sprintf("0x%02X",$val);
    echo 'Unexpected Character At Position ';
    echo $hex_pos.' , Value '.$hex_val."\r\n";
    echo "Analysing Process Teminated.";
    exit();
  }
}
?>