php - 如何在没有内存错误的情况下使用 var_dump + 输出缓冲？

Question

我在一个应用程序中使用调试辅助工具，该应用程序使用 var_dump() 和输出缓冲来捕获变量并显示它们。但是，我遇到了一个问题，即大型对象最终会占用缓冲区中的太多内存。

function getFormattedOutput(mixed $var) {
  if (isTooLarge($var)) { 
    return 'Too large! Abort!'; // What a solution *might* look like
  }

  ob_start();
  var_dump($var); // Fatal error:  Allowed memory size of 536870912 bytes exhausted
  $data = ob_get_clean();

  // Return the nicely-formated data to use later
  return $data
}

有什么办法可以防止这种情况发生吗？还是一种变通方法来检测它即将为特定变量输出大量信息？我真的无法控制哪些变量被传递到这个函数中。它可以是任何类型。

Answer 1

正如所有其他人都提到你所问的是不可能的。你唯一能做的就是尽量处理好它。

您可以尝试将其拆分为更小的部分，然后将其组合起来。我创建了一个小测试来尝试获取内存错误。显然，现实世界的示例可能表现不同，但这似乎可以解决问题。

<?php
define('mem_limit', return_bytes(ini_get('memory_limit'))); //allowed memory

/*
SIMPLE TEST CLASS
*/
class test { }
$loop = 260;
$t = new Test();
for ($x=0;$x<=$loop;$x++) {
  $v = 'test'.$x;
  $t->$v = new Test();
  for ($y=0;$y<=$loop;$y++) {
    $v2 = 'test'.$y;
    $t->$v->$v2 = str_repeat('something to test! ', 200);
  }
}
/* ---------------- */


echo saferVarDumpObject($t);

function varDumpToString($v) {
  ob_start();
  var_dump($v);
  $content = ob_get_contents();
  ob_end_clean();
  return $content;
}

function saferVarDumpObject($var) {
  if (!is_object($var) && !is_array($var))
    return varDumpToString($var);

  $content = '';
  foreach($var as $v) {
    $content .= saferVarDumpObject($v);
  }
  //adding these smaller pieces to a single var works fine.
  //returning the complete larger piece gives memory error

  $length = strlen($content);
  $left = mem_limit-memory_get_usage(true);

  if ($left>$length)
    return $content; //enough memory left

  echo "WARNING! NOT ENOUGH MEMORY<hr>";
  if ($left>100) {
    return substr($content, 0, $left-100); //100 is a margin I choose, return everything you have that fits in the memory
  } else {
    return ""; //return nothing.
  }  
}

function return_bytes($val) {
    $val = trim($val);
    $last = strtolower($val[strlen($val)-1]);
    switch($last) {
        // The 'G' modifier is available since PHP 5.1.0
        case 'g':
            $val *= 1024;
        case 'm':
            $val *= 1024;
        case 'k':
            $val *= 1024;
    }

    return $val;
}
?>

更新上面的版本仍然有一些错误。我重新创建它以使用一个类和一些其他功能

• 检查递归
• 修复单个大属性
• 模拟 var_dump 输出
• trigger_error on warning 以便能够捕获/隐藏它

如注释所示，类的资源标识符与 var_dump 的输出不同。据我所知，其他的都是一样的。

<?php  
/*
RECURSION TEST
*/
class sibling {
  public $brother;
  public $sister;
}
$brother = new sibling();
$sister = new sibling();
$brother->sister = $sister;
$sister->sister = $brother;
Dump::Safer($brother);


//simple class
class test { }

/*
LARGE TEST CLASS - Many items
*/
$loop = 260;
$t = new Test();
for ($x=0;$x<=$loop;$x++) {
  $v = 'test'.$x;
  $t->$v = new Test();
  for ($y=0;$y<=$loop;$y++) {
    $v2 = 'test'.$y;
    $t->$v->$v2 = str_repeat('something to test! ', 200);
  }
}
//Dump::Safer($t);
/* ---------------- */


/*
LARGE TEST CLASS - Large attribute
*/
$a = new Test();
$a->t2 = new Test();
$a->t2->testlargeattribute = str_repeat('1', 268435456 - memory_get_usage(true) - 1000000);
$a->smallattr1 = 'test small1';
$a->smallattr2 = 'test small2';
//Dump::Safer($a);
/* ---------------- */

class Dump
{
  private static $recursionhash;
  private static $memorylimit;
  private static $spacing;
  private static $mimicoutput = true;


  final public static function MimicOutput($v) {
    //show results similar to var_dump or without array/object information
    //defaults to similar as var_dump and cancels this on out of memory warning
    self::$mimicoutput = $v===false ? false : true;
  }

  final public static function Safer($var) {
    //set defaults
    self::$recursionhash = array();
    self::$memorylimit = self::return_bytes(ini_get('memory_limit'));

    self::$spacing = 0;

    //echo output
    echo self::saferVarDumpObject($var);
  }  

  final private static function saferVarDumpObject($var) {
    if (!is_object($var) && !is_array($var))
      return self::Spacing().self::varDumpToString($var);

    //recursion check
    $hash = spl_object_hash($var);
    if (!empty(self::$recursionhash[$hash])) {
      return self::Spacing().'*RECURSION*'.self::Eol();
    }
    self::$recursionhash[$hash] = true;


    //create a similar output as var dump to identify the instance
    $content = self::Spacing() . self::Header($var);
    //add some spacing to mimic vardump output
    //Perhaps not the best idea because the idea is to use as little memory as possible.
    self::$spacing++;
    //Loop trough everything to output the result
    foreach($var as $k=>$v) {
      $content .= self::Spacing().self::Key($k).self::Eol().self::saferVarDumpObject($v);
    }
    self::$spacing--;
    //decrease spacing and end the object/array
    $content .= self::Spacing().self::Footer().self::Eol();
    //adding these smaller pieces to a single var works fine.
    //returning the complete larger piece gives memory error

    //length of string and the remaining memory
    $length = strlen($content);
    $left = self::$memorylimit-memory_get_usage(true);

     //enough memory left?
    if ($left>$length)
      return $content;

    //show warning  
    trigger_error('Not enough memory to dump "'.get_class($var).'" memory left:'.$left, E_USER_WARNING);
    //stop mimic output to prevent fatal memory error
    self::MimicOutput(false);
    if ($left>100) {
      return substr($content, 0, $left-100); //100 is a margin I chose, return everything you have that fits in the memory
    } else {
      return ""; //return nothing.
    }  
  }

  final private static function Spacing() {
    return self::$mimicoutput ? str_repeat(' ', self::$spacing*2) : '';
  }

  final private static function Eol() {
    return self::$mimicoutput ? PHP_EOL : '';
  }

  final private static function Header($var) {
    //the resource identifier for an object is WRONG! Its always 1 because you are passing around parts and not the actual object. Havent foundnd a fix yet
    return self::$mimicoutput ? (is_array($var) ? 'array('.count($var).')' : 'object('.get_class($var).')#'.intval($var).' ('.count((array)$var).')') . ' {'.PHP_EOL : '';
  }

  final private static function Footer() {
    return self::$mimicoutput ? '}' : '';
  }

  final private static function Key($k) {
    return self::$mimicoutput ? '['.(gettype($k)=='string' ? '"'.$k.'"' : $k ).']=>' : '';
  }

  final private static function varDumpToString($v) {
    ob_start();
    var_dump($v);

    $length = strlen($v);
    $left = self::$memorylimit-memory_get_usage(true);

     //enough memory left with some margin?
    if ($left-100>$length) {
      $content = ob_get_contents();
      ob_end_clean();
      return $content;
    }
    ob_end_clean();

    //show warning  
    trigger_error('Not enough memory to dump "'.gettype($v).'" memory left:'.$left, E_USER_WARNING);

    if ($left>100) {
      $header = gettype($v).'('.strlen($v).')';
      return $header . substr($v, $left - strlen($header));
    } else {
      return ""; //return nothing.
    }  
  }

  final private static function return_bytes($val) {
      $val = trim($val);
      $last = strtolower($val[strlen($val)-1]);
      switch($last) {
          // The 'G' modifier is available since PHP 5.1.0
          case 'g':
              $val *= 1024;
          case 'm':
              $val *= 1024;
          case 'k':
              $val *= 1024;
      }

      return $val;
  }
}
?>