Zend captcha Image generates blank

问题:

The image captcha randomly displays a blank captch. Roughly 4 out of 10 attempts.

I have already discovered the problem and a post on the zend forum suggest the only fix is to edit the Zend Framework code.

Is there any way to fix this without editing the ZF code? How come Zend have not fixed this in the releases since then, I have a look in the change log but nothing related to this?

$w     = $this->getWidth();
$h     = $this->getHeight();
$fsize = $this->getFontSize();

$img_file   = $this->getImgDir() . $id . $this->getSuffix();
if(empty($this->_startImage)) {
    $img = imagecreatetruecolor($w, $h);
} else {
    $img = imagecreatefrompng($this->_startImage);
    if(!$img) {
        require_once 'Zend/Captcha/Exception.php';
        throw new Zend_Captcha_Exception("Can not load start image");
    }
    $w = imagesx($img);
    $h = imagesy($img);
}
$text_color = imagecolorallocate($img, 0, 0, 0);
$bg_color   = imagecolorallocate($img, 255, 255, 255);
imagefilledrectangle($img, 0, 0, $w-1, $h-1, $bg_color);
$textbox = imageftbbox($fsize, 0, $font, $word);
$x = ($w - ($textbox[2] - $textbox[0])) / 2;
$y = ($h - ($textbox[7] - $textbox[1])) / 2;

// Edit: check not over 100
if($x > 50){ $x = 50;}
if($y > 100){ $y = 100;}

imagefttext($img, $fsize, 0, $x, $y, $text_color, $font, $word);

Debugging with a die() proves this is the case:

die("img=".$img ." fsize=".$fsize. " x=".$x ." y=".$y . " h=".$h );
img=Resource id #159 fsize=24 x=1073741923.5 y=41 h=50

回答1:

According to the link provided, it may not be a Zend Framework bug, but something with imageftbbox. I would suggest extending Zend_Captcha_Image and copying the _generateImage function and setting $x = to something reasonable ( I saw 45 on the forum post ) when it is too big ( perhaps > 100 ). This allows you to put in the suggested fix / hack without changing the actual Zend Framework code.

回答2:

Are you running php 5.3.2 on Debian/Ubuntu by chance? There was a imageftbbox bug in PHP (not Zend) that causes it to return anomalous values on occasion.

I think it had to do with compiling a certain GD version using a 32-bit gcc. I saw this a large number of times with captcha images. The easy fix is to upgrade PHP to the latest version, or I think it was fixed in the next version of PHP.