快速远程PHP技术检测图像404

Question

What PHP script technique runs the fastest in detecting if a remote image does not exist before I include the image? I mean, I don't want to download all the bytes of the remote image -- just enough to detect if it exists.

And while on the subject but with just a slight deviation, I'd like to download just enough bytes to determine a JPEG's width and height information.

Speed is very important in my concern here on this system design I'm working on.

Answer 1

I've modified the @Volomike's code to get width too. Here you go...

function get_image_dim($sURL) {
  // note that for jpeg you may need to change 300 to a larger value,
  // as some height/width info is farther out in the header
  try {
    $hSock = @ fopen($sURL, 'rb');
    if ($hSock) {
      while(!feof($hSock)) {
        $vData = fread($hSock, 300);
        break;
      }
      fclose($hSock);
      if (strpos(' ' . $vData, 'JFIF')>0) {
        $vData = substr($vData, 0, 300);
        $asResult = unpack('H*',$vData);        
        $sBytes = $asResult[1];
        $width = 0;
        $height = 0;
        $hex_width = '';
        $hex_height = '';
        if (strstr($sBytes, 'ffc2')) {
          $hex_height = substr($sBytes, strpos($sBytes, 'ffc2') + 10, 4);
          $hex_width = substr($sBytes, strpos($sBytes, 'ffc2') + 14, 4);
        } else {
          $hex_height = substr($sBytes, strpos($sBytes, 'ffc0') + 10, 4);
          $hex_width = substr($sBytes, strpos($sBytes, 'ffc0') + 14, 4);
        }
        $width = hexdec($hex_width);
        $height = hexdec($hex_height);
        return array('width' => $width, 'height' => $height);
      } elseif (strpos(' ' . $vData, 'GIF')>0) {
        $vData = substr($vData, 0, 300);
        $asResult = unpack('h*',$vData);
        $sBytes = $asResult[1];
        $sBytesH = substr($sBytes, 16, 4);
        $height = hexdec(strrev($sBytesH));
        $sBytesW = substr($sBytes, 12, 4);
        $width = hexdec(strrev($sBytesW));
        return array('width' => $width, 'height' => $height);
      } elseif (strpos(' ' . $vData, 'PNG')>0) {
        $vDataH = substr($vData, 22, 4);
        $asResult = unpack('n',$vDataH);
        $height = $asResult[1];        
        $vDataW = substr($vData, 18, 4);
        $asResult = unpack('n',$vDataW);
        $width = $asResult[1];        
        return array('width' => $width, 'height' => $height);
      }
    }
  } catch (Exception $e) {}
  return FALSE;
}

So, using it we have...

// jpeg
$url = 'http://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Quality_comparison_jpg_vs_saveforweb.jpg/250px-Quality_comparison_jpg_vs_saveforweb.jpg';
// png
//$url = 'http://upload.wikimedia.org/wikipedia/commons/thumb/4/47/PNG_transparency_demonstration_1.png/280px-PNG_transparency_demonstration_1.png';
// gif
//$url = 'http://upload.wikimedia.org/wikipedia/commons/e/e2/Sunflower_as_gif_small.gif';

$dim = get_image_dim($url);
print_r($dim);