在 php 脚本上缓存图像

Question

我正在使用这里找到的这个很棒的随机发生器代码：http://alistapart.com/article/randomizer，但图像不会保存在浏览器的缓存中，这意味着它们会在网站重新加载时刷新。

是否可以将图像缓存在以下代码中？ 我使用这个脚本的原因是 css 上的 php 解析由于某种原因在我的服务器上不起作用。

<?php

$folder = '.';
$extList = array();
    $extList['gif'] = 'image/gif';
    $extList['jpg'] = 'image/jpeg';
    $extList['jpeg'] = 'image/jpeg';
    $extList['png'] = 'image/png';

$img = null;

if (substr($folder,-1) != '/') {
    $folder = $folder.'/';
}

if (isset($_GET['img'])) {
    $imageInfo = pathinfo($_GET['img']);
    if (
        isset( $extList[ strtolower( $imageInfo['extension'] ) ] ) &&
        file_exists( $folder.$imageInfo['basename'] )
    ) {
        $img = $folder.$imageInfo['basename'];
    }
} else {
    $fileList = array();
    $handle = opendir($folder);
    while ( false !== ( $file = readdir($handle) ) ) {
        $file_info = pathinfo($file);
        if (
            isset( $extList[ strtolower( $file_info['extension'] ) ] )
        ) {
            $fileList[] = $file;
        }
    }
    closedir($handle);

    if (count($fileList) > 0) {
        $imageNumber = time() % count($fileList);
        $img = $folder.$fileList[$imageNumber];
    }
}

if ($img!=null) {
    $imageInfo = pathinfo($img);
    $contentType = 'Content-type: '.$extList[ $imageInfo['extension'] ];
    header ($contentType);
    readfile($img);
} else {
    if ( function_exists('imagecreate') ) {
        header ("Content-type: image/png");
        $im = @imagecreate (100, 100)
            or die ("Cannot initialize new GD image stream");
        $background_color = imagecolorallocate ($im, 255, 255, 255);
        $text_color = imagecolorallocate ($im, 0,0,0);
        imagestring ($im, 2, 5, 5,  "IMAGE ERROR", $text_color);
        imagepng ($im);
        imagedestroy($im);
    }
}

?>

Answer 1

您可以通过在标题中指定缓存持续时间来指示用户的浏览器将您的页面缓存很长时间（最长一年，如下所示）：

header('Cache-Control: max-age=31556926');

但是，对此有两个警告。首先，浏览器不一定会遵循缓存指令，并且可能会选择下载图像的新副本。其次，这一行必须放在页面上的某处在任何内容之前。

Answer 2

生成E-tag 和Cache-Control 标头会帮助您喜欢这个

<?php
  $folder   = '.';
  $extList  = array( "gif", "jpg", "jpeg", "png" );
  $image    = false;

  if ( substr( $folder, -1 ) != '/' ) {
    $folder = $folder.'/';
  }

  if ( isset( $_GET["img"] ) ) {
    $imageExtn  = strtolower( pathinfo( $_GET["img"], PATHINFO_EXTENSION ) );
    $imageName  = basename( $_GET["img"] );
    if ( in_array( $imageExtn, $extList ) && file_exists( $folder.$imageName ) ) {
      $image  = $folder.$imageName;
    }
  }
  else {
    $fileList = array();
    $handle   = opendir( $folder );
    while( false !== ( $file = readdir( $handle ) ) ) {
      $fileExtn = strtolower( pathinfo( $file, PATHINFO_EXTENSION ) );
      if ( in_array( $fileExtn, $extList ) ) {
        $fileList[] = $file;
      }
    }
    closedir( $handle );

    if ( !empty( $fileList ) ) {
      $imageNumber  = time() % count( $fileList );
      $image  = $folder.$fileList[$imageNumber];
    }
  }

  if ( $image !== false ) {
    $contents = implode( "", file( $image ) );
    $md5  = md5( $contents );
    $mtime  = filemtime( $image );
    $etag = etag( $md5, $mtime );

    $r_mtime  = 0;
    $r_etag   = null;

    if ( isset( $_SERVER["HTTP_IF_MODIFIED_SINCE"] ) ) {
      $r_mtime  = strtotime( $_SERVER["HTTP_IF_MODIFIED_SINCE"] );
    }
    if ( isset( $_SERVER["HTTP_IF_NONE_MATCH"] ) ) {
      $r_etag   = trim( $_SERVER["HTTP_IF_NONE_MATCH"] );
    }

    if ( $mtime == $r_mtime && $r_etag == $etag ) {
      header( "HTTP/1.0 304 Not Modified", true, 304 );
      header( "HTTP/1.1 304 Not Modified", true, 304 );
      header( "Content-length: 0" );
      exit;
    }

    header( "Content-type: image/".strtolower( pathinfo( $image, PATHINFO_EXTENSION ) ) );
    header( "Last-Modified: ".gmdate( "D, d M Y H:i:s", $mtime )." GMT" );
    header( "ETag: ".$etag );
    header( "Expires: ".gmdate( "D, d M Y H:i:s", time()+3600 )." GMT" );
    header( "Cache-Control: max-age=3600" );
    header( "Cache-Control: public" );

    echo $contents;
    exit();
  }
  else {
    if ( function_exists( "imagecreate" ) ) {
      header( "Content-type: image/png" );
      $im = @imagecreate( 100, 100 ) or die( "Cannot initialize new GD image stream" );
      $background_color = imagecolorallocate( $im, 255, 255, 255 );
      $text_color = imagecolorallocate( $im, 0, 0, 0 );
      imagestring( $im, 2, 5, 5,  "IMAGE ERROR", $text_color );
      imagepng( $im );
      imagedestroy( $im );
    }
  }

  function etag( $string_1 = null, $string_2 = null, $quote = true ) {
    $quote  = ( $quote ) ? '"' : '';
    $etag   = sprintf( $quote."%s-%s".$quote, $string_1, $string_2 );
    return $etag;
  }
?>

Answer 3

一种解决方案是使用 cookie 来存储您发送给用户的图像，并始终发送该图像：

if(!isset($_COOKIE['imgCookie']))
{
    //runs if the user doesn't have the cookie
    //run randomizer code
    //setcookie('imgCookie',$imageNumber);
} else {
    //runs if the user already has the cookie
    $imagenumber=$_COOKIE['imgCookie'];
}
//run code for sending image to user