在PHP脚本中处理If-modified-since标头 [英] Handling If-modified-since header in a PHP-script
问题描述
我有一个PHP脚本，该脚本使用?img = 参数调用.
I have a PHP script which is called with an ?img= parameter.
该参数的值是图像的(加编码的)URL.
The value for that parameter is an (urlencoded) URL of an image.
我的脚本检查该图像是否已经存储在我的服务器上.
My script checks, if that image is already stored at my server.
如果不是，则将其下载.之后，它可以选择调整图像的大小并将其发送到STDOUT，即返回到请求的浏览器，并带有 Content-Type 和 Last-modified 标头:
If not - it downloads it. After that it optionally resizes the image and sends it to STDOUT, i.e. back to the requesting browser, prepended with Content-Type and Last-modified headers:
Connection:close
Content-Type:image/jpeg
Date:Fri, 01 Jun 2012 08:28:30 GMT
Last-Modified:Fri, 01 Jun 2012 08:02:44 GMT
Server:Apache/2.2.15 (CentOS)
Transfer-Encoding:chunked
X-Powered-By:PHP/5.3.3
这是解决一些跨域问题所必需的，并且自一年以来对我来说很有效:
This is needed to workaround some crossdomain issues and works well for me since over a year:
不过，我想添加一些功能来处理传入的 If-Modified-since 标头-发送 Not Modified 304 响应.
However I'd like to add functionality to handle the incoming If-Modified-since header - to send a Not Modified 304 response.
我的问题是:
1)在Apache中运行时，在PHP中甚至可以实现吗?
1) Is that even possible in PHP, when run in Apache?
2)如何在此处最好地处理(即解析和产生)PHP中的日期?
2) How to handle (i.e. parse and produce) the dates best in PHP here?
奖金问题)如何为调整大小后的图像添加 Content-Length 标头?
Bonus question) How to add a Content-Length header for the resized images?
下面是我的代码(我省略了CURL下载部分):
My code is below (I've omitted the CURL-downloading part):
<?php
define('CACHE_DIR', '/var/www/cached_avatars/');
$img = urldecode($_GET['img']);
$cached = CACHE_DIR . md5($img);
# omitted downloading part for brevity
$readfh = fopen($cached, 'rb');
if ($readfh) {
flock($readfh, LOCK_SH);
$size = getimagesize($cached);
$w = $size[0];
$h = $size[1];
$type = $size[2];
$mime = $size['mime'];
# find the downscale factor to fit image into $maxw x $maxh
$scale = max($w / $maxw, $h / $maxh);
header('Content-Type: ' . $size['mime']);
header('Last-Modified: ' . gmdate('D, d M Y H:i:s T', filemtime($cached)));
$length = filesize($cached);
$buf = fread($readfh, $length);
fclose($readfh);
# the image is smaller than $maxw x $maxh, do not scale up
if ($scale <= 1) {
header('Content-Length: ' . $length);
print($buf);
return;
}
$tw = $w / $scale;
$th = $h / $scale;
$image = imagecreatefromstring($buf);
$thumb = imagecreatetruecolor($tw, $th);
imagecopyresampled($thumb, $image, 0, 0, 0, 0, $tw, $th, $w, $h);
imagedestroy($image);
# How to add Content-Length here, after image resizing?
if (IMAGETYPE_JPEG == $type)
imagejpeg($thumb, null, 75);
else if (IMAGETYPE_PNG == $type)
imagepng($thumb, null, 9);
else if (IMAGETYPE_GIF == $type)
imagegif($thumb, null);
imagedestroy($thumb);
}
?>
推荐答案
在PHP中这绝对是可能的！
This is definitely possible in PHP!
当浏览器检查是否有修改时，它将发送If-Modified-Since标头；在PHP中，此值将在$_SERVER['HTTP_IF_MODIFIED_SINCE']中设置.
When the browser checks if there were modifications, it sends an If-Modified-Since header; in PHP this value would be set inside $_SERVER['HTTP_IF_MODIFIED_SINCE'].
要解码日期/时间值(我相信使用rfc822进行编码)，您可以使用strtotime()，因此:
To decode the date/time value (encoded using rfc822 I believe), you can just use strtotime(), so:
if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) &&
strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= filemtime($localFileName))
{
header('HTTP/1.0 304 Not Modified');
exit;
}
说明:如果If-Modified-Since标头是由浏览器发送的，并且日期/时间至少是您正在提供的文件的修改日期，则编写"304 Not Modified"标头并停止.
Explanation: if the If-Modified-Since header is sent by the browser AND the date/time is at least the modified date of the file you're serving, you write the "304 Not Modified" header and stop.
否则，脚本会照常继续.
Otherwise, the script continues as per normal.
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