当前位置：首页 > PHP

php 实现协商缓存

2026-02-16 03:18:45PHP

协商缓存实现原理

协商缓存通过服务器与浏览器之间的HTTP头交互实现，主要依赖Last-Modified/If-Modified-Since和ETag/If-None-Match两组头部。当资源未变化时返回304状态码，减少数据传输。

基于Last-Modified的实现

$filePath = 'path/to/resource.txt';
$lastModified = filemtime($filePath);
$ifModifiedSince = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? 
    strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) : 0;

header("Last-Modified: " . gmdate("D, d M Y H:i:s", $lastModified) . " GMT");

if ($lastModified <= $ifModifiedSince) {
    header("HTTP/1.1 304 Not Modified");
    exit;
}

header("Content-Type: text/plain");
readfile($filePath);

基于ETag的实现

$filePath = 'path/to/resource.txt';
$fileContent = file_get_contents($filePath);
$eTag = md5($fileContent);
$ifNoneMatch = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? 
    trim($_SERVER['HTTP_IF_NONE_MATCH']) : '';

header("ETag: $eTag");

if ($ifNoneMatch === $eTag) {
    header("HTTP/1.1 304 Not Modified");
    exit;
}

header("Content-Type: text/plain");
echo $fileContent;

组合使用两种策略

$filePath = 'path/to/resource.txt';
$lastModified = filemtime($filePath);
$fileContent = file_get_contents($filePath);
$eTag = md5($fileContent);

$ifModifiedSince = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? 
    strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) : 0;
$ifNoneMatch = isset($_SERVER['HTTP_IF_NONE_MATCH']) ? 
    trim($_SERVER['HTTP_IF_NONE_MATCH']) : '';

header("Last-Modified: " . gmdate("D, d M Y H:i:s", $lastModified) . " GMT");
header("ETag: $eTag");

if (($lastModified <= $ifModifiedSince) || ($ifNoneMatch === $eTag)) {
    header("HTTP/1.1 304 Not Modified");
    exit;
}

header("Content-Type: text/plain");
echo $fileContent;