php静态文件回到304-PHP Tutorial-php.cn

php静态文件回到304

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Release： 2016-06-13 12:10:54

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php静态文件返回304

有时一些静态文件（如图片）会由php输出，会发现请求都是200，静态文件每次都去服务器上请求太浪费资源了，这时如何让浏览器缓存图片呢？就需要我们在php中输出304了。

我们可以利用php中的 HTTP_IF_MODIFIED_SINCE 结合etag来干这事。Etag没有明确规定的格式，我们可以用文件修改时间的md5值，代码如下:

<span style="color: #0000ff;">private</span> <span style="color: #0000ff;">function</span> _addEtag(<span style="color: #800080;">$file</span><span style="color: #000000;">) {    </span><span style="color: #800080;">$last_modified_time</span> = <span style="color: #008080;">filemtime</span>(<span style="color: #800080;">$file</span><span style="color: #000000;">);     </span><span style="color: #800080;">$etag</span> = <span style="color: #008080;">md5_file</span>(<span style="color: #800080;">$file</span><span style="color: #000000;">);    </span><span style="color: #008000;">//</span><span style="color: #008000;"> always send headers </span>    <span style="color: #008080;">header</span>("Last-Modified: ".<span style="color: #008080;">gmdate</span>("D, d M Y H:i:s", <span style="color: #800080;">$last_modified_time</span>)." GMT"<span style="color: #000000;">);     </span><span style="color: #008080;">header</span>("Etag: <span style="color: #800080;">$etag</span>"<span style="color: #000000;">);     </span><span style="color: #008000;">//</span><span style="color: #008000;"> exit if not modified</span>    <span style="color: #0000ff;">if</span> (@<span style="color: #008080;">strtotime</span>(<span style="color: #800080;">$_SERVER</span>['HTTP_IF_MODIFIED_SINCE']) == <span style="color: #800080;">$last_modified_time</span> ||<span style="color: #000000;">     @</span><span style="color: #008080;">trim</span>(<span style="color: #800080;">$_SERVER</span>['HTTP_IF_NONE_MATCH']) == <span style="color: #800080;">$etag</span><span style="color: #000000;">) {         </span><span style="color: #008080;">header</span>("HTTP/1.1 304 Not Modified"<span style="color: #000000;">);         </span><span style="color: #0000ff;">exit</span><span style="color: #000000;">;     }}</span>

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在代码中可以在静态文件（如图片）输出之前调用即可。