How header() outputs image cache usage example-PHP Tutorial-php.cn

When we generate theverification code, we need to directly input the image, usually using header("Content-type: image/jpeg"); to achieve this. Here is a brief introduction.

In many developments, we try to use header("Content-type: image/jpeg"); to output pictures, and try to use some phpimage processingtechnology to allow the output Pictures are more intelligent and dynamic. But we often encounter new problems. Unless you specify different URL structures and use server technology to cache images, it is very likely that these output images will consume a lot of traffic. How to cache them and call the cache the next time the user visits? (The premise is that you want this image to remain unchanged)

// put this above any php image generation code: session_start(); header("Cache-Control: private, max-age=10800, pre-check=10800"); header("Pragma: private"); header("Expires: " . date(DATE_RFC822,strtotime(" 2 day")));

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Add the above code above header("Content-type: image/jpeg");, which will specify the cache time of the current page (two days) and use this cache time node on the next visit.
Next, determine whether there is already a cache. If so, use the cache.

Situation 1: If the browser already caches the current page, then use it directly.

// the browser will send a $_SERVER['HTTP_IF_MODIFIED_SINCE'] if it has a cached copy if(isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])){ // if the browser has a cached version of this image, send 304 header('Last-Modified: '.$_SERVER['HTTP_IF_MODIFIED_SINCE'],true,304); exit; }

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Scenario 2: The browser caches the current page. Although we have updated some image information, the source image itself has not changed, and we want to use the previous cache, so we also use the cache.

$img = "some_image.png"; if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && (strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == filemtime($img))) { // send the last mod time of the file back header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($img)).' GMT',true, 304); exit; }

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Of course, there are some special situations that we must consider, but the above code can basically lead our thinking. By the way, remember to put them all above header("Content-type: image/jpeg").
Let’s take a look at an example

高，则宽=目标宽, 高=目标宽的比例 * 原高 *4、如：高>宽，则高=目标高，宽=目标高的比例 * 原宽 **/ $image = "test.jpg"; $max_width = 200; $max_height = 200; $size = getimagesize($image); //得到图像的大小 $width = $size[0]; $height = $size[1]; $x_ratio = $max_width / $width; $y_ratio = $max_height / $height; if (($width <= $max_width) && ($height <= $max_height)) { $tn_width = $width; $tn_height = $height; } elseif (($x_ratio * $height) < $max_height) { $tn_height = ceil($x_ratio * $height); $tn_width = $max_width; } else { $tn_width = ceil($y_ratio * $width); $tn_height = $max_height; } $src = imagecreatefromjpeg($image); $dst = imagecreatetruecolor($tn_width, $tn_height); //新建一个真彩色图像 imagecopyresampled($dst, $src, 0, 0, 0, 0,$tn_width, $tn_height, $width, $height); //重采样拷贝部分图像并调整大小 header('Content-Type: image/jpeg'); imagejpeg($dst,null,100); imagedestroy($src); imagedestroy($dst); ?>

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