not-modified-field-based.php

<?php

/**
 * Not Modified field based
 * Warning: if you change the file and the field
 * `updatedAt` don't change, your users won't see the change
 * (except those who don't have a cache)
 */

$result = [
  'title'     => 'Hello world',
  'content'   => 'lorem lorem lorem lorem',
  'updatedAt' => 1510235856 // = time()
];

$lastModifiedTime = $result['updatedAt'];

// Generate etag from the last modified date.
$etag = 'W/"' . md5($lastModifiedTime) . '"';
// Generate gmd date
$gmdate = gmdate('D, d M Y H:i:s', $lastModifiedTime);

// Set headers (for response)
header('Last-Modified: ' . $gmdate . " GMT");
// If you want to fix a maximum lifetime
header('Cache-Control: public, max-age=604800');
header("Etag: $etag");

/**
 * Check request headers
 */

$ifModifiedSince = $_SERVER['HTTP_IF_MODIFIED_SINCE'] ?? null;
$ifNoneMatch = $_SERVER['HTTP_IF_NONE_MATCH'] ?? null;

if (
  ($ifModifiedSince !== null && strtotime($ifModifiedSince) === $lastModifiedTime) ||
  ($ifNoneMatch !== null && $etag === trim($ifNoneMatch))
  ) {
    // Okay browser, use your version from the cache.
    header('HTTP/1.1 304 Not Modified');
    exit();
}

sleep(2);
header("Content-type: application/json; charset=UTF-8");
echo json_encode($result);

not-modified-file-based.php

<?php

/**
 * Not Modified file based
 * If the php file change, the cache is invalided.
 */

// Current file
$file = __FILE__;
$lastModifiedTime = filemtime($file);

// Generate etag from the last modified date.
$etag = 'W/"' . md5($lastModifiedTime) . '"';

// Generate gmd date
$gmdate = gmdate('D, d M Y H:i:s', $lastModifiedTime);

// Set headers (for response)
header('Last-Modified: ' . $gmdate . " GMT");
// If you want to fix a maximum lifetime
header('Cache-Control: public, max-age=604800');
header("Etag: $etag");

/**
 * Check request headers
 */

$ifModifiedSince = $_SERVER['HTTP_IF_MODIFIED_SINCE'] ?? null;
$ifNoneMatch = $_SERVER['HTTP_IF_NONE_MATCH'] ?? null;

if (
  ($ifModifiedSince !== null && strtotime($ifModifiedSince) === $lastModifiedTime) ||
  ($ifNoneMatch !== null && $etag === trim($ifNoneMatch))
  ) {
    // Okay browser, use your version from the cache.
    header('HTTP/1.1 304 Not Modified');
    exit();
}

// Fake long response...
sleep(2);
echo "<h1>Hello world </h1>";