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Negotiate cache_expiration_time (#26)
* Add support for HTTP cache headers - `Cache-Control: max-age` minus `Age`, extendable by `$simplepie_cache_duration` - `Cache-Control: must-revalidate` will prevent `$simplepie_cache_duration` from extending past the `max-age` - `Cache-Control: no-cache` will return the current time - `Cache-Control: no-store` will return `0` - `Expires` but only if `Cache-Control: max-age` is absent * Refined logic * More doc * Add support for `s-maxage` * Typos * Pragmatism? * Typos * Remove support of s-maxage Seems to only make sense for CDNs * Move order of headers * Remove superfluous comments * Remove wrong comment * Workaround for buggy servers returning wrong cache-control headers for 304 responses * fix logic for 304 workaround * Fix whitespace * Minor simplification
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,79 @@ | ||
| <?php | ||
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| declare(strict_types=1); | ||
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| namespace SimplePie\HTTP; | ||
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| /** | ||
| * HTTP util functions | ||
| * FreshRSS | ||
| * @internal | ||
| */ | ||
| final class Utils | ||
| { | ||
| /** | ||
| * Extracts `max-age` from the `Cache-Control` HTTP headers | ||
| * | ||
| * @param array<string,mixed> $http_headers HTTP headers of the response | ||
| * @return int|null The `max-age` value or `null` if not found | ||
| * | ||
| * FreshRSS | ||
| */ | ||
| public static function get_http_max_age(array $http_headers): ?int | ||
| { | ||
| $cache_control = $http_headers['cache-control'] ?? null; | ||
| if (is_string($cache_control) && preg_match('/\bmax-age=(\d+)\b/', $cache_control, $matches)) { | ||
| return (int) $matches[1]; | ||
| } | ||
| return null; | ||
| } | ||
|
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| /** | ||
| * Negotiate the cache expiration time based on the HTTP response headers. | ||
| * Return the cache duration time in number of seconds since the Unix Epoch, accounting for: | ||
| * - `Cache-Control: max-age` minus `Age`, bounded by `$cache_duration_min` and `$cache_duration_max` | ||
| * - `Cache-Control: must-revalidate` will set `$cache_duration` to `$cache_duration_min` | ||
| * - `Cache-Control: no-cache` will return `time() + $cache_duration_min` | ||
| * - `Cache-Control: no-store` will return `time() + $cache_duration_min - 3` | ||
| * - `Expires` like `Cache-Control: max-age` but only if it is absent | ||
| * | ||
| * @param array<string,mixed> $http_headers HTTP headers of the response | ||
| * @param int $cache_duration Desired cache duration in seconds, potentially overridden by HTTP response headers | ||
| * @param int $cache_duration_min Minimal cache duration (in seconds), overriding HTTP response headers `Cache-Control` and `Expires`, | ||
| * @param int $cache_duration_max Maximal cache duration (in seconds), overriding HTTP response headers `Cache-Control: max-age` and `Expires`, | ||
| * @return int The negotiated cache expiration time in seconds since the Unix Epoch | ||
| * | ||
| * FreshRSS | ||
| */ | ||
| public static function negociate_cache_expiration_time(array $http_headers, int $cache_duration, int $cache_duration_min, int $cache_duration_max): int | ||
| { | ||
| $cache_control = $http_headers['cache-control'] ?? ''; | ||
| if ($cache_control !== '') { | ||
| if (preg_match('/\bno-store\b/', $cache_control)) { | ||
| return time() + $cache_duration_min - 3; // -3 to distinguish from no-cache if needed | ||
| } | ||
| if (preg_match('/\bno-cache\b/', $cache_control)) { | ||
| return time() + $cache_duration_min; | ||
| } | ||
| if (preg_match('/\bmust-revalidate\b/', $cache_control)) { | ||
| $cache_duration = $cache_duration_min; | ||
| } | ||
| if (preg_match('/\bmax-age=(\d+)\b/', $cache_control, $matches)) { | ||
| $max_age = (int) $matches[1]; | ||
| $age = $http_headers['age'] ?? ''; | ||
| if (is_numeric($age)) { | ||
| $max_age -= (int) $age; | ||
| } | ||
| return time() + min(max($max_age, $cache_duration), $cache_duration_max); | ||
| } | ||
| } | ||
| $expires = $http_headers['expires'] ?? ''; | ||
| if ($expires !== '') { | ||
| $expire_date = \SimplePie\Misc::parse_date($expires); | ||
| if ($expire_date !== false) { | ||
| return min(max($expire_date, time() + $cache_duration), time() + $cache_duration_max); | ||
| } | ||
| } | ||
| return time() + $cache_duration; | ||
| } | ||
| } |
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