Add Network::checkEtagModified method

diff --git a/src/Util/Network.php b/src/Util/Network.php
index 6c7fd731cbf711f096efab0990edcf88d5bf9329..6b73369d32a72dba3187741dcc0c97869aa0da8f 100644 (file)
--- a/src/Util/Network.php
+++ b/src/Util/Network.php
@@ -910,4 +910,46 @@ class Network
 
                return self::unparseURL($parsed);
        }
+
+       /**
+        * Generates ETag and Last-Modified response headers and checks them against
+        * If-None-Match and If-Modified-Since request headers if present.
+        *
+        * Blocking function, sends 304 headers and exits if check passes.
+        *
+        * @param string $etag          The page etag
+        * @param string $last_modified The page last modification UTC date
+        * @throws \Exception
+        */
+       public static function checkEtagModified(string $etag, string $last_modified)
+       {
+               $last_modified = DateTimeFormat::utc($last_modified, 'D, d M Y H:i:s') . ' GMT';
+
+               /**
+                * @see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26
+                */
+               $if_none_match     = filter_input(INPUT_SERVER, 'HTTP_IF_NONE_MATCH');
+               $if_modified_since = filter_input(INPUT_SERVER, 'HTTP_IF_MODIFIED_SINCE');
+               $flag_not_modified = null;
+               if ($if_none_match) {
+                       $result = [];
+                       preg_match('/^(?:W\/")?([^"]+)"?$/i', $etag, $result);
+                       $etagTrimmed = $result[1];
+                       // Lazy exact ETag match, could check weak/strong ETags
+                       $flag_not_modified = $if_none_match == '*' || strpos($if_none_match, $etagTrimmed) !== false;
+               }
+
+               if ($if_modified_since && (!$if_none_match || $flag_not_modified)) {
+                       // Lazy exact Last-Modified match, could check If-Modified-Since validity
+                       $flag_not_modified = $if_modified_since == $last_modified;
+               }
+
+               header('Etag: ' . $etag);
+               header('Last-Modified: ' . $last_modified);
+
+               if ($flag_not_modified) {
+                       header("HTTP/1.1 304 Not Modified");
+                       exit;
+               }
+       }
 }