[core] Returning 304 http code when returning cached data (#793)

index.php

@@ -195,6 +195,7 @@ try {
 		try {
 			$bridge->setCache($cache);
 			$bridge->setCacheTimeout($cache_timeout);
+			$bridge->dieIfNotModified();
 			$bridge->setDatas($params);
 		} catch(Error $e) {
 			http_response_code($e->getCode());
@@ -211,6 +212,7 @@ try {
 			$format = Format::create($format);
 			$format->setItems($bridge->getItems());
 			$format->setExtraInfos($bridge->getExtraInfos());
+			$format->setLastModified($bridge->getCacheTime());
 			$format->display();
 		} catch(Error $e) {
 			http_response_code($e->getCode());

lib/BridgeAbstract.php

@@ -292,4 +292,27 @@ abstract class BridgeAbstract implements BridgeInterface {
 	public function getCacheTimeout(){
 		return isset($this->cacheTimeout) ? $this->cacheTimeout : static::CACHE_TIMEOUT;
 	}
+
+	public function getCacheTime(){
+		return !is_null($this->cache) ? $this->cache->getTime() : false;
+	}
+
+	public function dieIfNotModified(){
+		if ((defined('DEBUG') && DEBUG === true)) return; // disabled in debug mode
+
+		$if_modified_since = isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : false;
+		if (!$if_modified_since) return; // If-Modified-Since value is required
+
+		$last_modified = $this->getCacheTime();
+		if (!$last_modified) return; // did not detect cache time
+
+		if (time() - $this->getCacheTimeout() > $last_modified) return; // cache timeout
+
+		$last_modified = (gmdate('D, d M Y H:i:s ', $last_modified) . 'GMT');
+
+		if ($if_modified_since == $last_modified) {
+			header('HTTP/1.1 304 Not Modified');
+			die();
+		}
+	}
 }

lib/FormatAbstract.php

@@ -7,6 +7,7 @@ abstract class FormatAbstract implements FormatInterface {
 		$contentType,
 		$charset,
 		$items,
+		$lastModified,
 		$extraInfos;
 
 	public function setCharset($charset){
@@ -27,11 +28,18 @@ abstract class FormatAbstract implements FormatInterface {
 		return $this;
 	}
 
+	public function setLastModified($lastModified){
+		$this->lastModified = $lastModified;
+	}
+
 	protected function callContentType(){
 		header('Content-Type: ' . $this->contentType);
 	}
 
 	public function display(){
+		if ($this->lastModified) {
+			header('Last-Modified: ' . gmdate('D, d M Y H:i:s ', $this->lastModified) . 'GMT');
+		}
 		echo $this->stringify();
 
 		return $this;