ApiController::actionRead PHP Method

    public function actionRead($resource_type, $id)
    {
        $ref = $this->getRef($resource_type, $id);
        $vid = $ref->getVersionId();
        // http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26
        $etagMatch = null;
        $modified = null;
        if (isset($_SERVER['HTTP_IF_NONE_MATCH'])) {
            $etagMatch = false;
            foreach (str_getcsv($_SERVER['HTTP_IF_NONE_MATCH']) as $tag) {
                if ($tag == $vid || $tag == '*') {
                    $etagMatch = true;
                    break;
                }
            }
        }
        if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {
            $since = strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']);
            if ($since === false) {
                $this->sendError("Failed to parse If-Modified-Since header: {$_SERVER['HTTP_IF_MODIFIED_SINCE']}");
            }
            $modified = $ref->getLastModified() > $since;
        }
        if ($etagMatch === null && $modified === false || $etagMatch === true && $modified !== true) {
            $this->sendResponse(304);
        }
        header('Content-Location: ' . $this->createAbsoluteUrl('api/') . '/' . Yii::app()->service->referenceToFhirUrl($ref) . "/_history/{$vid}");
        header("ETag: \"{$vid}\"");
        $this->sendResource($ref->resolve());
    }