std::string HttpRequest::VALID_REQUEST_HEADERS = ",accept,accept-charset,accept-encoding,accept-language,accept-datetime,access-control-request-headers,access-control-request-method,authorization,cache-control,connection,cookie,content-length,content-md5,content-type,date,expect,from,host,if-match,if-modified-since,if-none-match,if-range,if-unmodified-since,max-forwards,origin,pragma,proxy-authorization,range,referer,te,upgrade,user-agent,via,warning,transfer-encoding,sec-websocket-key,sec-websocket-version,sec-websocket-accept,sec-websocket-protocol,sec-websocket-extensions,alt-used,http2-settings,";
