fix(1902): correct the skb len

Fix #1902

When we contruct frames for HTTP/2 response and
reuse the same skbs from the backend (HTTP/1), we forget to adjust
the skb size according to the trailer headers (if exist) size, then it
comes with extra partial HTTP/1 response to the client. Then, the client
will send a `GOAWAY` to temepesta due to wrong frame size, and tempesta
sends back the `TCP RESET`.

fw/http.h

@@ -301,7 +301,8 @@ typedef struct {
 	TfwConn		*conn;						\
 	void (*destructor)(void *msg);					\
 	TfwStr		crlf;						\
-	TfwStr		body;
+	TfwStr		body;						\
+	int		trailers_len;
 
 
 static inline void

fw/http_msg.c

@@ -565,6 +565,11 @@ tfw_http_msg_hdr_close(TfwHttpMsg *hm)
 	/* Close just parsed header. */
 	parser->hdr.flags |= TFW_STR_COMPLETE;
 
+	/* Cumulate the trailer headers length */
+	if (parser->hdr.flags & TFW_STR_TRAILER)
+		hm->trailers_len += parser->hdr.len +
+			tfw_str_eolen(&parser->hdr);
+
 	/*
 	 * We make this frang check here, because it is the earliest
 	 * place where we can determine that new added header is violating
@@ -1050,7 +1055,8 @@ tfw_http_msg_cutoff_body_chunks(TfwHttpResp *resp)
 	int r;
 
 	r = ss_skb_cutoff_data(resp->body.skb, &resp->cut, 0,
-			       tfw_str_eolen(&resp->body));
+			       tfw_str_eolen(&resp->body) +
+			       ((TfwHttpMsg*)resp)->trailers_len);
 	if (unlikely(r))
 		return r;