[PATCH 3 of 4] QUIC: fixed congesion control in GSO mode

[Roman Arutyunyan]

# HG changeset patch
# User Roman Arutyunyan <arut at nginx.com>
# Date 1690450542 -14400
#      Thu Jul 27 13:35:42 2023 +0400
# Node ID d8a6ec55938e9a4f1a84c825d9c6abe13aa8b791
# Parent  0d12ada84c168c62e9bae847af2725641da583d0
QUIC: fixed congesion control in GSO mode.

In non-GSO mode, a datagram is sent if congestion window is not exceeded by the
time of send.  The window could be exceeded by a small amount after the send.
In GSO mode, congestion window was checked in a similar way, but for all
concatenated datagrams as a whole.  This could result in exceeding congestion
window by a lot.  Now congestion window is checked for every datagram in GSO
mode as well.

diff --git a/src/event/quic/ngx_event_quic_output.c b/src/event/quic/ngx_event_quic_output.c
--- a/src/event/quic/ngx_event_quic_output.c
+++ b/src/event/quic/ngx_event_quic_output.c
@@ -358,7 +358,7 @@ ngx_quic_create_segments(ngx_connection_
 
         len = ngx_min(segsize, (size_t) (end - p));
 
-        if (len && cg->in_flight < cg->window) {
+        if (len && cg->in_flight + (p - dst) < cg->window) {
 
             n = ngx_quic_output_packet(c, ctx, p, len, len);
             if (n == NGX_ERROR) {