QUIC: further limiting maximum QUIC packet size. quic-transport draft 29, section 14: QUIC depends upon a minimum IP packet size of at least 1280 bytes. This is the IPv6 minimum size [RFC8200] and is also supported by most modern IPv4 networks. Assuming the minimum IP header size, this results in a QUIC maximum packet size of 1232 bytes for IPv6 and 1252 bytes for IPv4. Since the packet size can change during connection lifetime, the ngx_quic_max_udp_payload() function is introduced that currently returns minimal allowed size, depending on address family.

--- a/src/event/ngx_event_quic.h
+++ b/src/event/ngx_event_quic.h
@@ -23,7 +23,8 @@
     /* 1 flags + 4 version + 2 x (1 + 20) s/dcid + 4 pn + 4 len + token len */
 
 #define NGX_QUIC_MAX_UDP_PAYLOAD_SIZE        65527
-#define NGX_QUIC_MAX_UDP_PAYLOAD_OUT         1300  /* TODO */
+#define NGX_QUIC_MAX_UDP_PAYLOAD_OUT         1252
+#define NGX_QUIC_MAX_UDP_PAYLOAD_OUT6        1232
 
 #define NGX_QUIC_DEFAULT_ACK_DELAY_EXPONENT  3
 #define NGX_QUIC_DEFAULT_MAX_ACK_DELAY       25