# HG changeset patch
# User Vladimir Homutov <vl@nginx.com>
# Date 1592297645 -10800
# Node ID 9fe7875ce4bb083865c6f2a6de27c451f35cf94d
# Parent  5bc9229ec4cfa5fa3555c68dd48b4091e6a0b81e
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.

diff --git a/src/event/ngx_event_quic.c b/src/event/ngx_event_quic.c
--- a/src/event/ngx_event_quic.c
+++ b/src/event/ngx_event_quic.c
@@ -157,6 +157,7 @@ static ngx_int_t ngx_quic_new_token(ngx_
 static ngx_int_t ngx_quic_validate_token(ngx_connection_t *c,
     ngx_quic_header_t *pkt);
 static ngx_int_t ngx_quic_init_connection(ngx_connection_t *c);
+static ngx_inline size_t ngx_quic_max_udp_payload(ngx_connection_t *c);
 static void ngx_quic_input_handler(ngx_event_t *rev);
 
 static void ngx_quic_close_connection(ngx_connection_t *c, ngx_int_t rc);
@@ -439,8 +440,8 @@ ngx_quic_add_handshake_data(ngx_ssl_conn
             return 0;
         }
 
-        if (qc->ctp.max_udp_payload_size > NGX_QUIC_MAX_UDP_PAYLOAD_OUT) {
-            qc->ctp.max_udp_payload_size = NGX_QUIC_MAX_UDP_PAYLOAD_OUT;
+        if (qc->ctp.max_udp_payload_size > ngx_quic_max_udp_payload(c)) {
+            qc->ctp.max_udp_payload_size = ngx_quic_max_udp_payload(c);
             ngx_log_debug0(NGX_LOG_DEBUG_EVENT, c->log, 0,
                           "quic client maximum packet size truncated");
         }
@@ -655,7 +656,7 @@ ngx_quic_new_connection(ngx_connection_t
     qc->streams.handler = handler;
 
     ctp = &qc->ctp;
-    ctp->max_udp_payload_size = NGX_QUIC_MAX_UDP_PAYLOAD_OUT;
+    ctp->max_udp_payload_size = ngx_quic_max_udp_payload(c);
     ctp->ack_delay_exponent = NGX_QUIC_DEFAULT_ACK_DELAY_EXPONENT;
     ctp->max_ack_delay = NGX_QUIC_DEFAULT_MAX_ACK_DELAY;
 
@@ -1122,6 +1123,21 @@ ngx_quic_init_connection(ngx_connection_
 }
 
 
+static ngx_inline size_t
+ngx_quic_max_udp_payload(ngx_connection_t *c)
+{
+    /* TODO: path MTU discovery */
+
+#if (NGX_HAVE_INET6)
+    if (c->sockaddr->sa_family == AF_INET6) {
+        return NGX_QUIC_MAX_UDP_PAYLOAD_OUT6;
+    }
+#endif
+
+    return NGX_QUIC_MAX_UDP_PAYLOAD_OUT;
+}
+
+
 static void
 ngx_quic_input_handler(ngx_event_t *rev)
 {
diff --git a/src/event/ngx_event_quic.h b/src/event/ngx_event_quic.h
--- 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