QUIC: disabled datagram fragmentation.

As per RFC 9000, Section 14:

  UDP datagrams MUST NOT be fragmented at the IP layer.

auto/unix

@@ -448,6 +448,54 @@ ngx_feature_test="setsockopt(0, IPPROTO_IPV6, IPV6_RECVPKTINFO, NULL, 0)"
 . auto/feature
 
 
+# IP packet fragmentation
+
+ngx_feature="IP_MTU_DISCOVER"
+ngx_feature_name="NGX_HAVE_IP_MTU_DISCOVER"
+ngx_feature_run=no
+ngx_feature_incs="#include <sys/socket.h>
+                  #include <netinet/in.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="(void) IP_PMTUDISC_DO;
+                  setsockopt(0, IPPROTO_IP, IP_MTU_DISCOVER, NULL, 0)"
+. auto/feature
+
+
+ngx_feature="IPV6_MTU_DISCOVER"
+ngx_feature_name="NGX_HAVE_IPV6_MTU_DISCOVER"
+ngx_feature_run=no
+ngx_feature_incs="#include <sys/socket.h>
+                  #include <netinet/in.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="(void) IPV6_PMTUDISC_DO;
+                  setsockopt(0, IPPROTO_IPV6, IPV6_MTU_DISCOVER, NULL, 0)"
+. auto/feature
+
+
+ngx_feature="IP_DONTFRAG"
+ngx_feature_name="NGX_HAVE_IP_DONTFRAG"
+ngx_feature_run=no
+ngx_feature_incs="#include <sys/socket.h>
+                  #include <netinet/in.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="setsockopt(0, IPPROTO_IP, IP_DONTFRAG, NULL, 0)"
+. auto/feature
+
+
+ngx_feature="IPV6_DONTFRAG"
+ngx_feature_name="NGX_HAVE_IPV6_DONTFRAG"
+ngx_feature_run=no
+ngx_feature_incs="#include <sys/socket.h>
+                  #include <netinet/in.h>"
+ngx_feature_path=
+ngx_feature_libs=
+ngx_feature_test="setsockopt(0, IPPROTO_IP, IPV6_DONTFRAG, NULL, 0)"
+. auto/feature
+
+
 ngx_feature="TCP_DEFER_ACCEPT"
 ngx_feature_name="NGX_HAVE_DEFERRED_ACCEPT"
 ngx_feature_run=no

src/core/ngx_connection.c

@@ -1009,6 +1009,78 @@ ngx_configure_listening_sockets(ngx_cycle_t *cycle)
             }
         }
 
+#endif
+
+#if (NGX_HAVE_IP_MTU_DISCOVER)
+
+        if (ls[i].quic && ls[i].sockaddr->sa_family == AF_INET) {
+            value = IP_PMTUDISC_DO;
+
+            if (setsockopt(ls[i].fd, IPPROTO_IP, IP_MTU_DISCOVER,
+                           (const void *) &value, sizeof(int))
+                == -1)
+            {
+                ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_socket_errno,
+                              "setsockopt(IP_MTU_DISCOVER) "
+                              "for %V failed, ignored",
+                              &ls[i].addr_text);
+            }
+        }
+
+#elif (NGX_HAVE_IP_DONTFRAG)
+
+        if (ls[i].quic && ls[i].sockaddr->sa_family == AF_INET) {
+            value = 1;
+
+            if (setsockopt(ls[i].fd, IPPROTO_IP, IP_DONTFRAG,
+                           (const void *) &value, sizeof(int))
+                == -1)
+            {
+                ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_socket_errno,
+                              "setsockopt(IP_DONTFRAG) "
+                              "for %V failed, ignored",
+                              &ls[i].addr_text);
+            }
+        }
+
+#endif
+
+#if (NGX_HAVE_INET6)
+
+#if (NGX_HAVE_IPV6_MTU_DISCOVER)
+
+        if (ls[i].quic && ls[i].sockaddr->sa_family == AF_INET6) {
+            value = IPV6_PMTUDISC_DO;
+
+            if (setsockopt(ls[i].fd, IPPROTO_IPV6, IPV6_MTU_DISCOVER,
+                           (const void *) &value, sizeof(int))
+                == -1)
+            {
+                ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_socket_errno,
+                              "setsockopt(IPV6_MTU_DISCOVER) "
+                              "for %V failed, ignored",
+                              &ls[i].addr_text);
+            }
+        }
+
+#elif (NGX_HAVE_IP_DONTFRAG)
+
+        if (ls[i].quic && ls[i].sockaddr->sa_family == AF_INET6) {
+            value = 1;
+
+            if (setsockopt(ls[i].fd, IPPROTO_IPV6, IPV6_DONTFRAG,
+                           (const void *) &value, sizeof(int))
+                == -1)
+            {
+                ngx_log_error(NGX_LOG_ALERT, cycle->log, ngx_socket_errno,
+                              "setsockopt(IPV6_DONTFRAG) "
+                              "for %V failed, ignored",
+                              &ls[i].addr_text);
+            }
+        }
+
+#endif
+
 #endif
     }