# HG changeset patch
# User Roman Arutyunyan <arut@nginx.com>
# Date 1599658529 -10800
# Node ID eece8e35e64d6ca0006c890c071d6d92ed40934e
# Parent  702f1d2581a497d5d82e0e4eec37f81bd5619585
QUIC: allowed old DCID for initial packets until first ACK.

If a packet sent in response to an initial client packet was lost, then
successive client initial packets were dropped by nginx with the unexpected
dcid message logged.  This was because the new DCID generated by the server was
not available to the client.

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
@@ -1991,21 +1991,34 @@ ngx_quic_early_input(ngx_connection_t *c
 static ngx_int_t
 ngx_quic_check_peer(ngx_quic_connection_t *qc, ngx_quic_header_t *pkt)
 {
-    ngx_str_t             *dcid;
     ngx_queue_t           *q;
+    ngx_quic_send_ctx_t   *ctx;
     ngx_quic_client_id_t  *cid;
 
-    dcid = ngx_quic_pkt_zrtt(pkt->flags) ? &qc->odcid : &qc->dcid;
-
-    if (pkt->dcid.len != dcid->len) {
-        ngx_log_error(NGX_LOG_INFO, pkt->log, 0, "quic unexpected quic dcidl");
-        return NGX_ERROR;
-    }
-
-    if (ngx_memcmp(pkt->dcid.data, dcid->data, dcid->len) != 0) {
-        ngx_log_error(NGX_LOG_INFO, pkt->log, 0, "quic unexpected quic dcid");
-        return NGX_ERROR;
-    }
+    ctx = ngx_quic_get_send_ctx(qc, ssl_encryption_initial);
+
+    if (ngx_quic_pkt_zrtt(pkt->flags)
+        || (ngx_quic_pkt_in(pkt->flags) && ctx->largest_ack == (uint64_t) -1))
+    {
+        if (pkt->dcid.len == qc->odcid.len
+            && ngx_memcmp(pkt->dcid.data, qc->odcid.data, qc->odcid.len) == 0)
+        {
+            goto found;
+        }
+    }
+
+    if (!ngx_quic_pkt_zrtt(pkt->flags)) {
+        if (pkt->dcid.len == qc->dcid.len
+            && ngx_memcmp(pkt->dcid.data, qc->dcid.data, qc->dcid.len) == 0)
+        {
+            goto found;
+        }
+    }
+
+    ngx_log_error(NGX_LOG_INFO, pkt->log, 0, "quic unexpected quic dcid");
+    return NGX_ERROR;
+
+found:
 
     for (q = ngx_queue_head(&qc->client_ids);
          q != ngx_queue_sentinel(&qc->client_ids);