1 files changed, 83 insertions, 0 deletions
diff --git a/ssl/quic/quic_statm.c b/ssl/quic/quic_statm.c
new file mode 100644
index 0000000000..35f5722735
--- /dev/null
+++ b/ssl/quic/quic_statm.c
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2022 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include "internal/quic_statm.h"
+
+void ossl_statm_update_rtt(OSSL_STATM *statm,
+                           OSSL_TIME ack_delay,
+                           OSSL_TIME override_latest_rtt)
+{
+    OSSL_TIME adjusted_rtt, latest_rtt = override_latest_rtt;
+
+    /* Use provided RTT value, or else last RTT value. */
+    if (ossl_time_is_zero(latest_rtt))
+        latest_rtt = statm->latest_rtt;
+    else
+        statm->latest_rtt = latest_rtt;
+
+    if (!statm->have_first_sample) {
+        statm->min_rtt              = latest_rtt;
+        statm->smoothed_rtt         = latest_rtt;
+        statm->rtt_variance         = ossl_time_divide(latest_rtt, 2);
+        statm->have_first_sample    = 1;
+        return;
+    }
+
+    /* Update minimum RTT. */
+    if (ossl_time_compare(latest_rtt, statm->min_rtt) < 0)
+        statm->min_rtt = latest_rtt;
+
+    /*
+     * Enforcement of max_ack_delay is the responsibility of
+     * the caller as it is context-dependent.
+     */
+
+    adjusted_rtt = latest_rtt;
+    if (ossl_time_compare(latest_rtt, ossl_time_add(statm->min_rtt, ack_delay)) >= 0)
+        adjusted_rtt = ossl_time_subtract(latest_rtt, ack_delay);
+
+    statm->rtt_variance = ossl_time_divide(ossl_time_add(ossl_time_multiply(3, statm->rtt_variance),
+                                                         ossl_time_abs_difference(statm->smoothed_rtt,
+                                                                              adjusted_rtt)), 4);
+    statm->smoothed_rtt = ossl_time_divide(ossl_time_add(ossl_time_multiply(7, statm->smoothed_rtt),
+                                                         adjusted_rtt), 8);
+}
+
+/* RFC 9002 kInitialRtt value. RFC recommended value. */
+#define K_INITIAL_RTT               (ossl_time_multiply(OSSL_TIME_MS, 333))
+
+int ossl_statm_init(OSSL_STATM *statm)
+{
+    statm->smoothed_rtt             = K_INITIAL_RTT;
+    statm->latest_rtt               = OSSL_TIME_ZERO;
+    statm->min_rtt                  = OSSL_TIME_INFINITY;
+    statm->rtt_variance             = ossl_time_divide(K_INITIAL_RTT, 2);
+    statm->have_first_sample        = 0;
+    statm->max_ack_delay            = OSSL_TIME_INFINITY;
+    return 1;
+}
+
+void ossl_statm_destroy(OSSL_STATM *statm)
+{
+    /* No-op. */
+}
+
+void ossl_statm_set_max_ack_delay(OSSL_STATM *statm, OSSL_TIME max_ack_delay)
+{
+    statm->max_ack_delay = max_ack_delay;
+}
+
+void ossl_statm_get_rtt_info(OSSL_STATM *statm, OSSL_RTT_INFO *rtt_info)
+{
+    rtt_info->min_rtt           = statm->min_rtt;
+    rtt_info->latest_rtt        = statm->latest_rtt;
+    rtt_info->smoothed_rtt      = statm->smoothed_rtt;
+    rtt_info->rtt_variance      = statm->rtt_variance;
+    rtt_info->max_ack_delay     = statm->max_ack_delay;
+}