1 files changed, 71 insertions, 0 deletions
diff --git a/src/vendor/golang.org/x/net/quic/rtt.go b/src/vendor/golang.org/x/net/quic/rtt.go
new file mode 100644
index 0000000000..0dc9bf5bf2
--- /dev/null
+++ b/src/vendor/golang.org/x/net/quic/rtt.go
@@ -0,0 +1,71 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package quic
+
+import (
+	"time"
+)
+
+type rttState struct {
+	minRTT          time.Duration
+	latestRTT       time.Duration
+	smoothedRTT     time.Duration
+	rttvar          time.Duration // RTT variation
+	firstSampleTime time.Time     // time of first RTT sample
+}
+
+func (r *rttState) init() {
+	r.minRTT = -1 // -1 indicates the first sample has not been taken yet
+
+	// "[...] the initial RTT SHOULD be set to 333 milliseconds."
+	// https://www.rfc-editor.org/rfc/rfc9002.html#section-6.2.2-1
+	const initialRTT = 333 * time.Millisecond
+
+	// https://www.rfc-editor.org/rfc/rfc9002.html#section-5.3-12
+	r.smoothedRTT = initialRTT
+	r.rttvar = initialRTT / 2
+}
+
+func (r *rttState) establishPersistentCongestion() {
+	// "Endpoints SHOULD set the min_rtt to the newest RTT sample
+	// after persistent congestion is established."
+	// https://www.rfc-editor.org/rfc/rfc9002#section-5.2-5
+	r.minRTT = r.latestRTT
+}
+
+// updateSample is called when we generate a new RTT sample.
+// https://www.rfc-editor.org/rfc/rfc9002.html#section-5
+func (r *rttState) updateSample(now time.Time, handshakeConfirmed bool, spaceID numberSpace, latestRTT, ackDelay, maxAckDelay time.Duration) {
+	r.latestRTT = latestRTT
+
+	if r.minRTT < 0 {
+		// First RTT sample.
+		// "min_rtt MUST be set to the latest_rtt on the first RTT sample."
+		// https://www.rfc-editor.org/rfc/rfc9002.html#section-5.2-2
+		r.minRTT = latestRTT
+		// https://www.rfc-editor.org/rfc/rfc9002.html#section-5.3-14
+		r.smoothedRTT = latestRTT
+		r.rttvar = latestRTT / 2
+		r.firstSampleTime = now
+		return
+	}
+
+	// "min_rtt MUST be set to the lesser of min_rtt and latest_rtt [...]
+	// on all other samples."
+	// https://www.rfc-editor.org/rfc/rfc9002.html#section-5.2-2
+	r.minRTT = min(r.minRTT, latestRTT)
+
+	// https://www.rfc-editor.org/rfc/rfc9002.html#section-5.3-16
+	if handshakeConfirmed {
+		ackDelay = min(ackDelay, maxAckDelay)
+	}
+	adjustedRTT := latestRTT - ackDelay
+	if adjustedRTT < r.minRTT {
+		adjustedRTT = latestRTT
+	}
+	rttvarSample := abs(r.smoothedRTT - adjustedRTT)
+	r.rttvar = (3*r.rttvar + rttvarSample) / 4
+	r.smoothedRTT = ((7 * r.smoothedRTT) + adjustedRTT) / 8
+}