From 5a5e6c6d3a98ae8a2d181170a73a49f7c63b8324 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Wed, 25 Dec 2024 17:30:47 +0300
Subject: [PATCH] add simple rtt estimator

Signed-off-by: Roman Khimov <roman@nspcc.ru>
---
 context.go |  4 ++++
 dbft.go    |  5 +++++
 rtt.go     | 26 ++++++++++++++++++++++++++
 send.go    |  2 ++
 4 files changed, 37 insertions(+)
 create mode 100644 rtt.go

diff --git a/context.go b/context.go
index 1ad088da..84139c20 100644
--- a/context.go
+++ b/context.go
@@ -91,6 +91,9 @@ type Context[H Hash] struct {
 	lastBlockTime      time.Time // Wall clock time of when the last block was first seen (used for timer adjustments).
 	lastBlockIndex     uint32
 	lastBlockView      byte
+
+	prepareSentTime time.Time
+	rttEstimates    rtt
 }
 
 // N returns total number of validators.
@@ -236,6 +239,7 @@ func (c *Context[H]) PreBlock() PreBlock[H] {
 
 func (c *Context[H]) reset(view byte, ts uint64) {
 	c.MyIndex = -1
+	c.prepareSentTime = time.Time{}
 	c.lastBlockTimestamp = ts
 
 	if view == 0 {
diff --git a/dbft.go b/dbft.go
index 9a1b0748..126954a2 100644
--- a/dbft.go
+++ b/dbft.go
@@ -153,6 +153,7 @@ func (d *DBFT[H]) initializeConsensus(view byte, ts uint64) {
 		var ts = d.Timer.Now()
 		var diff = ts.Sub(d.lastBlockTime)
 		timeout -= diff
+		timeout -= d.rttEstimates.avg / 2
 		timeout = max(0, timeout)
 	}
 	d.changeTimer(timeout)
@@ -482,6 +483,10 @@ func (d *DBFT[H]) onPrepareResponse(msg ConsensusPayload[H]) {
 		}
 	}
 
+	if d.IsPrimary() && !d.prepareSentTime.IsZero() && !d.recovering {
+		d.rttEstimates.addTime(time.Since(d.prepareSentTime))
+	}
+
 	d.extendTimer(2)
 
 	if !d.Context.WatchOnly() && !d.CommitSent() && (!d.isAntiMEVExtensionEnabled() || !d.PreCommitSent()) && d.RequestSentOrReceived() {
diff --git a/rtt.go b/rtt.go
new file mode 100644
index 00000000..ae5a06e1
--- /dev/null
+++ b/rtt.go
@@ -0,0 +1,26 @@
+package dbft
+
+import (
+	"time"
+)
+
+const rttLength = 7 * 10
+
+type rtt struct {
+	times [rttLength]time.Duration
+	idx   int
+	avg   time.Duration
+}
+
+func (r *rtt) addTime(new time.Duration) {
+	var old = r.times[r.idx]
+
+	if old != 0 {
+		new = min(new, 2*old) // Too long delays should be normalized, we don't want to overshoot.
+	}
+
+	r.avg = r.avg + (new-old)/time.Duration(len(r.times))
+	r.avg = max(0, r.avg) // Can't be less than zero.
+	r.times[r.idx] = new
+	r.idx = (r.idx + 1) % len(r.times)
+}
diff --git a/send.go b/send.go
index cc9c5082..70c12e4c 100644
--- a/send.go
+++ b/send.go
@@ -27,6 +27,8 @@ func (d *DBFT[H]) sendPrepareRequest() {
 	d.PreparationPayloads[d.MyIndex] = msg
 	d.broadcast(msg)
 
+	d.prepareSentTime = d.Timer.Now()
+
 	delay := d.SecondsPerBlock << (d.ViewNumber + 1)
 	if d.ViewNumber == 0 {
 		delay -= d.SecondsPerBlock