From 1ec873f917cbbfd27b9dfc633f26d93dc02d70c9 Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Thu, 19 Apr 2018 17:36:12 +0900
Subject: [PATCH] use binary search to check if an ACK acks a packet

---
 internal/wire/ack_frame.go      | 15 +++++++--------
 internal/wire/ack_frame_test.go |  2 ++
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/internal/wire/ack_frame.go b/internal/wire/ack_frame.go
index d1ee229b..61fdfb70 100644
--- a/internal/wire/ack_frame.go
+++ b/internal/wire/ack_frame.go
@@ -3,6 +3,7 @@ package wire
 import (
 	"bytes"
 	"errors"
+	"sort"
 	"time"
 
 	"github.com/lucas-clemente/quic-go/internal/protocol"
@@ -202,17 +203,15 @@ func (f *AckFrame) LowestAcked() protocol.PacketNumber {
 
 // AcksPacket determines if this ACK frame acks a certain packet number
 func (f *AckFrame) AcksPacket(p protocol.PacketNumber) bool {
-	if p < f.LowestAcked() || p > f.LargestAcked() { // this is just a performance optimization
+	if p < f.LowestAcked() || p > f.LargestAcked() {
 		return false
 	}
 
-	// TODO: this could be implemented as a binary search
-	for _, ackRange := range f.AckRanges {
-		if p >= ackRange.Smallest && p <= ackRange.Largest {
-			return true
-		}
-	}
-	return false
+	i := sort.Search(len(f.AckRanges), func(i int) bool {
+		return p >= f.AckRanges[i].Smallest
+	})
+	// i will always be < len(f.AckRanges), since we checked above that p is not bigger than the largest acked
+	return p <= f.AckRanges[i].Largest
 }
 
 func encodeAckDelay(delay time.Duration) uint64 {
diff --git a/internal/wire/ack_frame_test.go b/internal/wire/ack_frame_test.go
index f8a052d4..9e29c8db 100644
--- a/internal/wire/ack_frame_test.go
+++ b/internal/wire/ack_frame_test.go
@@ -314,12 +314,14 @@ var _ = Describe("ACK Frame (for IETF QUIC)", func() {
 			}
 			Expect(f.AcksPacket(4)).To(BeFalse())
 			Expect(f.AcksPacket(5)).To(BeTrue())
+			Expect(f.AcksPacket(6)).To(BeTrue())
 			Expect(f.AcksPacket(7)).To(BeTrue())
 			Expect(f.AcksPacket(8)).To(BeTrue())
 			Expect(f.AcksPacket(9)).To(BeFalse())
 			Expect(f.AcksPacket(14)).To(BeFalse())
 			Expect(f.AcksPacket(15)).To(BeTrue())
 			Expect(f.AcksPacket(18)).To(BeTrue())
+			Expect(f.AcksPacket(19)).To(BeTrue())
 			Expect(f.AcksPacket(20)).To(BeTrue())
 			Expect(f.AcksPacket(21)).To(BeFalse())
 		})