use the same ACK frame struct in the send path, remove ACK frame pool (#3831)

internal/ackhandler/received_packet_tracker.go

@@ -169,16 +169,18 @@ func (h *receivedPacketTracker) GetAckFrame(onlyIfQueued bool) *wire.AckFrame {
 		}
 	}
 
-	ack := wire.GetAckFrame()
+	// This function always returns the same ACK frame struct, filled with the most recent values.
+	ack := h.lastAck
+	if ack == nil {
+		ack = &wire.AckFrame{}
+	}
+	ack.Reset()
 	ack.DelayTime = utils.Max(0, now.Sub(h.largestObservedReceivedTime))
 	ack.ECT0 = h.ect0
 	ack.ECT1 = h.ect1
 	ack.ECNCE = h.ecnce
 	ack.AckRanges = h.packetHistory.AppendAckRanges(ack.AckRanges)
 
-	if h.lastAck != nil {
-		wire.PutAckFrame(h.lastAck)
-	}
 	h.lastAck = ack
 	h.ackAlarm = time.Time{}
 	h.ackQueued = false

internal/wire/ack_frame_pool.go

@@ -1,24 +0,0 @@
-package wire
-
-import "sync"
-
-var ackFramePool = sync.Pool{New: func() any {
-	return &AckFrame{}
-}}
-
-func GetAckFrame() *AckFrame {
-	f := ackFramePool.Get().(*AckFrame)
-	f.AckRanges = f.AckRanges[:0]
-	f.ECNCE = 0
-	f.ECT0 = 0
-	f.ECT1 = 0
-	f.DelayTime = 0
-	return f
-}
-
-func PutAckFrame(f *AckFrame) {
-	if cap(f.AckRanges) > 4 {
-		return
-	}
-	ackFramePool.Put(f)
-}

internal/wire/ack_frame_pool_test.go

@@ -1,29 +0,0 @@
-package wire
-
-import (
-	"math/rand"
-	"time"
-
-	. "github.com/onsi/ginkgo/v2"
-	. "github.com/onsi/gomega"
-)
-
-var _ = Describe("ACK Frame (for IETF QUIC)", func() {
-	It("gets an ACK frame from the pool", func() {
-		for i := 0; i < 100; i++ {
-			ack := GetAckFrame()
-			Expect(ack.AckRanges).To(BeEmpty())
-			Expect(ack.ECNCE).To(BeZero())
-			Expect(ack.ECT0).To(BeZero())
-			Expect(ack.ECT1).To(BeZero())
-			Expect(ack.DelayTime).To(BeZero())
-
-			ack.AckRanges = make([]AckRange, rand.Intn(10))
-			ack.ECNCE = 1
-			ack.ECT0 = 2
-			ack.ECT1 = 3
-			ack.DelayTime = time.Hour
-			PutAckFrame(ack)
-		}
-	})
-})