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// 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.
//go:build go1.21
package quic
import (
// A sentPacket tracks state related to an in-flight packet we sent,
// to be committed when the peer acks it or resent if the packet is lost.
type sentPacket struct {
num packetNumber
size int // size in bytes
time time.Time // time sent
ackEliciting bool //
inFlight bool //
acked bool // ack has been received
lost bool // packet is presumed lost
// Frames sent in the packet.
// This is an abbreviated version of the packet payload, containing only the information
// we need to process an ack for or loss of this packet.
// For example, a CRYPTO frame is recorded as the frame type (0x06), offset, and length,
// but does not include the sent data.
// This buffer is written by packetWriter.append* and read by Conn.handleAckOrLoss.
b []byte
n int // read offset into b
var sentPool = sync.Pool{
New: func() any {
return &sentPacket{}
func newSentPacket() *sentPacket {
sent := sentPool.Get().(*sentPacket)
return sent
// recycle returns a sentPacket to the pool.
func (sent *sentPacket) recycle() {
func (sent *sentPacket) reset() {
*sent = sentPacket{
b: sent.b[:0],
// The append* methods record information about frames in the packet.
func (sent *sentPacket) appendNonAckElicitingFrame(frameType byte) {
sent.b = append(sent.b, frameType)
func (sent *sentPacket) appendAckElicitingFrame(frameType byte) {
sent.ackEliciting = true
sent.inFlight = true
sent.b = append(sent.b, frameType)
func (sent *sentPacket) appendInt(v uint64) {
sent.b = appendVarint(sent.b, v)
func (sent *sentPacket) appendOffAndSize(start int64, size int) {
sent.b = appendVarint(sent.b, uint64(start))
sent.b = appendVarint(sent.b, uint64(size))
// The next* methods read back information about frames in the packet.
func (sent *sentPacket) next() (frameType byte) {
f := sent.b[sent.n]
return f
func (sent *sentPacket) nextInt() uint64 {
v, n := consumeVarint(sent.b[sent.n:])
sent.n += n
return v
func (sent *sentPacket) nextRange() (start, end int64) {
start = int64(sent.nextInt())
end = start + int64(sent.nextInt())
return start, end
func (sent *sentPacket) done() bool {
return sent.n == len(sent.b)