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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
// A sentPacketList is a ring buffer of sentPackets.
//
// Processing an ack for a packet causes all older packets past a small threshold
// to be discarded (RFC 9002, Section 6.1.1), so the list of in-flight packets is
// not sparse and will contain at most a few acked/lost packets we no longer
// care about.
type sentPacketList struct {
nextNum packetNumber // next packet number to add to the buffer
off int // offset of first packet in the buffer
size int // number of packets
p []*sentPacket
}
// start is the first packet in the list.
func (s *sentPacketList) start() packetNumber {
return s.nextNum - packetNumber(s.size)
}
// end is one after the last packet in the list.
// If the list is empty, start == end.
func (s *sentPacketList) end() packetNumber {
return s.nextNum
}
// discard clears the list.
func (s *sentPacketList) discard() {
*s = sentPacketList{}
}
// add appends a packet to the list.
func (s *sentPacketList) add(sent *sentPacket) {
if s.nextNum != sent.num {
panic("inserting out-of-order packet")
}
s.nextNum++
if s.size >= len(s.p) {
s.grow()
}
i := (s.off + s.size) % len(s.p)
s.size++
s.p[i] = sent
}
// nth returns a packet by index.
func (s *sentPacketList) nth(n int) *sentPacket {
index := (s.off + n) % len(s.p)
return s.p[index]
}
// num returns a packet by number.
// It returns nil if the packet is not in the list.
func (s *sentPacketList) num(num packetNumber) *sentPacket {
i := int(num - s.start())
if i < 0 || i >= s.size {
return nil
}
return s.nth(i)
}
// clean removes all acked or lost packets from the head of the list.
func (s *sentPacketList) clean() {
for s.size > 0 {
sent := s.p[s.off]
if !sent.acked && !sent.lost {
return
}
sent.recycle()
s.p[s.off] = nil
s.off = (s.off + 1) % len(s.p)
s.size--
}
s.off = 0
}
// grow increases the buffer to hold more packaets.
func (s *sentPacketList) grow() {
newSize := len(s.p) * 2
if newSize == 0 {
newSize = 64
}
p := make([]*sentPacket, newSize)
for i := 0; i < s.size; i++ {
p[i] = s.nth(i)
}
s.p = p
s.off = 0
}
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