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package sequencer
import (
"errors"
"time"
"github.com/osm/quake/packet/command"
)
var ErrRateLimit = errors.New("rate limit reached")
type State byte
const (
Disconnected State = 0
Handshake State = 1
Connecting State = 2
Connected State = 3
)
type Sequencer struct {
ping int16
lastWrite time.Time
state State
incomingSeq uint32
incomingAck uint32
lastReliableSeq uint32
outgoingSeq uint32
isIncomingAckReliable bool
isOutgoingSeqReliable bool
isIncomingSeqReliable bool
outgoingCommands []command.Command
outgoingCommandsBuf []command.Command
}
func New(opts ...Option) *Sequencer {
s := Sequencer{
ping: 999,
}
for _, opt := range opts {
opt(&s)
}
return &s
}
func (s *Sequencer) SetState(state State) { s.state = state }
func (s *Sequencer) GetState() State { return s.state }
func (s *Sequencer) SetPing(ping int16) { s.ping = ping }
func (s *Sequencer) GetPing() int16 { return s.ping }
func (s *Sequencer) Reset() {
s.incomingSeq = 0
s.incomingAck = 0
s.lastReliableSeq = 0
s.outgoingSeq = 0
s.isIncomingAckReliable = false
s.isOutgoingSeqReliable = false
s.isIncomingSeqReliable = false
s.outgoingCommands = []command.Command{}
s.outgoingCommandsBuf = []command.Command{}
}
func (s *Sequencer) Process(
incomingSeq, incomingAck uint32,
cmds []command.Command,
) (uint32, uint32, []command.Command, error) {
s.incoming(incomingSeq, incomingAck)
return s.outgoing(cmds)
}
func (s *Sequencer) incoming(incomingSeq, incomingAck uint32) {
isIncomingSeqReliable := incomingSeq>>31 == 1
isIncomingAckReliable := incomingAck>>31 == 1
incomingSeq = incomingSeq & 0x7fffffff
incomingAck = incomingAck & 0x7fffffff
if incomingSeq < s.incomingSeq {
return
}
if isIncomingAckReliable == s.isOutgoingSeqReliable {
s.outgoingCommandsBuf = []command.Command{}
}
if isIncomingSeqReliable {
s.isIncomingSeqReliable = !s.isIncomingSeqReliable
}
s.incomingSeq = incomingSeq
s.incomingAck = incomingAck
s.isIncomingAckReliable = isIncomingAckReliable
}
func (s *Sequencer) outgoing(cmds []command.Command) (uint32, uint32, []command.Command, error) {
s.outgoingCommands = append(s.outgoingCommands, cmds...)
if s.state == Connected && time.Since(s.lastWrite).Milliseconds() < int64(s.ping) {
return 0, 0, nil, ErrRateLimit
}
var isReliable bool
if s.incomingAck > s.lastReliableSeq &&
s.isIncomingAckReliable != s.isOutgoingSeqReliable {
isReliable = true
}
if len(s.outgoingCommandsBuf) == 0 && len(s.outgoingCommands) > 0 {
s.outgoingCommandsBuf = s.outgoingCommands
s.isOutgoingSeqReliable = !s.isOutgoingSeqReliable
isReliable = true
s.outgoingCommands = []command.Command{}
}
outgoingSeq := s.outgoingSeq
if isReliable {
outgoingSeq = s.outgoingSeq | (1 << 31)
}
outgoingAck := s.incomingSeq
if s.isIncomingSeqReliable {
outgoingAck = s.incomingSeq | (1 << 31)
}
outgoingCmds := []command.Command{}
s.outgoingSeq++
if isReliable {
outgoingCmds = append(outgoingCmds, s.outgoingCommandsBuf...)
s.lastReliableSeq = s.outgoingSeq
}
s.lastWrite = time.Now()
return outgoingSeq, outgoingAck, outgoingCmds, nil
}
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