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package quic
import (
"crypto/rand"
"net"
"slices"
"time"
"github.com/quic-go/quic-go/internal/ackhandler"
"github.com/quic-go/quic-go/internal/protocol"
"github.com/quic-go/quic-go/internal/utils"
"github.com/quic-go/quic-go/internal/wire"
)
type pathID int64
const invalidPathID pathID = -1
// Maximum number of paths to keep track of.
// If the peer probes another path (before the pathTimeout of an existing path expires),
// this probing attempt is ignored.
const maxPaths = 3
// If no packet is received for a path for pathTimeout,
// the path can be evicted when the peer probes another path.
// This prevents an attacker from churning through paths by duplicating packets and
// sending them with spoofed source addresses.
const pathTimeout = 5 * time.Second
type path struct {
id pathID
addr net.Addr
lastPacketTime time.Time
pathChallenge [8]byte
validated bool
rcvdNonProbing bool
}
type pathManager struct {
nextPathID pathID
// ordered by lastPacketTime, with the most recently used path at the end
paths []*path
getConnID func(pathID) (_ protocol.ConnectionID, ok bool)
retireConnID func(pathID)
logger utils.Logger
}
func newPathManager(
getConnID func(pathID) (_ protocol.ConnectionID, ok bool),
retireConnID func(pathID),
logger utils.Logger,
) *pathManager {
return &pathManager{
paths: make([]*path, 0, maxPaths+1),
getConnID: getConnID,
retireConnID: retireConnID,
logger: logger,
}
}
// Returns a path challenge frame if one should be sent.
// May return nil.
func (pm *pathManager) HandlePacket(
remoteAddr net.Addr,
t time.Time,
pathChallenge *wire.PathChallengeFrame, // may be nil if the packet didn't contain a PATH_CHALLENGE
isNonProbing bool,
) (_ protocol.ConnectionID, _ []ackhandler.Frame, shouldSwitch bool) {
var p *path
for i, path := range pm.paths {
if addrsEqual(path.addr, remoteAddr) {
p = path
p.lastPacketTime = t
// already sent a PATH_CHALLENGE for this path
if isNonProbing {
path.rcvdNonProbing = true
}
if pm.logger.Debug() {
pm.logger.Debugf("received packet for path %s that was already probed, validated: %t", remoteAddr, path.validated)
}
shouldSwitch = path.validated && path.rcvdNonProbing
if i != len(pm.paths)-1 {
// move the path to the end of the list
pm.paths = slices.Delete(pm.paths, i, i+1)
pm.paths = append(pm.paths, p)
}
if pathChallenge == nil {
return protocol.ConnectionID{}, nil, shouldSwitch
}
}
}
if len(pm.paths) >= maxPaths {
if pm.paths[0].lastPacketTime.Add(pathTimeout).After(t) {
if pm.logger.Debug() {
pm.logger.Debugf("received packet for previously unseen path %s, but already have %d paths", remoteAddr, len(pm.paths))
}
return protocol.ConnectionID{}, nil, shouldSwitch
}
// evict the oldest path, if the last packet was received more than pathTimeout ago
pm.retireConnID(pm.paths[0].id)
pm.paths = pm.paths[1:]
}
var pathID pathID
if p != nil {
pathID = p.id
} else {
pathID = pm.nextPathID
}
// previously unseen path, initiate path validation by sending a PATH_CHALLENGE
connID, ok := pm.getConnID(pathID)
if !ok {
pm.logger.Debugf("skipping validation of new path %s since no connection ID is available", remoteAddr)
return protocol.ConnectionID{}, nil, shouldSwitch
}
frames := make([]ackhandler.Frame, 0, 2)
if p == nil {
var pathChallengeData [8]byte
rand.Read(pathChallengeData[:])
p = &path{
id: pm.nextPathID,
addr: remoteAddr,
lastPacketTime: t,
rcvdNonProbing: isNonProbing,
pathChallenge: pathChallengeData,
}
pm.nextPathID++
pm.paths = append(pm.paths, p)
frames = append(frames, ackhandler.Frame{
Frame: &wire.PathChallengeFrame{Data: p.pathChallenge},
Handler: (*pathManagerAckHandler)(pm),
})
pm.logger.Debugf("enqueueing PATH_CHALLENGE for new path %s", remoteAddr)
}
if pathChallenge != nil {
frames = append(frames, ackhandler.Frame{
Frame: &wire.PathResponseFrame{Data: pathChallenge.Data},
Handler: (*pathManagerAckHandler)(pm),
})
}
return connID, frames, shouldSwitch
}
func (pm *pathManager) HandlePathResponseFrame(f *wire.PathResponseFrame) {
for _, p := range pm.paths {
if f.Data == p.pathChallenge {
// path validated
p.validated = true
pm.logger.Debugf("path %s validated", p.addr)
break
}
}
}
// SwitchToPath is called when the connection switches to a new path
func (pm *pathManager) SwitchToPath(addr net.Addr) {
// retire all other paths
for _, path := range pm.paths {
if addrsEqual(path.addr, addr) {
pm.logger.Debugf("switching to path %d (%s)", path.id, addr)
continue
}
pm.retireConnID(path.id)
}
clear(pm.paths)
pm.paths = pm.paths[:0]
}
type pathManagerAckHandler pathManager
var _ ackhandler.FrameHandler = &pathManagerAckHandler{}
// Acknowledging the frame doesn't validate the path, only receiving the PATH_RESPONSE does.
func (pm *pathManagerAckHandler) OnAcked(f wire.Frame) {}
func (pm *pathManagerAckHandler) OnLost(f wire.Frame) {
pc, ok := f.(*wire.PathChallengeFrame)
if !ok {
return
}
for i, path := range pm.paths {
if path.pathChallenge == pc.Data {
pm.paths = slices.Delete(pm.paths, i, i+1)
pm.retireConnID(path.id)
break
}
}
}
func addrsEqual(addr1, addr2 net.Addr) bool {
if addr1 == nil || addr2 == nil {
return false
}
a1, ok1 := addr1.(*net.UDPAddr)
a2, ok2 := addr2.(*net.UDPAddr)
if ok1 && ok2 {
return a1.IP.Equal(a2.IP) && a1.Port == a2.Port
}
return addr1.String() == addr2.String()
}
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