syncthing/lib/stun/filter.go

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// Copyright (C) 2019 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at https://mozilla.org/MPL/2.0/.
package stun
import (
"bytes"
"net"
"sync"
"time"
)
const (
stunFilterPriority = 10
otherDataPriority = 100
)
type stunFilter struct {
ids map[string]time.Time
mut sync.Mutex
}
func (f *stunFilter) Outgoing(out []byte, _ net.Addr) {
if !f.isStunPayload(out) {
panic("not a stun payload")
}
f.mut.Lock()
f.ids[string(out[8:20])] = time.Now().Add(time.Minute)
f.reap()
f.mut.Unlock()
}
func (f *stunFilter) ClaimIncoming(in []byte, _ net.Addr) bool {
if f.isStunPayload(in) {
f.mut.Lock()
_, ok := f.ids[string(in[8:20])]
f.reap()
f.mut.Unlock()
return ok
}
return false
}
func (*stunFilter) isStunPayload(data []byte) bool {
// Need at least 20 bytes
if len(data) < 20 {
return false
}
// First two bits always unset, and should always send magic cookie.
return data[0]&0xc0 == 0 && bytes.Equal(data[4:8], []byte{0x21, 0x12, 0xA4, 0x42})
}
func (f *stunFilter) reap() {
now := time.Now()
for id, timeout := range f.ids {
if timeout.Before(now) {
delete(f.ids, id)
}
}
}