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// Copyright 2016 Cong Ding
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package stun
import (
"crypto/rand"
"encoding/binary"
"errors"
"math"
)
type packet struct {
types uint16
length uint16
transID []byte // 4 bytes magic cookie + 12 bytes transaction id
attributes []attribute
}
func newPacket() (*packet, error) {
v := new(packet)
v.transID = make([]byte, 16)
binary.BigEndian.PutUint32(v.transID[:4], magicCookie)
_, err := rand.Read(v.transID[4:])
if err != nil {
return nil, err
}
v.attributes = make([]attribute, 0, 10)
v.length = 0
return v, nil
}
func newPacketFromBytes(packetBytes []byte) (*packet, error) {
if len(packetBytes) < 20 {
return nil, errors.New("Received data length too short.")
}
if len(packetBytes) > math.MaxUint16+20 {
return nil, errors.New("Received data length too long.")
}
pkt := new(packet)
pkt.types = binary.BigEndian.Uint16(packetBytes[0:2])
pkt.length = binary.BigEndian.Uint16(packetBytes[2:4])
pkt.transID = packetBytes[4:20]
pkt.attributes = make([]attribute, 0, 10)
packetBytes = packetBytes[20:]
for pos := uint16(0); pos+4 < uint16(len(packetBytes)); {
types := binary.BigEndian.Uint16(packetBytes[pos : pos+2])
length := binary.BigEndian.Uint16(packetBytes[pos+2 : pos+4])
end := pos + 4 + length
if end < pos+4 || end > uint16(len(packetBytes)) {
return nil, errors.New("Received data format mismatch.")
}
value := packetBytes[pos+4 : end]
attribute := newAttribute(types, value)
pkt.addAttribute(*attribute)
pos += align(length) + 4
}
return pkt, nil
}
func (v *packet) addAttribute(a attribute) {
v.attributes = append(v.attributes, a)
v.length += align(a.length) + 4
}
func (v *packet) bytes() []byte {
packetBytes := make([]byte, 4)
binary.BigEndian.PutUint16(packetBytes[0:2], v.types)
binary.BigEndian.PutUint16(packetBytes[2:4], v.length)
packetBytes = append(packetBytes, v.transID...)
for _, a := range v.attributes {
buf := make([]byte, 2)
binary.BigEndian.PutUint16(buf, a.types)
packetBytes = append(packetBytes, buf...)
binary.BigEndian.PutUint16(buf, a.length)
packetBytes = append(packetBytes, buf...)
packetBytes = append(packetBytes, a.value...)
}
return packetBytes
}
func (v *packet) getSourceAddr() *Host {
return v.getRawAddr(attributeSourceAddress)
}
func (v *packet) getMappedAddr() *Host {
return v.getRawAddr(attributeMappedAddress)
}
func (v *packet) getChangedAddr() *Host {
return v.getRawAddr(attributeChangedAddress)
}
func (v *packet) getOtherAddr() *Host {
return v.getRawAddr(attributeOtherAddress)
}
func (v *packet) getRawAddr(attribute uint16) *Host {
for _, a := range v.attributes {
if a.types == attribute {
return a.rawAddr()
}
}
return nil
}
func (v *packet) getXorMappedAddr() *Host {
addr := v.getXorAddr(attributeXorMappedAddress)
if addr == nil {
addr = v.getXorAddr(attributeXorMappedAddressExp)
}
return addr
}
func (v *packet) getXorAddr(attribute uint16) *Host {
for _, a := range v.attributes {
if a.types == attribute {
return a.xorAddr(v.transID)
}
}
return nil
}
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