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package proto
import (
"encoding/binary"
"errors"
"strconv"
"github.com/pion/stun"
)
// ChannelNumber represents CHANNEL-NUMBER attribute.
//
// The CHANNEL-NUMBER attribute contains the number of the channel.
//
// RFC 5766 Section 14.1
type ChannelNumber uint16 // encoded as uint16
func (n ChannelNumber) String() string { return strconv.Itoa(int(n)) }
// 16 bits of uint + 16 bits of RFFU = 0.
const channelNumberSize = 4
// AddTo adds CHANNEL-NUMBER to message.
func (n ChannelNumber) AddTo(m *stun.Message) error {
v := make([]byte, channelNumberSize)
binary.BigEndian.PutUint16(v[:2], uint16(n))
// v[2:4] are zeroes (RFFU = 0)
m.Add(stun.AttrChannelNumber, v)
return nil
}
// GetFrom decodes CHANNEL-NUMBER from message.
func (n *ChannelNumber) GetFrom(m *stun.Message) error {
v, err := m.Get(stun.AttrChannelNumber)
if err != nil {
return err
}
if err = stun.CheckSize(stun.AttrChannelNumber, len(v), channelNumberSize); err != nil {
return err
}
_ = v[channelNumberSize-1] // asserting length
*n = ChannelNumber(binary.BigEndian.Uint16(v[:2]))
// v[2:4] is RFFU and equals to 0.
return nil
}
// See https://tools.ietf.org/html/rfc5766#section-11:
//
// 0x4000 through 0x7FFF: These values are the allowed channel
// numbers (16,383 possible values).
const (
MinChannelNumber = 0x4000
MaxChannelNumber = 0x7FFF
)
// ErrInvalidChannelNumber means that channel number is not valid as by RFC 5766 Section 11.
var ErrInvalidChannelNumber = errors.New("channel number not in [0x4000, 0x7FFF]")
// isChannelNumberValid returns true if c in [0x4000, 0x7FFF].
func isChannelNumberValid(c uint16) bool {
return c >= MinChannelNumber && c <= MaxChannelNumber
}
// Valid returns true if channel number has correct value that complies RFC 5766 Section 11 range.
func (n ChannelNumber) Valid() bool {
return isChannelNumberValid(uint16(n))
}
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