基于MQTT协议谈谈物联网开发

type FixedHeader struct {

    MessageType    byte
    Dup            bool
    Qos            byte
    Retain          bool
    RemainingLength int
}

func boolToByte(b bool) byte {
switch b {
case true:
return 1
default:
return 0
}
}
//编码固定头部
func (fh *FixedHeader) pack() bytes.Buffer {
var header bytes.Buffer
header.WriteByte(fh.MessageType<<4 | boolToByte(fh.Dup)<<3 | fh.Qos<<1 | boolToByte(fh.Retain))
header.Write(encodeLength(fh.RemainingLength))
return header
}
//解码固定头部
func (fh *FixedHeader) unpack(typeAndFlags byte, r io.Reader) {
fh.MessageType = typeAndFlags >> 4
fh.Dup = (typeAndFlags>>3)&0x01 > 0
fh.Qos = (typeAndFlags >> 1) & 0x03
fh.Retain = typeAndFlags&0x01 > 0
fh.RemainingLength = decodeLength(r)
}
//编码剩余长度
func encodeLength(length int) []byte {
var encLength []byte
for {
digit := byte(length % 128)
length /= 128
if length > 0 {
digit |= 0x80
}
encLength = append(encLength, digit)
if length == 0 {
break
}
}
return encLength
}
//解码剩余长度
func decodeLength(r io.Reader) int {
var rLength uint32
var multiplier uint32
b := make([]byte, 1)
for {
io.ReadFull(r, b)
digit := b[0]
rLength |= uint32(digit&127) << multiplier
if (digit & 128) == 0 {
break
}
multiplier += 7
}
return int(rLength)
}

type ConnectPacket struct {
FixedHeader
ProtocolName string
ProtocolVersion byte
CleanSession bool
WillFlag bool
WillQos byte
WillRetain bool
UsernameFlag bool
PasswordFlag bool
ReservedBit byte
KeepaliveTimer uint16

ClientIdentifier string
WillTopic string
WillMessage []byte
Username string
Password []byte
}
//连接报文编码
func (c *ConnectPacket) Write(w io.Writer) error {
var body bytes.Buffer
var err error
body.Write(encodeString(c.ProtocolName))
body.WriteByte(c.ProtocolVersion)
body.WriteByte(boolToByte(c.CleanSession)<<1 | boolToByte(c.WillFlag)<<2 | c.WillQos<<3 | boolToByte(c.WillRetain)<<5 | boolToByte(c.PasswordFlag)<<6 | boolToByte(c.UsernameFlag)<<7)
body.Write(encodeUint16(c.KeepaliveTimer))
body.Write(encodeString(c.ClientIdentifier))
if c.WillFlag {
body.Write(encodeString(c.WillTopic))
body.Write(encodeBytes(c.WillMessage))
}
if c.UsernameFlag {
body.Write(encodeString(c.Username))
}
if c.PasswordFlag {
body.Write(encodeBytes(c.Password))
}
c.FixedHeader.RemainingLength = body.Len()
packet := c.FixedHeader.pack()
packet.Write(body.Bytes())
_, err = packet.WriteTo(w)

return err
}
//连接报文解码
func (c *ConnectPacket) Unpack(b io.Reader) {
c.ProtocolName = decodeString(b)
c.ProtocolVersion = decodeByte(b)
options := decodeByte(b)
c.ReservedBit = 1 & options
c.CleanSession = 1&(options>>1) > 0
c.WillFlag = 1&(options>>2) > 0
c.WillQos = 3 & (options >> 3)
c.WillRetain = 1&(options>>5) > 0
c.PasswordFlag = 1&(options>>6) > 0
c.UsernameFlag = 1&(options>>7) > 0
c.KeepaliveTimer = decodeUint16(b)
c.ClientIdentifier = decodeString(b)
if c.WillFlag {
c.WillTopic = decodeString(b)
c.WillMessage = decodeBytes(b)
}
if c.UsernameFlag {
c.Username = decodeString(b)
}
if c.PasswordFlag {
c.Password = decodeBytes(b)
}
}