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package protocol
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import (
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"bytes"
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"encoding/binary"
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"fmt"
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"git.noahlan.cn/noahlan/nnet/packet"
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"git.noahlan.cn/noahlan/ntool-biz/nmodbus/util"
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)
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type RTUPacker struct {
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buf *bytes.Buffer
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byteOrder binary.ByteOrder
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}
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func NewRTUPacker(byteOrder binary.ByteOrder) *RTUPacker {
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p := &RTUPacker{
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buf: bytes.NewBuffer(nil),
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byteOrder: byteOrder,
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}
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return p
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}
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func (d *RTUPacker) Pack(header interface{}, data []byte) ([]byte, error) {
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modbusHeader, ok := header.(*ModbusHeader)
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if !ok {
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return nil, packet.ErrWrongPacketType
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}
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bs := make([]byte, 2)
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bs[0] = modbusHeader.Address
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bs[1] = modbusHeader.Function
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bs = append(bs, data...)
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// calc CRC
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pLen := len(bs)
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crc := util.Checksum(bs[0:pLen])
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bs = append(bs, []byte{0, 0}...)
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d.byteOrder.PutUint16(bs[pLen:pLen+2], crc)
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return bs, nil
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}
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func (d *RTUPacker) Unpack(data []byte) ([]packet.IPacket, error) {
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d.buf.Write(data)
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//nlog.Debugf("接收RTU数据: %x", data)
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var (
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packets []packet.IPacket
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err error
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)
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pLen := d.buf.Len()
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if pLen < 5 {
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return packets, fmt.Errorf("RTU Frame error: packet less than 5 bytes")
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}
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// ModbusRTU 串口通讯 发送端在发送报文时，一帧结束后必须有3.5个字符周期的间隔时间（4.01ms）
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// 本质上不会发生粘包的情况，故此可以直接读取一个完整的包
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// 否则无法处理粘包状况，这是由于协议帧没有描述具体包长度的字节
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bs := d.buf.Next(d.buf.Len())
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// check crc 取[0:len-2]进行计算,与最后一个字节对比（最后一个字节为crc校验码）
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crcExpect := d.byteOrder.Uint16(bs[pLen-2 : pLen])
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crcCalc := util.Checksum(bs[0 : pLen-2])
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if crcCalc != crcExpect {
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return nil, fmt.Errorf("RTU Frame error: CRC (expected 0x%x, got 0x%x)", crcExpect, crcCalc)
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}
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p := NewRTUPacket()
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p.Address = bs[0]
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p.Function = bs[1]
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p.Data = bs[2 : pLen-2]
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p.CRC = crcExpect
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packets = append(packets, p)
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d.buf.Reset()
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return packets, err
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}
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