plc4go/protocols/df1/readwrite/model/StaticHelper.go

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *
 *   https://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 model

import (
	"context"

	"github.com/apache/plc4x/plc4go/spi/utils"
)

// crc16df1Update accumulates CRC-16/DF-1 (CRC-16/ARC variant) over data.
// Parameters: poly=0x8005, init=0x0000, reflectIn=true, reflectOut=true, finalXor=0.
// The reflected polynomial is 0xA001.
func crc16df1Update(crc uint16, data []byte) uint16 {
	const refPoly uint16 = 0xA001
	for _, b := range data {
		crc ^= uint16(b)
		for range 8 {
			if crc&1 != 0 {
				crc = (crc >> 1) ^ refPoly
			} else {
				crc >>= 1
			}
		}
	}
	return crc
}

func CrcCheck(ctx context.Context, destinationAddress uint8, sourceAddress uint8, command DF1Command) func() (uint16, error) {
	return func() (uint16, error) {
		df1Crc := uint16(0)
		df1Crc = crc16df1Update(df1Crc, []byte{destinationAddress, sourceAddress})
		bytes, err := command.Serialize()
		if err != nil {
			return 0, err
		}
		df1Crc = crc16df1Update(df1Crc, bytes)
		df1Crc = crc16df1Update(df1Crc, []byte{0x03})
		return df1Crc, nil
	}
}

func DataTerminate(ctx context.Context, io utils.ReadBuffer) func([]byte) bool {
	return func([]byte) bool {
		rbbb := io.(utils.ReadBufferByteBased)
		// The byte sequence 0x10 followed by 0x03 indicates the end of the message,
		// so if we would read this, we abort the loop and stop reading data.
		return rbbb.PeekByte(0) == 0x10 && rbbb.PeekByte(1) == 0x03
	}
}

func ReadData(ctx context.Context, io utils.ReadBuffer) func(context.Context) (uint8, error) {
	return func(context.Context) (uint8, error) {
		rbbb := io.(utils.ReadBufferByteBased)
		// If we read a 0x10, this has to be followed by another 0x10, which is how
		// this value is escaped in DF1, so if we encounter two 0x10, we simply ignore the first.
		if rbbb.PeekByte(0) == 0x10 && rbbb.PeekByte(1) == 0x10 {
			_, _ = io.ReadUint8("", 8)
		}
		data, _ := io.ReadUint8("", 8)
		return data, nil
	}
}

func WriteData(ctx context.Context, io utils.WriteBuffer, element byte) error {
	if element == 0x10 {
		// If a value is 0x10, this has to be duplicated in order to be escaped.
		if err := io.WriteUint8("", 8, element); err != nil {
			return err
		}
	}
	return io.WriteUint8("", 8, element)
}

func DataLength(ctx context.Context, data []byte) uint16 {
	length := uint16(0)
	for _, datum := range data {
		if datum == 0x10 {
			// If a value is 0x10, this has to be duplicated which increases the message size by one.
			length++
		}
		length++
	}
	return length
}