feat: replace iot adapter with mqtt command pipeline

backend/iot-server/internal/protocol/frame.go

@@ -0,0 +1,173 @@
+// Package protocol 实现《气体探测器通讯协议》V1.8 的二进制帧编解码。
+package protocol
+
+import (
+	"crypto/aes"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"time"
+)
+
+const (
+	StartByte      = byte(0x5E)
+	EndByte        = byte(0x5B)
+	FixedBodyBytes = 29 // key 到有效数据长度，不含载荷和校验。
+)
+
+var (
+	ErrFrameTooShort   = errors.New("数据帧长度不足")
+	ErrBoundary        = errors.New("起始符或结束符无效")
+	ErrLength          = errors.New("帧长度不匹配")
+	ErrChecksum        = errors.New("LRC8 校验失败")
+	ErrPayloadLength   = errors.New("数据包有效长度无效")
+	ErrEncryptedLength = errors.New("密文长度不是 16 字节的倍数")
+)
+
+// Frame 是设备原始帧的强类型表示；多字节整数均按大端序传输。
+type Frame struct {
+	KeyID        byte
+	Version      byte
+	Control      byte
+	DeviceKind   byte
+	DeviceType   byte
+	DeviceModel  [3]byte
+	DeviceID     [8]byte
+	PacketNumber uint16
+	Sequence     byte
+	Final        bool
+	DeviceTime   time.Time
+	Payload      []byte
+}
+
+// Keyring 按协议支持 0 号明文和 1/2/3 号 AES-128 密钥。
+type Keyring map[byte][]byte
+
+// Encode 构造可直接作为 MQTT payload 发布的厂商二进制帧。
+func Encode(frame Frame, keys Keyring) ([]byte, error) {
+	payload, err := cryptPayload(frame.KeyID, frame.Payload, keys, false)
+	if err != nil {
+		return nil, err
+	}
+	body := make([]byte, FixedBodyBytes+len(payload))
+	body[0], body[1], body[2] = frame.KeyID, frame.Version, frame.Control
+	body[3], body[4] = frame.DeviceKind, frame.DeviceType
+	copy(body[5:8], frame.DeviceModel[:])
+	copy(body[8:16], frame.DeviceID[:])
+	binary.BigEndian.PutUint16(body[16:18], frame.PacketNumber)
+	body[18] = frame.Sequence
+	if frame.Final {
+		body[19] = 1
+	}
+	encodeBCDTime(body[20:27], frame.DeviceTime)
+	binary.BigEndian.PutUint16(body[27:29], uint16(len(frame.Payload)))
+	copy(body[29:], payload)
+
+	frameLength := len(body) + 1 // 加上校验字节，不含起始符、长度字段和结束符。
+	if frameLength > 0xffff {
+		return nil, fmt.Errorf("帧过长: %d", frameLength)
+	}
+	result := make([]byte, 0, frameLength+4)
+	result = append(result, StartByte, byte(frameLength>>8), byte(frameLength))
+	result = append(result, body...)
+	result = append(result, LRC8(result[1:]), EndByte)
+	return result, nil
+}
+
+// Decode 校验边界、长度、LRC8 和 AES 后返回有效载荷。
+func Decode(raw []byte, keys Keyring) (Frame, error) {
+	var frame Frame
+	if len(raw) < FixedBodyBytes+5 {
+		return frame, ErrFrameTooShort
+	}
+	if raw[0] != StartByte || raw[len(raw)-1] != EndByte {
+		return frame, ErrBoundary
+	}
+	declared := int(binary.BigEndian.Uint16(raw[1:3]))
+	if declared+4 != len(raw) {
+		return frame, ErrLength
+	}
+	if LRC8(raw[1:len(raw)-2]) != raw[len(raw)-2] {
+		return frame, ErrChecksum
+	}
+	body := raw[3 : len(raw)-2]
+	frame.KeyID, frame.Version, frame.Control = body[0], body[1], body[2]
+	frame.DeviceKind, frame.DeviceType = body[3], body[4]
+	copy(frame.DeviceModel[:], body[5:8])
+	copy(frame.DeviceID[:], body[8:16])
+	frame.PacketNumber = binary.BigEndian.Uint16(body[16:18])
+	frame.Sequence, frame.Final = body[18], body[19] == 1
+	frame.DeviceTime = decodeBCDTime(body[20:27])
+	validLength := int(binary.BigEndian.Uint16(body[27:29]))
+	plain, err := cryptPayload(frame.KeyID, body[29:], keys, true)
+	if err != nil {
+		return frame, err
+	}
+	if validLength > len(plain) {
+		return frame, ErrPayloadLength
+	}
+	frame.Payload = append([]byte(nil), plain[:validLength]...)
+	return frame, nil
+}
+
+// LRC8 返回连续字节和的二进制补码低字节。
+func LRC8(data []byte) byte {
+	var sum byte
+	for _, value := range data {
+		sum += value
+	}
+	return ^sum + 1
+}
+
+func cryptPayload(keyID byte, input []byte, keys Keyring, decrypt bool) ([]byte, error) {
+	if keyID == 0 {
+		size := len(input)
+		if !decrypt && size%aes.BlockSize != 0 {
+			size += aes.BlockSize - size%aes.BlockSize
+		}
+		result := make([]byte, size)
+		copy(result, input)
+		return result, nil
+	}
+	key := keys[keyID]
+	if len(key) != aes.BlockSize {
+		return nil, fmt.Errorf("%d 号 AES 密钥必须为 16 字节", keyID)
+	}
+	if decrypt && len(input)%aes.BlockSize != 0 {
+		return nil, ErrEncryptedLength
+	}
+	size := len(input)
+	if !decrypt && size%aes.BlockSize != 0 {
+		size += aes.BlockSize - size%aes.BlockSize
+	}
+	output := make([]byte, size)
+	copy(output, input)
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+	for offset := 0; offset < len(output); offset += aes.BlockSize {
+		if decrypt {
+			block.Decrypt(output[offset:offset+aes.BlockSize], input[offset:offset+aes.BlockSize])
+		} else {
+			block.Encrypt(output[offset:offset+aes.BlockSize], output[offset:offset+aes.BlockSize])
+		}
+	}
+	return output, nil
+}
+
+func encodeBCDTime(dst []byte, value time.Time) {
+	if value.IsZero() {
+		value = time.Now()
+	}
+	parts := []int{value.Year() / 100, value.Year() % 100, int(value.Month()), value.Day(), value.Hour(), value.Minute(), value.Second()}
+	for index, part := range parts {
+		dst[index] = byte((part/10)<<4 | part%10)
+	}
+}
+
+func decodeBCDTime(src []byte) time.Time {
+	n := func(value byte) int { return int(value>>4)*10 + int(value&0x0f) }
+	year := n(src[0])*100 + n(src[1])
+	return time.Date(year, time.Month(n(src[2])), n(src[3]), n(src[4]), n(src[5]), n(src[6]), 0, time.Local)
+}