feat: write protocol acknowledgements from go gateway

go/vehicle-gateway/internal/protocol/gb32960/response.go

@@ -0,0 +1,80 @@
+package gb32960
+
+import (
+	"encoding/binary"
+	"errors"
+	"time"
+
+	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
+)
+
+var ErrResponseFrameTooShort = errors.New("gb32960 response frame too short")
+
+const (
+	responseSuccess = byte(0x01)
+	responseCommand = byte(0xfe)
+	encryptNone     = byte(0x01)
+)
+
+// AutoResponse builds the protocol ACK for accepted upstream GB/T 32960 frames.
+// The ACK is written only after the caller has durably published the frame.
+func AutoResponse(raw []byte, env envelope.FrameEnvelope) ([]byte, bool, error) {
+	if env.ParseStatus == envelope.ParseBadFrame {
+		return nil, false, nil
+	}
+	if len(raw) < headerLen+1 {
+		return nil, false, ErrResponseFrameTooShort
+	}
+	if raw[3] != responseCommand {
+		return nil, false, nil
+	}
+	command := raw[2]
+	if !shouldRespond(command) {
+		return nil, false, nil
+	}
+
+	body := []byte(nil)
+	if timestamp := responseTime(raw, command); !timestamp.IsZero() {
+		body = encodeGBTime(timestamp)
+	}
+	return buildResponse(raw[0], command, responseSuccess, raw[4:21], body), true, nil
+}
+
+func shouldRespond(command byte) bool {
+	switch command {
+	case 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08:
+		return true
+	default:
+		return false
+	}
+}
+
+func responseTime(raw []byte, command byte) time.Time {
+	bodyLen := len(raw) - headerLen - 1
+	if bodyLen >= 6 {
+		return parseGBTime(raw[headerLen : headerLen+6])
+	}
+	return time.Now().In(time.FixedZone("Asia/Shanghai", 8*3600))
+}
+
+func encodeGBTime(t time.Time) []byte {
+	local := t.In(time.FixedZone("Asia/Shanghai", 8*3600))
+	return []byte{
+		byte(local.Year() - 2000),
+		byte(local.Month()),
+		byte(local.Day()),
+		byte(local.Hour()),
+		byte(local.Minute()),
+		byte(local.Second()),
+	}
+}
+
+func buildResponse(start byte, command byte, responseFlag byte, vin17 []byte, body []byte) []byte {
+	out := make([]byte, 0, headerLen+len(body)+1)
+	out = append(out, start, start, command, responseFlag)
+	out = append(out, vin17[:17]...)
+	out = append(out, encryptNone, 0, 0)
+	binary.BigEndian.PutUint16(out[22:24], uint16(len(body)))
+	out = append(out, body...)
+	return append(out, bcc(out[2:]))
+}