Read serial number and model name over UDP

go.mod

@@ -0,0 +1,3 @@
+module git.netflux.io/rob/goodwe-go
+
+go 1.18

main.go

@@ -0,0 +1,114 @@
+package main
+
+import (
+	"bufio"
+	"encoding/binary"
+	"encoding/hex"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"strings"
+)
+
+const (
+	readBufSizeBytes = 4_096
+)
+
+func main() {
+	var ipAddr string
+	flag.StringVar(&ipAddr, "ipaddr", "", "IP address/port")
+	flag.Parse()
+
+	if ipAddr == "" {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	fmt.Println("ipAddr", ipAddr)
+
+	conn, err := net.Dial("udp", ipAddr)
+	if err != nil {
+		log.Fatalf("error dialing: %s", err)
+	}
+	defer conn.Close()
+
+	resp, err := sendAA55Command(conn, "010200", "0182")
+	if err != nil {
+		log.Fatalf("error sending command: %s", err)
+	}
+
+	modelName := strings.TrimSpace(string(resp[12:22]))
+	serialNum := string(resp[38:54])
+
+	log.Printf("modelName = %q, serialNum = %q\n", modelName, serialNum)
+}
+
+func sendAA55Command(conn io.ReadWriter, payload, expectedResponseType string) ([]byte, error) {
+	bytes, err := hex.DecodeString("AA55C07F" + payload)
+	if err != nil {
+		return nil, fmt.Errorf("error decoding hex string: %s", err)
+	}
+
+	bytes = append(bytes, checksum(bytes)...)
+
+	_, err = fmt.Fprint(conn, string(bytes))
+	if err != nil {
+		return nil, fmt.Errorf("error writing to socket: %s", err)
+	}
+
+	log.Printf("sent data to socket: %X", bytes)
+
+	p := make([]byte, readBufSizeBytes)
+	n, err := bufio.NewReader(conn).Read(p)
+	if err != nil {
+		return nil, fmt.Errorf("error reading from socket: %s", err)
+	}
+
+	return validateResponse(p[:n], expectedResponseType)
+}
+
+const (
+	aa55ResponseLengthIndex  = 6
+	aa55ResponseLengthOffset = 9
+)
+
+func validateResponse(p []byte, expectedResponseType string) ([]byte, error) {
+	if len(p) < 8 {
+		return nil, fmt.Errorf("response truncated")
+	}
+
+	expectedLen := int(p[aa55ResponseLengthIndex] + aa55ResponseLengthOffset)
+	if len(p) != expectedLen {
+		return nil, fmt.Errorf("unexpected response length %d (expected %d)", len(p), expectedLen)
+	}
+
+	responseType := hex.EncodeToString(p[4:6])
+	if responseType != expectedResponseType {
+		return nil, fmt.Errorf("unexpected response type `%s` (expected `%s`)", responseType, expectedResponseType)
+	}
+
+	var s uint16
+	for _, b := range p[:len(p)-2] {
+		s += uint16(b)
+	}
+	expSum := binary.BigEndian.Uint16(p[len(p)-2:])
+	if s != expSum {
+		return nil, fmt.Errorf("invalid response checksum %d (expected %d)", s, expSum)
+	}
+
+	return p, nil
+}
+
+func checksum(p []byte) []byte {
+	var v uint16
+	for _, byte := range p {
+		v += uint16(byte)
+	}
+
+	c := make([]byte, 4)
+	binary.BigEndian.PutUint16(c, v)
+	return c
+}