Add an xC relay protocol analyzer

xR/xR.go

@@ -0,0 +1,134 @@
+// Copyright (c) 2025, Přemysl Eric Janouch <p@janouch.name>
+// SPDX-License-Identifier: 0BSD
+
+package main
+
+import (
+	"encoding/binary"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"os"
+	"time"
+)
+
+var (
+	debug          = flag.Bool("debug", false, "enable debug output")
+	version        = flag.Bool("version", false, "show version and exit")
+	projectName    = "xR"
+	projectVersion = "?"
+)
+
+func now() string {
+	return time.Now().UTC().Format(time.RFC3339Nano)
+}
+
+func relayReadFrame(r io.Reader) bool {
+	var length uint32
+	if err := binary.Read(
+		r, binary.BigEndian, &length); errors.Is(err, io.EOF) {
+		return false
+	} else if err != nil {
+		log.Fatalln("Event receive failed: " + err.Error())
+	}
+	b := make([]byte, length)
+	if _, err := io.ReadFull(r, b); errors.Is(err, io.EOF) {
+		return false
+	} else if err != nil {
+		log.Fatalln("Event receive failed: " + err.Error())
+	}
+
+	m := struct {
+		When   string `json:"when"`
+		Binary []byte `json:"raw"`
+		RelayEventMessage
+	}{
+		When:   now(),
+		Binary: b,
+	}
+
+	if after, ok := m.RelayEventMessage.ConsumeFrom(b); !ok {
+		log.Println("Event deserialization failed")
+	} else if len(after) != 0 {
+		log.Println("Event deserialization failed: trailing data")
+		return true
+	}
+
+	j, err := json.Marshal(m)
+	if err != nil {
+		log.Fatalln("Event marshalling failed: " + err.Error())
+	}
+	fmt.Printf("%s\n", j)
+	return true
+}
+
+func run(addressConnect string) {
+	conn, err := net.Dial("tcp", addressConnect)
+	if err != nil {
+		log.Println("Connection failed: " + err.Error())
+		return
+	}
+	defer conn.Close()
+
+	// We can only support this one protocol version
+	// that proto.go has been generated for.
+	m := RelayCommandMessage{CommandSeq: 0, Data: RelayCommandData{
+		Variant: &RelayCommandDataHello{Version: RelayVersion},
+	}}
+
+	b, ok := m.AppendTo(make([]byte, 4))
+	if !ok {
+		log.Fatalln("Command serialization failed")
+	}
+	binary.BigEndian.PutUint32(b[:4], uint32(len(b)-4))
+	if _, err := conn.Write(b); err != nil {
+		log.Fatalln("Command send failed: " + err.Error())
+	}
+
+	// You can differentiate the direction by the presence
+	// of .data.command or .data.event.
+	if *debug {
+		j, err := json.Marshal(struct {
+			When   string `json:"when"`
+			Binary []byte `json:"raw"`
+			RelayCommandMessage
+		}{
+			When:                now(),
+			Binary:              b,
+			RelayCommandMessage: m,
+		})
+		if err != nil {
+			log.Fatalln("Command marshalling failed: " + err.Error())
+		}
+		fmt.Printf("%s\n", j)
+	}
+
+	for relayReadFrame(conn) {
+	}
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(),
+			"Usage: %s [OPTION...] CONNECT\n\n", os.Args[0])
+		flag.PrintDefaults()
+	}
+	flag.Parse()
+	if *version {
+		fmt.Printf("%s %s (relay protocol version %d)\n",
+			projectName, projectVersion, RelayVersion)
+		return
+	}
+
+	if flag.NArg() != 1 {
+		flag.Usage()
+		os.Exit(1)
+	}
+
+	// TODO(p): This program should be able to run as a filter as well.
+	run(flag.Arg(0))
+}