feat: Started on a proxy server to intercept game packets

connector/handle_game_connection.go

@@ -0,0 +1,16 @@
+package connector
+
+import (
+	"io"
+)
+
+// This is the size that Netty apparently uses to read from the incoming
+// connection at a time
+//
+// This is documented in a mod that removes this limit:
+// https://www.curseforge.com/minecraft/mc-mods/xl-packets
+const nettyMaxPacketSize = 2_097_152 // 16MiB
+
+func handleGameConnection(conn io.Reader) {
+	panic("Unhandled game traffic")
+}

connector/listen_port.go

@@ -0,0 +1,77 @@
+package connector
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+
+	log "github.com/sirupsen/logrus"
+
+	"github.com/spf13/cobra"
+)
+
+var (
+	inputPort  int
+	outputPort int
+)
+
+func init() {
+	ProxyPortCommand.Flags().IntVar(&inputPort, "in", -1, "The input port, or the port to listen to a server on")
+	ProxyPortCommand.Flags().IntVar(&outputPort, "out", -1, "The output port, or the port for the client to listen on")
+	ProxyPortCommand.MarkFlagRequired("in")
+	ProxyPortCommand.MarkFlagRequired("out")
+}
+
+var ProxyPortCommand = &cobra.Command{
+	Use:   "proxy",
+	Short: "Proxies the connection between the input and output ports",
+	RunE: func(cmd *cobra.Command, args []string) error {
+
+		// Listen for connections to the local server
+		l, err := net.Listen("tcp", fmt.Sprintf(":%d", inputPort))
+		if err != nil {
+			return err
+		}
+
+		log.Infof("Listening for incoming connections on port %d", inputPort)
+		for {
+			conn, err := l.Accept()
+			if err != nil {
+				return err
+			}
+
+			go handleConn(conn)
+		}
+	},
+}
+
+func handleConn(conn net.Conn) {
+	defer conn.Close()
+	log.Infof("Received connection from %v", conn.RemoteAddr())
+	// Open a connection to the remote server
+	serverConn, err := net.Dial("tcp", fmt.Sprintf(":%d", outputPort))
+	if err != nil {
+		panic(err)
+	}
+	defer serverConn.Close()
+
+	var sidecarServerDataStream bytes.Buffer
+
+	// Divert any data read from the server to be copied into the sidecar data stream
+	serverReader := io.TeeReader(serverConn, &sidecarServerDataStream)
+
+	go handleGameConnection(&sidecarServerDataStream)
+
+	// Start copying data from the server to the client
+	go func() {
+		if _, err := io.Copy(conn, serverReader); err != nil {
+			panic(err)
+		}
+	}()
+
+	// Copy data from the client to the server
+	if _, err := io.Copy(serverConn, conn); err != nil {
+		panic(err)
+	}
+}