clonetool/listen.go

package main

import (
	"crypto/tls"
	"flag"
	"fmt"
	"net"
	"os"
	"strings"
	"time"
)

// cmdListen runs clonetool in listen mode: it waits for inbound TLS
// connections (see nettransport.go), authenticates each with the shared
// password, and serves whatever role the peer requests (control for the
// manager's stat calls, source-stream/sink for the data transfer). This is the
// no-ssh path for a host — typically a Windows source — that this machine and
// the destination connect *to* instead of being reached over ssh.
func cmdListen(args []string) error {
	fs := flag.NewFlagSet("listen", flag.ContinueOnError)
	bind := fs.String("bind", ":9000", "address to listen on, e.g. :9000 or 0.0.0.0:9000")
	password := fs.String("password", "", "shared password (or set CLONETOOL_PASSWORD, or --password-file)")
	passwordFile := fs.String("password-file", "", "read the shared password from this file")
	if err := fs.Parse(args); err != nil {
		return err
	}
	pw, err := resolvePassword(*password, *passwordFile)
	if err != nil {
		return err
	}
	if pw == "" {
		return fmt.Errorf("listen: a password is required (--password, --password-file, or CLONETOOL_PASSWORD)")
	}

	tlsCfg, err := newServerTLSConfig()
	if err != nil {
		return fmt.Errorf("listen: tls setup: %w", err)
	}
	ln, err := net.Listen("tcp", *bind)
	if err != nil {
		return fmt.Errorf("listen on %s: %w", *bind, err)
	}
	defer ln.Close()
	fmt.Fprintf(os.Stderr, "clonetool listening on %s (%s); press Ctrl-C to stop\n", ln.Addr(), versionString())

	for {
		raw, err := ln.Accept()
		if err != nil {
			return fmt.Errorf("accept: %w", err)
		}
		go serveListenConn(raw, tlsCfg, pw)
	}
}

// serveListenConn handles one accepted connection: TLS + password auth, then a
// single role request that it dispatches. Each connection is one role; the
// manager and the destination open separate connections.
func serveListenConn(raw net.Conn, tlsCfg *tls.Config, password string) {
	remote := raw.RemoteAddr().String()
	defer raw.Close()

	conn := tls.Server(raw, tlsCfg)
	const handshakeTimeout = 30 * time.Second
	_ = conn.SetDeadline(time.Now().Add(handshakeTimeout))
	if err := conn.Handshake(); err != nil {
		fmt.Fprintf(os.Stderr, "listen: %s: tls handshake: %v\n", remote, err)
		return
	}
	fr, fw, err := serverAuth(conn, password, handshakeTimeout)
	if err != nil {
		fmt.Fprintf(os.Stderr, "listen: %s: %v\n", remote, err)
		return
	}
	_ = conn.SetDeadline(time.Time{}) // transfers set their own pacing

	req, err := readCtrlFrame(fr)
	if err != nil {
		fmt.Fprintf(os.Stderr, "listen: %s: read role request: %v\n", remote, err)
		return
	}
	if req.Type != msgRole {
		_ = fw.WriteJSON(CtrlMsg{Type: msgRoleErr, Message: fmt.Sprintf("expected a role request, got %q", req.Type)})
		return
	}
	if err := dispatchRole(req, fr, fw, remote); err != nil {
		fmt.Fprintf(os.Stderr, "listen: %s: role %s: %v\n", remote, req.Role, err)
	}
}

func dispatchRole(req CtrlMsg, fr *FrameReader, fw *FrameWriter, remote string) error {
	switch req.Role {
	case roleControl:
		fmt.Fprintf(os.Stderr, "listen: %s: control session\n", remote)
		return runControlAgent(fr, fw)
	case roleSourceStream:
		fmt.Fprintf(os.Stderr, "listen: %s: source-stream %s\n", remote, req.Path)
		return runSourceStreamRole(fr, fw, req.Path, req.Base, req.Size, req.BlockSize)
	case roleSink:
		fmt.Fprintf(os.Stderr, "listen: %s: sink %s\n", remote, req.Path)
		return runSinkRole(fr, fw, req.Path, req.Base, req.Size, req.BlockSize)
	default:
		_ = fw.WriteJSON(CtrlMsg{Type: msgRoleErr, Message: fmt.Sprintf("unknown role %q", req.Role)})
		return fmt.Errorf("unknown role %q", req.Role)
	}
}

// resolvePassword picks the shared password from, in order: --password-file, an
// inline --password, then the CLONETOOL_PASSWORD environment variable. A
// trailing newline in a password file is stripped.
func resolvePassword(inline, file string) (string, error) {
	if file != "" {
		b, err := os.ReadFile(file)
		if err != nil {
			return "", fmt.Errorf("read password file: %w", err)
		}
		return strings.TrimRight(string(b), "\r\n"), nil
	}
	if inline != "" {
		return inline, nil
	}
	return os.Getenv("CLONETOOL_PASSWORD"), nil
}