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telnetd.go
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telnetd.go
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// Copyright © 2015-2016 Platina Systems, Inc. All rights reserved.
// Use of this source code is governed by the GPL-2 license described in the
// LICENSE file.
// This telnet daemon is only run from an embedded machine's /init, not
// /usr/bin/goes start
package telnetd
import (
"bytes"
"fmt"
"io"
"net"
"os"
"os/signal"
"syscall"
"github.com/creack/pty"
"github.com/platinasystems/goes/cmd"
"github.com/platinasystems/goes/internal/telnet/command"
"github.com/platinasystems/goes/internal/telnet/option"
"github.com/platinasystems/goes/lang"
)
type Command struct{}
func (Command) String() string { return "telnetd" }
func (Command) Usage() string { return "telnetd" }
func (Command) Apropos() lang.Alt {
return lang.Alt{
lang.EnUS: "telnet server daemon",
}
}
func (Command) Kind() cmd.Kind { return cmd.Daemon }
func (Command) Main(args ...string) error {
ln, err := net.Listen("tcp", ":23")
if err != nil {
return err
}
defer ln.Close()
signal.Ignore(syscall.SIGCHLD)
dir := "/"
if fi, err := os.Stat("/root"); err == nil && fi.IsDir() {
dir = "/root"
}
for {
conn, err := ln.Accept()
if err != nil {
return err
}
optionNegotiation(conn)
pts, tty, err := pty.Open()
if err != nil {
return err
}
proc, err := os.StartProcess("/bin/goes",
[]string{"goes"},
&os.ProcAttr{
Dir: dir,
Env: []string{
"PATH=/usr/bin:/bin",
"TERM=xterm",
},
Files: []*os.File{
tty,
tty,
tty,
},
Sys: &syscall.SysProcAttr{
Setsid: true,
Setctty: true,
Ctty: 0,
Pgid: 0,
},
})
tty.Close()
if err != nil {
fmt.Fprintln(os.Stderr, err)
pts.Close()
continue
}
go func() { io.Copy(conn, pts) }()
go nullFilteredCopy(pts, conn)
go func() {
proc.Wait()
pts.Close()
conn.Close()
}()
}
}
func optionNegotiation(conn net.Conn) error {
ack := make([]byte, 1024)
conn.Write([]byte{command.IAC, command.WILL, option.ECHO})
n, err := conn.Read(ack)
if err != nil {
return err
}
if 0 != bytes.Compare(ack[:n],
[]byte{command.IAC, command.DO, option.ECHO}) {
conn.Write([]byte("telnet WILL ECHO Failed"))
return nil
}
conn.Write([]byte{
command.IAC, command.DONT, option.ECHO,
command.IAC, command.WILL, option.SGA,
})
n, err = conn.Read(ack)
if err != nil {
return err
}
if 0 != bytes.Compare(ack[:n],
[]byte{command.IAC, command.DO, option.SGA}) {
conn.Write([]byte("telnet WILL SGA failed"))
return nil
}
conn.Write([]byte{command.IAC, command.DO, option.SGA})
n, err = conn.Read(ack)
if err != nil {
return err
}
if 0 != bytes.Compare(ack[:n],
[]byte{command.IAC, command.WILL, option.SGA}) {
conn.Write([]byte("telnet DO SGA failed"))
return nil
}
conn.Write([]byte{command.IAC, command.WONT, option.LINEMODE})
return nil
}
func nullFilteredCopy(w io.Writer, r io.Reader) {
buf := make([]byte, 4096)
for {
n, err := r.Read(buf)
if err != nil {
return
}
if n <= 0 {
continue
}
if buf[n-1] == 0 {
n -= 1
}
if _, err = w.Write(buf[:n]); err != nil {
return
}
}
}