burble.dn42/modemulator
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initial release

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This commit is contained in:
Simon Marsh 2022-09-27 13:46:36 +01:00
parent 7f4c08c89b
commit 4f8ef2757d
Signed by: burble
GPG Key ID: 0FCCD13AE1CF7ED8
4 changed files with 841 additions and 0 deletions
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1
.gitignore vendored
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@ -72,3 +72,4 @@ flycheck_*.el
# Go workspace file
go.work
modemulator

7
go.mod Normal file
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@ -0,0 +1,7 @@
module modemulator
go 1.19
require github.com/sirupsen/logrus v1.9.0
require golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 // indirect

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go.sum Normal file
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@ -0,0 +1,15 @@
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/sirupsen/logrus v1.9.0 h1:trlNQbNUG3OdDrDil03MCb1H2o9nJ1x4/5LYw7byDE0=
github.com/sirupsen/logrus v1.9.0/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 h1:0A+M6Uqn+Eje4kHMK80dtF3JCXC4ykBgQG4Fe06QRhQ=
golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

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modemulator.go Normal file
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//////////////////////////////////////////////////////////////////////////
package main
//////////////////////////////////////////////////////////////////////////
import (
"bytes"
"errors"
"fmt"
log "github.com/sirupsen/logrus"
"io"
"net"
"os"
"os/signal"
"regexp"
"strconv"
"strings"
"time"
)
//////////////////////////////////////////////////////////////////////////
// some config options
const PPS_TARGET = 10
const SERVER_BIND = ""
const SERVER_PORT_INDEX = 10000
const TELNET_SERVER = "localhost"
var BAUDS []uint = []uint{
300,
1200,
2400,
4800,
9600,
14400,
19200,
28800,
33600,
56000,
115000,
}
var AddressBook map[string]string = map[string]string{
"54311": "shell.fr-par1.burble.dn42:23",
"42": "localhost:23",
}
var OnlyNumbers *regexp.Regexp = regexp.MustCompile("([^0-9]+)")
// global data and structures
var Listeners []net.Listener
type TCode uint
const (
TN_NORM TCode = 65535
TN_IAC TCode = 255
TN_DONT TCode = 254
TN_DO TCode = 253
TN_WONT TCode = 252
TN_WILL TCode = 251
TN_SB TCode = 250
TN_GA TCode = 249
TN_EL TCode = 248
TN_EC TCode = 247
TN_AYT TCode = 246
TN_AO TCode = 245
TN_IP TCode = 244
TN_BRK TCode = 243
TN_DM TCode = 242
TN_NOP TCode = 241
TN_SE TCode = 240
)
type DTEMode uint
const (
DTE_COMMAND DTEMode = iota
DTE_COMMAND_A
DTE_COMMAND_AT
DTE_ATTN_1
DTE_ATTN_2
DTE_ATTN_3
DTE_CONNECTED
)
type Modem struct {
baud uint
dce net.Conn
mode DTEMode
echo bool
cmdBuff *bytes.Buffer
dteBuff []byte
connected bool
dte net.Conn
state TCode
readSlot time.Time
writeSlot time.Time
dceBuff []byte
}
var Modems map[string]*Modem
//////////////////////////////////////////////////////////////////////////
// utility function to set the log level
func setLogLevel(levelStr string) {
if level, err := log.ParseLevel(levelStr); err != nil {
// failed to set the level
// set a sensible default and, of course, log the error
log.SetLevel(log.InfoLevel)
log.WithFields(log.Fields{
"loglevel": levelStr,
"error": err,
}).Error("Failed to set requested log level")
} else {
// set the requested level
log.SetLevel(level)
}
}
//////////////////////////////////////////////////////////////////////////
// listen on required ports
func Listen() {
for _, baud := range BAUDS {
port := SERVER_PORT_INDEX + (baud / 100)
bind := SERVER_BIND + ":" + strconv.Itoa(int(port))
log.WithFields(log.Fields{
"bind": bind,
"baud": baud,
}).Debug("Listening on socket")
listener, err := net.Listen("tcp", bind)
if err != nil {
log.WithFields(log.Fields{
"bind": bind,
"baud": baud,
"error": err,
}).Fatal("Failed to bind listening port")
}
Listeners = append(Listeners, listener)
// spin off a thread waiting for new connections
go func(p uint, b uint) {
for {
conn, err := listener.Accept()
if err != nil {
if errors.Is(err, net.ErrClosed) {
log.WithFields(log.Fields{
"port": p,
}).Debug("Listener closed")
return
} else {
log.WithFields(log.Fields{
"port": p,
"error": err,
}).Error("Listen Error")
return
}
}
// initialise modem and start listening for commands
modem := &Modem{}
go modem.DTEReceive(b, conn)
}
}(port, baud)
}
}
//////////////////////////////////////////////////////////////////////////
// modem utility functions
func (m *Modem) disconnect() {
if m.connected {
m.dce.Close()
}
m.connected = false
m.mode = DTE_COMMAND
}
func (m *Modem) Shutdown() {
m.disconnect()
m.dte.Close()
}
func (m *Modem) bytesPerTimeslot() uint {
return (m.baud / (PPS_TARGET * 9)) + 1
}
func (m *Modem) createBuffers() {
m.dteBuff = make([]byte, m.baud)
m.dceBuff = make([]byte, m.bytesPerTimeslot())
if m.cmdBuff == nil {
m.cmdBuff = new(bytes.Buffer)
m.cmdBuff.Grow(80)
}
}
func (m *Modem) dteWrite(data []byte) {
if _, err := m.dte.Write(data); err != nil {
m.Shutdown()
}
}
func (m *Modem) dceWrite(data []byte) {
// step through the data in chunks
csize := int(m.bytesPerTimeslot())
for scan := 0; scan < len(data); {
// wait if necessary until we can send
now := time.Now()
if m.writeSlot.After(now) {
wtime := m.writeSlot.Sub(now)
fmt.Printf("waiting %d for write slot\n", wtime)
time.Sleep(wtime)
}
// send the data
end := scan + csize
if end > len(data) {
end = len(data)
}
chunk := data[scan:end]
if _, err := m.dce.Write(chunk); err != nil {
m.disconnect()
m.noCarrier()
return
}
scan += len(chunk)
// set the next available timeslot
tlen := time.Duration((9 * 1000 * 1000 * 1000 * len(chunk)) / int(m.baud))
fmt.Printf("%d chars, next write slot in %d\n", len(chunk), tlen)
m.writeSlot = now.Add(tlen)
}
}
func (m *Modem) tnWrite(codes []TCode) {
b := make([]byte, len(codes))
for i, c := range codes {
b[i] = byte(c)
}
m.dceWrite(b)
}
func (m *Modem) cmdOK() {
m.dteWrite([]byte("OK\r\n"))
}
func (m *Modem) cmdError() {
m.dteWrite([]byte("ERROR\r\n"))
}
func (m *Modem) noCarrier() {
m.dteWrite([]byte("NO CARRIER\r\n"))
}
func (m *Modem) connect(dial string) error {
endpoint, found := AddressBook[dial]
if !found {
return errors.New("Address not found:" + dial)
}
conn, err := net.Dial("tcp", endpoint)
if err != nil {
log.WithFields(log.Fields{
"error": err,
}).Error("Telnet connection failed")
m.connected = false
return err
}
m.dce = conn
m.connected = true
m.mode = DTE_CONNECTED
return nil
}
//////////////////////////////////////////////////////////////////////////
// Modem receive thread
func (m *Modem) DTEReceive(baud uint, dte net.Conn) {
remote := dte.RemoteAddr().String()
log.WithFields(log.Fields{
"remote": remote,
}).Info("Accepting new modem")
// initialise state
m.baud = baud
m.dte = dte
m.createBuffers()
m.atCmd("z")
// register
Modems[remote] = m
defer func() {
log.WithFields(log.Fields{
"remote": remote,
}).Debug("Shutting down modem")
m.Shutdown()
delete(Modems, remote)
}()
for {
// read some data
if m.mode == DTE_ATTN_3 {
// potential hangup, set a read deadline
m.dte.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
}
// do the read
available, err := m.dte.Read(m.dteBuff)
if m.mode == DTE_ATTN_3 {
// clear the deadline and return to connected state
m.dte.SetReadDeadline(time.Time{})
if (err != nil) && errors.Is(err, os.ErrDeadlineExceeded) {
// back to command mode
m.mode = DTE_COMMAND
m.cmdOK()
err = nil
} else {
// no attention
m.mode = DTE_CONNECTED
m.dce.Write([]byte("+++"))
}
}
if err != nil {
if errors.Is(err, io.EOF) || errors.Is(err, net.ErrClosed) {
log.WithFields(log.Fields{
"remote": remote,
}).Info("Modem DTE closed")
return
} else {
log.WithFields(log.Fields{
"remote": remote,
"error": err,
}).Error("DTE Read error")
return
}
}
for scan := 0; scan < available; {
switch m.mode {
case DTE_COMMAND:
// waiting for AT
start := scan
for ; scan < available; scan++ {
if m.dteBuff[scan] == 'a' || m.dteBuff[scan] == 'A' {
m.mode = DTE_COMMAND_A
scan++
break
}
}
// echo characters if required
if m.echo {
m.dteWrite(m.dteBuff[start:scan])
}
case DTE_COMMAND_A:
// have A, is next byte a T ?
if m.dteBuff[scan] == 't' || m.dteBuff[scan] == 'T' {
// yes, start AT command mode
m.mode = DTE_COMMAND_AT
scan++
// echo char if needed
if m.echo {
m.dteWrite(m.dteBuff[scan-1 : scan])
}
} else {
// not a T, reset the mode
m.mode = DTE_COMMAND
}
case DTE_COMMAND_AT:
// have AT, waiting for \r
eol := false
start := scan
for ; scan < available; scan++ {
if m.dteBuff[scan] == '\r' {
// signal EOL
eol = true
break
}
}
data := m.dteBuff[start:scan]
// echo characters if required
if m.echo {
m.dteWrite(data)
}
// add to command buffer
if (m.cmdBuff.Len() + len(data)) > 80 {
// nah too long
m.cmdBuff.Reset()
m.cmdError()
} else {
m.cmdBuff.Write(data)
}
// parse AT command if EOL
if eol {
scan++
m.dteWrite([]byte("\r\n"))
cmd := m.cmdBuff.String()
log.WithFields(log.Fields{
"remote": remote,
"cmd": cmd,
}).Debug("ATCMD")
m.atCmd(cmd)
m.cmdBuff.Reset()
if m.mode != DTE_CONNECTED {
m.mode = DTE_COMMAND
}
}
case DTE_CONNECTED:
// stream to DCE
start := scan
for ; scan < available; scan++ {
if m.dteBuff[scan] == '+' {
m.mode = DTE_ATTN_1
break
}
}
// write data so far
data := m.dteBuff[start:scan]
m.dceWrite(data)
if scan < available {
// + was received, skip over it
scan++
}
case DTE_ATTN_1:
if m.dteBuff[scan] == '+' {
m.mode = DTE_ATTN_2
scan++
} else {
// no attention, send suitable number of +
m.mode = DTE_CONNECTED
m.dceWrite([]byte("+"))
}
case DTE_ATTN_2:
if m.dteBuff[scan] == '+' {
scan++
if scan < available {
// more bytes were available, no hangup
m.mode = DTE_CONNECTED
m.dceWrite([]byte("+++"))
} else {
// wait for pause
m.mode = DTE_ATTN_3
}
} else {
// no attention, send suitable number of +
m.mode = DTE_CONNECTED
m.dceWrite([]byte("++"))
}
}
}
}
}
//////////////////////////////////////////////////////////////////////////
// action AT command
func (m *Modem) atCmd(cmd string) {
cmd = strings.ToLower(strings.TrimSpace(cmd))
l := len(cmd)
// cope with zero length commands
if l == 0 {
m.cmdError()
return
}
switch cmd[0] {
case 'd':
// dial
if m.connected || l < 4 {
m.cmdError()
return
}
// remove any non-digit characters
dial := OnlyNumbers.ReplaceAllString(cmd, "")
log.WithFields(log.Fields{
"dial": dial,
}).Debug("Dial number")
if err := m.connect(dial); err != nil {
m.noCarrier()
return
}
// show connect string
cstr := "CONNECT " + strconv.Itoa(int(m.baud)) + "\r\n"
m.dte.Write([]byte(cstr))
// start dce read thread
go m.dceTelnet()
case 'h':
// hangup
switch {
case l == 1 || cmd[1] == '0':
m.disconnect()
m.cmdOK()
default:
m.cmdError()
}
case 'e':
// enable/disable echo
switch {
case l == 1 || cmd[1] == '0':
m.echo = false
m.cmdOK()
case cmd[1] == '1':
m.echo = true
m.cmdOK()
default:
m.cmdError()
}
case 'o':
if l == 1 {
if m.connected {
m.mode = DTE_CONNECTED
m.cmdOK()
} else {
m.noCarrier()
}
} else {
m.cmdError()
}
case 'z':
if l == 1 || cmd[1] == '0' {
m.disconnect()
m.echo = true
m.mode = DTE_COMMAND
m.cmdBuff.Reset()
m.cmdOK()
} else {
m.cmdError()
}
default:
m.cmdOK()
}
}
//////////////////////////////////////////////////////////////////////////
// DCE read thread
func (m *Modem) dceTelnet() {
defer func() {
log.WithFields(log.Fields{
"remote": m.dte.RemoteAddr().String(),
}).Debug("Shutting down DCE")
m.disconnect()
m.noCarrier()
}()
// suppress GA (3)
// binary transmission (0)
// echo (1)
m.tnWrite([]TCode{
TN_IAC, TN_WILL, TCode(3),
TN_IAC, TN_DO, TCode(3),
TN_IAC, TN_WILL, TCode(0),
TN_IAC, TN_DO, TCode(0),
TN_IAC, TN_WONT, TCode(1),
TN_IAC, TN_DO, TCode(1),
})
m.state = TN_NORM
for {
// wait if necessary until we can read
now := time.Now()
if m.readSlot.After(now) {
rtime := m.readSlot.Sub(now)
fmt.Printf("waiting %d for read slot\n", rtime)
time.Sleep(rtime)
}
// read some data
available, err := m.dce.Read(m.dceBuff)
// set the next available timeslot
tlen := time.Duration((9 * 1000 * 1000 * 1000 * len(m.dceBuff)) / int(m.baud))
fmt.Printf("%d chars, next read slot in %d\n", len(m.dceBuff), tlen)
m.readSlot = now.Add(tlen)
if err != nil {
if errors.Is(err, io.EOF) || errors.Is(err, net.ErrClosed) {
log.WithFields(log.Fields{
"remote": m.dte.RemoteAddr().String(),
}).Info("Telnet DCE closed")
return
} else {
log.WithFields(log.Fields{
"remote": m.dte.RemoteAddr().String(),
"error": err,
}).Error("DCE Read error")
return
}
}
// parse the read data for control chars
for scan := 0; scan < available; {
switch m.state {
case TN_NORM:
// normal data processing, scan for IAC code
start := scan
for ; scan < available; scan++ {
if TCode(m.dceBuff[scan]) == TN_IAC {
m.state = TN_IAC
break
}
}
// write data so far
data := m.dceBuff[start:scan]
m.dte.Write(data)
if scan < available {
// TN_IAC was received, skip over it
scan++
}
case TN_IAC:
// have received IAC look for the next code
code := TCode(m.dceBuff[scan])
scan++
switch code {
case TN_IAC:
// actually send 255
m.dte.Write([]byte{byte(TN_IAC)})
case TN_WILL:
m.state = TN_WILL
case TN_WONT:
m.state = TN_WONT
case TN_DO:
m.state = TN_DO
case TN_DONT:
m.state = TN_DO
default:
log.WithFields(log.Fields{
"code": code,
}).Debug("Un-implemented TN code")
m.state = TN_NORM
}
case TN_WILL:
code := TCode(m.dceBuff[scan])
m.state = TN_NORM
scan++
switch code {
case 0:
// ignore binary confirmation
case 1:
// ignore echo
case 3:
// ignore GA confirmation
default:
// refuse any other WILL codes
m.tnWrite([]TCode{TN_IAC, TN_DONT, code})
log.WithFields(log.Fields{
"code": code,
}).Debug("Un-implemented TN_WILL")
}
case TN_WONT:
code := TCode(m.dceBuff[scan])
m.state = TN_NORM
scan++
switch code {
default:
log.WithFields(log.Fields{
"code": code,
}).Debug("Un-implemented TN_WONT")
}
case TN_DO:
code := TCode(m.dceBuff[scan])
m.state = TN_NORM
scan++
switch code {
case 0:
// ignore binary confirmation
case 3:
// ignore GA confirmation
default:
// refuse any DO codes
m.tnWrite([]TCode{TN_IAC, TN_WONT, code})
log.WithFields(log.Fields{
"code": code,
}).Debug("Un-implemented TN_DO")
}
case TN_DONT:
code := TCode(m.dceBuff[scan])
m.state = TN_NORM
scan++
switch code {
default:
// confirm won't do any codes
m.tnWrite([]TCode{TN_IAC, TN_WONT, code})
log.WithFields(log.Fields{
"code": code,
}).Debug("Un-implemented TN_DONT")
}
default:
log.WithFields(log.Fields{
"state": m.state,
}).Debug("Unknown TN state")
}
}
}
}
//////////////////////////////////////////////////////////////////////////
// everything starts here
func main() {
log.SetLevel(log.DebugLevel)
log.Info("modemulator starting")
// startup
Modems = make(map[string]*Modem)
Listen()
// graceful shutdown via SIGINT (^C)
csig := make(chan os.Signal, 1)
signal.Notify(csig, os.Interrupt)
// and block
<-csig
log.Info("Server shutting down")
// shutdown listeners here
for _, listener := range Listeners {
listener.Close()
}
// shutdown active modems
for _, modem := range Modems {
modem.Shutdown()
}
// nothing left to do
log.Info("Shutdown complete, all done")
os.Exit(0)
}
//////////////////////////////////////////////////////////////////////////
// end of code