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connection.go
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connection.go
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package telnetlib
import (
"bytes"
"io"
"io/ioutil"
"net"
"sync"
"time"
log "github.com/Sirupsen/logrus"
)
type connOpts struct {
conn net.Conn
fsm *telnetFSM
cmdHandler CmdHandlerFunc
dataHandler DataHandlerFunc
serverOpts map[byte]bool
clientOpts map[byte]bool
optCallback func(byte, byte)
}
type TelnetConn struct {
// conn is the underlying connection
conn net.Conn
readCh chan []byte
writeCh chan []byte
srvrOptsLock sync.Mutex
unackedServerOpts map[byte]bool
clientOptsLock sync.Mutex
unackedClientOpts map[byte]bool
//server *TelnetServer
serverOpts map[byte]bool
clientOpts map[byte]bool
// dataRW is the data buffer. It is written to by the FSM and read from by the data handler
dataRW io.ReadWriter
cmdBuffer bytes.Buffer
fsm *telnetFSM
handlerWriter io.WriteCloser
// cmdHandler is the command handler for the telnet server
// it is a callback function when receiving commands issued by the telnet client
// it is wrapped by the cmdHandlerWrapper
cmdHandler CmdHandlerFunc
// dataHandler is the data handler of the telnet server
// it is a call back function when recieving data from the telnet client
// it is wrapped by the dataHandlerWrapper
dataHandler DataHandlerFunc
// used in the dataHandlerWrapper to notify that the telnet connection is closed
dataHandlerCloseCh chan chan struct{}
// used in the dataHandlerWrapper to notify that data has been writeen to the dataRW buffer
dataWrittenCh chan bool
// callBack function for receiving an option during negotiation
optionCallback func(byte, byte)
// connWriteDoneCh closes the write loop when the telnet connection is closed
connWriteDoneCh chan chan struct{}
// negotiationDone notifies that telnet negotiation has been done
negotiationDone chan struct{}
closedMutex sync.Mutex
closed bool
}
// Safely read/write concurrently to the data Buffer
// databuffer is written to by the FSM and it is read from by the dataHandler
type dataReadWriter struct {
dataBuffer bytes.Buffer
dataMux *sync.Mutex
}
func (drw *dataReadWriter) Read(p []byte) (int, error) {
drw.dataMux.Lock()
defer drw.dataMux.Unlock()
return drw.dataBuffer.Read(p)
}
func (drw *dataReadWriter) Write(p []byte) (int, error) {
drw.dataMux.Lock()
defer drw.dataMux.Unlock()
return drw.dataBuffer.Write(p)
}
type connectionWriter struct {
ch chan []byte
}
func (cw *connectionWriter) Write(b []byte) (int, error) {
if cw.ch != nil {
cw.ch <- b
}
return len(b), nil
}
func (cw *connectionWriter) Close() error {
close(cw.ch)
cw.ch = nil
return nil
}
func newTelnetConn(opts connOpts) *TelnetConn {
tc := &TelnetConn{
conn: opts.conn,
readCh: make(chan []byte),
writeCh: make(chan []byte),
unackedServerOpts: make(map[byte]bool),
unackedClientOpts: make(map[byte]bool),
cmdHandler: opts.cmdHandler,
dataHandler: opts.dataHandler,
dataHandlerCloseCh: make(chan chan struct{}),
dataWrittenCh: make(chan bool),
serverOpts: opts.serverOpts,
clientOpts: opts.clientOpts,
optionCallback: opts.optCallback,
connWriteDoneCh: make(chan chan struct{}),
negotiationDone: make(chan struct{}),
closed: false,
}
if tc.optionCallback == nil {
tc.optionCallback = tc.handleOptionCommand
}
tc.handlerWriter = &connectionWriter{
ch: tc.writeCh,
}
tc.dataRW = &dataReadWriter{
dataMux: new(sync.Mutex),
}
fsm := opts.fsm
fsm.tc = tc
tc.fsm = fsm
for k := range tc.serverOpts {
tc.unackedServerOpts[k] = true
}
for k := range tc.clientOpts {
tc.unackedClientOpts[k] = true
}
return tc
}
func (c *TelnetConn) writeLoop() {
log.Debugf("entered write loop")
for {
select {
case writeBytes := <-c.writeCh:
c.conn.Write(writeBytes)
case ch := <-c.connWriteDoneCh:
ch <- struct{}{}
return
}
}
}
func (c *TelnetConn) startNegotiation() {
c.srvrOptsLock.Lock()
for k := range c.serverOpts {
log.Infof("sending WILL %d", k)
c.unackedServerOpts[k] = true
c.sendCmd(Will, k)
}
c.srvrOptsLock.Unlock()
c.clientOptsLock.Lock()
for k := range c.clientOpts {
log.Infof("sending DO %d", k)
c.unackedClientOpts[k] = true
c.sendCmd(Do, k)
}
c.clientOptsLock.Unlock()
select {
case <-c.negotiationDone:
log.Infof("Negotiation finished")
return
case <-time.After(10 * time.Second):
log.Infof("Negotiation failed. Exiting")
c.Close()
c.closed = true
return
}
}
// Close closes the telnet connection
func (c *TelnetConn) Close() {
log.Infof("Closing the connection")
c.conn.Close()
c.closeConnLoopWrite()
c.closeDatahandler()
c.handlerWriter.Close()
log.Infof("telnet connection closed")
c.closedMutex.Lock()
defer c.closedMutex.Unlock()
c.closed = true
}
func (c *TelnetConn) closeConnLoopWrite() {
connLoopWriteCh := make(chan struct{})
c.connWriteDoneCh <- connLoopWriteCh
<-connLoopWriteCh
log.Infof("connection loop write-side closed")
}
func (c *TelnetConn) closeDatahandler() {
dataCh := make(chan struct{})
c.dataHandlerCloseCh <- dataCh
<-dataCh
}
func (c *TelnetConn) sendCmd(cmd byte, opt byte) {
b := []byte{Iac, cmd, opt}
log.Infof("Sending command: %v %v", cmd, opt)
c.writeCh <- b
}
func (c *TelnetConn) handleOptionCommand(cmd byte, opt byte) {
c.clientOptsLock.Lock()
defer c.clientOptsLock.Unlock()
c.srvrOptsLock.Lock()
defer c.srvrOptsLock.Unlock()
if cmd == Will || cmd == Wont {
if _, ok := c.clientOpts[opt]; !ok {
c.sendCmd(Dont, opt)
return
}
if _, ok := c.unackedClientOpts[opt]; ok {
delete(c.unackedClientOpts, opt)
if len(c.unackedClientOpts) == 0 && len(c.unackedServerOpts) == 0 {
close(c.negotiationDone)
}
} else {
c.sendCmd(Do, opt)
}
}
if cmd == Do || cmd == Dont {
if _, ok := c.serverOpts[opt]; !ok {
c.sendCmd(Wont, opt)
return
}
if _, ok := c.unackedServerOpts[opt]; ok {
log.Infof("removing from the unack list")
delete(c.unackedServerOpts, opt)
if len(c.unackedClientOpts) == 0 && len(c.unackedServerOpts) == 0 {
close(c.negotiationDone)
}
} else {
log.Infof("Sending WILL command")
c.sendCmd(Will, opt)
}
}
}
func (c *TelnetConn) dataHandlerWrapper(w io.Writer, r io.Reader) {
defer func() {
log.Infof("data handler closed")
}()
for {
select {
case ch := <-c.dataHandlerCloseCh:
ch <- struct{}{}
return
case <-c.dataWrittenCh:
if b, err := ioutil.ReadAll(r); err == nil {
c.dataHandler(w, b, c)
}
}
}
}
func (c *TelnetConn) cmdHandlerWrapper(w io.Writer, r io.Reader) {
if cmd, err := ioutil.ReadAll(r); err == nil {
c.cmdHandler(w, cmd, c)
}
}
// IsClosed returns true if the connection is already closed
func (c *TelnetConn) IsClosed() bool {
c.closedMutex.Lock()
defer c.closedMutex.Unlock()
return c.closed
}