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package server
import (
"dtail/config"
"dtail/logger"
"dtail/server/handlers"
"dtail/server/user"
"dtail/ssh/server"
"dtail/version"
"errors"
"fmt"
"io"
"net"
"sync"
gossh "golang.org/x/crypto/ssh"
)
// Server is the main server data structure.
type Server struct {
// Various server statistics counters.
stats stats
// SSH server configuration.
sshServerConfig *gossh.ServerConfig
// To control the max amount of concurrent cats (which can cause a lot of I/O on the server)
catLimiterCh chan struct{}
// To control the max amount of concurrent tails
tailLimiterCh chan struct{}
// Ask to shutdown the server
stop chan struct{}
}
// New returns a new server.
func New() *Server {
logger.Info("Creating server", version.String())
s := Server{
sshServerConfig: &gossh.ServerConfig{},
catLimiterCh: make(chan struct{}, config.Server.MaxConcurrentCats),
tailLimiterCh: make(chan struct{}, config.Server.MaxConcurrentTails),
stop: make(chan struct{}),
}
s.sshServerConfig.PasswordCallback = s.controlUserCallback
s.sshServerConfig.PublicKeyCallback = server.PublicKeyCallback
private, err := gossh.ParsePrivateKey(server.PrivateHostKey())
if err != nil {
logger.FatalExit(err)
}
s.sshServerConfig.AddHostKey(private)
return &s
}
// Start the server.
func (s *Server) Start(wg *sync.WaitGroup) int {
defer wg.Done()
logger.Info("Starting server")
bindAt := fmt.Sprintf("%s:%d", config.Server.SSHBindAddress, config.Common.SSHPort)
logger.Info("Binding server", bindAt)
listener, err := net.Listen("tcp", bindAt)
if err != nil {
logger.FatalExit("Failed to open listening TCP socket", err)
}
go s.stats.periodicLogServerStats(s.stop)
for {
conn, err := listener.Accept() // Blocking
if err != nil {
logger.Error("Failed to accept incoming connection", err)
continue
}
if err := s.stats.serverLimitExceeded(); err != nil {
logger.Error(err)
conn.Close()
continue
}
go s.handleConnection(conn)
}
}
func (s *Server) handleConnection(conn net.Conn) {
logger.Info("Handling connection")
sshConn, chans, reqs, err := gossh.NewServerConn(conn, s.sshServerConfig)
if err != nil {
logger.Error("Something just happened", err)
return
}
s.stats.incrementConnections()
go gossh.DiscardRequests(reqs)
for newChannel := range chans {
go s.handleChannel(sshConn, newChannel)
}
}
func (s *Server) handleChannel(sshConn gossh.Conn, newChannel gossh.NewChannel) {
user := user.New(sshConn.User(), sshConn.RemoteAddr().String())
logger.Info(user, "Invoking channel handler")
if newChannel.ChannelType() != "session" {
err := errors.New("Don'w allow other channel types than session")
logger.Error(user, err)
newChannel.Reject(gossh.Prohibited, err.Error())
return
}
channel, requests, err := newChannel.Accept()
if err != nil {
logger.Error(user, "Could not accept channel", err)
return
}
if err := s.handleRequests(sshConn, requests, channel, user); err != nil {
logger.Error(user, err)
sshConn.Close()
}
}
func (s *Server) handleRequests(sshConn gossh.Conn, in <-chan *gossh.Request, channel gossh.Channel, user *user.User) error {
logger.Info(user, "Invoking request handler")
for req := range in {
var payload = struct{ Value string }{}
gossh.Unmarshal(req.Payload, &payload)
switch req.Type {
case "shell":
var handler handlers.Handler
switch user.Name {
case config.ControlUser:
handler = handlers.NewControlHandler(user)
default:
handler = handlers.NewServerHandler(user, s.catLimiterCh, s.tailLimiterCh)
}
// Bi-directionally connect SSH stream to SSH handler
brokenPipe1 := make(chan struct{})
go func() {
defer close(brokenPipe1)
io.Copy(channel, handler)
}()
brokenPipe2 := make(chan struct{})
go func() {
defer close(brokenPipe2)
io.Copy(handler, channel)
}()
// Ensure to close all fd's and stop all goroutines once ssh connection terminated
go func() {
defer s.stats.decrementConnections()
defer handler.Close()
if err := sshConn.Wait(); err != nil && err != io.EOF {
logger.Error(user, err)
}
logger.Info(user, "Good bye Mister!")
}()
// Close the underlying ssh socket when server shuts down
go func() {
select {
case <-s.stop:
logger.Debug(user, "Server initiating shutdown on handler")
case <-handler.Wait():
logger.Debug(user, "Handler initiating shutdown by its own")
case <-brokenPipe1:
logger.Debug(user, "Broken pipe1")
case <-brokenPipe2:
logger.Debug(user, "Broken pipe2")
}
sshConn.Close()
logger.Info(user, "Closed SSH connection")
}()
// Only serving shell type
req.Reply(true, nil)
default:
req.Reply(false, nil)
return fmt.Errorf("Closing SSH connection as unknown request recieved|%s|%v",
req.Type, payload.Value)
}
}
return nil
}
func (*Server) controlUserCallback(c gossh.ConnMetadata, authPayload []byte) (*gossh.Permissions, error) {
user := user.New(c.User(), c.RemoteAddr().String())
if user.Name == config.ControlUser && string(authPayload) == config.ControlUser {
logger.Debug(user, "Initiating master control program")
return nil, nil
}
return nil, fmt.Errorf("Not authorized")
}
// Stop the server.
func (s *Server) Stop() {
close(s.stop)
s.stats.waitForConnections()
}
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