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server.go
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server.go
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package internal
import (
"context"
"fmt"
"io"
"net"
"os"
"os/exec"
"time"
gssh "github.com/charmbracelet/ssh"
"github.com/owenthereal/upterm/host/api"
"github.com/owenthereal/upterm/server"
"github.com/owenthereal/upterm/upterm"
"github.com/owenthereal/upterm/utils"
"github.com/oklog/run"
"github.com/olebedev/emitter"
uio "github.com/owenthereal/upterm/io"
log "github.com/sirupsen/logrus"
"golang.org/x/crypto/ssh"
)
type Server struct {
Command []string
CommandEnv []string
ForceCommand []string
Signers []ssh.Signer
AuthorizedKeys []ssh.PublicKey
EventEmitter *emitter.Emitter
KeepAliveDuration time.Duration
Stdin *os.File
Stdout *os.File
Logger log.FieldLogger
ReadOnly bool
}
func (s *Server) ServeWithContext(ctx context.Context, l net.Listener) error {
writers := uio.NewMultiWriter(5)
cmdCtx, cmdCancel := context.WithCancel(ctx)
defer cmdCancel()
cmd := newCommand(
s.Command[0],
s.Command[1:],
s.CommandEnv,
s.Stdin,
s.Stdout,
s.EventEmitter,
writers,
)
ptmx, err := cmd.Start(cmdCtx)
if err != nil {
return fmt.Errorf("error starting command: %w", err)
}
var g run.Group
{
ctx, cancel := context.WithCancel(ctx)
teh := terminalEventHandler{
eventEmitter: s.EventEmitter,
logger: s.Logger,
}
g.Add(func() error {
return teh.Handle(ctx)
}, func(err error) {
cancel()
})
}
{
g.Add(func() error {
return cmd.Run()
}, func(err error) {
cmdCancel()
})
}
{
ctx, cancel := context.WithCancel(ctx)
sh := sessionHandler{
forceCommand: s.ForceCommand,
ptmx: ptmx,
eventEmmiter: s.EventEmitter,
writers: writers,
keepAliveDuration: s.KeepAliveDuration,
ctx: ctx,
logger: s.Logger,
readonly: s.ReadOnly,
}
ph := publicKeyHandler{
AuthorizedKeys: s.AuthorizedKeys,
EventEmmiter: s.EventEmitter,
Logger: s.Logger,
}
var ss []gssh.Signer
for _, signer := range s.Signers {
ss = append(ss, signer)
}
server := gssh.Server{
HostSigners: ss,
Handler: sh.HandleSession,
Version: upterm.HostSSHServerVersion,
PublicKeyHandler: ph.HandlePublicKey,
ConnectionFailedCallback: func(conn net.Conn, err error) {
s.Logger.WithError(err).Error("connection failed")
},
}
g.Add(func() error {
return server.Serve(l)
}, func(err error) {
// kill ssh sessionHandler
cancel()
// shut down ssh server
_ = server.Shutdown(ctx)
})
}
return g.Run()
}
type publicKeyHandler struct {
AuthorizedKeys []ssh.PublicKey
EventEmmiter *emitter.Emitter
Logger log.FieldLogger
}
func (h *publicKeyHandler) HandlePublicKey(ctx gssh.Context, key gssh.PublicKey) bool {
checker := server.UserCertChecker{}
auth, pk, err := checker.Authenticate(ctx.User(), key)
if err != nil {
h.Logger.WithError(err).Error("error parsing auth request from cert")
return false
}
// TODO: sshproxy already rejects unauthorized keys
// Does host still need to check them?
if len(h.AuthorizedKeys) == 0 {
emitClientJoinEvent(h.EventEmmiter, ctx.SessionID(), auth, pk)
return true
}
for _, k := range h.AuthorizedKeys {
if utils.KeysEqual(k, pk) {
emitClientJoinEvent(h.EventEmmiter, ctx.SessionID(), auth, pk)
return true
}
}
h.Logger.Info("unauthorized public key")
return false
}
type sessionHandler struct {
forceCommand []string
ptmx *pty
eventEmmiter *emitter.Emitter
writers *uio.MultiWriter
keepAliveDuration time.Duration
ctx context.Context
logger log.FieldLogger
readonly bool
}
func (h *sessionHandler) HandleSession(sess gssh.Session) {
sessionID := sess.Context().Value(gssh.ContextKeySessionID).(string)
defer emitClientLeftEvent(h.eventEmmiter, sessionID)
ptyReq, winCh, isPty := sess.Pty()
if !isPty {
_, _ = io.WriteString(sess, "PTY is required.\n")
_ = sess.Exit(1)
}
var (
g run.Group
err error
ptmx = h.ptmx
)
// simulate openssh keepalive
{
ctx, cancel := context.WithCancel(h.ctx)
g.Add(func() error {
ticker := time.NewTicker(h.keepAliveDuration)
defer ticker.Stop()
for {
select {
case <-ticker.C:
if _, err := sess.SendRequest(upterm.OpenSSHKeepAliveRequestType, true, nil); err != nil {
h.logger.WithError(err).Debug("error pinging client to keepalive")
}
case <-ctx.Done():
return ctx.Err()
}
}
}, func(err error) {
cancel()
})
}
if len(h.forceCommand) > 0 {
var cmd *exec.Cmd
ctx, cancel := context.WithCancel(h.ctx)
defer cancel()
cmd, ptmx, err = startAttachCmd(ctx, h.forceCommand, ptyReq.Term)
if err != nil {
h.logger.WithError(err).Error("error starting force command")
_ = sess.Exit(1)
return
}
{
// reattach output
g.Add(func() error {
_, err := io.Copy(sess, uio.NewContextReader(ctx, ptmx))
return ptyError(err)
}, func(err error) {
cancel()
ptmx.Close()
})
}
{
g.Add(func() error {
return cmd.Wait()
}, func(err error) {
cancel()
ptmx.Close()
})
}
} else {
// output
if err := h.writers.Append(sess); err != nil {
_ = sess.Exit(1)
return
}
defer h.writers.Remove(sess)
}
{
// pty
ctx, cancel := context.WithCancel(h.ctx)
tee := terminalEventEmitter{h.eventEmmiter}
g.Add(func() error {
for {
select {
case win := <-winCh:
tee.TerminalWindowChanged(sessionID, ptmx, win.Width, win.Height)
case <-ctx.Done():
return ctx.Err()
}
}
}, func(err error) {
tee.TerminalDetached(sessionID, ptmx)
cancel()
})
}
// if a readonly session has been requested, don't connect stdin
if h.readonly {
// write to client to notify them that they have connected to a read-only session
_, _ = io.WriteString(sess, "\r\n=== Attached to read-only session ===\r\n\r\n")
} else {
// input
ctx, cancel := context.WithCancel(h.ctx)
g.Add(func() error {
_, err := io.Copy(ptmx, uio.NewContextReader(ctx, sess))
return err
}, func(err error) {
cancel()
})
}
if err := g.Run(); err != nil {
if exitError, ok := err.(*exec.ExitError); ok {
_ = sess.Exit(exitError.ExitCode())
} else {
_ = sess.Exit(1)
}
} else {
_ = sess.Exit(0)
}
}
func emitClientJoinEvent(eventEmmiter *emitter.Emitter, sessionID string, auth *server.AuthRequest, pk ssh.PublicKey) {
c := &api.Client{
Id: sessionID,
Version: auth.ClientVersion,
Addr: auth.RemoteAddr,
PublicKeyFingerprint: utils.FingerprintSHA256(pk),
}
eventEmmiter.Emit(upterm.EventClientJoined, c)
}
func emitClientLeftEvent(eventEmmiter *emitter.Emitter, sessionID string) {
eventEmmiter.Emit(upterm.EventClientLeft, sessionID)
}
func startAttachCmd(ctx context.Context, c []string, term string) (*exec.Cmd, *pty, error) {
cmd := exec.CommandContext(ctx, c[0], c[1:]...)
cmd.Env = append(os.Environ(), fmt.Sprintf("TERM=%s", term))
pty, err := startPty(cmd)
return cmd, pty, err
}