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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssh
// Session implements an interactive session described in
// "RFC 4254, section 6".
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"io/ioutil"
"sync"
)
type Signal string
// POSIX signals as listed in RFC 4254 Section 6.10.
const (
SIGABRT Signal = "ABRT"
SIGALRM Signal = "ALRM"
SIGFPE Signal = "FPE"
SIGHUP Signal = "HUP"
SIGILL Signal = "ILL"
SIGINT Signal = "INT"
SIGKILL Signal = "KILL"
SIGPIPE Signal = "PIPE"
SIGQUIT Signal = "QUIT"
SIGSEGV Signal = "SEGV"
SIGTERM Signal = "TERM"
SIGUSR1 Signal = "USR1"
SIGUSR2 Signal = "USR2"
)
var signals = map[Signal]int{
SIGABRT: 6,
SIGALRM: 14,
SIGFPE: 8,
SIGHUP: 1,
SIGILL: 4,
SIGINT: 2,
SIGKILL: 9,
SIGPIPE: 13,
SIGQUIT: 3,
SIGSEGV: 11,
SIGTERM: 15,
}
type TerminalModes map[uint8]uint32
// POSIX terminal mode flags as listed in RFC 4254 Section 8.
const (
tty_OP_END = 0
VINTR = 1
VQUIT = 2
VERASE = 3
VKILL = 4
VEOF = 5
VEOL = 6
VEOL2 = 7
VSTART = 8
VSTOP = 9
VSUSP = 10
VDSUSP = 11
VREPRINT = 12
VWERASE = 13
VLNEXT = 14
VFLUSH = 15
VSWTCH = 16
VSTATUS = 17
VDISCARD = 18
IGNPAR = 30
PARMRK = 31
INPCK = 32
ISTRIP = 33
INLCR = 34
IGNCR = 35
ICRNL = 36
IUCLC = 37
IXON = 38
IXANY = 39
IXOFF = 40
IMAXBEL = 41
ISIG = 50
ICANON = 51
XCASE = 52
ECHO = 53
ECHOE = 54
ECHOK = 55
ECHONL = 56
NOFLSH = 57
TOSTOP = 58
IEXTEN = 59
ECHOCTL = 60
ECHOKE = 61
PENDIN = 62
OPOST = 70
OLCUC = 71
ONLCR = 72
OCRNL = 73
ONOCR = 74
ONLRET = 75
CS7 = 90
CS8 = 91
PARENB = 92
PARODD = 93
TTY_OP_ISPEED = 128
TTY_OP_OSPEED = 129
)
// A Session represents a connection to a remote command or shell.
type Session struct {
// Stdin specifies the remote process's standard input.
// If Stdin is nil, the remote process reads from an empty
// bytes.Buffer.
Stdin io.Reader
// Stdout and Stderr specify the remote process's standard
// output and error.
//
// If either is nil, Run connects the corresponding file
// descriptor to an instance of ioutil.Discard. There is a
// fixed amount of buffering that is shared for the two streams.
// If either blocks it may eventually cause the remote
// command to block.
Stdout io.Writer
Stderr io.Writer
ch Channel // the channel backing this session
started bool // true once Start, Run or Shell is invoked.
copyFuncs []func() error
errors chan error // one send per copyFunc
// true if pipe method is active
stdinpipe, stdoutpipe, stderrpipe bool
// stdinPipeWriter is non-nil if StdinPipe has not been called
// and Stdin was specified by the user; it is the write end of
// a pipe connecting Session.Stdin to the stdin channel.
stdinPipeWriter io.WriteCloser
exitStatus chan error
}
// SendRequest sends an out-of-band channel request on the SSH channel
// underlying the session.
func (s *Session) SendRequest(name string, wantReply bool, payload []byte) (bool, error) {
return s.ch.SendRequest(name, wantReply, payload)
}
func (s *Session) Close() error {
return s.ch.Close()
}
// RFC 4254 Section 6.4.
type setenvRequest struct {
Name string
Value string
}
// Setenv sets an environment variable that will be applied to any
// command executed by Shell or Run.
func (s *Session) Setenv(name, value string) error {
msg := setenvRequest{
Name: name,
Value: value,
}
ok, err := s.ch.SendRequest("env", true, Marshal(&msg))
if err == nil && !ok {
err = errors.New("ssh: setenv failed")
}
return err
}
// RFC 4254 Section 6.2.
type ptyRequestMsg struct {
Term string
Columns uint32
Rows uint32
Width uint32
Height uint32
Modelist string
}
// RequestPty requests the association of a pty with the session on the remote host.
func (s *Session) RequestPty(term string, h, w int, termmodes TerminalModes) error {
var tm []byte
for k, v := range termmodes {
kv := struct {
Key byte
Val uint32
}{k, v}
tm = append(tm, Marshal(&kv)...)
}
tm = append(tm, tty_OP_END)
req := ptyRequestMsg{
Term: term,
Columns: uint32(w),
Rows: uint32(h),
Width: uint32(w * 8),
Height: uint32(h * 8),
Modelist: string(tm),
}
ok, err := s.ch.SendRequest("pty-req", true, Marshal(&req))
if err == nil && !ok {
err = errors.New("ssh: pty-req failed")
}
return err
}
// RFC 4254 Section 6.5.
type subsystemRequestMsg struct {
Subsystem string
}
// RequestSubsystem requests the association of a subsystem with the session on the remote host.
// A subsystem is a predefined command that runs in the background when the ssh session is initiated
func (s *Session) RequestSubsystem(subsystem string) error {
msg := subsystemRequestMsg{
Subsystem: subsystem,
}
ok, err := s.ch.SendRequest("subsystem", true, Marshal(&msg))
if err == nil && !ok {
err = errors.New("ssh: subsystem request failed")
}
return err
}
// RFC 4254 Section 6.7.
type ptyWindowChangeMsg struct {
Columns uint32
Rows uint32
Width uint32
Height uint32
}
// WindowChange informs the remote host about a terminal window dimension change to h rows and w columns.
func (s *Session) WindowChange(h, w int) error {
req := ptyWindowChangeMsg{
Columns: uint32(w),
Rows: uint32(h),
Width: uint32(w * 8),
Height: uint32(h * 8),
}
_, err := s.ch.SendRequest("window-change", false, Marshal(&req))
return err
}
// RFC 4254 Section 6.9.
type signalMsg struct {
Signal string
}
// Signal sends the given signal to the remote process.
// sig is one of the SIG* constants.
func (s *Session) Signal(sig Signal) error {
msg := signalMsg{
Signal: string(sig),
}
_, err := s.ch.SendRequest("signal", false, Marshal(&msg))
return err
}
// RFC 4254 Section 6.5.
type execMsg struct {
Command string
}
// Start runs cmd on the remote host. Typically, the remote
// server passes cmd to the shell for interpretation.
// A Session only accepts one call to Run, Start or Shell.
func (s *Session) Start(cmd string) error {
if s.started {
return errors.New("ssh: session already started")
}
req := execMsg{
Command: cmd,
}
ok, err := s.ch.SendRequest("exec", true, Marshal(&req))
if err == nil && !ok {
err = fmt.Errorf("ssh: command %v failed", cmd)
}
if err != nil {
return err
}
return s.start()
}
// Run runs cmd on the remote host. Typically, the remote
// server passes cmd to the shell for interpretation.
// A Session only accepts one call to Run, Start, Shell, Output,
// or CombinedOutput.
//
// The returned error is nil if the command runs, has no problems
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the remote server does not send an exit status, an error of type
// *ExitMissingError is returned. If the command completes
// unsuccessfully or is interrupted by a signal, the error is of type
// *ExitError. Other error types may be returned for I/O problems.
func (s *Session) Run(cmd string) error {
err := s.Start(cmd)
if err != nil {
return err
}
return s.Wait()
}
// Output runs cmd on the remote host and returns its standard output.
func (s *Session) Output(cmd string) ([]byte, error) {
if s.Stdout != nil {
return nil, errors.New("ssh: Stdout already set")
}
var b bytes.Buffer
s.Stdout = &b
err := s.Run(cmd)
return b.Bytes(), err
}
type singleWriter struct {
b bytes.Buffer
mu sync.Mutex
}
func (w *singleWriter) Write(p []byte) (int, error) {
w.mu.Lock()
defer w.mu.Unlock()
return w.b.Write(p)
}
// CombinedOutput runs cmd on the remote host and returns its combined
// standard output and standard error.
func (s *Session) CombinedOutput(cmd string) ([]byte, error) {
if s.Stdout != nil {
return nil, errors.New("ssh: Stdout already set")
}
if s.Stderr != nil {
return nil, errors.New("ssh: Stderr already set")
}
var b singleWriter
s.Stdout = &b
s.Stderr = &b
err := s.Run(cmd)
return b.b.Bytes(), err
}
// Shell starts a login shell on the remote host. A Session only
// accepts one call to Run, Start, Shell, Output, or CombinedOutput.
func (s *Session) Shell() error {
if s.started {
return errors.New("ssh: session already started")
}
ok, err := s.ch.SendRequest("shell", true, nil)
if err == nil && !ok {
return errors.New("ssh: could not start shell")
}
if err != nil {
return err
}
return s.start()
}
func (s *Session) start() error {
s.started = true
type F func(*Session)
for _, setupFd := range []F{(*Session).stdin, (*Session).stdout, (*Session).stderr} {
setupFd(s)
}
s.errors = make(chan error, len(s.copyFuncs))
for _, fn := range s.copyFuncs {
go func(fn func() error) {
s.errors <- fn()
}(fn)
}
return nil
}
// Wait waits for the remote command to exit.
//
// The returned error is nil if the command runs, has no problems
// copying stdin, stdout, and stderr, and exits with a zero exit
// status.
//
// If the remote server does not send an exit status, an error of type
// *ExitMissingError is returned. If the command completes
// unsuccessfully or is interrupted by a signal, the error is of type
// *ExitError. Other error types may be returned for I/O problems.
func (s *Session) Wait() error {
if !s.started {
return errors.New("ssh: session not started")
}
waitErr := <-s.exitStatus
if s.stdinPipeWriter != nil {
s.stdinPipeWriter.Close()
}
var copyError error
for range s.copyFuncs {
if err := <-s.errors; err != nil && copyError == nil {
copyError = err
}
}
if waitErr != nil {
return waitErr
}
return copyError
}
func (s *Session) wait(reqs <-chan *Request) error {
wm := Waitmsg{status: -1}
// Wait for msg channel to be closed before returning.
for msg := range reqs {
switch msg.Type {
case "exit-status":
wm.status = int(binary.BigEndian.Uint32(msg.Payload))
case "exit-signal":
var sigval struct {
Signal string
CoreDumped bool
Error string
Lang string
}
if err := Unmarshal(msg.Payload, &sigval); err != nil {
return err
}
// Must sanitize strings?
wm.signal = sigval.Signal
wm.msg = sigval.Error
wm.lang = sigval.Lang
default:
// This handles keepalives and matches
// OpenSSH's behaviour.
if msg.WantReply {
msg.Reply(false, nil)
}
}
}
if wm.status == 0 {
return nil
}
if wm.status == -1 {
// exit-status was never sent from server
if wm.signal == "" {
// signal was not sent either. RFC 4254
// section 6.10 recommends against this
// behavior, but it is allowed, so we let
// clients handle it.
return &ExitMissingError{}
}
wm.status = 128
if _, ok := signals[Signal(wm.signal)]; ok {
wm.status += signals[Signal(wm.signal)]
}
}
return &ExitError{wm}
}
// ExitMissingError is returned if a session is torn down cleanly, but
// the server sends no confirmation of the exit status.
type ExitMissingError struct{}
func (e *ExitMissingError) Error() string {
return "wait: remote command exited without exit status or exit signal"
}
func (s *Session) stdin() {
if s.stdinpipe {
return
}
var stdin io.Reader
if s.Stdin == nil {
stdin = new(bytes.Buffer)
} else {
r, w := io.Pipe()
go func() {
_, err := io.Copy(w, s.Stdin)
w.CloseWithError(err)
}()
stdin, s.stdinPipeWriter = r, w
}
s.copyFuncs = append(s.copyFuncs, func() error {
_, err := io.Copy(s.ch, stdin)
if err1 := s.ch.CloseWrite(); err == nil && err1 != io.EOF {
err = err1
}
return err
})
}
func (s *Session) stdout() {
if s.stdoutpipe {
return
}
if s.Stdout == nil {
s.Stdout = ioutil.Discard
}
s.copyFuncs = append(s.copyFuncs, func() error {
_, err := io.Copy(s.Stdout, s.ch)
return err
})
}
func (s *Session) stderr() {
if s.stderrpipe {
return
}
if s.Stderr == nil {
s.Stderr = ioutil.Discard
}
s.copyFuncs = append(s.copyFuncs, func() error {
_, err := io.Copy(s.Stderr, s.ch.Stderr())
return err
})
}
// sessionStdin reroutes Close to CloseWrite.
type sessionStdin struct {
io.Writer
ch Channel
}
func (s *sessionStdin) Close() error {
return s.ch.CloseWrite()
}
// StdinPipe returns a pipe that will be connected to the
// remote command's standard input when the command starts.
func (s *Session) StdinPipe() (io.WriteCloser, error) {
if s.Stdin != nil {
return nil, errors.New("ssh: Stdin already set")
}
if s.started {
return nil, errors.New("ssh: StdinPipe after process started")
}
s.stdinpipe = true
return &sessionStdin{s.ch, s.ch}, nil
}
// StdoutPipe returns a pipe that will be connected to the
// remote command's standard output when the command starts.
// There is a fixed amount of buffering that is shared between
// stdout and stderr streams. If the StdoutPipe reader is
// not serviced fast enough it may eventually cause the
// remote command to block.
func (s *Session) StdoutPipe() (io.Reader, error) {
if s.Stdout != nil {
return nil, errors.New("ssh: Stdout already set")
}
if s.started {
return nil, errors.New("ssh: StdoutPipe after process started")
}
s.stdoutpipe = true
return s.ch, nil
}
// StderrPipe returns a pipe that will be connected to the
// remote command's standard error when the command starts.
// There is a fixed amount of buffering that is shared between
// stdout and stderr streams. If the StderrPipe reader is
// not serviced fast enough it may eventually cause the
// remote command to block.
func (s *Session) StderrPipe() (io.Reader, error) {
if s.Stderr != nil {
return nil, errors.New("ssh: Stderr already set")
}
if s.started {
return nil, errors.New("ssh: StderrPipe after process started")
}
s.stderrpipe = true
return s.ch.Stderr(), nil
}
// newSession returns a new interactive session on the remote host.
func newSession(ch Channel, reqs <-chan *Request) (*Session, error) {
s := &Session{
ch: ch,
}
s.exitStatus = make(chan error, 1)
go func() {
s.exitStatus <- s.wait(reqs)
}()
return s, nil
}
// An ExitError reports unsuccessful completion of a remote command.
type ExitError struct {
Waitmsg
}
func (e *ExitError) Error() string {
return e.Waitmsg.String()
}
// Waitmsg stores the information about an exited remote command
// as reported by Wait.
type Waitmsg struct {
status int
signal string
msg string
lang string
}
// ExitStatus returns the exit status of the remote command.
func (w Waitmsg) ExitStatus() int {
return w.status
}
// Signal returns the exit signal of the remote command if
// it was terminated violently.
func (w Waitmsg) Signal() string {
return w.signal
}
// Msg returns the exit message given by the remote command
func (w Waitmsg) Msg() string {
return w.msg
}
// Lang returns the language tag. See RFC 3066
func (w Waitmsg) Lang() string {
return w.lang
}
func (w Waitmsg) String() string {
str := fmt.Sprintf("Process exited with status %v", w.status)
if w.signal != "" {
str += fmt.Sprintf(" from signal %v", w.signal)
}
if w.msg != "" {
str += fmt.Sprintf(". Reason was: %v", w.msg)
}
return str
}