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communicator.go
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communicator.go
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package ssh
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"os"
"path/filepath"
"sync"
"time"
"golang.org/x/crypto/ssh"
)
// RemoteCmd represents a remote command being prepared or run.
type RemoteCmd struct {
// Command is the command to run remotely. This is executed as if
// it were a shell command, so you are expected to do any shell escaping
// necessary.
Command string
// Stdin specifies the process's standard input. If Stdin is
// nil, the process reads from an empty bytes.Buffer.
Stdin io.Reader
// Stdout and Stderr represent the process's standard output and
// error.
//
// If either is nil, it will be set to ioutil.Discard.
Stdout io.Writer
Stderr io.Writer
// This will be set to true when the remote command has exited. It
// shouldn't be set manually by the user, but there is no harm in
// doing so.
Exited bool
// Once Exited is true, this will contain the exit code of the process.
ExitStatus int
// Internal fields
exitCh chan struct{}
// This thing is a mutex, lock when making modifications concurrently
sync.Mutex
}
// SetExited is a helper for setting that this process is exited. This
// should be called by communicators who are running a remote command in
// order to set that the command is done.
func (r *RemoteCmd) SetExited(status int) {
r.Lock()
defer r.Unlock()
if r.exitCh == nil {
r.exitCh = make(chan struct{})
}
r.Exited = true
r.ExitStatus = status
close(r.exitCh)
}
// Wait waits for the remote command to complete.
func (r *RemoteCmd) Wait() {
// Make sure our condition variable is initialized.
r.Lock()
if r.exitCh == nil {
r.exitCh = make(chan struct{})
}
r.Unlock()
<-r.exitCh
}
type SSHCommunicator struct {
client *ssh.Client
config *Config
conn net.Conn
address string
}
// Config is the structure used to configure the SSH communicator.
type Config struct {
// The configuration of the Go SSH connection
SSHConfig *ssh.ClientConfig
// Connection returns a new connection. The current connection
// in use will be closed as part of the Close method, or in the
// case an error occurs.
Connection func() (net.Conn, error)
// NoPty, if true, will not request a pty from the remote end.
NoPty bool
// SSHAgentConn is a pointer to the UNIX connection for talking with the
// ssh-agent.
SSHAgentConn net.Conn
}
// New creates a new packer.Communicator implementation over SSH. This takes
// an already existing TCP connection and SSH configuration.
func New(address string, config *Config) (result *SSHCommunicator, err error) {
// Establish an initial connection and connect
result = &SSHCommunicator{
config: config,
address: address,
}
if err = result.reconnect(); err != nil {
result = nil
return
}
return
}
func (c *SSHCommunicator) Start(cmd *RemoteCmd) (err error) {
session, err := c.newSession()
if err != nil {
return
}
// Setup our session
session.Stdin = cmd.Stdin
session.Stdout = cmd.Stdout
session.Stderr = cmd.Stderr
if !c.config.NoPty {
// Request a PTY
termModes := ssh.TerminalModes{
ssh.ECHO: 0, // do not echo
ssh.TTY_OP_ISPEED: 14400, // input speed = 14.4kbaud
ssh.TTY_OP_OSPEED: 14400, // output speed = 14.4kbaud
}
if err = session.RequestPty("xterm", 80, 40, termModes); err != nil {
return
}
}
log.Printf("starting remote command: %s", cmd.Command)
err = session.Start(cmd.Command + "\n")
if err != nil {
return
}
// Start a goroutine to wait for the session to end and set the
// exit boolean and status.
go func() {
defer session.Close()
err := session.Wait()
exitStatus := 0
if err != nil {
exitErr, ok := err.(*ssh.ExitError)
if ok {
exitStatus = exitErr.ExitStatus()
}
}
log.Printf("remote command exited with '%d': %s", exitStatus, cmd.Command)
cmd.SetExited(exitStatus)
}()
return
}
func (c *SSHCommunicator) Upload(path string, input io.Reader) error {
// The target directory and file for talking the SCP protocol
targetDir := filepath.Dir(path)
targetFile := filepath.Base(path)
// On windows, filepath.Dir uses backslash separators (ie. "\tmp").
// This does not work when the target host is unix. Switch to forward slash
// which works for unix and windows
targetDir = filepath.ToSlash(targetDir)
scpFunc := func(w io.Writer, stdoutR *bufio.Reader) error {
return scpUploadFile(targetFile, input, w, stdoutR)
}
return c.scpSession("scp -vt "+targetDir, scpFunc)
}
func (c *SSHCommunicator) UploadDir(dst string, src string, excl []string) error {
log.Printf("Upload dir '%s' to '%s'", src, dst)
scpFunc := func(w io.Writer, r *bufio.Reader) error {
uploadEntries := func() error {
f, err := os.Open(src)
if err != nil {
return err
}
defer f.Close()
entries, err := f.Readdir(-1)
if err != nil {
return err
}
return scpUploadDir(src, entries, w, r)
}
if src[len(src)-1] != '/' {
log.Printf("No trailing slash, creating the source directory name")
return scpUploadDirProtocol(filepath.Base(src), w, r, uploadEntries)
}
// Trailing slash, so only upload the contents
return uploadEntries()
}
return c.scpSession("scp -rvt "+dst, scpFunc)
}
func (c *SSHCommunicator) Download(string, io.Writer) error {
panic("not implemented yet")
}
func (c *SSHCommunicator) newSession() (session *ssh.Session, err error) {
log.Println("opening new ssh session")
if c.client == nil {
err = errors.New("client not available")
} else {
session, err = c.client.NewSession()
}
if err != nil {
log.Printf("ssh session open error: '%s', attempting reconnect", err)
if err := c.reconnect(); err != nil {
return nil, err
}
return c.client.NewSession()
}
return session, nil
}
func (c *SSHCommunicator) reconnect() (err error) {
if c.conn != nil {
c.conn.Close()
}
// Set the conn and client to nil since we'll recreate it
c.conn = nil
c.client = nil
log.Printf("reconnecting to TCP connection for SSH")
c.conn, err = c.config.Connection()
if err != nil {
// Explicitly set this to the REAL nil. Connection() can return
// a nil implementation of net.Conn which will make the
// "if c.conn == nil" check fail above. Read here for more information
// on this psychotic language feature:
//
// http://golang.org/doc/faq#nil_error
c.conn = nil
log.Printf("reconnection error: %s", err)
return
}
log.Printf("handshaking with SSH")
sshConn, sshChan, req, err := ssh.NewClientConn(c.conn, c.address, c.config.SSHConfig)
if err != nil {
log.Printf("handshake error: %s", err)
}
if sshConn != nil {
c.client = ssh.NewClient(sshConn, sshChan, req)
}
return
}
func (c *SSHCommunicator) scpSession(scpCommand string, f func(io.Writer, *bufio.Reader) error) error {
session, err := c.newSession()
if err != nil {
return err
}
defer session.Close()
// Get a pipe to stdin so that we can send data down
stdinW, err := session.StdinPipe()
if err != nil {
return err
}
// We only want to close once, so we nil w after we close it,
// and only close in the defer if it hasn't been closed already.
defer func() {
if stdinW != nil {
stdinW.Close()
}
}()
// Get a pipe to stdout so that we can get responses back
stdoutPipe, err := session.StdoutPipe()
if err != nil {
return err
}
stdoutR := bufio.NewReader(stdoutPipe)
// Set stderr to a bytes buffer
stderr := new(bytes.Buffer)
session.Stderr = stderr
// Start the sink mode on the other side
// TODO(mitchellh): There are probably issues with shell escaping the path
log.Println("Starting remote scp process: ", scpCommand)
if err := session.Start(scpCommand); err != nil {
return err
}
// Call our callback that executes in the context of SCP. We ignore
// EOF errors if they occur because it usually means that SCP prematurely
// ended on the other side.
log.Println("Started SCP session, beginning transfers...")
if err := f(stdinW, stdoutR); err != nil && err != io.EOF {
return err
}
// Close the stdin, which sends an EOF, and then set w to nil so that
// our defer func doesn't close it again since that is unsafe with
// the Go SSH package.
log.Println("SCP session complete, closing stdin pipe.")
stdinW.Close()
stdinW = nil
// Wait for the SCP connection to close, meaning it has consumed all
// our data and has completed. Or has errored.
log.Println("Waiting for SSH session to complete.")
err = session.Wait()
if err != nil {
if exitErr, ok := err.(*ssh.ExitError); ok {
// Otherwise, we have an ExitErorr, meaning we can just read
// the exit status
log.Printf("non-zero exit status: %d", exitErr.ExitStatus())
// If we exited with status 127, it means SCP isn't available.
// Return a more descriptive error for that.
if exitErr.ExitStatus() == 127 {
return errors.New(
"SCP failed to start. This usually means that SCP is not\n" +
"properly installed on the remote system.")
}
}
return err
}
log.Printf("scp stderr (length %d): %s", stderr.Len(), stderr.String())
return nil
}
// checkSCPStatus checks that a prior command sent to SCP completed
// successfully. If it did not complete successfully, an error will
// be returned.
func checkSCPStatus(r *bufio.Reader) error {
code, err := r.ReadByte()
if err != nil {
return err
}
if code != 0 {
// Treat any non-zero (really 1 and 2) as fatal errors
message, _, err := r.ReadLine()
if err != nil {
return fmt.Errorf("Error reading error message: %s", err)
}
return errors.New(string(message))
}
return nil
}
func scpUploadFile(dst string, src io.Reader, w io.Writer, r *bufio.Reader) error {
// Create a temporary file where we can copy the contents of the src
// so that we can determine the length, since SCP is length-prefixed.
tf, err := ioutil.TempFile("", "packer-upload")
if err != nil {
return fmt.Errorf("Error creating temporary file for upload: %s", err)
}
defer os.Remove(tf.Name())
defer tf.Close()
log.Println("Copying input data into temporary file so we can read the length")
if _, err := io.Copy(tf, src); err != nil {
return err
}
// Sync the file so that the contents are definitely on disk, then
// read the length of it.
if err := tf.Sync(); err != nil {
return fmt.Errorf("Error creating temporary file for upload: %s", err)
}
// Seek the file to the beginning so we can re-read all of it
if _, err := tf.Seek(0, 0); err != nil {
return fmt.Errorf("Error creating temporary file for upload: %s", err)
}
fi, err := tf.Stat()
if err != nil {
return fmt.Errorf("Error creating temporary file for upload: %s", err)
}
// Start the protocol
log.Println("Beginning file upload...")
fmt.Fprintln(w, "C0644", fi.Size(), dst)
if err := checkSCPStatus(r); err != nil {
return err
}
if _, err := io.Copy(w, tf); err != nil {
return err
}
fmt.Fprint(w, "\x00")
if err := checkSCPStatus(r); err != nil {
return err
}
return nil
}
func scpUploadDirProtocol(name string, w io.Writer, r *bufio.Reader, f func() error) error {
log.Printf("SCP: starting directory upload: %s", name)
fmt.Fprintln(w, "D0755 0", name)
err := checkSCPStatus(r)
if err != nil {
return err
}
if err := f(); err != nil {
return err
}
fmt.Fprintln(w, "E")
if err != nil {
return err
}
return nil
}
func scpUploadDir(root string, fs []os.FileInfo, w io.Writer, r *bufio.Reader) error {
for _, fi := range fs {
realPath := filepath.Join(root, fi.Name())
// Track if this is actually a symlink to a directory. If it is
// a symlink to a file we don't do any special behavior because uploading
// a file just works. If it is a directory, we need to know so we
// treat it as such.
isSymlinkToDir := false
if fi.Mode()&os.ModeSymlink == os.ModeSymlink {
symPath, err := filepath.EvalSymlinks(realPath)
if err != nil {
return err
}
symFi, err := os.Lstat(symPath)
if err != nil {
return err
}
isSymlinkToDir = symFi.IsDir()
}
if !fi.IsDir() && !isSymlinkToDir {
// It is a regular file (or symlink to a file), just upload it
f, err := os.Open(realPath)
if err != nil {
return err
}
err = func() error {
defer f.Close()
return scpUploadFile(fi.Name(), f, w, r)
}()
if err != nil {
return err
}
continue
}
// It is a directory, recursively upload
err := scpUploadDirProtocol(fi.Name(), w, r, func() error {
f, err := os.Open(realPath)
if err != nil {
return err
}
defer f.Close()
entries, err := f.Readdir(-1)
if err != nil {
return err
}
return scpUploadDir(realPath, entries, w, r)
})
if err != nil {
return err
}
}
return nil
}
// ConnectFunc is a convenience method for returning a function
// that just uses net.Dial to communicate with the remote end that
// is suitable for use with the SSH communicator configuration.
func ConnectFunc(network, addr string) func() (net.Conn, error) {
return func() (net.Conn, error) {
c, err := net.DialTimeout(network, addr, 15*time.Second)
if err != nil {
return nil, err
}
if tcpConn, ok := c.(*net.TCPConn); ok {
tcpConn.SetKeepAlive(true)
}
return c, nil
}
}